Toxoplasma is a genus of parasitic eukaryotes that includes only one reliably studied species - Toxoplasma gondii. This microorganism is able to invade any animal or human cells, including nervous, epithelial, brain and cardiac tissue. For life, he does not need oxygen, because he is anaerobic. The main host of Toxoplasma is the feline, in whose body it goes through several stages of development, turning into an adult cyst. Cats are a kind of incubator, releasing eukaryotic eggs along with feces. And a variety of warm-blooded animals, including humans, can be chosen as an intermediate host.
Disease caused by a pathogen
Toxoplasmosis, whose life cycle goes through several stages, causes a disease called toxoplasmosis. In humans, this disease usually proceeds surprisingly mildly and without severe symptoms. But if you get an infection during pregnancy or during a period when immunity is reduced (for example, in the presence of HIV), then it can cause serious consequences and even lead toto death.
Structure of a microorganism
The shape of an adult is like a crescent. In front are special processes, with the help of which Toxoplasma sticks to the internal organs of the host. It does not have organelles, but even without them it can move perfectly by sliding, and also penetrate into tissue cells in a corkscrew fashion.
Scheme of the life cycle of a microorganism
The life cycle of Toxoplasma can be briefly described by two different states:
- finding it in the intestines of a cat;
- exit of eggs to the external environment.
It is possible that the entire development of the microbe can take place only in the body of the same cat. In an adult individual, the parasite is formed gradually, passing from one phase of development to another. The life cycle of Toxoplasma, the scheme of which is shown in the picture, consists of successive forms acquired by the pathogen. As he grows up, lasting several years, he goes through four of them: trophozoite - pseudocyst - tissue cyst - oocyst (fertilized egg). The formation of a mature individual also takes place in several stages:
- schizogony - division of the cell nucleus and the formation of many daughter merozoites;
- budding - the formation of two new microorganisms in the shell of one mother cell;
- gametogony - sexual reproduction by fusion;
- sporogony - separation of the zygote formed after sexual reproduction.
Life cycle phases: asexual
The asexual part of life takes place in the intermediate host. This could be, again, a cat or any other warm-blooded animal, bird, or reptile. Once in the body, trophozoites invade muscle and brain cells, where they form cell vacuoles with brandisoites, which, in turn, turn into pseudocysts. Toxoplasma gondii cannot be detected by the human or animal immune system, as the cysts hide inside the body's native cells. And its resistance to antibacterial drugs is so different that sometimes it is impossible to destroy all the cysts in the tissues. Reproducing inside vacuoles, it produces rapidly multiplying tachyzoites by division. The native cell of the host bursts, and mobile parasites come out, affecting an increasing number of he althy cells. Tachyzoites can be identified by the immune system and destroyed, but this is not enough to stop their spread.
Toxoplasma: life cycle. Sexual phase
The sexual and final phase of the life cycle of the microbe takes place in the body of cats - both domestic and wild. Tissue cysts can be ingested by a cat with an infected bird or mouse. They, bypassing the stomach, affect the epithelial cells of the small intestine. There they reproduce sexually, resulting in oocysts with two spores and four single-celled embryos of the parasite, called sporozoites.
With the faeces, the finished eggs are released into the environment. They retain the ability to live in the ground, sand up to 2 years,if external factors do not favor their further development. Animals or people can easily swallow the oocyst by eating unwashed fruits or vegetables, uncooked or raw meat. They become sources of infection for other hosts, including humans. Toxoplasma gondii invades the intestinal cells and, together with the bloodstream, spreads throughout the body. In the internal organs, most often in the brain, cysts form, each of which contains hundreds of cystozoites - mononuclear microbes.
Routes of infection
Unlike cats, a sick person does not release pathogen cysts into the outside world, like other representatives of the fauna. Toxoplasma is a microorganism whose eggs can be found almost anywhere: on lawns, in fields, in the ground, grass, sand. Wherever cats have gone to defecate.
You can catch the pathogen:
- From a sick cat, if her saliva, urine or feces got on the covers, the integrity of which is broken. Therefore, be sure to wash your hands with soap and water before eating and after cleaning the litter box.
- When eating half-baked poultry or livestock meat (lamb, pork), vegetables, berries, herbs and fruits not well washed.
- Flies and cockroaches that come into contact with cat feces are also carriers. After contact with food, a person can become infected by eating spoiled food.
But catching toxoplasmosis from a normal house cat is not as easy as one might imagine.
First, the cat must be a carrier of Toxoplasma.
Second,cysts are removed in a certain period of time. Usually for several weeks along with the cat's feces, but only once in the life of the animal.
Symptoms of infection
Most of the time, you don't feel any symptoms, but sometimes you get sick, like the flu. After a few days or months, the acute stage of the disease gradually turns into a chronic one. In immunocompromised patients, the infection can cause toxoplasmic encephalitis, pneumonia, or other inflammatory conditions from which the person dies. During pregnancy, Toxoplasma, whose life cycle goes through several stages and is not disturbed by the pathogen migrating from the intermediate host to the main one, crosses the placenta and infects the fetus. Often this leads to intrauterine death of the baby or miscarriage. It is noticed that infection contributes to a change in the behavior of the host. The microorganism "makes" rats or mice less afraid of cats and even look for places to live.
The parasite does this in order to move on to the next phase of its life cycle if the cat eats easy prey. The relationship between schizophrenia and the presence of Toxoplasma in the body has been studied. Studies have shown that the presence of an infection can affect the development of paranoia or other psychological changes.
Tests
After primary infection, a person develops a stable and lifelong immunity to the microorganism. Immunoglobulins come to the rescue in the fight against infection. Antibodies capable of:
- neutralize the toxins produced by the parasite;
- to communicate with pathogen cells;
- penetrate the placenta, partially forming a passive defense in the fetus.
Toxoplasma IgG is detected in blood serum, cerebrospinal fluid, lung sputum and other biological secrets. If these antibodies are found in the amount of 7/16 hl., then an additional study is carried out by polymer chain reaction to identify the activity of the infection. The presence of an acute period of the disease - primary infection - is evidenced by the presence of pathogen DNA in biological media. It should be noted that it is not possible to detect Toxoplasma in the blood plasma in all cases, even with increased invasion.
Interpretation of results
Toxoplasma IgG with a “+” sign and IgM with a “-” indicates the development of strong immunity for life. Both indicators with a “+” sign indicate the presence of a primary infection. And if IgM is positive, but IgG is negative, then during pregnancy this may mean intrauterine infection of the fetus. The absence of antibodies of the lgm group in the blood always indicates a negative result. Even if the infection did take place, it happened a long time ago. Therefore, at the moment it no longer poses any danger to humans.
Toxoplasma, whose life cycle is so complex, is the causative agent of a serious disease. But in fact, almost any person in the world who lives side by sideside by side with a cat, manages to “meet” it in childhood. The asymptomatic acute period of the disease does not attract attention, and the chronic form or carriage does not harm the person and other people around him. Toxoplasma is dangerous only when the pregnant woman was not previously infected, but picked up the infection while carrying a child. Therefore, in childhood or at the stage of family planning, you should not limit yourself to communicating with cats - it is better to have your own pet so that the body develops lifelong protection against infection. This will help preserve the he alth of the unborn fetus and protect it from fatal pathology.
