Toxoplasma Gondii
Toxoplasma Gondii
Toxoplasma Gondii
TOXOPLASMA GONDII
Toxoplasma Gondii
Scientific classification
T. gondii
tachyzoites
Kingdom:
Protista
Phylum:
Apicomplexa
Class:
Conoidasida
Subclass:
Coccidiasina
Order:
Eucoccidiorida
Family:
Sarcocystidae
Genus:
Toxoplasma
Species:
T. gondii
There are many intermediate hosts, including man rodent and farm
animals.
Man
Rat
farm animals
Definitive host
Oocyst contains
two sporocysts
with 4
sporozoites
Intermediate host
MORPHOLOGY
Tachyzoite3-7 micrometre in length
Oval to crescent shaped with a pointed anterior end and a rounded
posterior end..
Ovoid nucleus at the posterior end
It is the actively multiplying form (tachy = fast, zoite = organism)
and can invade any cell in the host
Toxoplasma gondii
tachyzoites
(Giemsa stain).
Tissue cyst
After repeated divisions, tachyzoites become encysted in the body,
pseudocyst
Pseudocyst of toxoplasma
Oocysts
In the environment, cysts take 48-72 hours to sporulate and become
infective.
Mature oocysts measure 10-12 m in diameter and contain two sporocysts. .
Cats may excrete millions of oocysts after ingesting as few as 1 bradyzoite or 1
tissue cyst, and many tissue cysts may be present in one infected mouse.
Oocysts are shed for only a short period (1-2 weeks) in the life of the cat,
Epidemiology
Very common throughout the world; up to 50+% in other
Mode of infection
Life Cycle
The sexual cycle takes place exclusively in the intestinal enterocytes of
many members of the cat family
1) Ingestion of tissue cysts,
2) The parasites invade the enterocytes and divide repeatedly
3) Differentiate into microgametocytes and macrogametocytes.
4 ) The gametocytes fuse to form a zygote or oocyst that is shed into
the environment with the cats faeces.
5) The oocyst undergoes meiosis, producing eight infectious
sporozoites that are resistant to environmental damage and may
persist for years in a moist environment.
6)Ingestion (by a secondary host such as a mouse),
F. Unsporulated oocyst in
fecal float of cat feces.
G. Sporulated oocyst with a
thin oocyst wall (large arrow),
2 sporocysts (arrowheads).
Each sporocyst has 4
sporozoites
Pathophysiology
Oocysts are ingested in material contaminated by feces from acutely
infected cats.
Sporozoites are released from oocysts and enter gastrointestinal
cells. They multiply, rupture cells, and infect contiguous cells. They are
transported via the lymphatics and disseminated hematogenously
throughout the tissues.
Tachyzoites proliferate, producing necrotic foci surrounded by a
cellular reaction. With the development of a normal immune response,
tachyzoites disappear from tissues.
In immunodeficient individuals and in some apparently
immunologically healthy patients, the acute infection progresses and
may cause potentially lethal consequences such as pneumonitis,
myocarditis, or necrotizing encephalitis
When a mother acquires the infection during gestation, the organism
may be disseminated hematogenously to the placenta. When this
occurs, infection may be transmitted to the fetus transplacentally or
during vaginal delivery
Clinical
1) Majority are asymptomatic In humans, severe disease is usually
observed only in congenitally infected children and in immunosuppressed
individuals, including patients with acquired immune deficiency
syndrome (AIDS).
2. Acute Toxoplasmosis:
Fever,
Lymphadenopathy Any node can be infected, but the deep cervical
nodes are the most commonly involved. Infected nodes are tender and
discrete but not painful; the infection resolves spontaneously in weeks or
months
Fatigue,
Muscle pains,
Sore throat, and
Headache
Rarely cause specific organ inflammation, e.g. encephalitis,
myocarditis.
3. Reactivation toxoplasmosis:
occurs in immunosuppressed such as AIDS,
transplant and cancer patients:
CNS disease occurs in 50% of patients
encephalitis,
meningoencephalitis,
Hemiparesis,
seizures, and
mental status changes
Patients report visual changes.
Myocarditis and pneumonitis
5. Congenital toxoplasmosis:
Transmission from mother to fetus when mother has developed
acute toxoplasmosis during pregnancy --- increased transmission
rate in third trimester, but increased severity of fetal disease in
first trimester.
Infection in the first trimester - approximately 17% of fetuses are
infected, and disease in the infant is usually severe.
Infection in the third trimester --65% of fetuses are infected, and
involvement is mild or inapparent at birth.
These different rates of transmission are most likely related to
placental blood flow, the virulence and amount of T
gondii acquired, and the immunologic ability of the
mother to restrict parasitemia
Congenital toxoplasmosis
Presents as
Hydrocephalus,
Hepatomegaly,
Cerebral calcifications,
Mental retardation
Choreoretinitis -Focal lesion in retina presenting as
Decreased visual acuity;
Rarely occurs during acute toxoplasmosis.
LABDIAGNOSIS
DemonstrationoftheT. gondiiorganism in blood, body fluids, or tissue.
IsolationofT. gondiifrom amniotic fluid is diagnostic of congenital infection
by mouse inoculation.
Lymphocytetransformationto T. gondii antigens is an indicator of previous
toxoplasmosis in adults
DetectionofT. gondiiantigenin blood or body fluids by enzyme-linked
immunosorbent assay (ELISA) technique indicates acute infection.
The Sabin-Feldmandyetest
Sensitive and specific neutralization test.
It measures IgG antibody and is the standard reference test for toxoplasmosis.
Live virulent tachyzoites of T gondii are used as antigen and are exposed to
dilutions of the test serum and to a complement accessory factor resembling
complement that is obtained from Toxoplasma-antibody free-human serum.
Its main disadvantages are its high cost and the human hazard of using live
organisms.
more sensitive and specific than the results from other IgM
tests.
Diagnosis in pregnancy
Diagnosis is primarily made by serologic investigations.
Antibody Detection
The detection of Toxoplasma-specific antibodies is the primary
diagnostic method to determine infection with Toxoplasma.
Test kits are commercially available to detect T. gondii specific
IgG, IgM , IgA or IgE antibodies.
All suspected patients should be initially tested for the presence
of Toxoplasma-specific IgG antibodies to determine their immune
status.
The presence of IgG antibodies only means exposure because
asymptomatic humans can develop very high (>100,000) and
titres may remain elevated for several years or even whole life if
repeated exposures are encountered.
A 8-fold rise in antibody titre, taken two weeks apart, is
indicative of a recent infection,
IgM antibodies are short-lived, and they appear before IgG
antibodies
Treatment
1)Sulfonamides and
2) Pyrimethamine (Daraprim) are two drugs widely used to treat toxoplasmosis
in humans.
helpful when given in the acute stage of the disease,
usually they will not eradicate infection when active multiplication of the
parasite occurs.
Precautions
1) Meat should be cooked to 66C throughout before eating.
2) Hands should be washed with soap and water after handling meat.
3) Raw meat should never be fed to cats; only dry or canned food or cooked
meat should be fed.
4) Cats should be kept indoors and litter boxes changed daily.
5) Cat feces should be flushed down the toilet or burned.
6) Litter pans should be cleaned by immersing them in boiling water.
7) Gloves should be used while working in the garden.