Parasite 27, 36 (2020)
Ó M. Boussinesq et al., published by EDP Sciences, 2020
https://doi.org/10.1051/parasite/2020036
Available online at:
www.parasite-journal.org
RESEARCH ARTICLE
OPEN
ACCESS
Effects of an injectable long-acting formulation of ivermectin
on Onchocerca ochengi in zebu cattle
Michel Boussinesq1,*, Peter Enyong2, Patrick Chounna-Ndongmo2, Abdel-Jelil Njouendou2, Sébastien David Pion1,
Anthony Rech3, Christophe Roberge3, Georges Gaudriault3,a, and Samuel Wanji2
1
2
3
Recherches Translationnelles sur le VIH et les Maladies Infectieuses (TransVIHMI), UMI233 IRD-U1175 INSERM-Université
de Montpellier, BP 64501, 34394 Montpellier Cedex 5, France
Research Foundation for Tropical Diseases and the Environment, PO Box 474, Buea, Cameroon
MedinCell S.A., 3 Rue des Frères Lumière, 34830 Jacou, France
Received 3 August 2019, Accepted 5 May 2020, Published online 18 May 2020
Abstract – The availability of a safe macrofilaricidal drug would help to accelerate onchocerciasis elimination. A trial
was conducted in Cameroon to evaluate the effects of a subcutaneous injectable long-acting formulation of ivermectin
(LAFI) on the microfilariae (mf) and adult stages of Onchocerca ochengi. Ten zebu cattle naturally infected with the
parasite were injected subcutaneously with either 500 mg (group A, N = 4), or 1000 mg long-acting ivermectin
(group B, N = 4) or the vehicle (group C, N = 2). Skin samples were collected from each animal before, and 6, 12,
and 24 months after treatment to measure microfilarial densities (MFDs). Nodules excised before, and 6 and 12 months
after treatment were examined histologically to assess the adult worms’ viability and reproductive status. Blood
samples were collected at pre-determined time-points to obtain pharmacokinetic data. Before treatment, the average
O. ochengi MFDs were similar in the three groups. Six months after treatment, all animals in groups A and B were
free of skin mf, whereas those in group C still showed high MFDs (mean = 324.5 mf/g). Only one ivermectin-treated
animal (belonging to group A) had skin mf 12 months after treatment (0.9 mf/g). At 24 months, another animal in
group A showed skin mf (10.0 mf/g). The histologic examination of nodules at 6 and 12 months showed that LAFI
was not macrofilaricidal but had a strong effect on embryogenesis. The new LAFI regimen might be an additional tool
to accelerate the elimination of human onchocerciasis in specific settings.
Key words: Onchocerciasis, Onchocerca ochengi, Ivermectin, Long-acting formulation, Microfilaricidal effect,
Macrofilaricidal effect.
Résumé – Effets d’une formulation injectable d’ivermectine à activité prolongée sur Onchocerca ochengi chez
les bovins zébu. La disponibilité d’un médicament macrofilaricide et sans danger permettrait d’accélérer l’élimination
de l’onchocercose. Un essai a été mené au Cameroun pour évaluer les effets d’une formulation injectable en souscutané d’ivermectine à activité prolongée (FIAP) sur les microfilaires (mf) et les stades adultes d’Onchocerca
ochengi. Dix vaches zébu infectées naturellement par le parasite ont reçu une injection sous-cutanée de 500 mg
(groupe A, N = 4) ou de 1000 mg d’ivermectine à activité prolongée (groupe B, N = 4) ou le véhicule (groupe C,
N = 2). Des échantillons de peau ont été collectés de chaque animal avant, puis 6, 12 et 24 mois après traitement
pour mesurer les densités microfilariennes (DMF). Des nodules prélevés avant et 6 et 12 mois après traitement ont
été examinés histologiquement pour évaluer la viabilité et le statut reproductif des vers adultes. Des échantillons de
sang ont été prélevés pour obtenir des données de pharmacocinétique. Avant traitement, les DMF à O. ochengi
étaient similaires dans les 3 groupes. Six mois après traitement, aucun des animaux des groupes A et B ne
présentait de mf dermiques, alors que ceux du groupe C présentaient encore des DMF élevées (moyenne :
324,5 mf/g). Parmi les animaux traités par ivermectine, un seul (du groupe A) avait des mf dermiques 12 mois
après traitement (0,9 mf/g). A 24 mois, un autre animal du groupe A avait des mf (10,0 mf/g). L’examen
histologique des nodules collectés à 6 et 12 mois montrait que la FIAP n’était pas macrofilaricide mais avait un
effet marqué sur l’embryogénèse. La nouvelle FIAP pourrait représenter un outil pour accélérer l’élimination de
l’onchocercose dans certaines circonstances spécifiques.
*Corresponding author: michel.boussinesq@ird.fr
a
Present address: Deinove S.A., ZAC Euromédecine II, Cap Sigma, 1682 Rue de la Valsière, 34790 Grabels, France.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
2
M. Boussinesq et al.: Parasite 2020, 27, 36
Introduction
The main control strategy for onchocerciasis is currently
based on mass treatment with ivermectin (IVM) targeting the
most affected populations, i.e. those (called meso-hyperendemic)
where more than 20% of the adults present subcutaneous
nodules containing Onchocerca volvulus adult worms. In
Africa, community-directed treatment with IVM (CDTI) has
led to the elimination of onchocerciasis as a public health
problem in most of the treated areas. However, to reach the
new World Health Organization’s objective of elimination of
the infection [47], interventions might have to be expanded to
the so-far untreated hypoendemic zones, and alternative
treatment strategies (ATS, i.e., differing from annual CDTI)
implemented [11]. Such strategies include the use of new drugs
or new formulations of existing drugs.
IVM has two main effects on O. volvulus. First, it induces
rapid destruction of the larval stage of the parasites (microfilariae [mf]) which are the cause of the immune reactions leading
to the ocular and skin manifestations of the disease (microfilaricidal effect). Second, IVM treatment interrupts for 3–4 months
the release of new mf by the adult female worms (embryostatic
effect) [8]. However, as IVM has a limited effect on the lifespan
of adult worms, CDTI has to be repeated every 6 or 12 months
to maintain microfilarial densities (MFD) below the level associated with clinical manifestations. One of the ATSs that could
be used to accelerate elimination of onchocerciasis would be to
treat the whole population, or only those individuals currently
infected with O. volvulus, with a macrofilaricidal drug, i.e. a
drug that kills or permanently sterilizes the adult worms.
Presently, the only macrofilaricidal drug which can be distributed on a large scale without major risks of adverse effects is
doxycycline. Daily treatment with this antibiotic for 4–6 weeks
eliminates the Wolbachia symbiotic bacteria present in the adult
worms, which leads to the sterilization and progressive death of
the latter [45]. The main problem related to this strategy is the
duration of the treatment, and research is ongoing to identify
other drugs that could be macrofilaricidal using a regimen of
two weeks or less. Three candidates have recently been tested
as part of phase 1 trials. The first is oxfendazole [1], which
belongs to the benzimidazole family and could have the advantage of killing the adult worms without affecting the mf, and
thus would not induce adverse effects, particularly in case of
coinfection with Loa loa [27, 48]. Ongoing trials (phase 1
and phase 2 against Trichuris trichiura) will enable us to evaluate its possible toxicity [25]. This point is key because the
development of another benzimidazole to treat filariases,
flubendazole, was interrupted in 2017 because its toxicity associated with effective doses was considered unacceptable [30].
The second macrofilaricidal candidate is emodepside, whose
efficacy was demonstrated in pre-clinical trials [29], and which
was evaluated in two phase 1 trials, one using single ascending
doses [24], and the other using multiple ascending doses
(https://clinicaltrials.gov/ct2/show/NCT03383614). The last
candidate is a drug called TylAMac (Tylosin Analogue
Macrofilaricide, ABBV-4083), which is a macrolide antibiotic
effective against Wolbachia [41, 43], and which was also
evaluated in a phase 1 trial terminated in 2018 (https://www.
dndi.org/diseases-projects/portfolio/abbv-4083/). All these
candidates are thus only at an initial stage of clinical
development.
The present study was conducted following the observation
that three-monthly doses of IVM induce excess mortality in
adult worms, when compared to annual doses [22], this excess
mortality actually being due to a significant decrease in the
adult worms’ lifespan [46]. As the plasma half-life of IVM in
man ranges between 12 h and 56 h following oral administration [26], we hypothesized that longer and continuous exposure
of the parasite to the drug could have a stronger macrofilaricidal
effect. Presently, several commercial long-acting formulations
of IVM exist, one of the best known being the subcutaneous
injectable formulation IvomecÒ Gold for cattle [15]. In this context, we tested the long-term efficacy (two years) of an injectable long-acting IVM formulation on the cattle-Onchocerca
ochengi filarial model. This model is widely used to assess
the effects of potentially filaricidal drugs because O. ochengi
is taxonomically close to O. volvulus, and because the adult
stages of both species live in subcutaneous nodules [32]. The
tested formulation is based on the proprietary drug delivery
platform BEPOÒ, which uses bioresorbable block copolymers
as functional excipients to control the release of IVM. In this
study, an assessment was made of the effect of the slow release
of IVM on the skin MFD by counting mf in skin biopsies, and
on the fertility and the viability of the adult worms, by histological examination of sections of excised subcutaneous nodules.
Materials and methods
Animals
Ten Gudali zebu cattle (Bos indicus) were purchased in
villages near Ngaoundere (Adamaoua region of Cameroon)
where transmission of O. ochengi is ongoing [44]. They were
selected on the basis of their sex (female), age (three years)
and presence of at least 10 subcutaneous nodules between the
udder and the umbilicus, and in the inguinal region. The
animals were not weighed, and no girth measurement was made
to estimate their weight, but given the age of the cows, one can
assume that weight ranged between 250 kg and 330 kg [2].
They were transported to the field research station of the
Research Foundation for Tropical Diseases and the Environment (REFOTDE) located near Modeka, in the South–West
region, on the right bank of the Mungo River. Each animal
was identified using an individual number printed on labels
attached at one ear. The interval of time between the departure
of the cows from the Adamaoua region and the first examination round (and administration of treatment) was six weeks.
Treatment description
The injectable long-acting formulation of IVM was prepared by Medincell using their proprietary drug delivery
platform BEPOÒ [23, 37]. A diblock (PEG–PLA) and a
triblock (PLA–PEG–PLA) bioresorbable copolymer were
allowed to dissolve overnight in a biocompatible solvent,
dimethyl sulfoxide (DMSO), with gentle mixing on a roller
mixer at room temperature. Then, 40 mL of the obtained
M. Boussinesq et al.: Parasite 2020, 27, 36
vehicle were sterile filtered into a 50 mL glass bottle and kept
refrigerated before shipment. The rest of the vehicle (approx.
160 mL) was used to prepare the IVM formulation; preweighed IVM powder was added to the vehicle and allowed
to gently dissolve on a roller mixer at room temperature. The
final solution of IVM was sterile filtered into a 250 mL glass
bottle and kept refrigerated prior to shipment. The composition
of the formulation was 7.5 w/w% IVM, 40 w/w% of copolymers and 52.5 w/w% of DMSO.
Treatment and follow-up of adverse effects
Four animals (group A) were injected subcutaneously, just
behind the shoulder, with 500 mg IVM, four others (group B)
with 1000 mg IVM, and two others (group C) with the vehicle
only. Injections were made by a veterinarian using a 16-gauge
needle and the volume injected was about 5.8 mL for the
500 mg dose or 2 5.8 mL for the 1000 mg dose (5.8 mL
behind each shoulder). As the animals’ weight was about
250–330 kg, the IVM doses administered in the two treated
groups were 1.5–2.0 mg/kg and 3.0–4.0 mg/kg, respectively.
Upon administration, the initially liquid formulation turned into
a solid depot in the subcutaneous space, where IVM was
released progressively by diffusion through the formed polymeric matrix. Any anomaly at the injection site(s) and relevant
clinical signs (apathy, loss of appetite, tremors, locomotion problems, etc.) were monitored during the three days following the
injection, and then at day 7.
Pharmacokinetics
The blood sampling schedule was the following: in the
vehicle group (group C): pre-dose ( 1 h) and no subsequent
sampling; in the IVM treated groups: pre-dose ( 1 h) and
multiple post-dose sampling (6 h, D2, D7, D14, D30, D90,
D150, D180, D240, D300, D330, and D360).
At each time-point, atleast 4 mL of blood were withdrawn
from the jugular vein or from a vein on the tail and transferred
in ethylenediaminetetraacetic acid (EDTA) tubes to prevent
coagulation. Samples were placed on ice before being
centrifuged.
Blood collection tubes were promptly centrifuged at
2500 g for 10 min at room temperature and plasma was split
in two aliquots of 500 lL in previously labelled polypropylene
tubes (aliquots A and B (back-up sample)). Tubes with plasma
specimens were frozen and stored at 80 °C until being shipped
in dry ice containers to Europe. The samples were analyzed at
the Echevarne Laboratory, Barcelona, Spain, using a liquid
chromatography coupled with tandem mass spectrometry
(LC/MS/MS) method. The bioanalytical method was validated
based on the following criteria (Selectivity, Recovery,
Carry-over, Calibration range and Response function, Limit of
Quantification, Precision and Accuracy, Dilution Integrity,
Matrix effect, Stability in samples, and Reference Solutions
Stability). The Liquid Chromatography system was coupled to
tandem mass spectrometry (Triple Quadrupole) with Electrospray Probe. Specifically, the chromatography was performed
using a Synergi MAX204 RP column (100 Å, 100 3 mm,
3
2.5 lm) and a C18 guard cartridge (4 2 mm). The mobile
phases were: A = 50 mM ammonium acetate (pH 4.5) and
B = acetonitrile. The other conditions were: isocratic elution
A/B (10:90); flow rate: 0.5 mL/min; injection volume: 10 lL;
autosampler temperature: 4 °C; column temperature: 40 °C;
and flush port: methanol. The detection consisted in multiple
reaction monitoring (MRM) in positive mode. IVM was detected
for m/z 892.400 > 307.200. The lower limit of quantification
(LLOQ) for the method used was 0.1 ng of IVM per mL.
The analysis of the pharmacokinetic parameters (mean
Cmax, Tmax, Clast, and AUC0–tlast) was undertaken with the help
of WinNonlin, Phoenix 64, version 8.0 software.
Skin biopsies and nodulectomies
One skin biopsy was collected from each animal just
before the subcutaneous injection (day 0, D0), and another
one after 6, 12, and 24 months (M6, M12, and M24).
Nodulectomies were performed at the same time as skin biopsies
on D0, M6, and M12. To collect these samples, the animals were
put in lateral recumbency, on a mattress, and maintained in this
position with ropes, for a maximum of 1 h. All sample collections were performed by a veterinarian, after shaving of the skin
and under local anaesthesia. Skin biopsies (surface area about
1 cm2) were taken from the area between the udder and the
umbilicus, i.e. where the O. ochengi microfilarial densities are
the highest [44]. Nodules were collected surgically. In some
instances, more than one nodule was collected from a given
animal at a given time-point. Nodules were placed in tubes
containing 10 mL of fixative (10% formalin) until further
processing. After nodulectomy, the wound was sutured and
the animal received an intramuscular injection of antibiotics
(streptomycin and penicillin G) with no action on the
Wolbachia bacterial endosymbionts hosted by filariae. Stitches
were removed after seven days.
Microscopic examination of skin biopsies
The skin biopsies were left to incubate for 24 h at room
temperature in 24-well plates, each well containing 300 lL of
sterile RPMI 1640, and weighed with a 10 mg precision just
before examination. The medium containing the mf which
had emerged during the incubation period was pipetted and
placed on microscopic slides and examined at 40 and 100
magnification. Four species of bovine Onchocerca are present
in North Cameroon (O. ochengi, O. gutturosa, O. dukei, and
O. armillata [44]), and mf were identified according to their
size and aspect [6, 44]. No mf of O. armillata (length: 300–
380 lm; width: 5.0–6.8 lm; characteristic bulging anterior
end) was seen. Microfilariae of the three other species were
observed: O. ochengi (length: 280–300 lm; width: 6–8 lm;
rounded anterior end); O. gutturosa (length: 225–270 lm;
width: 3.5–4.5 lm; rounded anterior end and tapering posterior
end); and O. dukei (length: 220–260 lm; width: 5.0–6.5 lm;
thinner anterior third of the body). Mf of each these three
species were counted by two independent microscopists who
had no information on the treatment received by the animal
from which the biopsy was taken. The individual MFD were
calculated as the arithmetic mean of the two counts and
4
M. Boussinesq et al.: Parasite 2020, 27, 36
expressed as the number of mf per gram of skin. As mf of
O. dukei were seen in only one animal at D0, with a low
MFD (16.0/g), the results presented below distinguish only
O. ochengi mf and “non O. ochengi” (i.e., O. gutturosa +
O. dukei) mf. The MFD in each treatment group were
calculated as the arithmetic means of individual MFD.
Histological processing of nodules and
assessment of worm viability and fertility
The nodules were embedded in paraffin wax, and 6 lm
sections were stained with hematoxylin and eosin. Two of the
authors (MB and SW) examined the sections independently
and without having any information on the treatment arm of
the animals. The nodules collected at each round of nodulectomies were examined separately. When the observers did not
agree on the classification of the worms in a nodule, the slides
were re-examined until a consensus was reached.
The reproductive status of the adult worms was assessed by
the presence of oocytes and of embryos (morulas, coiled mf,
and stretched mf). Live embryos were distinguished from
degenerating ones [14]. Worms with uteri containing live
embryos of any stage were considered fertile.
Figure 1. Plasma concentration-time profiles of IVM following
subcutaneous injection of a long-acting formulation in cattle (N = 4
per group). LLOQ = lower limit of quantification.
Table 1. Mean pharmacokinetic (PK) parameters in the two groups
of animals treated with IVM.
PK parameters
Value
Results
Safety
After injection of the ~5.8 mL of liquid (5.8 mL 2 for
animals treated with 1000 mg IVM), a small bump (diameter:
~1 cm) could be palpated at the injection site. No side effects
were recorded in any of the cows during the follow-up period.
Cmax (ng/mL)
Tmax (days)
Clast (ng/mL)
AUC0–tlast (ng day/mL)
Pharmacokinetics
Following the subcutaneous injection of the long-acting formulation of IVM in cattle, the obtained plasma-concentration
time profiles were characterized by rapid absorption of the drug
associated with a peak plasma concentration (Cmax) followed by
sustained plasma concentrations for at least one year (Fig. 1).
Mean Cmax, Tmax, Clast and AUC0–tlast are presented in
Table 1. As expected, there was a dose-dependent increase in
the mean Cmax and mean AUC0–tlast, the 3–4 mg/kg dose leading to a 2.2 times higher mean Cmax and a 2.5 times higher
mean AUC0–tlast compared to the 1.5–2 mg/kg dose group.
Consequently, steady IVM plasma concentrations were maintained in the range 5.52–10.28 ng/mL between days 90 and
365 for the 3–4 mg/kg dose and 1.65–4.15 ng/mL for the
1.5–2 mg/kg dose in the same period.
Microfilarial densities
The individual and mean MFDs for O. ochengi are shown
in Table 2 and those for non-ochengi Onchocerca are presented
in Table 3. At D0, one of the cows of group B (cow number 3)
did not present O. ochengi mf. After excluding this animal,
the mean O. ochengi MFDs were 367.0 mf/g in the nine
remaining cows (standard deviation [SD] = 398.6), and
Mean
SD
CV (%)
Median
Mean
SD
Mean
SD
Treatment group
500 mg
(1.5–2 mg/kg)
16.3
5.4
33.2
2.00
3.10
1.23
1239
636
1000 mg
(3–4 mg/kg)
36.2
6.9
19.1
0.25
6.02
1.55
3116
581
Cmax = maximum observed plasma concentration; Tmax = time of
maximum observed plasma concentration; Clast = last measurable
concentration (above the quantification limit); AUC0–tlast = area
under the concentration-time curve to the last measurable concentration; SD = standard deviation; CV = coefficient of variation.
471.6 (SD = 540.1), 296.5 (SD = 188.2), and 263.8
(SD = 196.2) mf/g in cows of groups A, B, and C, respectively.
The pre-treatment non-ochengi MFDs were 332.3
(SD = 386.9), 230.9 (SD = 193.9), and 17.3 (SD = 2.6) in
groups A, B, and C, respectively.
The O. ochengi mean MFD increased gradually from D0 to
M24 in animals in group C: 324.5, 850.4, and 1399.0 mf/g at
M6, M12, and M24 (SD = 50.5, 532.9, and 1168.3), respectively. The non-ochengi MFDs in this control group fluctuated
between 33.7 mf/g and 56.7 mf/g.
At M6, no mf (O. ochengi or non-ochengi) was found in the
skin samples taken from the cows treated with IVM. At M12,
only one animal treated with IVM was found positive for
O. ochengi, with only one mf seen in the incubation liquid
(MFD: 0.9 mf/g). The cow was the one that had the highest
pre-treatment MFD and belonged to group A (thus treated with
the “low” dose of IVM). At M24, none of the cows treated with
5
M. Boussinesq et al.: Parasite 2020, 27, 36
Table 2. Onchocerca ochengi MFD per gram of skin in each animal and each treatment group at D0, M6, M12, and M24. Post-treatmentpositive results are shown in bold.
Groupa
A
A
A
A
B
B
B
B
C
C
ID
4
9
28
294
Meanb
3
92
147
255
Meanb
254
256
Meanb
D0
W
0.73
0.34
0.25
0.22
No. Oo
15
177
334
2
0.30
0.18
0.62
0.44
0
6
287
173
0.45
0.37
207
25
M6
MFD Oo
20.5
520.6
1336.0
9.1
471.6
0
33.3
462.9
393.2
296.5
460.0
67.6
263.8
W
0.18
0.31
0.24
0.99
No. Oo
0
0
0
0
0.44
0.30
0.47
0.16
0
0
0
0
0.32
0.50
120
137
M12
MFD Oo
0
0
0
0
0
0
0
0
0
0
375.0
274.0
324.5
W
1.90
1.00
1.10
1.30
No. Oo
0
0
1
0
1.10
1.10
0.30
1.50
0
0
0
0
0.90
0.40
1110
187
M24
MFD Oo
0
0
0.9
0
0.2
0
0
0
0
0
1233.3
467.5
850.4
W
0.92
0.70
0.87
1.47
No. Oo
0
7
0
0
0.32
0.86
1.36
0.13
0
0
0
0
0.52
0.52
120
1335
MFD Oo
0
10.0
0
0
2.5
0
0
0
0
0
230.8
2567.3
1399.0
Abbreviations: ID = animal identity number; W = weight of skin specimen (in grams); No. Oo = total number of microfilariae of Onchocerca
ochengi having emerged from the skin specimen; MFD Oo = O. ochengi microfilarial density per gram of skin.
a
A = 500 mg IVM; B = 1000 mg IVM; C = Control (vehicle only).
b
Arithmetic mean of the individual Onchocerca ochengi microfilarial densities in the group (in group B, the mean was calculated after
excluding animal #3, which did not present O. ochengi microfilariae before treatment).
Table 3. Non-O. ochengi (O. gutturosa and O. dukei) MFD per gram of skin in each animal and each treatment group at D0, M6, M12, and
M24. Post-treatment-positive results are shown in bold.
Groupa
A
A
A
A
B
B
B
B
C
C
ID
4
9
28
294
Meanb
3
92
147
255
Meanb
254
256
Meanb
D0
W
0.73
0.34
0.25
0.22
No. Ogd
2
90
20
216
0.30
0.18
0.62
0.44
11
92
40
137
0.45
0.37
9
5
M6
MFD Ogd
2.7
264.7
80.0
981.8
332.3
36.7
511.1
64.5
311.4
230.9
20.0
14.7
17.3
W
0.18
0.31
0.24
0.99
No. Ogd
0
0
0
0
0.44
0.30
0.47
0.16
0
0
0
0
0.32
0.50
21
7
M12
MFD Ogd
0
0
0
0
0
0
0
0
0
0
65.6
14.0
39.8
W
1.90
1.00
1.10
1.30
No. Ogd
0
0
0
0
1.10
1.10
0.30
1.50
0
0
0
0
0.90
0.40
0
27
M24
MFD Ogd
0
0
0
0
0
0
0
0
0
0
0
67.5
33.7
W
0.92
0.70
0.87
1.47
No. Ogd
0
0
0
0
0.32
0.86
1.36
0.13
0
0
0
0
0.52
0.52
59
0
MFD Ogd
0
0
0
0
0
0
0
0
0
0
113.5
0
56.7
Abbreviations: ID = animal identity number; W = weight of skin specimen (in grams); No. Ogd = total number of microfilariae of Onchocerca
gutturosa or O. dukei having emerged from the skin specimen; MFD Ogd = O. gutturosa + O. dukei microfilarial density per gram of skin.
a
A = 500 mg IVM; B = 1000 mg IVM; C = Control (vehicle only).
b
Arithmetic mean of the individual Onchocerca ochengi microfilarial densities in the group.
IVM showed non-ochengi skin mf but, again, one cow in group
A showed O. ochengi mf (MFD: 10.0 mf/g). This cow was the
one that had the second highest pre-treatment MFD: 520.6 mf/g.
The cow found positive at M12 was negative at M24.
Reproductive status and viability of adult worms
Sixteen nodules containing 24 female worms were collected
on D0, just before treatment. Six of the females (25%) contained live embryos in their uteri and were thus considered
fertile, and 19 (79.2%) contained live embryos or oocytes and
were thus fertile or potentially fertile (results in Table 4). Similar percentages (29.0 and 74.2%, respectively) were obtained by
combining all the untreated female worms (thus including the
worms collected at M6 and M12 from animals in group C).
On M6 and M12, none of the female worms collected from
the treated groups (N = 11 on M6 and 13 on M12) contained
live embryos in their uteri. The proportion of potentially fertile
females (shedding oocytes), which was fairly high on M6 in the
treated groups (90.9%), decreased to 38.5% at M12.
During the course of this study, no dead female worms
were observed in the treated groups of cows at M6 and M12
M. Boussinesq et al.: Parasite 2020, 27, 36
6
Table 4. Results of the histological examination of nodules.
Time point
D0
M6
M12
M6
M12
All naïve
wormsb
a
b
Treatment
No.
group(s)a nodules
A
6
B
6
C
5
A+B+C
16
A
7
B
5
C
3
A
8
B
7
C
5
A+B
12
A+B
15
24
No. female
worms
12
7
5
24
6
5
1
8
5
6
11
13
31
No.
fertile
1
2
3
6
0
0
1
0
0
2
0
0
9
No. shedding
oocytes
8
3
2
13
5
5
0
3
2
1
10
5
14
No.
empty
2
1
0
3
1
0
0
5
3
1
1
8
4
No.
dead
1
1
0
2
0
0
0
0
0
2
0
0
4
% fertile
females
8.3
28.6
60.0
25.0
0
0
100
0
0
33.3
0
0
29.0
% worms fertile
or shedding oocytes
75.0
71.4
100
79.2
83.3
100
100
37.5
40.0
50.0
90.9
38.5
74.2
A = 500 mg IVM; B = 1000 mg IVM; C = control (vehicle only).
All worms (groups A, B, and C) collected at D0 and worms in group C collected at M6 and M12.
(total number of females observed at these time-points: N = 11
and N = 13, respectively). Conversely, 4 of the 31 untreated
female worms (worms observed at D0 in nodules collected
from the three groups, plus worms observed at M6 and M12
in nodules from group C) were dead (12.9%). These results
suggest that the subcutaneous injectable long-acting formulation of IVM did not have a detectable macrofilaricidal effect
on the adult worms.
Male worms were not counted because their numbers were
very low in the examined histologic sections. In addition, some
sections were of sub-optimal quality and enabled only assessment of female worms.
Discussion
Wahl et al. [44] assessed the anatomic distribution of
O. ochengi mf in the hide of eight cows infected with this parasite. At the sites of highest concentration (near the umbilicus
and in the inguinal region) the MFD recorded after 4-h incubation in RPMI was 221 mf/g. As the MFD increases by 1.5–2.0
when the incubation time increases from 4 h to 24 h [44], this
MFD was similar to that recorded during the present study
(367.0 mf/g).
Our results show that the in-situ forming depot containing
IVM used in this study maintained the Onchocerca sp. mf at
extremely low levels for two years. None of the cows treated
with IVM presented skin mf at M6, and only one was mfpositive at M12 (with 0.9 mf/g), and another at M24 (with
10.0 mf/g). Both the cows with post-treatment-positive biopsies
had been treated with the low dose (500 mg) of IVM. These
results were obtained by examining a single fairly large biopsy
(180–730 mg), and not smaller biopsies (mean weight: 54 mg)
taken from three different sites, as done in another study [36].
By doing so (mainly to limit the time the animals were held
down in an uncomfortable position), we could not account for
variation in MFD in the skin [44], but given the considerable
decrease in the MFD observed in the IVM-treated animals, the
results would have probably been similar by examining more
than one biopsy.
Interestingly, in cows in group C, the MFD increased gradually from D0 to M24, both for O. ochengi (from 264 mf/g
to 1399 mf/g) and non-O. ochengi (from 17.3 mf/g to
56.7 mf/g). As the REFOTDE field research station is located
in an area where there is probably no transmission of bovine
Onchocerca spp., this increase might be due to the fact that
pre-adult or young adult stages which were present at D0 developed during the following two years to adult worms producing
mf. This increase in the MFD in group C makes the persistent
absence of mf for two years in most of the cows in groups A
and B even more remarkable.
The possibility that the decrease in the MFD could be due,
at last partly, to other treatments received by the animals before
their departure from the Adamaoua region has to be considered.
Even though little quantitative information is available on the
veterinary drug market in this area, it is known that levamisole,
albendazole and IVM are widely used by cattle herders to treat
intestinal nematode infections in their animals [20]. Levamisole
has no significant effect on the microfilariae and macrofilariae
of O. volvulus [3], and this is probably also the case for
O. ochengi. A single dose of albendazole (400 mg) has little
effect on the O. volvulus MFD and adult-worm reproductive
activity [5], but treatment with 800 mg daily for three or seven
days, or with 1200 mg daily for three days leads to a gradual
decrease in the MFDs, which are reduced by 24–66% one year
after treatment [4]; the latter regimens have no macrofilaricidal
effect, and the effect on the MFD is due to an embryotoxic
effect (i.e., preventing the embryos from developing in the uteri
to the stretched mf stage). Regarding IVM, it is known that
O. volvulus MFDs are reduced by 99% of pre-treatment levels
1–2 months after treatment, and then re-increase progressively
[8]. As the dynamics are probably similar for O. ochengi
[36], if the drug had been given just before the animals’ departure from the Adamaoua region, then the O. ochengi MFD
would have been close to their nadir when the cows underwent
pre-treatment biopsy six weeks later. As most of the study
M. Boussinesq et al.: Parasite 2020, 27, 36
animals showed significant O. ochengi or non-ochengi MFD at
that time, we can assume that they had not been treated with
IVM recently; and should this be the case, then such treatment
could not explain the subsequent decrease in the MFD. These
considerations, together with the fact that the substantial
decrease in the MFD was seen only in those cows that received
IVM, lead us to believe that any treatment received by the animals before the study had only a minimal influence, if any, on
the results observed.
The prolonged effect of the formulation on the MFD could
be due to an embryotoxic (see above) and/or an embryostatic
effect (preventing the release of mf from the adult female
worms), and/or a persisting microfilaricidal effect (destruction
of the mf after their release from the females’ uteri), and/or a
macrofilaricidal effect (killing of the adult worms). As the main
objective of the study was to investigate the effects of the formulation on the adult worms, we did not collect skin samples
within the first weeks following treatment to evaluate the (probable) microfilaricidal effect. The histologic examination of
nodules collected at M6 and M12 provided information on
the effects of the formulation on the adult worms’ viability
and reproductive status. This showed that all the female worms
collected at M6 and M12 from the cows treated with IVM were
alive, showing that the formulation had no macrofilaricidal
effect. These results are similar to those obtained, also using
the bovine-O. ochengi model, with repeated monthly doses of
subcutaneous IVM at 500 lg/kg [12]. However, the females
from animals treated with IVM did not contain live embryos
in their uteri, demonstrating that the treatment had a strong
effect on the parasite’s fertility. In addition, the fact that the proportion of worms shedding oocytes decreased markedly
between M6 and M12 suggests that permanent exposure to
IVM for one year might sterilize the worms. No nodules were
collected at M24, but the fact that one (and only one) cow treated with IVM showed skin mf at that time-point suggests that
the condition of the worms at M24 was probably similar to that
observed at M12.
Given these results, one may wonder what role the in-situ
forming depot evaluated as part of this study could play to
accelerate the elimination of human onchocerciasis, and thus
whether it would be worth assessing this formulation in phase
1 clinical trials. The long-term effect of the IVM-releasing
depot on O. ochengi MFD was remarkable and a comparable
effect would probably be obtained with O. volvulus. However,
a similar effect on the MFD, and thus on the transmission of
O. volvulus, could be obtained with annual oral treatment with
moxidectin (MOX), a drug whose plasma half-life is 20–43
days, i.e. much longer than that of IVM (12–56 h) [35]. The
question to be answered is “what would be the advantage of
treating with an injectable long-acting formulation of IVM,
instead of annual oral doses of MOX?” As IVM seems to have
a prophylactic effect on Onchocerca sp. [40, 42], i.e. prevents
the development of the parasite up to the adult stage, a sustained-release formulation might protect people from new infections for many months. A solid implant containing IVM was
shown to be effective in preventing experimental infection of
dogs with Dirofilaria immitis larvae [18]. The prophylactic
effect of MOX on Onchocerca sp. is unknown. Injectable
long-acting formulations of MOX (ProHeart 6 and ProHeart 12)
7
are used to prevent canine infection with D. immitis [34] but,
given the half-life of the drug, oral treatment with MOX would
probably need to be repeated every 2–3 months to have any
prophylactic effect against O. volvulus. In this case, an IVMcontaining subcutaneous depot might be advantageous. The
prophylactic effect of an injectable long-acting formulation of
IVM on O. ochengi could be tested using the same protocol
as that used for IVM [42], i.e. by comparing the incidence of
infection in two groups of calves living in an area where the
parasite is transmitted, one treated with the IVM formulation,
and one receiving only the vehicle.
In addition, macrocyclic lactones like IVM and MOX are
also effective against soil-transmitted helminths (STH) and
ectoparasites such as scabies and lice [7]. A yearly single subcutaneous injection of a long-acting formulation of IVM might
be as efficient to prevent clinical manifestations of STH as
two- or three-monthly doses of MOX. Regarding scabies, in
vitro assays suggest that the concentration of MOX required
to kill the mites might be lower than that of IVM [33], and trials
using a porcine model suggest that a single oral dose of MOX is
more effective than two consecutive IVM doses [10]. Collateral
benefits of a sustained-release formulation of IVM would also
include an effect on the longevity of mosquitoes and other
insects biting treated people. Studies are being conducted to
develop long-acting formulations of IVM that could help
decrease the density of Anopheles sp. and thus the transmission
of malaria, and an oral ultra-long-acting drug delivery system
containing IVM was developed to reach this objective [9].
A subcutaneous IVM-releasing depot could have the same
effect, with the significant advantage of showing sustained
release over up to a year. In addition, when the malaria vectors
are zoophagic, treatment of cattle could play a significant role
toward reducing vector density, and thus malaria transmission
[16]. Conversely, repeated doses of MOX might well have little
impact on malaria transmission because MOX seems to be less
active than IVM on malaria vectors [13, 21].
The fact that the long-acting formulation of IVM used as
part of this study does not seem to be macrofilaricidal for
O. volvulus is disappointing. However, it seems to sterilize
the female worms, and this, added to other effects against
soil-transmitted helminths and some ectoparasites and vectors
of serious diseases like malaria, makes the concept of a longacting formulation of IVM a potentially highly valuable alternative to the existing methods, including the use of oral IVM
(and/or MOX) tablets.
Of course, any decision regarding treatment with longacting formulations has to be taken considering possible risks
associated with long-term exposure to these drugs. For IVM
long-acting formulations, one of the risks is the possible
accelerated selection of IVM-resistant parasites, including
Onchocerca sp. or intestinal nematodes [39]. Studies have suggested that the embryostatic effect of IVM against O. volvulus
could be reduced in populations treated repeatedly with IVM,
but this phenomenon might not be due to genetic selection,
but to other processes that remain to be clarified [19]. Regarding intestinal nematodes, the risk of resistance is certainly
higher than for filariae, but it could be prevented by treating
the host simultaneously with another anthelmintic such as a
benzimidazole. The second point to consider is the management
8
M. Boussinesq et al.: Parasite 2020, 27, 36
of drug-drug interactions (DDIs) in subjects already treated
with another drug, or who have to start treatment with another
drug after injection of the IVM long-acting formulation.
A review of the interactions of IVM (and other macrocyclic
lactones) with ATP-binding cassette transporters suggests that
co-administration of IVM with drugs such as the antifungal
drug ketoconazole, the antihypertensive, and antiarrhythmic
drug verapamil, or the anti-diarrheal drug loperamide can
increase the IVM AUC by 2-fold [31]. In addition, in vitro or
animal model studies suggest possible DDIs between IVM
and antibiotics or antiretroviral drugs, and further investigations
should be conducted to investigate the possibility of in vivo
interactions in humans [28]. This being said, one must recall
here that the depot formed by the IVM-long acting formulation
used as part of this study can be easily removed if necessary, to
prevent adverse effects due to DDIs.
Presently, the major indications for subcutaneous implantable devices or injectable long-acting formulations in humans
include contraception (implants containing levonorgestrel or
etonogestrel or in-situ formed depots containing medroxyprogesterone acetate (MPA)), treatment of schizophrenia (in-situ
formed depot containing risperidone), treatment of prostate cancer (implants or depot containing goserelin, leuprolide, or histrelin), and treatment of opioid abuse (in-situ formed depot
containing buprenorphine) [38]. SayanaÒ Press, a formulation
containing 104 mg MPA in a 0.65 mL suspension and which
can be injected subcutaneously by trained community health
workers or self-injected, is a very popular family planning
method in Africa [17]. More than one million doses have been
used so far. It would certainly be useful to conduct socioanthropologic studies in population where onchocerciasis and
malaria are endemic to evaluate the acceptability of a subcutaneous injection of a long-acting formulation of IVM that is fully
bioresorbable and would therefore not require depot removal
upon completion of the release period.
Conflicts of interest
The patent related to the formulation used during this study
belongs to MedinCell S.A. There is no conflict of interest
between the co-authors and present or past affiliation with
MedinCell and the co-authors affiliated at the Institut de
Recherche pour le Développement (IRD) and the Research
Foundation for Tropical Diseases and the Environment
(REFODTE). Co-authors affiliated with IRD or REFODTE
have no specific interest (i.e., shares) or commercial relationship
(i.e., consulting) with MedinCell. In the event of a commercial
development of the long-acting formulation of IVM described
in the present publication, MedinCell would benefit from the
outcomes of the present study. However, the co-authors with
present or past affiliation at MedinCell did not contribute to
the examination of the skin samples or the onchocercal nodules
collected as part of this study, nor to the data analysis and interpretation of results.
Acknowledgements. This study was co-funded by the Institut de
Recherche pour le Développement (IRD, Marseille, France),
MedinCell (Jacou, France) and the Research Foundation for Tropical
Diseases and the Environment (REFOTDE, Buea, Cameroon).
We thank the REFOTDE personnel for their help in the field, as well
as Dr. Elizabeth Hene, veterinarian, and Lucy Enow and Emilia
Ayompe, veterinary assistants, for having performed the skin snips
and the nodulectomies of the animals. We thank the personnel of
the Echevarne Laboratory, Barcelona, Spain, for having performed
the pharmacokinetic analyses.
References
1. An G, Murry DJ, Gajurel K, Bach T, Deye G, Stebounova LV,
Codd EE, Horton J, Gonzalez AE, Garcia HH, Ince D,
Hodgson-Zingman D, Nomicos EYH, Conrad T, Kennedy J,
Jones W, Gilman RH, Winokur P. 2019. Pharmacokinetics,
safety, and tolerability of oxfendazole in healthy volunteers: a
randomized, placebo-controlled first-in-human single-dose
Escalation Study. Antimicrobial Agents and Chemotherapy,
63, e02255-18.
2. Assana E, Doba E, Awah-Ndukum J, Soh GB, Mohamadou A,
Mebanga AS, Zoli AP. 2018. Formule de barymétrie pour
l’estimation du poids chez les zébus Goudali au Cameroun.
Bulletin of Animal Health and Production in Africa, 66, 469–480.
3. Awadzi K, Schulz-Key H, Howells RE, Haddock DR, Gilles
HM. 1982. The chemotherapy of onchocerciasis. VIII. Levamisole and its combination with the benzimidazoles. Annals of
Tropical Medicine and Parasitology, 76, 459–473.
4. Awadzi K, Hero M, Opoku O, Büttner DW, Gilles HM. 1991.
The chemotherapy of onchocerciasis. XV. Studies with
albendazole. Tropical Medicine and Parasitology, 42, 356–360.
5. Awadzi K, Edwards G, Duke BO, Opoku NO, Attah SK, Addy
ET, Ardrey AE, Quartey BT. 2003. The co-administration of
ivermectin and albendazole – safety, pharmacokinetics and
efficacy against Onchocerca volvulus. Annals of Tropical
Medicine and Parasitology, 97, 165–178.
6. Bain O. 1981. Le genre Onchocerca : hypothèses sur son
évolution et clé dichotomique des espèces. Annales de
Parasitologie Humaine et Comparée, 56, 503–526.
7. Barda B, Ame SM, Ali SM, Albonico M, Puchkov M,
Huwyler J, Hattendorf J, Keiser J. 2018. Efficacy and
tolerability of moxidectin alone and in co-administration with
albendazole and tribendimidine versus albendazole plus oxantel
pamoate against Trichuris trichiura infections: a randomised,
non-inferiority, single-blind trial. Lancet Infectious Diseases,
18, 864–873.
8. Basáñez MG, Pion SD, Boakes E, Filipe JA, Churcher TS,
Boussinesq M. 2008. Effect of single-dose ivermectin on
Onchocerca volvulus: a systematic review and meta-analysis.
Lancet Infectious Diseases, 8, 310–322.
9. Bellinger AM, Jafari M, Grant TM, Zhang S, Slater HC, Wenger
EA, Mo S, Lee YL, Mazdiyasni H, Kogan L, Barman R,
Cleveland C, Booth L, Bensel T, Minahan D, Hurowitz HM, Tai
T, Daily J, Nikolic B, Wood L, Eckhoff PA, Langer R, Traverso
G. 2016. Oral, ultra-long-lasting drug delivery: application
toward malaria elimination goals. Science Translational Medicine, 8, 365ra157.
10. Bernigaud C, Fang F, Fischer K, Lespine A, Aho LS,
Dreau D, Kelly A, Sutra JF, Moreau F, Lilin T, Botterel F,
Guillot J, Chosidow O. 2016. Preclinical study of single-dose
moxidectin, a new oral treatment for scabies: efficacy, safety,
and pharmacokinetics compared to two-dose ivermectin in a
porcine model. PLoS Neglected Tropical Diseases, 10,
e0005030.
11. Boussinesq M, Fobi G, Kuesel AC. 2018. Alternative treatment
strategies to accelerate the elimination of onchocerciasis.
International Health, 10(Suppl. 1), i40–i48.
M. Boussinesq et al.: Parasite 2020, 27, 36
12. Bronsvoort BM, Renz A, Tchakouté V, Tanya VN, Ekale D,
Trees AJ. 2005. Repeated high doses of avermectins cause
prolonged sterilisation, but do not kill, Onchocerca ochengi
adult worms in African cattle. Filaria Journal, 4, 8.
13. Butters MP, Kobylinski KC, Deus KM, da Silva IM, Gray M,
Sylla M, Foy BD. 2012. Comparative evaluation of systemic
drugs for their effects against Anopheles gambiae. Acta Tropica,
121, 34–43.
14. Büttner DW, Albiez EJ, von Essen J, Erichsen J. 1988.
Histological examination of adult Onchocerca volvulus and
comparison with the collagenase technique. Tropical Medicine
and Parasitology, 39(Suppl. 4), 390–417.
15. Cady SM, Cheifetz PM, Galeska I. 2013. Veterinary long-acting
injections and implants, in Long Acting Animal Health Drug
Products, Rathborne MJ, McDowell A, Editors. Springer:
Boston, MA. p. 271–294.
16. Chaccour CJ, Ngha’bi K, Abizanda G, Irigoyen Barrio A,
Aldaz A, Okumu F, Slater H, Del Pozo JL, Killeen G. 2018.
Targeting cattle for malaria elimination: marked reduction of
Anopheles arabiensis survival for over six months using a slowrelease ivermectin implant formulation. Parasites and Vectors,
11, 287.
17. Cover J, Blanton E, Ndiaye D, Walugembe F, Lamontagne DS.
2014. Operational assessments of SayanaÒ Press provision in
Senegal and Uganda. Contraception, 89, 374–378.
18. Cunningham CP, Brown JM, Jacobson GA, Brandon MR,
Martinod SR. 2006. Evaluation of a covered-rod silicone
implant containing ivermectin for long-term prevention of
heartworm infection in dogs. American Journal of Veterinary
Research, 67, 1564–1569.
19. Doyle SR, Bourguinat C, Nana-Djeunga HC, Kengne-Ouafo
JA, Pion SDS, Bopda J, Kamgno J, Wanji S, Che H, Kuesel
AC, Walker M, Basáñez MG, Boakye DA, Osei-Atweneboana
MY, Boussinesq M, Prichard RK, Grant WN. 2017. Genomewide analysis of ivermectin response by Onchocerca volvulus
reveals that genetic drift and soft selective sweeps contribute to
loss of drug sensitivity. PLoS Neglected Tropical Diseases, 11,
e0005816.
20. Ebene Njongui J, Onyali Ikechuku O, Mingoas JP, Mfopit
Mouliom Y, Aboubakar Dandjouma AK, Manchang TK,
Toukala JP, Akuro A, Nwosu CO. 2016. Management of cattle
parasitism and use of anthelmintics in mixed farming systems in
the Vina Division, Cameroon. International Journal of Livestock
Research, 6, 59–72.
21. Fritz ML, Walker ED, Miller JR. 2012. Lethal and sublethal
effects of avermectin/milbemycin parasiticides on the African
malaria vector, Anopheles arabiensis. Journal of Medical
Entomology, 49, 326–331.
22. Gardon J, Boussinesq M, Kamgno J, Gardon-Wendel N,
Demanga-Ngangue Duke BO. 2002. Effects of standard and
high doses of ivermectin on adult worms of Onchocerca
volvulus: a randomised controlled trial. Lancet, 360, 203–210.
23. Gaudriault G, Inventor. 2011. Biodegradable drug delivery
compositions. US Patent 9,023,897 B2.
24. Gillon JYA, van den Berg F, Dequatre Cheeseman K,
Hopchet N, Delhomme S, Peña Rossi C, Monnot F, StrubWourgaft N, Rodriguez ML, Don R. 2018. A single-center,
first-in-human, randomized, double-blind, placebo-controlled,
parallel-group study to investigate the safety, tolerability and
pharmacokinetics of escalading doses of emodepside (BAY444400) in healthy male subjects. American Journal of Tropical
Medicine and Hygiene, 99(Suppl. 4), 168.
25. Gonzalez AE, Codd EE, Horton J, Garcia HH, Gilman RH.
2019. Oxfendazole: a promising agent for the treatment and
control of helminth infections in humans. Expert Review of
Anti-Infective Therapy, 17, 51–56.
9
26. Guzzo CA, Furtek CI, Porras AG, Chen C, Tipping R,
Clineschmidt CM, Sciberras DG, Hsieh JY, Lasseter KC.
2002. Safety, tolerability, and pharmacokinetics of escalating
high doses of ivermectin in healthy adult subjects. Journal of
Clinical Pharmacology, 42, 1122–1133.
27. Hübner MP, Martin C, Specht S, Koschel M, Dubben B,
Frohberger SJ, Ehrens A, Fendler M, Struever D, VallarinoLhermitte N, Gokool S, Townson S, Hoerauf A, Scandale I.
2018. Oxfendazole treatment has a macrofilaricidal efficacy
against the filarial nematode Litomosoides sigmodontis in vivo
and inhibits Onchocerca gutturosa adult worm motility in
vitro. American Journal of Tropical Medicine and Hygiene,
99(Suppl. 4), 656–657.
28. Kigen G, Edwards G. 2017. Drug-transporter mediated interactions between anthelminthic and antiretroviral drugs across the
Caco-2 cell monolayers. BMC Pharmacology and Toxicology,
18, 20.
29. Kulke D, Townson S, Bloemker D, Frohberger S, Specht S,
Scandale I, Glenschek-Sieberth M, Harder A, Hoerauf A,
Hübner MP. 2017. Comparison of the in vitro susceptibility to
emodepside of microfilariae, third stage larvae and adult worms
of related filarial nematodes. American Journal of Tropical
Medicine and Hygiene, 97(Suppl. 5), 563.
30. Lachau-Durand S, Lammens L, van der Leede BJ, Van Gompel J,
Bailey G, Engelen M, Lampo A. 2019. Preclinical toxicity and
pharmacokinetics of a new orally bioavailable flubendazole
formulation and the impact for clinical trials and risk/benefit to
patients. PLoS Neglected Tropical Diseases, 13, e0007026.
31. Lespine A, Alvinerie M, Vercruysse J, Prichard RK, Geldhof P.
2008. ABC transporter modulation: a strategy to enhance the
activity of macrocyclic lactone anthelmintics. Trends in
Parasitology, 24, 293–298.
32. Makepeace BL, Tanya VN. 2016. 25 years of the Onchocerca
ochengi model. Trends in Parasitology, 32, 966–978.
33. Mounsey KE, Walton SF, Innes A, Cash-Deans S, McCarthy JS.
2017. In vitro efficacy of moxidectin versus ivermectin against
Sarcoptes scabiei. Antimicrobial Agents and Chemotherapy, 61,
e00381-17.
34. Nolan TJ, Lok JB. 2012. Macrocyclic lactones in the treatment
and control of parasitism in small companion animals. Current
Pharmaceutical Biotechnology, 13, 1078–1094.
35. Opoku NO, Bakajika DK, Kanza EM, Howard H, Mambandu
GL, Nyathirombo A, Nigo MM, Kasonia K, Masembe SL,
Mumbere M, Kataliko K, Larbelee JP, Kpawor M, Bolay KM,
Bolay F, Asare S, Attah SK, Olipoh G, Vaillant M, Halleux
CM, Kuesel AC. 2018. Single dose moxidectin versus
ivermectin for Onchocerca volvulus infection in Ghana, Liberia,
and the Democratic Republic of the Congo: a randomised,
controlled, double-blind phase 3 trial. Lancet, 392, 1207–1216.
36. Renz A, Trees AJ, Achu-Kwi D, Edwards G, Wahl G. 1995.
Evaluation of suramin, ivermectin and CGP 20376 in a new
macrofilaricidal drug screen, Onchocerca ochengi in African
cattle. Tropical Medicine and Parasitology, 46, 31–37.
37. Roberge C, Cros JM, Serindoux J, Cagnon ME, Samuel R,
Vrlinic T, Berto P, Rech A, Richard J, Lopez-Noriega A. 2020.
BEPOÒ: bioresorbable diblock mPEG-PDLLA and triblock
PDLLA-PEG-PDLLA based in situ forming depots with
flexible drug delivery kinetics modulation. Journal of Controlled Release, 319, 416–427.
38. Stewart S, Domínguez-Robles J, Donnelly R, Larrañeta E. 2018.
Implantable polymeric drug delivery devices: classification,
manufacture, materials, and clinical applications. Polymers, 10,
1379.
39. Sutherland IA, Leathwick DM. 2011. Anthelmintic resistance in
nematode parasites of cattle: a global issue? Trends in
Parasitology, 27, 176–181.
10
M. Boussinesq et al.: Parasite 2020, 27, 36
40. Taylor HR, Trpis M, Cupp EW, Brotman B, Newland HS,
Soboslay PT, Greene BM. 1988. Ivermectin prophylaxis against
experimental Onchocerca volvulus infection in chimpanzees.
American Journal of Tropical Medicine and Hygiene, 39, 86–90.
41. Taylor MJ, von Geldern TW, Ford L, Hübner MP, Marsh K,
Johnston KL, Sjoberg HT, Specht S, Pionnier N, Tyrer HE,
Clare RH, Cook DAN, Murphy E, Steven A, Archer J,
Bloemker D, Lenz F, Koschel M, Ehrens A, Metuge HM,
Chunda VC, Ndongmo Chounna PW, Njouendou AJ, Fombad
FF, Carr R, Morton HE, Aljayyoussi G, Hoerauf A, Wanji S,
Kempf DJ, Turner JD, Ward SA. 2019. Preclinical development
of an oral anti-Wolbachia macrolide drug for the treatment of
lymphatic filariasis and onchocerciasis. Science Translational
Medicine, 11, eaau2086.
42. Tchakouté VL, Bronsvoort M, Tanya V, Renz A, Trees AJ.
1999. Chemoprophylaxis of Onchocerca infections: in a
controlled, prospective study ivermectin prevents calves becoming infected with O. ochengi. Parasitology, 118(Pt 2), 195–199.
43. von Geldern TW, Morton HE, Clark RF, Brown BS, Johnston
KL, Ford L, Specht S, Carr RA, Stolarik DF, Ma J, Rieser MJ,
Struever D, Frohberger SJ, Koschel M, Ehrens A, Turner JD,
Hübner MP, Hoerauf A, Taylor MJ, Ward SA, Marsh K, Kempf
DJ. 2019. Discovery of ABBV-4083, a novel analog of Tylosin
44.
45.
46.
47.
48.
A that has potent anti-Wolbachia and anti-filarial activity. PLoS
Neglected Tropical Diseases, 13, e0007159.
Wahl G, Achu-Kwi MD, Mbah D, Dawa O, Renz A. 1994.
Bovine onchocercosis in North Cameroon. Veterinary Parasitology, 52, 297–311.
Walker M, Specht S, Churcher TS, Hoerauf A, Taylor MJ,
Basáñez MG. 2015. Therapeutic efficacy and macrofilaricidal
activity of doxycycline for the treatment of river blindness.
Clinical Infectious Diseases, 60, 1199–1207.
Walker M, Pion SDS, Fang H, Gardon J, Kamgno J, Basáñez
MG, Boussinesq M. 2017. Macrofilaricidal efficacy of repeated
doses of ivermectin for the treatment of river blindness. Clinical
Infectious Diseases, 65, 2026–2034.
World Health Organization. 2012. Accelerating work to overcome the global impact of neglected tropical diseases: a
roadmap for implementation: executive summary. Geneva:
World Health Organization. WHO/HTM/NTD/2012.1.
Zahner H, Schares G. 1993. Experimental chemotherapy of
filariasis: comparative evaluation of the efficacy of filaricidal
compounds in Mastomys coucha infected with Litomosoides
carinii, Acanthocheilonema viteae, Brugia malayi and
B. pahangi. Acta Tropica, 52, 221–266.
Cite this article as: Boussinesq M, Enyong P, Chounna-Ndongmo P, Njouendou A-J, Pion SD, Rech A, Roberge C, Gaudriault G &
Wanji S. 2020. Effects of an injectable long-acting formulation of ivermectin on Onchocerca ochengi in zebu cattle. Parasite 27, 36.
An international open-access, peer-reviewed, online journal publishing high quality papers
on all aspects of human and animal parasitology
Reviews, articles and short notes may be submitted. Fields include, but are not limited to: general, medical and veterinary parasitology;
morphology, including ultrastructure; parasite systematics, including entomology, acarology, helminthology and protistology, and molecular
analyses; molecular biology and biochemistry; immunology of parasitic diseases; host-parasite relationships; ecology and life history of
parasites; epidemiology; therapeutics; new diagnostic tools.
All papers in Parasite are published in English. Manuscripts should have a broad interest and must not have been published or submitted
elsewhere. No limit is imposed on the length of manuscripts.
Parasite (open-access) continues Parasite (print and online editions, 1994-2012) and Annales de Parasitologie Humaine et Comparée
(1923-1993) and is the official journal of the Société Française de Parasitologie.
Editor-in-Chief:
Jean-Lou Justine, Paris
Submit your manuscript at
http://parasite.edmgr.com/