1. TOXOPLASMA GONDII HISTORY
Toxoplasma gondii is an obligate intracelluler coccidian parasite, first described in 1908 by Nicolle and manceaux in spleen and liver smear of a small north African rodent called gondii. Its importance as human pathogen was recognized later when janku in 1923 observed the cyst in the retina of child with hydrocephalus and microphthalmia.
The name toxoplasma is derived from Greek word taxon means arc or bow meaning curved shape of trophozoite
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2. General features Is an obligate intracellular parasite
Mode of reproduction is by sexual and asexual
-trophozoite and tissue cyst represent asexual multiplication
-oocyte represent sexual reproduction
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3. morphology Trophozoite Tissue cyst oocyte
T.gondii occur in three forms
Trophozoite
Tissue cyst
oocyte
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4. Trophozoite
Is a crescent shaped with one end pointed and the other end rounded
It measures 3µm by 7µm
Has ovoid nucleus situated near the blunt end of the parasite
Stains well with Giemsa stain
Formed during acute phase of infection
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5. Tissue cyst
Formed during chronic phase of infection and can be found in muscles and various tissues and organs like brain
Has slow multiplication within the host cell
The cyst is rounded or oval measures µm in size and contain numerous bradyzoites
cyst reach various tissues and organs through blood and lymphatic dissemination
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6. oocyte It is spherical or ovoid in shape
It measures about 10-20µm in size and contain sporoblast
Freshly oocyte is not infectious, it become infectious only after development in soil and water for a few days
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7. Life cycle and pathogenesis
Life cycle of T.gondii consist of three stages
Tachyzoites, the rapidly multiplying trophozoites which invade and multiply within cells
Bradyzoites,the slowly multiplying forms inside tissue cyst seen during latent and chronic infection
Sporozoites inside oocysts, which are shed in cat feces and remain in the environment
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8. Life cycle and pathog ….
In cats which are the definitive hosts. Both schizogony and gametogony take place in the epithelial cells of the small intestine. This is known as enteric cycle.
the oocysts produced by gametogony are shed in faeces.They develop into infective forms in soil or water. They may be ingested by felines to repeat the cycle.
When ingested by other animals or birds which are intermediate hosts. The oocysts release sporozoites which infect the intestinal epithelial cells. Here,they multiply by endodyogeny to form tachyzoites.
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9. Life cycle cont……..
The host cell ruptures releasing numerous trophozoite which spread through blood and lymph infecting any type of nucleated cell in various tissues and organs. Which is known as exoenteric cycle.
Human infection is obtained through the following
Eating uncooked or undercooked infected meat containing tissue cyst
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10. Lifecycle and pathogenesis…..
Ingestion of mature oocyst through food, water or fingers contaminated with cat feaces directly or indirectly
Intrauterine infection from infected mothers to babies.
Rarely by blood transfusion or transplantation from infected donors
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11. Clinical features Most human infection are asymptomatic
Clinical toxoplasmosis may be congenital or acquired
Congenital toxoplasmosis-this results when infection is transmitted transplacentaly from mother to foetus, the risk of infection rises with the progress of gestation from 25% when mother acquire primary infection in the first trimester to 65% in the third trimester. Severity of infection to the foetal damage is highest when infection is transmitted in earlier pregnancy.
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12. Mother with chronic or latent Toxoplasma infection acquired earlier do not ordinary infect their babies, but in some women with latent or chronic infection , the tissue cyst may be reactivated during pregnancy and liberate trophozoites which may reach the fetus in vitro. Most infected newborn are asymptomatic at birth and may remain so throughout. Some develop clinical manifestation after some years.
its manifestations are may be: blindness, deafness,epilepsy or mental retardation and chorioretinitis, and other acute toxoplasmosis like jaundice and diarrhea
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13. Acquired Toxoplasmosis
Infection acquired postnataly and is asymptomatic
Most common clinical manifestation includes:
Lymphadenopathy, the cervical lymph nodes affected, fever, headache, myalgia, and splenomegaly, the illness may resemble mild flu and is self limited. Toxoplasmosis involving the central nervous system is usually fatal.
Toxoplasmosis is severe in immunodefficient particularly AIDS patient
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14. Clinical features Lymphadenopathy Fever Headache Myalgia and
Acquired toxoplasmosis-infection is acquired postnatal and is mostly asymptomatic and may present in different forms, most common manifestation are
Lymphadenopathy
Fever
Headache
Myalgia and
Spleenalmegaly are often present
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15. Epidemiology
The infection is worldwide be found whener there are cats.
Hosts are numerous spp of mammals, reptiles and birds.
It is a zoonotic disease acquired through food or water contaminated with mature oocyte or tissue cyst.
Can be acquired by laboratory infection
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16. Epidemiology …….. Incubation period is usually one to three weeks.
The outcome of infection depends on the immune status of the infected person
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17. Diagnosis Sabin-Feldman test Indirect immunoflorecent
microscopic demonstration of parasite is by isolation or serological test
Serology includes
Sabin-Feldman test
Indirect immunoflorecent
Indirect haemoglutination
Complement fixation
ELISA
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18. Prevention Proper cooking of meat
Eradication is unlikely because the disease is widely disseminated in nature but some simple measures can be used to reduce the risk of infection which include
Proper cooking of meat
Washing of hands before eating to safeguard against soil contamination of fingers
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19. Treatment and control
Combined treatment with pyrimethamine and sulphonamides or cotrimoxazole may lead to clinical cure
Spiromycin and clindamycin have also been used
NOTE: treatment is effective only against trophozoites and not cysts.
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20. References
Paniker ck jayaram,Medical parasitology,(2002) 5th edition,new delhi.
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