Toxoplasmosis: detection of antibodies IgM and IgG to toxoplasma in blood

Antibodies of IgM class to toxoplasma in serum are absent.

Toxoplasmosis is a disease caused by the obligate intracellular protozoan Toxoplasma gondii, which has a complex development cycle. The final owner of toxoplasm can be a domestic cat, as well as wild representatives of the cat family. When a cat is infected with alimentary pathways, parasites enter the epithelial cells of the intestine, where after several asexual generations, macro- and microgametes are formed. The sexual process is completed by the formation of oocysts, which are excreted into the external environment. Man is an intermediate host of the parasite, but does not isolate the causative agent into the external environment and does not pose an epidemic threat to others. In the human body, toxoplasm multiplies only asexually and go through two stages of development:

• endositis - a rapidly multiplying intracellular form, which causes cell destruction and an inflammatory reaction; the presence of endozoites is characteristic of the acute stage of toxoplasmosis;
• cysts - spherical parasite shape, surrounded by a dense shell and adapted to prolonged existence in the human body; they are localized in the brain, the retina of the eye, muscles and do not cause an inflammatory reaction; the presence of cysts is characteristic of the chronic stage of toxoplasmosis; cysts continue to grow slowly, their rupture and destruction leads to a recurrence of organ damage.

The main way of infection with toxoplasmosis is oral (the use of raw meat, vegetables and berries contaminated with soil, through dirty hands when contacting cats). However, for clinical practice, the congenital pathway of infection is equally important - intrauterine infection of the fetus from the pregnant woman through the placenta. It is proved fetal infection only from women with a primary infection acquired during this pregnancy. When a woman is infected in the first trimester of pregnancy, congenital toxoplasmosis in a child is recorded in 15-20% of cases, it is severe. When infected in the third trimester of pregnancy, 65% of the newborns are infected. In women with chronic or latent toxoplasmosis, the transmission of the causative agent to the fetus is not proven.

It is necessary to distinguish between toxoplasmic (carrier) infection from toxoplasmosis proper (disease), so the main thing in laboratory diagnostics is not the fact of the detection of a positive immune response (antibody), but the clarification of the nature of the course of the process - carriage or illness. Complex detection of antibodies of classes IgM and IgG makes it possible to quickly confirm or deny the diagnosis. The main method at present is ELISA, which allows detecting antibodies of classes IgM and IgG.

IgM antibodies to toxoplasm appear in the acute period of infection (in the first week at a titer of 1:10), peak within a month (2-3 weeks after infection) and disappear after 2-3 months (at the earliest - after 1 month ). They are detected in 75% of congenital infected newborns and in 97% of infected adults. Negative results of IgM antibody detection allow to exclude acute infection lasting less than 3 weeks, but do not exclude infection of a longer term. When reinfection, the IgM antibody titer rises again (in the presence of immunodeficiency it does not increase; in such cases, a computer or magnetic resonance imaging of the brain that reveals multiple dense rounded foci is shown for diagnosis). The presence of rheumatoid factor and / or antinuclear antibodies in the blood of patients can lead to false positive results of the study. In individuals with immunodeficiency, IgM antibodies in the acute period of infection are usually absent.

Early diagnosis of toxoplasmosis is especially important for pregnant women due to the risk of intrauterine infection of the fetus, which can lead to fetal death (spontaneous abortion) or the birth of a child with serious lesions. Specific treatment of women in the early stages of the infectious process reduces the risk of fetal damage by 60%. Since antibodies of the IgM class do not penetrate the placenta, their detection in the blood of the newborn indicates an innate infection.

Antibodies of class IgG to toxoplasm appear during the period of convalescence and in the ill are saved up to 10 years. The determination of antibodies of IgG class is used for diagnostics of the period of convalescence of toxoplasmosis and evaluation of the intensity of post-vaccination immunity. False positive results can be obtained from patients with systemic lupus erythematosus and rheumatoid arthritis.

Persons with positive antibody titers for toxoplasmosis are recommended to re-conduct serological tests 10-14 days later to establish the dynamics of the disease. The absence of an increase in antibody titers indicates a chronic toxoplasmosis. The increase of titers by 3-4 dilutions of serum testifies to the active course of the invasion.

Indications for the appointment of serological tests for toxoplasmosis:

• pregnant women according to indications, with seroconversion;
• patients with toxoplasmosis who receive specific treatment;
• children born from mothers with a history of toxoplasmosis;
• epidemically significant contingents: veterinary and other specialists associated with working with cats and dogs;
• patients with clinical manifestations, characteristic of toxoplasmosis.