Toxoplasma: the life cycle of the causative agent of toxoplasmosis Toxoplasma gondii

Toxoplasma is a genus of parasitic eukaryotes, which includes only one reliably studied species - Toxoplasma gondii. This microorganism is able to penetrate into any cells of the animal or human, including the nervous, epithelial, cerebral and cardiac tissue. For life, he does not need oxygen, because he is anaerobic. The main host of toxoplasma are representatives of the cat family, in the body of which it passes several stages of development, turning into an adult cyst. Cats are a kind of incubator, highlighting, together with feces, eukaryote eggs. And as an intermediate host, a variety of warm-blooded animals, including humans, can be selected.

Illness caused by the pathogen

Toxoplasma, the life cycle of which passes several stages, causes a disease called toxoplasmosis. In humans, this disease usually occurs surprisingly easily and without significant symptoms. But if you get an infection during pregnancy or at a time when your immunity is reduced (for example, if you have HIV), it can cause serious consequences and even lead to death.

Structure of the microorganism

The shape of an adult is similar to a crescent moon. At the front there are special processes, with which toxoplasma adheres to the internal organs of the host. It does not have organelles, but without them it can perfectly move by sliding, and also be introduced into the cells of tissues with a corkscrew.

Diagram of microorganism life cycle

The life cycle of toxoplasm can be briefly described by two different states:

• Finding it in the intestines of a cat;
• The yield of eggs in the external environment.

It is possible that the entire development of the microbe can only take place in the body of the same cat. In an adult, the parasite forms gradually, passing from one phase of development to another. The life cycle of toxoplasm, the scheme of which is represented in the picture, consists of successive forms, acquired by the pathogen. As he grows up for several years, he goes through four: 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 a number of daughter merozoites;
• Budding - the formation of two new microorganisms in the shell of a single mother cell;
• Gametogony - sexual reproduction by fusion;
• Sporogony - separation of the zygote formed after sexual reproduction .

Life-cycle phases: asexual

The sexless part of life proceeds in the intermediate host. It can be, again, a cat or any other warm-blooded animal, a bird or a reptile. Trophozoites, once ingested, are introduced into muscle and brain cells, where cell vacuoles with the Brandizoites are formed, which in turn turn into pseudocysts. Toxoplasma gondii can not be detected by the immune system of a person or animal, as the cysts are hidden inside the native cells of the body. And its resistance to antibacterial drugs is so different that sometimes it is impossible to destroy all cysts in tissues. By multiplying inside the vacuoles, it by division produces rapidly multiplying tachyzoites. The host cell of the host bursts, and the mobile parasites come out, hitting an increasing number of healthy 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 swallowed by a cat with an infected bird or mouse. They, having passed the stomach, affect the epithelial cells of the small intestine. There they multiply already by the sexual way, as a result of which oocysts with two spores and four unicellular embryos of the parasite, called sporozoites, appear.

Together with the feces, ready-made eggs are released into the environment. They retain their 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 an oocyst, absorbing unwashed fruits or vegetables, not roasted or raw meat. They are the sources of infection of other hosts, including humans. Toxoplasma gondii is introduced into the cells of the intestine and, together with the blood flow, spreads throughout the body. In the internal organs, most often in the brain, cysts are formed, each of which contains hundreds of cystozoites - mononuclear microbes.

Ways of infection

Unlike cats, a sick person does not distinguish the cysts of the pathogen in the surrounding world, like other representatives of the fauna. Toxoplasma is a microorganism whose eggs can be found almost everywhere: on lawns, in fields, in the ground, grass, sand. In any places where cats went to defecate.

You can catch the pathogen:

• From a sick cat, if its saliva, urine or feces have fallen on the covers, the integrity of which is broken. Therefore, it is necessary to wash hands with soap before meals and after harvesting the cat's tray.
• When eating semi-tender meat of poultry or livestock (lamb, pork), not enough well-washed vegetables, berries, greens and fruits.
• The carriers also come from flies, cockroaches contacting with faeces. After their contact with food, a person can become infected by using spoiled food.

But to catch toxoplasmosis from an ordinary domestic cat is not as easy as you might imagine.

First, it is necessary that the cat be a carrier of toxoplasm.

Secondly, cysts are excreted in a certain period of time. Usually for several weeks with the feces of a cat, but only once in the life of the animal.

Symptoms of infection

Most people do not feel any symptoms, but sometimes the health condition is violated, as in the case of the flu. After a few days or months, the acute stage of the disease gradually changes into a chronic one. In patients with immunodeficiency, the infection can cause toxoplasmic encephalitis, pneumonia or other inflammatory processes, from which a person dies. During pregnancy toxoplasm, the life cycle of which passes several stages and is not disturbed in the process of migrating the pathogen from the intermediate host to the main one, penetrates the placenta and affects the fetus. Often this leads to a fetal death of the baby or a 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 of their residence. The parasite does this in order to move to the next phase of the life cycle, if the cat eats easy prey. The relationship between schizophrenia and the presence of toxoplasma in the body was studied. Studies have shown that the presence of infection can affect the development of paranoia or other psychological changes.

Analyzes

After primary infection in humans, a permanent and lifelong immunity to the microorganism is formed. Immunoglobulins come to the aid in the fight against infection. Antibodies are capable of:

• Neutralize the toxins that the parasite produces;
• To contact the cells of the pathogen;
• Penetrate through the placenta, partially forming the fetus passive protection.

Toxoplasma IgG is detected in serum, cerebrospinal fluid, pulmonary sputum and other biological secrets. If these antibodies are detected in an amount of 7/16 hl, an additional study is carried out by a polymer chain reaction to detect infection activity. The presence of an acute period of the disease - the primary infection - is indicated by the presence of the DNA of the pathogen in biological media. It should be noted that toxoplasma can not be detected in the blood plasma in all cases, even with increased invasion.

Interpretation of results

Toxoplasma IgG with the sign "+" and IgM c "-" indicates the development of a lasting immunity for life. Both indicators with a "+" sign indicate the presence of primary infection. And if IgM with a plus, but IgG with a minus, then during pregnancy it can mean intrauterine infection of the fetus. Absence of IgG antibodies in the blood always indicates a negative result. Even if the infection took place, it happened a long time ago. Therefore, at the moment, there is no danger for man anymore.

Toxoplasma, whose life cycle is so complex, is the causative agent of a serious illness. But in fact, almost any person in the world who lives side by side with a cat, has time to "meet" it even in childhood. The asymptomatic acute period of the disease does not attract attention, and chronic form or carrier does not harm the person and other people around him. Toxoplasma is dangerous only when the pregnant woman was not infected earlier, but picked up the infection while the child is pregnant. Therefore, in childhood or at the stage of family planning, you should not limit yourself in communicating with cats - it is better to have your pet, so that the body has developed a lifelong protection against infection. This will help to preserve the health of the future fetus and protect it from deadly pathology.