Toxoplasmosis, Biology

Toxoplasmosis, one of the important parasitic zoonoses, occurs all over the world, and is caused by a protozoan parasite Toxoplasma gondii. Its definitive hosts are cats (and other members of the cat family) and the intermediate stages occur in a wide range of animals including domesticated animals and man.

Toxoplasma infection is widespread throughout the world but its incidence may vary in different geographical areas. Toxoplasmosis in man may occur as a congenital or as an acquired infection. The majority of congenital infections occur when the mother acquires infection during pregnancy. Postnatally, toxoplasmosis can be acquired either by ingestion of food contaminated by mature oocysts or by eating uncooked or raw infected meat (cattle, sheep, rabbits and pigs).

Cats and other members of felidae family are the key animals involved in the epidemiology of postnatal toxoplasmosis. After primary infection cats can shed oocysts for about two weeks and millions of these can be present in a single sample of stool. Coprophagous invertebrates like cockroaches and flies may spread oocysts mechanically.Infection may also occur due to laboratory and autopsy accidents and handling of infected meat. Other possible means of transmission are venereal, ingestion of milk, from eggs and by organ transplant.

Clinical features:
Congenital infection is more serious. It may result in abortion, miscarriage, still birth or birth of child with cerebral calcification, chorio-retinitis, hydrocephalus or microcephalus, anemia, jaundice, hepatomegaly and lymphadenitis. Acquired infection in man is usually mild. Lymphadenitis is the common manifestation with or without fever, malaise and rash, but infection persists for longer duration.

Laboratory diagnosis: Two important methods of diagnosis are discussed here.Demonstration and isolation of parasite: Biopsy material (lymph node and muscle) or impression smears can be used for detection of parasite by simple staining or fluorescent staining technique. Toxoplasma can be isolated by inoculating laboratory animals. Young albino mice are highly susceptible and are therefore most commonly used.

Demonstration of antibodies:
As isolation of parasites from all material is difficult and diagnosis largely depend on serological tests. Of the numerous tests available, complement fixation test, direct haemagglutination test indirect immunofluorescence test and enzyme – linked immunosorbent assay are reported to be suitable.

Control and prevention:
Man is infected by Toxoplasma from tissue-cysts in meat, oocysts in soil and transplacentally in mother’s womb. So, proper cooking of meat is essential. Proper feeding and management of pet cats and elimination of stray cats. Proper disposal of cat’s faeces is important to check the spread. Immunoprophylaxis of animals against toxoplasmosis also helps in preventing the disease .Routine serological check-up and treatment of infected mothers are essential for protecting the foetus.

Posted Date: 9/20/2012 3:14:25 AM | Location : United States

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