Toxoplasmosis: an overview

Toxoplasmosis is a zoonotic protozoal disease characterized by chronic course, polymorphism of clinical manifestations, primary lesion of the central nervous system, eyes, liver and lungs.

Toxoplasmosis is a widespread disease caused by the intracellular parasite Toxoplasma gondii. Infection of the person basically occurs alimentary by the use of the food infected by toxoplasma, or at contact to the infected cats.

In most cases, toxoplasmosis is asymptomatic. In the presence of clinical signs, they may be similar to those in mononucleosis or influenza-like diseases. However, even subclinical infection can subsequently lead to the appearance of signs of damage to certain organs, for example neurological diseases, pathology of the organ of vision,

Toxoplasmosis is an opportunistic AIDS-associated infection. Against the background of immunodeficiency in patients with HIV infection can develop acute encephalitis, which often becomes the cause of death of the patient.

Congenital toxoplasmosis is acquired by transplacental transmission of the parasite to the fetus during a woman's primary disease with toxoplasmosis during pregnancy. This can lead to serious consequences (miscarriage, CNS damage, deformities, etc.).

It has been established that severe forms of fetal damage occur during primary infection of the pregnant woman during organogenesis.

According to the literature, women who have been infected or have had toxoplasmosis before pregnancy do not transmit toxoplasm to the fetus.

The absence of specific symptoms in toxoplasmosis does not allow to diagnose this disease without the results of laboratory testing.

The guidelines recommend the main methods of serological diagnosis, the most available and used in clinical laboratories, as well as a list of drugs and schemes for their administration for the treatment of toxoplasmosis.

Timely implementation of preventive measures, examination of women before the planned pregnancy, timely initiated specific treatment can avoid toxoplasmosis.

ICD-10 codes

• Q58. Toxoplasmosis. Included: infection caused by Toxoplasma gondii. Excluded: congenital toxoplasmosis (P37.1).
• B58.0. Toxoplasmosis oculopathy.
• B58.1. Toxoplasmosis hepatitis (K77.0).
• B58.2. Toxoplasmosis meningoencephalitis (G05.2).
• 858.3. Pulmonary toxoplasmosis (J17.3).
• B58.8. Toxoplasmosis with damage to other organs.
• B58.9. Toxoplasmosis, unspecified.

Epidemiology of toxoplasmosis

Toxoplasmosis is primarily a natural focal infestation, i.e. Zoonosis of wild animals (Zasukhin DN, 1952, Jirovec, 1952). However, toxoplasmosis at the present time (from the epidemiological point of view) should be considered a zoonosis of agricultural and domestic animals. The person is involved in the circulation of the pathogen, as a rule, in the locality, i. In the sanitary focus of toxoplasmosis. There are grounds to believe that the most frequent factor in the transmission of the causative agent to humans is the meat of invasive farm animals. The geological mechanism for the transmission of invasion to humans is realized, apparently, much less often. However, this should not minimize the epidemiological significance of cats.

Recently, it was found that in those areas where there are no cats, for example on some Pacific islands, toxoplasmosis is not found (Wallace et al., 1972). This undoubtedly testifies not only to the fact that the cat is the most important direct source of human infection, but also that without it the agricultural animals are not infected, from which the person becomes infected indirectly. At the same time in settlements where there are cats, toxoplasmosis affects a wide variety of groups of residents, including strict vegetarians, who can not get infected except from a cat. Thus, there is every reason to assert that cats in epidemiology of toxoplasmosis occupy a central place. If we could prevent the contamination of the environment with oocysts, the invasion of farm animals would gradually cease, and a synanthropic focus would be doomed to extinction. It is pertinent to note that a person as a source of infection in the epidemiological sense does not play any significant role. Rare, in general, cases of transplacental transmission of infestation (no more than 1% of all cases of human infection with toxoplasmosis) and, undoubtedly, even more rare cases of infection in the provision of obstetric and surgical care (if at all), with blood transfusion, as well as organ transplantation do not change the validity of this assumption.

The incidence of toxoplasmosis in connection with the difficulties of recognizing clinically pronounced, and furthermore subclinical toxoplasmosis, remains unknown in all countries, including so far in Ukraine.

[1], [2], [3], [4], [5], [6], [7],

Pathways of infection with toxoplasmosis

Oral

The main way of infection occurs by oocysts with the use of vegetables, berries, raw water, in contact with cats and soil, cysts or tachyzoites - with unprocessed meat and raw milk.

Contact

Occurs through mucous and damaged skin, possible with close contact with sick animals.

[8], [9], [10]

Congenital (transplacental)

Intrauterine infection of the fetus occurs through the placenta. The source of infection is a pregnant woman with a fresh infection, when there is parasitaemia, and the pathogen gets through the placenta, where the primary focus of infection is formed, where toxoplasma from the hematogenous way enter the fetus.

[11], [12], [13], [14], [15]

Transplantation

Occurs when organ transplants from a donor with toxoplasmosis. The transmission of the pathogen during blood transfusion or leukocytes has also been proven.

The incidence of toxoplasmosis in various countries (France, Holland, USA, etc.) often depends on the degree of consumption of half-baked meat dishes in culinary practice (up to 90% in France, in the Netherlands - 45-80%, USA - 18-20%) .

To better understand the epidemiology of infection caused by T. Gondii, it is necessary to establish the source of infection, possible ways and factors of infection. These data will allow the development of a specific prevention strategy and, if necessary, treatment of toxoplasmosis in a particular case.

It is quite logical to assume that the differences in the intensity of immunity in these cases are associated, first of all, with the unequal social status of the surveyed groups and the different risk of their infection and re-invasion with toxoplasmosis.

What causes toxoplasmosis?

Toxoplasmosis is caused by Toxoplasma gondii (subdomination of Protozoa, type Apicomplecxa, order Coccidia, suborder Eimeriina., Family Eimeriidae).

In the human body and animals, T. Gondii passes through several stages of development: trophozoite (endozoite, tachizoite), cysts (cystoseite, bradizoite), and oocysts. Trophozoites with a size of 4-7x2-4 μm resemble the shape of a crescent moon. Cysts are covered with a dense shell, up to 100 microns in size. Oocysts are oval in shape, 10-12 microns in diameter.

According to genotyping data, three groups of toxoplasmic strains are distinguished. Representatives of the first group cause congenital toxoplasmosis in animals. In humans, strains of the second and third groups of toxoplasm are detected, and representatives of the latter group are more often detected in patients with HIV infection. The antigenic structure of various stages of development of toxoplasm has been determined and it has been established that trophozoites and cysts have both common and characteristic antigens only for each of them.

Pathogenesis of toxoplasmosis

From the place of implantation (most often - hollow digestive organs) toxoplasma with lymph flow enters the regional lymph nodes, where they multiply and cause the development of lymphadenitis. Then, parasites enter the blood in large quantities and are spread throughout the body}, resulting in foci of lesions in the nervous system, liver, spleen, lymph nodes, skeletal muscles, myocardium, eyes. Due to the multiplication of trophozoites, the infected cells are destroyed. Around the foci of necrosis and the accumulation of toxoplasm formed specific granulomas. Under the normal immune response of the organism, trophozoites disappear from the tissues and the process of formation of cysts begins (the inflammatory reaction around them is weak). Disease toxoplasmosis passes from the acute phase to the chronic, and even more often - into chronic carriage with the preservation of cysts in the tissues of organs.

What are the symptoms of toxoplasmosis?

The incubation period of toxoplasmosis lasts from several weeks to several months. Depending on the mechanism of infection, the acquired and congenital toxoplasmosis is isolated.

Acquired toxoplasmosis usually proceeds without symptoms (up to 99% of all cases of T. Gondii infection ). These are healthy people, usually with a low level of antitoxoplasma antibodies that do not need any medical supervision or treatment. In persons with a normal immune response, in most cases, toxoplasmosis proceeds in a latent form. Manifest toxoplasmosis occurs in acute (up to 0.01% infected) and chronic (1-5%) form, with a tendency to relapse and exacerbation.

How is toxoplasmosis diagnosed?

Toxoplasmosis is diagnosed on the basis of epidemiological risk factors for infection and clinical and laboratory diagnosis data .

Parasitological methods (the investigation of biopsies of lymph nodes and other organs) are not widely used because of their complexity and laboriousness. Specific antibodies of IgM and IgG classes to toxoplasm antigens are detected in repeated serological tests: ELISA, RNGA and RIF (but they are not sufficiently informative in AIDS patients): conduct an intracutaneous test with toxoplasmin (native or recombinant). When analyzing and interpreting the results of serological diagnosis, one should take into account the "immunological" incubation - the appearance of antibodies on parasite antigens only through a certain latent period - and evaluate the results of the studies in dynamics. Skin test indicates infection with toxoplasm, but does not give information about the nature of the course of the disease. Pregnant women with positive serological reactions spend ultrasound of the fetus in dynamics.

How is toxoplasmosis treated?

Acquired chronic toxoplasmosis with a latent form does not need treatment. The effectiveness of etiotropic drugs for chronic toxoplasmosis is low, as chemotherapy and antibiotics practically do not affect endozoites in tissue cysts. In chronic toxoplasmosis, treatment is indicated only with exacerbation of the process and with miscarriage (treatment is performed outside the gestation period).

What is the prognosis of toxoplasmosis?

Acquired toxoplasmosis has a favorable prognosis, because the latent form predominates without clinical manifestations. Septic forms observed in AIDS patients and in patients with an immunodeficiency state of another etiology are severe and can result in death.