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Toxoplasmosis

Toxoplasmosis is a parasitic disease caused by the parasite Toxoplasma gondii. It infects most animals and causes human parasitic diseases, but the primary host is the felid (cat) family. People usually get infected by eating raw or undercooked meat, or more rarely, by contact with cat faeces. more...

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At least one third of the world population may have contracted a toxoplasmosis infection in their lifetime but, after the acute infection has passed, the parasite rarely causes any symptoms in otherwise healthy adults. However, people with a weakened immune system are particularly susceptible, such as people infected with HIV. The parasite can cause encephalitis (inflammation of the brain) and neurologic diseases and can affect the heart, liver, and eyes (chorioretinitis).

Transmission

Transmission may occur through:

  • Ingestion of raw or partly cooked meat, especially pork, lamb, or venison, or by hand to mouth contact after handling undercooked meat. Infection prevalence is higher in countries that traditionally eat undercooked meat, such as France. This seems to be by far the most common route of infection.
  • Accidental ingestion of contaminated cat faeces. This can occur through hand to mouth contact following gardening, cleaning a cat's litter box, children's sandpits, or touching anything that has come into contact with cat faeces.
  • Contamination of knives, utensils, cutting boards and other foods that have had contact with raw meat.
  • Drinking water contaminated with Toxoplasma.
  • Ingestion of raw or unpasteurized milk and milk products, particularly those containing goat's milk.
  • The reception of an infected organ transplant or blood transfusion, although this is extremely rare.

The cyst form of the parasite is extremely hardy, capable of surviving exposure to cooling down to subzero temperatures and chemical disinfectants such as bleach and can survive in the environment for over a year. It is, however, susceptible to high temperatures, and is killed by cooking. Cats excrete the pathogen for a number of weeks or months after contracting the disease, generally by eating an infected rodent. Even then, cat faeces are not generally contagious for the first day or two after excretion, after which the cyst 'ripens' and becomes potentially pathogenic.

Although the pathogen has been detected on the fur of cats, the pathogen has not been found in a 'ripe' form, and direct infection from handling cats is generally believed to be very rare.

Pregnancy precautions

Congenital toxoplasmosis is a special form in which an unborn child is infected via the placenta. This is the reason that pregnant women should be checked to see if they have a titer to toxoplasmosis. A titer indicates previous exposure and largely ensures the unborn baby's safety. If a woman receives her first exposure to Toxoplasma while pregnant then the baby is at particular risk. A woman with no previous exposure should avoid handling raw meat, exposure to cat faeces, and gardening (a common place to find cat faeces). Most cats are not actively shedding oocysts and so are not a danger, but the risk may be reduced further by having the litterbox emptied daily (oocysts require longer than a single day to become infective), and/or by having someone else empty the litterbox.

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STANDARDIZATION AND USES OF IgG ANTIBODIES AVIDITY ASSAYS IN THE LABORATORIAL DIAGNOSIS OF ANIMAL TOXOPLASMOSIS
From Revista do Instituto de Medicina Tropical de Sao Paulo, 7/1/05 by Meireles, Luciana Regina

MEIRELES, Luciana Regina - Padronização e aplicaçães da avidez de anticorpos IgG no diagnóstico laboratorial da toxoplasmose animal. Sõo Paulo, 2005. (Tese de doutoramento - Instituto de Ciências Biomédicas da Universidade de Sõo Paulo).

Toxoplasmosis is a highly prevalent zoonosis in which the risk of transmission and elucidation of epidemic outbreaks depends on the determination of the time of the infection. The parasitological tools that detect the presence of T. gondii are time-consuming, with low sensibility, and serology is the most useful and powerful tool in the diagnosis of these infections. Antibody avidity has been used for the determination of the time of T. gondii infection in human infections and we devised the standardization of those reactions in animals involved in the transmission of the disease such as: cats (oocysts producers); sheep, cattle and rabbits (tissues cysts harboring animals); or dogs (environmental sentinels). The tests show that the IgG avidity as determined by ELISA, by tilers ratio (AVT) presented no interference of antigen concentration in plates, reaction absorbance or liter of the serum, being a general fact in the studied species. Simpler avidity measures in a single sample maintain the discrimination only inside the same mammal species. The maturation of the IgG avidity is proportional to the time of infection, allowing the discrimination between acute and chronic infections, not affecting tissue cysts prevalence. The progress of the infection is slower in felines, but the oocysts excretion occurs only in the acute stage, with low avidity antibodies. During immunizations, the maturation of IgG avidity is faster than in the infection, though it has low antibody tilers. However, when the animals are challenged, they present stronger response of high avidity antibodies and higher tissue inflammatory response, with low number of tissue cysts. The IgG avidity is directly related to the proliferation of blood lymphocytes induced by parasite antigens, both in infection or immunization. The evolution of the serum IgG avidity in toxoplasmosis is a general process in mammals, and its measure is proportional to the time of the infection and the efficiency of an immunization, indirectly reflecting in the immunological memory of the host to the agent.

Luciana Regina Meireles

Laboratório de Protozoologia

Inst. Med. Tropical de S. Paulo

Av. Enéas de C. Aguiar, 470

05403-000 - Sõo Paulo/SP, Brasil

Irmeirel@usp.br

Copyright Instituto de Medicina Tropical de Sao Paulo Jul/Aug 2005
Provided by ProQuest Information and Learning Company. All rights Reserved

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