Toxoplasma Gondii (TOX) is a parasite disease that happens in both animal and human populations. TOX has a worldwide distribution that causes 1/3 of infection among humans globally and 12.3% in China.
TOX is an obligate intracellular parasite that lives in all nucleated cells of substrates. Feline and other Felidae animals are the primary hosts of TOX. Because of its sexual reproduction only takes place in epithelial cells of the small intestine to feline and other Felidae animals. It has a wide range of secondary hosts. Other than humans, cats, pigs, cows, sheep, dogs, and many other animals often get infected by Tox as well.
Canine and feline TOX are usually recessive infections. However, there are cases of clinical symptoms or even some that lead to death. Continuous fever of body temperature above 40℃, vomiting and diarrhea are the common symptoms of Feline TOX. Chronic conditions include flagging, thinning, Anemia, etc. Fetal death and abortion might happen to a pregnant feline. It is hard to diagnose canine TOX, and often mixed with CDV, because of the lack of sensitiveness of clinical symptoms and characteristics.
7-8 days after the TOX infection, IgM was produced as the earliest antibody. Thus, IgM detection was often used at an early diagnosis of TOX. The IgG level reaches the peak and stays 2-4 months after infection. However, the positive results of IgG do not ensure the infection. IgA antibody is one of the significant markers at the early stage of TOX infection. After the disappearance and before the production of IgG, IgA test can increase the detection rate of acute TOX infection.
The subject of the TOX antibody test is commonly Circulating antigen (CAg) or CAg immune complex. There are numerous productions of tachyzoite, cyst, metabolites or pyrolysis products of the parasites which are CAg, at the early stage, acute stage or active stage of TOX infection. CAg is the direct evidence of the existence of TOX pathogen, and also the countable index of the TOX diagnoses because it is produced before IgG and IgM. CAg is not only an indicator of TOX infection but also a good way to evaluate the treatment. The serum antibody level can be low or even has no production of a specific antibody when TOX infection happens to congenital toxoplasmosis or individuals with an immunodeficiency. It is essential to the test that the positive result of CAg would factually reflect the infection level.