Acta vet. scand. 2001, Suppl. 94, 31-42.
Disease Surveillance Strategies in Swine
By E. Rautiainen1, K. Konradsson2, B. Lium3, S. Mortensen4, P. Wallgren5
1National
Veterinary and Food Research Institute, Regional Laboratory in Seinäjoki, P.O. Box 198, FIN-60101
Seinäjoki, Finland, 2Tilraunastod Haskola Islands, Keldum v/ Vesturlandsveg, IL-110 Reykjavik, Iceland, 3Norwegian Pig Health Service, Veterinærinstituttet, Boks 8156 dep., N-0033 Oslo, Norway, 4Danish Slaughterhouses, Axelborg, Axeltorv 3, DK-1609 Copenhagen V, Denmark, 5National Veterinary Institute, P.O. Box 7073,
SE-75007 Uppsala, Sweden.
Pig production systems in the Nordic countries
The volume and the structure of pig production
in different Nordic countries is described in
table 1. The volume of the production is clearly
largest in Denmark countries, and 80% of the
Danish production is exported. The infrastructure in Denmark and Sweden is similar with respect to the proportional number of nucleus and
multiplying herds. Finland and Norway still
have a relatively high number of nucleus herds.
The pig population in Iceland is minor, excluding nucleus or multiplying herds. There is no
export of pigs or pig products from Iceland.
Therefore no official disease surveillance programs have existed until today. However, import of pigs to Iceland has been very strictly
ruled. The latest imports took place in 1994 and
1996 from Norway and Finland, respectively. It
is believed that the health status of Icelandic
pigs is similar to that of Norway and Finland.
Random sampling of pigs from the majority of
herds during 1993-1999 supports that suggestion with respect to the epidemic pig diseases.
National surveillance systems of List A and
List B diseases (OIE)
Today, all Nordic countries are considered free
from Aujeszky´s disease (AD), transmissible
gastroenteritis (TGE), classical swine fever
(CSF), and swine vesicular disease (SVD). The
aim of the surveillance for these diseases is to
document freedom from disease within the national pig populations. The numbers of samples
analysed annually for these diseases, and the
strategies for collection are shown in table 2.
Table 1. Approximate numbers of different kinds of pig herds, total number of sows and annual number of pigs slaughtered
in Nordic countries in 1998.
Denmark
Nucleus herds
Multiplying herds
Conventional herds
- farrowing
- farrowing-to-finishing
- finishing
- sow pool systems
Total no. of sows (thousands)
Annual no. of pigs
Slaughtered (mill.)
Sweden
60
230
40
150
2.800
5.500
10.000
1.000
5.100
760
5.800
30
274
21
3.9
Finland
150
20
2.300
1.400
1.800
8
185a
2.2
Norway
110b
Iceland
85
-
500
3.400
2.000
1
65
54
4
1.3
0.065
a
Gilts older than 200 days of age included
b Aspirant herds included
Acta vet. scand. Suppl. 94 - 2001
32
Table 2. Approximate numbers of annual surveillane samples analysed for serum antibodies to the
causative agents of Aujeszky´s disease (AD), transmissble gastroenteritis (TGE), classical swine fever
(CSF), and swine vesicular disease (SVD) in Nordic
countries. In 1998, these countries were considered
free of all these disease.
AD
TGE
CSF
SVD
a
b
c
d
e
Denmark
Sweden
Finland
Norway
30.000a
1.500e
30.000
3.000
5.000b
3.000
3.000
3.000
9.800c
9.800
2.900
2.600
4.700d
4.700
-
A systematic sample comprising 10% of boars and 5% of
sows slaughtered or exported for slaughter; in border areas
all boars and 10 % of sows intended for slaughter are sampled.
A systematic sample from slaughtered sows and fatteners.
The sample comprises all boars slaughtered annually, all
sows slaughtered during April and May (corresponding to
10% of total sows slaughtered), and a systematic sample
(n=3000) from fatteners.
All elite breeding and multiplying herds (n=200), and a
stratified random selection (n=290; fattening herds Underrepresented) of the rest of the pig herds are tested; samples
are collected first and foremost from sows.
Samples from exported live animals.
AD has never been reported in Finland, Norway
and Iceland. Denmark and Sweden have eradicated the disease in 1991 and 1996, respectively. The AD free status has been confirmed
by the EU commission and by the EFTA´s Supervisory Authority (Norway). An annual
surveillance for the disease are required in each
country.
TGE has never been reported in Denmark, Sweden, Norway or Iceland. In Finland, two cases
of TGE of foreign origin were found in 1981.
The infection was immediately eradicated. Finland and Norway have been granted additional
guarantees relating to TGE by the EFTA´s Supervisory Authority. These decisions require an
annual surveillance of the disease and reporting
of the results.
The surveillance for CSF and SVD in Denmark, Sweden, and Finland is based on deciActa vet. scand. Suppl. 94 - 2001
sions of the EU commission.
Salmonella infections in pig
Denmark
Aim of the surveillance and organisation
The aim of the Danish Salmonella surveillance
program is to reduce the prevalence of
Salmonella in slaughter pig herds and pork.
Target population includes all herds producing
more than 100 slaughter pigs per year. The
number of such herds is about 16000. A permanent program, launched by the Danish Ministry of Agriculture, was established in 1995.
The compulsory program is administered by
the Danish Meat and Bacon Council.
In addition to surveillance and control of
Salmonella in breeding and multiplying herds
and in finishing herds, the program involves
control of Salmonella in feed stuffs, and control
measures at the abattoirs. These parts of the
program are beyond the scope of this paper.
Sampling
Meat juice samples are collected at random
from each herd participating in the program.
Between eight and sixty meat samples are collected from each herd every quarter of the year.
The sample size is predetermined by the number of pigs delivered for slaughter
The system is based on the identification of
each herd by a unique code (the Central Herd
Registration; CHR) that identifies a herd as the
smallest epidemiological unit of trace-back
within a given geographical location. Each
year, all farmers are obliged by law to inform
the CHR register about ownership, herd type
and number of pigs. The per-herd systematic
sampling frequency is based on a monthly update from Central Zoonoses Register (ZOOR),
which is part of the CHR register. ZOOR receives monthly information of the number of
pigs slaughtered per herd, and of the actual
samples obtained. Around 800 000 meat juice
samples are examined annually at the Danish
33
Veterinary Laboratory.
Tests and testing procedures
An indirect enzyme-linked immunosorbent assay (ELISA) based on a combination of the
lipopolysaccharide (LPS) antigens O:1, 4, 5, 6,
7, and 12 is used. This ELISA (Exiqon, Denmark) is presumed to be able to detect O-antigens from at least 93 % of all serovars presently
occurring in Danish pigs. In experimental studies using S. typhimurium and S. infantis, the
sensitivities have been >95 % and the specificities 100%, respectively. Using results obtained
with serum as the gold standard, relative sensitivities from 0.81 to 0.89 have been demonstrated when meat juice samples have been
analysed. The results of the examination are
summarized monthly for individual herds.
Based on the proportions of sero-reactors during the last three months, the herds are assigned
to one of three levels. Level 1 herds have no or
very few sero-reactors. Level 2 herds have a relatively high proportion of sero-reactors (from
>50% in the smallest to >10 % in the largest
herds), whereas level 3 herds have an unacceptably high proportion of seroreactors (>50 % for
most herd sizes). Both the herd owners and the
slaughter companies are informed monthly
about the Salmonella level of the herds.
Consequences in the case of assignment to level
2 or 3
Herds assigned to levels 2 and 3 are requested
by the slaughter company to seek advice on
how to reduce the prevalence of Salmonella. A
sufficient number of faecal samples must be
collected and analyzed in order to clarify the
distribution of Salmonella in the herd. Based on
the results obtained, the herd owner, a veterinarian, and a pig consultant elaborate a herdspecific intervention plan. The recommended
measures of the control of disease spread are
implementation of all-in/all-out practices in
growing and finishing barns, cleaning and dis-
infection between batches, and strict control
over the risks to introduce external sources of
Salmonella.
The slaughter companies collect a penalty per
pig delivered if the plan is not elaborated and
received by the slaughter companies within 35
days. If a herd remains in level 2 or 3 for more
than 6 months, the owner must again seek advice on how to reduce the Salmonella prevalence in the herd. In addition, a slaughtering fee
is charged to all herds assigned to level 3 for
more than 6 months. The fee would be collected
until the herd is reassigned to level 1 or 2. All
changes in levels are approved by the Danish
Veterinary Service. The slaughter companies
update ZOOR about compliance regarding advisory visits.
Current status
The prevalence of seropositive meat juice samples varied between 4% and 7% from 1995 to
the end of 1997. A significant decrease was observed from October 1997, to June 1998, reaching a minimum at 2.3%. Since then, the number
of seropositive meat juice samples has remained below 3%. The percentage of herds designated at level 2 and level 3 have ranged from
2.4% to 4.3% and 1.1% to 2.3%, respectively.
From February 1998 the number of level 2
herds has remained below 3% and the number
of level 3 herds has varied between 1.2 % and
1.8%.
From June 1995 to August 1998, about 25% of
the herds (3955 out of 16000) have been required to seek advice on how to reduce the
Salmonella prevalence in the herd. In 1747
herds (44% of the total surveyed), the high
prevalence of Salmonella lasted more than six
months. In 233 herds (5,9%), the Salmonella
has been so persistent that five to seven requirements to seek advice have been required. In order to reduce the number of herds with chronic
Salmonella problems, teams of “second opinActa vet. scand. Suppl. 94 - 2001
34
ion” advisers have been established. Severe
penalties are placed on herds that do not follow
the advice of these teams.
Sweden, Finland and Norway
Aims of the surveillance and organisation
Sweden, Finland, and Norway have a similar
national Salmonella control program. The aims
of those programs are to maintain a low prevalence of Salmonella in pigs and pig products, to
provide reliable recording for the Salmonella
status in the pig populations and to prevent increased occurrence of Salmonella. Salmonella
infections in pigs have always been notifiable in
these countries. The national programs were introduced in 1995.
In addition to surveillance of Salmonella in intestinal lymph nodes at abattoirs, the programs
involve surveillance for Salmonella by faecal
samples in nucleus, multiplying herds (Sweden
and Norway) as well as in sow pool herds (Sweden). In Finland, all boars intended for semen
collection centres are individually examined for
Salmonella.
In the national programs, Salmonella is also
controlled in cattle and poultry, and in fresh
meat of cattle and swine. Moreover, great efforts are made within feed industries aiming not
to introduce Salmonella to the animals by feed.
In addition, both in Sweden and Finland there
are voluntary slaughter company activities aiming at certifying herds free from Salmonella.
However, these parts of Salmonella control are
beyond the scope of this review.
The affiliation to the surveillance program is
compulsory in each country. In Sweden and
Finland, the costs of sampling and analyses are
paid by the industry and the pig producers.
Confirmatory analyses are paid by the Animal
Health Authorities. In Norway, all costs of the
program are paid by the Norwegian Animal
Health Authority. Follow-up of the control program is carried out by the national veterinary
Acta vet. scand. Suppl. 94 - 2001
institutes in each country.
Samples from live animals are collected by the
local official veterinarians. At the slaughterhouses, samples are collected by the meat inspection team under the control of an official
veterinarian. The analyses are performed by the
municipal food control laboratories and by the
slaughterhouse laboratories. All Salmonella
isolates are confirmed and typed by the national
reference laboratories. Animal Health Authorities (provincial veterinarians and local official
veterinarians) are responsible for the measures
taken at Salmonella findings.
Sampling of faecal samples from pig herds
In Sweden, faecal samples are collected from
50 individual sows. At laboratory 10 cultivations are made, each representing a pool of 5
samples. In Finland, two pooled faecal samples
are collected from 10 pens with animals aged 5
weeks to 6 months. In Norway, pooled faecal
samples (representing at least 5 individuals in
each pen) are collected from 3 to 20 pens with
animals aged 2-6 months.
Sampling of intestinal lymph nodes at abattoirs
The total number of individuals tested in each
country is calculated to be sufficient to detect
Salmonella at a prevalence level of 0.1 % in the
whole pig population with a confidence interval
of 95%. The targeted annual sample size in
Sweden and Finland is 6000, and in Norway
3000. In Sweden, the daily sample size is equal
at all major slaughterhouses (n = 11). In Finland
and Norway, sampling is stratified to all slaughterhouses and systematically distributed evenly
over the year. The numbers of pigs to be sampled at each slaughterhouse is pre-determined
by the number of pigs slaughtered during the
previous year. The number of slaughterhouses
comprising about 99% of pigs slaughtered is 12
and 30 in Finland and Norway, respectively. All
other establishments are treated as one slaugh-
Samples collected during weeks 19-52.
Sweden: 10 pooled samples per herd. Each cultivation represents 5 sows and is pooled at the laboratory; Finland: 2 pooled samples per herd. Each Cultivation represents a
pooled sample from 5 pens with growing/finishing pigs; Norway: 3-20 samples per herd. Each cultivation represents 5 Growing/finishing pigs in a pen.
c In Finland only nucleus herds included.
d Samples from sows included.
e Two positive samples from a same herd.
n.a. Information not available.
b
a
0 / 178
0 / 114
0 / 167
0 / 35
n.a.
-
1 / 175
-
0 / 191
0 / 23
0 / 197
-
1 / 137
0 / 30
2 / 139
0 / 185
Faecal herd samplesb from
nucleus and
multiplyingc herds
n.a.
sow pool herds
n.a.
0 / 147
-
0 / 3104d
3 / 3070
5 / 3247
7 / 3074
0 / 2905d 3 / 3914
2 / 2614 4 / 3165
0 / 2818d 6e / 3382 6 / 3209
Lymph node samples from
sows and boars
2 / 1361a 9 / 2725
3e / 2009 8 / 2627
a
d
fattening pigs
1 / 1721 10 / 2792 4 / 3207 1 / 2699 5 / 2683
Norway
Finland
1998
Sweden
Norway
1997
Finland
Sweden
Norway
1996
Finland
Sweden
Norway
1995
Consequences of a positive test result
All Salmonella isolations lead to restrictions at
the farm imposed by the official veterinarian,
aiming t to prevent transmission to other herds
and to prevent contamination of food products.
Individual faecal samples are taken from sows
and boars and from pens with growing and finishing pigs. If Salmonella is demonstrated, actions are taken to eliminate the infection from
the herd. In addition, an investigation aiming at
finding the source of the infection or contamination is initiated. Special hygienic measures
are undertaken at the abattoirs when animals
from a Salmonella infected herd are sent to
slaughter.
The restrictions of a previously Salmonella infected herd may be removed when individual
faecal samples from all sows and boars, and
pooled samples from all pens with growing and
finishing pigs are tested twice with an interval
of at least 30 days and no Salmonella is detected. In herds with fattening pigs the restrictions are released when all animals have been
slaughtered and the premises have been disinfected according to the instructions of the official veterinarian.
Finland
Tests and testing procedures
The nucleus and multiplying herds are tested
once a year. The sow pool herds (Sweden) are
tested twice a year. The surveillance at slaughterhouses is continuous. Bacteriological examinations are performed according to the Nordic
Committee on Food Analysis (NMKL) Method
No. 71 (1991). In Finland, also ISO-method
6579 (1990) can be used. All positive samples
are confirmed and serotyped by national reference laboratories.
Sweden
terhouse. The minimum number of samples
collected annually in each slaughterhouse is 59.
In each country, five lymph nodes are always
pooled before the bacteriological examination.
Table 3. Summary of the national Salmonella control program in pig herds in Sweden, Finland and Norway during 1995-1998 (number of positive Samples / total number of samples).
35
Acta vet. scand. Suppl. 94 - 2001
36
Current status
Results of the continuous surveillance in 19951998 are shown in table 3. In Sweden, Salmonella has been detected in 0.04%-0.18% of
the lymph node samples annually. In spite of
confirmatory analyses, Salmonella was only
demonstratedby faecal samples in one herd during 1996. During 1997, Salmonella was
demonstrated in faecal samples of one multiplying herd.
In Finland, Salmonella has been detected in
0.10%-0.34% of lymph node samples annually.
Salmonella has not been re-isolated in faecal
samples of such herds. In 1997, Salmonella was
found in faecal samples of 2 nucleus herds (S.
enteritidis FT 8; S. typhimurium FT 1). In the
latter herd, Salmonella could also be re-isolated
once (S. typhimurium var. Copenhagen). Both
herds became clean very soon.
In Norway, Salmonella was not detected in any
lymph node samples or faecal samples during
1996-1998. In 1995, Salmonella was found in
faecal samples of one multiplying herd (S. agona) and in 4 lymph node samples (0.12 %).
Salmonella was not demonstrated by cultivation in these herds.
Iceland
In Iceland, 447 faecal samples were taken from
29 herds during 1991-1995. One herd has been
found positive for S. typhimurium and the herd
was slaughtered out.
Porcine Reproductive and Respiratory
Syndrome (PRRS)
Denmark
Aim of the monitoring and organisation
Isolation of PRRS-virus is notifiable in Denmark. Notification is a prerequisite for export of
meat from non-outbreak herds to a few markets.
Acta vet. scand. Suppl. 94 - 2001
Serological monitoring of herd infection status
is compulsory in nucleus and multiplying herds
(n=360), and voluntary in production herds.
The aim of the monitoring is to assist the trade
of live pigs between herds of similar infection
status. The secondary purposes include monitoring of national and regional levels of PRRSvirus infection. This information may be used
to make decisions on national PRRS policies,
regional PRRS policies by farmer groups, and
to make decisions related to cost-benefit of
eradication procedures at the farm level. A
PRRS-database was developed in February
1996. The database is administered by the Danish Meat and Bacon Council, which also pays
for administration and distribution of information. Farmers pay for sample collection and diagnostic services.
The monitoring of nucleus and multiplying
herds is based on serum samples collected from
the herds. Samples are analysed for antibodies
at the Danish Veterinary Institute for Virus Research. Monitoring of production herds is based
on serum samples or on meat juice samples collected at the slaughterhouses. The latter samples are analysed for antibodies to PRRS at the
Danish Veterinary Laboratory.
Sampling
From all breeding and multiplying herds, 10
serum samples are collected monthly from randomly chosen growing and finishing pigs. From
production herds, 20 serum samples are collected annually. Alternatively, 40 meat juice
samples are collected systematically throughout the year. A unique herd code (Central Herd
Registration code) provides basic herd information for any diagnostic investigation.
Tests and testing procedures
The serum samples from nucleus and multiplying herds are analysed monthly for presence of
antibodies to PRRS by a blocking-ELISA
37
aimed at detecting antibodies to both European
and US sub-types of PRRS virus. Meat juice
samples from production herds are analysed for
PRRS-antibodies by an indirect ELISA. A positive result indicate that the herd has been infected by PRRS-virus.
Consequences of a positive test result
A “PRRS suspect” herd status is assigned when
the positive predictive value of meat juice test
results exceeds the values corresponding to
those obtained in 2 positive samples out of 10.
Actions following assignment of “PRRS suspect” herd status include notification of the
farmer, the herd veterinarian and trade organisations, and collection of 10 additional meat
juice samples intended for clarification of
PRRS herd status. If the herd is infected the
farmer must not sell pigs to PRRS herds.
Certification
The PRRS database does not certify the infection status of the herds in legal terms. The
farmer himself is responsible for providing information of the true infection status of his herd
in relation to his customers. The SPF company
certify the PRRS status of the herds, and if required it demands herds to participate in the
PRRS database.
Record keeping
The Central Herd Register in the Ministry of
Food, Agriculture and Fisheries provide basic
herd information for the PRRS database. By his
signature, the individual farmer represents his
herd in the database. He authorises that diagnostic results from the laboratories are forwarded to the database, and that trade companies, the herd veterinarian and the swine
specialists gain access to the PRRS herd infection status. The diagnostic results are kept for
indefinitely unless the farmer requests removal
of his herd from the database.
Current status
The estimated PRRS prevalence was 25% in
nucleus and multiplying herds, 45% in farrowing and farrow-to-finish herds and 50% in finishing herds in May 1999. During 1996-1998
the estimated annual PRRS incidence was 7.5%
in nucleus and multiplying herds and 8-10% in
production herds, respectively.
Sweden, Finland and Norway
Aims of the surveillance programs, target
population and organisation
PRRS is a notifiable disease in Sweden, Finland, and Norway, and has never been reported
in any of these countries. Each country has a
surveillance program aiming to document freedom from PRRS in the nucleus and multiplying
herds. In Sweden and Norway, surveillance is
made also in the rest of the pig population.
In Sweden, PRRS has been screened since
1993, and since 1998 PRRS is included in the
control program of the Swedish Animal Health
Service. The target population in this program
includes all nucleus and multiplying herds, all
boars entering the semen collection centres, pig
herds in Southern Sweden, as well as sows sent
to slaughter. Blood samples are collected at the
herds and affiliation to the program is compulsory for the breeding and multiplying herds. At
slaughterhouses, blood samples are collected
by the meat inspection team under the control
of an official veterinarian. All samples are analysed at the National Veterinary Institute in
Uppsala for antibodies to PRRS.
In Finland, PRRS was screened in the entire
pig population in 1996. PRRS surveillance was
included in the National Health Control Program for breeding herds in 1997. In addition, all
boars entering the semen collection centres are
tested. Both programs are administered by the
Animal Health Authority. At slaughterhouses,
blood samples are collected by the meat inspecActa vet. scand. Suppl. 94 - 2001
38
tion team under the control of the official veterinarian. Samples for antibodies are analysed
at the National Veterinary and Food Research
Institute in Helsinki. The boar samples are analysed for presence of antibodies to PRRS at the
Danish Veterinary Institute for Virus Research,
Lindholm, Denmark.
In Norway, a surveillance program for PRRS
started in 1995 and all pig herds comprise the
target population of the program. In addition,
all boars entering the semen collection centres
are tested. The program is administered by the
Animal Health Authority. In pig herds, blood
samples are collected by the local official veterinarians. Samples are analysed for antibodies to
PRRS at the Danish Veterinary Institute for
Virus Research, Lindholm, Denmark.
In each country, the surveillance is paid by the
national Animal Health Authority, who is also
responsible for the measures in case of interventions.
In Norway, the total group of farms from which
the random selection is made consists of all pig
herds receiving state support (including 82 wild
boar farms). Some of the largest pig herds do
not receive state support, but are still included
in the program.
All nucleus and multiplying herds are investigated annually, while a random sample of 290
herds is taken from the rest of the pig herds,
weighted to give the highest proportion in farrowing and farrow-to-finish herds. A higher
proportion of farms is selected from counties
considered to be high risk areas (south-eastern
and south-western part of Norway). In farrowing or farrow-to-finish herds, 10 blood samples
are collected from sows, whereas 10 finishing
pigs are sampled in fattening herds. In wild
boar farms, 5 samples are collected from sows.
The number of herds to be tested annually
varies between 470 and 510, and the total sample size is 4700-5000.
Sampling
In Swedish nucleus and multiplying herds 20
pigs are tested 1-2 times annually. The samples
are collected from animals aged 5-12 months
dispersed among different sections of the herd.
In the Southern part of Sweden (considered to
be a high risk area), 20 pigs are tested annually
in 50 randomly selected production herds. In
addition, 1000 randomly selected slaughtered
sows from the rest of the pig herds in the country are tested annually. The total sample size
varies between 5000 and 6000 samples annually.
In Finland, an annual sample size of 1300-2600
is collected randomly throughout the year from
pigs that are slaughtered from progeny testing
stations (no. of stations 6, total no. of test pigs
4200 in 1998). All nucleus herds send test pigs
to the stations. During 1998, 1903 samples
were collected from testing stations, and 690
samples from breeding boars.
Tests and testing procedures
Samples other than boar samples are analysed
for antibodies to PRRS-virus with a blockingELISA differing between the European and the
US subtypes of the virus (IDEXX® Laboratories, Maine, USA). Boars are tested for PRRSantibodies with an immunoperoxidase monolayer assay (IPMA).
Acta vet. scand. Suppl. 94 - 2001
Consequences of a positive test result
If positive reactions are detected, the herd will
immediately be closed and new blood samples
from at least 20 pigs of different ages will be
analyzed. In case of clinical symptoms, pigs
will be euthanised and sent for necropsy. A confirmed infection with the virus will initiate an
attempt to eradicated the infection by “stamping out”. A restriction area with a minimum of
3 km radius will be determined around the infected herd. A comprehensive epizootiologic
investigation will be performed to detect the
39
source of the infection and the possible spread
of the infection from the positive herd to neighbouring and other contact herds.
Current status
Antibodies to PRRS-virus have not been detected in any of the samples collected in Sweden, Finland, and Norway. These results, together with absence of clinical cases, support
the evidence of freedom from PRRS in these
countries.
Iceland
PRRS is a notifiable disease in Iceland. No clinical cases have been reported and no antibodies
to PRRS-virus have been detected.
Swine Enzootic Pneumonia (SEP)
Denmark
Swine enzootic pneumonia, caused by Mycoplasma hyopneumoniae (M. hyopneumoniae), is widely prevalent in Danish swine
herds. It is believed that the organism is present
in all herds that are not explicit monitored for
the absence of M. hyopneumoniae (SPF herds).
The SPF-system is an optional program that declare presence or absence of 5-6 diseases in
herds. Approximately 3000 herds participate
(about 25% of total production), and approximately 1000 of these herds are free from M. hyopneumoniae. Herd health status is controlled
by veterinarians 4-12 times per year and by
blood sampling (yearly sampling in production
herds, monthly sampling in nucleus and multiplying herds). Conventional nucleus and multiplying herds are not required to be free from M.
hyopneumoniae, but the trade of live pigs is assisted between herds of similar infection status.
Vaccination against M.hyopneumoniae is common in production herds.
Sweden
The SPF herds of the country (about 1% of the
production) are controlled with respect to M.
hyopneumoniae, and declared free from that organism. No specific monitoring program do occur within the conventional herds. Since most
of the nucleus herds are known to be infected
with M. hyopneumoniae, the organism should
be regarded to be present in the production
herds. The negative effects of M. hyopneumoniae are reduced by introducing age segregated
rearing systems from birth to slaughter. During
1997, 40% of the pigs reared to market weight
were raised within such systems. In addition,
the efficacy of vaccinations against M. hyopneumoniae, and definition of optimal time
points for such vaccinations, are presently evaluated.
Finland and Norway
Aim of the surveillance
Both Finland and Norway have a national
surveillance program for nucleus herds, and
freedom of M. hyopneumoniae is a presumption
for those herds to sell breeding animals. The
aim of the surveillance is to keep all nucleus
herds free from M. hyopneumoniae. In Norway,
also multiplying herds are included in the program. In addition, in both countries there are
extensive voluntary slaughter company activities aiming at certifying conventional herds free
from the infection. This trend may end up to a
situation where, based on national decisions, it
is possible to eradicate M. hyopneumoniae from
the entire pig population. The serological
surveillance in nucleus herds started in 1992
and 1993 in Finland and Norway, respectively,
and in conventional herds in 1994 and 1997, respectively.
Organisation
Finland
The M. hyopneumoniae surveillance in nucleus
herds is part of the National Health Control
Program for such herds. The program is adminActa vet. scand. Suppl. 94 - 2001
40
istered by the Animal Health Authority and it is
compulsory for all nucleus herds. When joining
the program, the herds have to pay for the analyses. Thereafter, analyses are paid by the Animal Health Authority. Colostrum samples are
collected and sent to the analysis by the herd
owners. All samples are analysed at the National Veterinary and Food Research Institute,
Regional Laboratory in Seinäjoki. If antibodies
are detected, provincial veterinarians and local
official veterinarians are responsible for measures taken.
The surveillance of conventional herds is based
on desicions of individual slaughter companies.
Every slaughterhouse company administers it´s
own health control program without any formal
coordination between the different programs.
Basically, the programs are based on similar
control strategies as the program for nucleus
herds. Most slaughterhouse companies pay the
costs of the analyses, when herds are joining
their health control programs.
Norway
The M. hyopneumoniae surveillance program
for nucleus and multiplying herds is based on
decisions made by the Norwegian Pig Breeding
Association and The Norwegian Pig Health
Service. The program is compulsory, and the
costs of the program are paid by a special fund
based on a tax that all farmers have to pay per
kg pork delivered to the slaughterhouse. The
surveillance program for conventional herds is
based on decisions made by the slaughterhouse
organisations, and the costs of the program are
paid by the farmers and in some areas by the
slaughterhouse companies.
Both surveillance programs are administered
by the Norwegian Pig Health Service.
Colostrum samples are collected by the farmers. Blood samples are collected at the abattoirs. Both colostrum and blood samples are
analysed at the National Veterinary Institute,
Acta vet. scand. Suppl. 94 - 2001
Oslo. If antibodies are detected the Norwegian
Pig Health Service is responsible for measures
taken.
Sampling
Finland
A condition of joining with the program for nucleus herds is that colostrum samples from up
to 50 sows are analysed for antibodies to M. hyopneumoniae. Thereafter, 15-25 colostrum
samples are analysed biannually. A condition of
joining with the programs for conventional
herds is that colostrum samples from up to 30
sows are analysed. In most cases, no further
sampling takes place unless clinical symptoms
indicate M. hyopneumoniae infection.
Norway
The nucleus and multiplying herds were originally screened for M. hyopneumoniae antibodies by analyzing 60 and 40 blood samples from
sows or slaughtered pigs, respectively. Biannually, 10 colostrum or blood samples from sows
are collected and analysed. Conventional herds
may be certified free from M. hyopneumoniae
when a minimum of 20 colostrum samples or
20 blood samples from slaughtered finishing
pigs are analysed and no antibodies to M. hyopneumoniae are detected. Thereafter, 10
colostrum or blood samples are analysed once a
year.
Consequences of a positive result
Both serum and colostrum samples are analyzed for the presence of antibodies to M. hyopneumoniae by a monoclonal blocking ELISA
(Mycoplasma hyopneumoniae ELISA®, DAKO
A/S, Glostrup, Denmark). If an nucleus or multiplying herd tests positive, confirmatory tests
will take place. If the infection is confirmed, the
herd can not sell breeding animals any more.
An eradication program will take place after the
acute phase of the infection. In Finland, such a
41
program is supported economically by the Animal Health Authority. If a conventional herd
looses it´s M. hyopneumoniae free status, negative economical consequences will take place.
The price of pigs delivered for fattening is reduced by 7-10% and 4% in Finland and Norway, respectively.
Certification
Both in Finland and Norway, all nucleus herds
(and multiplying herds in Norway) are certified
free from M. hyopneumoniae, if the requirements of the surveillance programs are met,
clinical symptoms indicating SEP are not detected during the quarterly veterinary visits and
the prevalence of pneumonia recorded at meat
inspection remains low.
Regulated control of disease spread
In Finland, the nucleus herds are allowed to buy
breeding animals from other similar certified
herds. At such occasions, great attention has to
be paid on common practises for the prevention
of possible disease spread. In Norway, the nucleus herds have been totally closed for several
years. Multiplying herds are allowed to buy
purebred sows from only one single certified
nucleus herd.
Current status
Finland
In 1995, all nucleus herds were screened and 4
herds were concluded to be infected. Since
then, one herd has been reinfected annually.
The surveillance in the nucleus herds during
1996 to 1998 is shown in table 4. During 1991,
the prevalence of sow herds with antibodies to
M. hyopneumoniae was 30% and 8% in Western and in Southwestern Finland, respectively.
Since then the number of colostrum and blood
samples collected from conventional farrowing
herds has been steadily increasing. Today, at
least one half of the total of 2 300 conventional
Table 4. Summary of the Mycoplasma hyopneumoniae
surveillance in Finnish nucleus pig herds (n=150) during
1996-1998 (number of samples with antibodies in blocking-ELISA / total number of samples).
1996
Colostrum
samples
Confirmatory
blood samples
a
b
c
d
e
1997
1998
49a / 4958 22b / 5427 15d / 3808
0 / 119
18c / 298
17e / 345
44 positive samples from 1 herd; other positive samples
single positives in a herd
7 positive samples from 1 herd; other positive samples single positives in a herd
all positive samples from 1 herd
8 positive samples from 1 herd; other positive samples
single positives in a herd
all positive samples from 1 herd
farrowing herds are certified by the slaughterhouse companies as M. hyopneumoniae free
herds.
Norway
All nucleus and multiplying herds were
screened during 1994-1996 (table 5.) Eleven of
the total of 189 herds were concluded to be infected. Since then, 2 nucleus and 3 multiplying
herds have been reinfected. Two of the multiplying herds were infected by breeding sows
bought from one of the infected nucleus herds.
Preliminary studies in about 700 conventional
herds indicate that the prevalence of farrowing
and farrow-to-finish herds infected with M. hyopneumoniae varies between 5 and 40% in different counties of Norway.
Iceland
SEP is present in the majority of Icelandic pig
herds.
Progressive Atrophic Rhinitis (PAR)
In Denmark, toxin producing strains of Pasteurella multocida, the causative agent of progressive atrophic rhinitis, are monitored twice
Acta vet. scand. Suppl. 94 - 2001
42
Table 5. Summary of the screening of Norwegian nucleus and multiplying pig herds for Antibodies in blocking ELISA to Mycoplasma hyopneumoniae in blood samples during 1994-1996.
Total no. of
samples
No. of samples
with antibodies (%)
No. of herds with a
confirmed infection (%)
Elite breeding herds (n=110)
7101
177 (2.5)
5 (4.5)
Multiplying herds (n=79)
3078
156 (5.1)
6 (7.6)
every winter season in nucleus and multiplying
herds. These herds are defined free of the disease. One herd test is based on collection of 20
nasal swab samples pooled 2 and 2 in 10 veils.
Samples are analysed for P. multocida toxin
(Pasteurella multocida toxin ELISA®, DAKO
A/S, Glostrup, Denmark).
In Sweden, toxin producing strains of P. multocida were eradicated from the nucleus herds
during 1993-94. The nucleus and multiplying
herds are defined free from infections with
toxin producing strains of P. multocida since
1995, which also is proven by annual control.
Between 5000 and 8000 nasal swab samples are
analysed annually for P. multocida toxin by
ELISA.
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