Table of contents:
- Toxoplasmosis in humans
- Study history
- Reservoir and sources of pathogen
- Etiology and developmental cycle of the pathogen
- Main clinical signs
- General information about toxoplasmosis research
Video: Toxoplasmosis In Humans: Signs, Symptoms And Treatment
Toxoplasmosis in humans is a dangerous infectious disease that infects both humans and animals. The life cycle of Toxoplasma is provided by two hosts - the final and intermediate.
The content of the article:
- 1 Toxoplasmosis in humans
- 2 Study history
- 3 Reservoir and sources of pathogen
- 4 Etiology and developmental cycle of the pathogen
- 5 Main clinical signs
- 6 General information about toxoplasmosis research
Toxoplasmosis in humans
Toxoplasmosis is a widespread parasitic infection of humans and vertebrates, which is characterized by an extreme polymorphism of clinical manifestations in cases of a manifest form of the disease and the possibility of long-term chronic carriage.
The important social significance of this infection is determined by the fact that, due to the possibility of a transplacental transmission route, it occupies one of the leading places among the infectious agents of perinatal pathology of the TORCH group of infections, causing severe congenital diseases in children and a decrease in fertility.
The increased interest in the problem of toxoplasmosis is currently associated with its role as an opportunistic parasitosis in HIV infection in the development of its final phase - AIDS. Against the background of HIV-induced immunodeficiency, latent toxoplasmosis exacerbates and gives rise to disseminating infection with damage primarily to the central nervous system in the terminal phase, the so-called neuro-AIDS.
The causative agent of toxoplasmosis Toxoplasma gondii was discovered for the first time in 1908 by the French researchers Nicoll et Manceaux in Tunisia in the North African rodent Chenodactylus gondii and Splendore in Brazil in rabbits. The form of the parasite (crescent, orange slice) is the basis of the generic name - toxon in Greek - arch, arch, specific - gondii is associated with the name of the host - a rodent.
Toxoplasmosis in humans. The first information about the possible pathogenic role of Toxoplasma for humans is associated with the works of A. Castellani (1913, 1914) in Ceylon and A.I. Fedorovich (1916) in Russia, who discovered parasites like Toxoplasma in the study of spleen smears and blood test for malaria.
A reliable description of toxoplasmosis in humans was made by the Czech ophthalmologist Janky (Janky, 1923), who observed a case of severe pathology in a newborn who died with symptoms of hydrocephalus, left-sided microphthalmos, bilateral macular coloboma. Microscopic examination of sections of the membranes of the eye revealed parasites similar to those previously described in animals.
In Ukraine, the study of different sides of the problem of toxoplasmosis is associated with the names of A.K. Korovitsky, A.E. Grigorashenko, M.N. Melnik, A.G. Papa. A. Sokol, I. I. Grishchenko, N. I. Shpaka and others.
Reservoir and sources of pathogen
Mainly cats and other representatives of felines, in the body of which the sexual development cycle of the parasite passes and which should be recognized as its final hosts. However, tocosoplasmosis was found in almost all surveyed species of mammals and birds, which are intermediate hosts of the parasite.
Murine rodents, hares, in which toxoplasmosis takes on the character of large and severe epizootics, are especially often affected. By becoming prey to cats, rodents maintain the life cycle of Toxoplasma. Intermediate hosts, including humans, do not pose an epidemiological danger.
Etiology and developmental cycle of the pathogen
Toxoplasmosis in humans. The causative agent of toxoplasmosis, Toxoplasma gondii, belongs to the subkingdom Protozoa, type Apicomplexa, class Sporozoa, subclass Coccidia, order Eucoccidiida, suborder Eimerina.
Toxoplasmas are conditionally pathogenic protozoa with an intracellular parasitic pattern, common on all continents, in countries with different climatic and geographical conditions. This can be explained by the presence of a wide range of hosts among hundreds of species of mammals and birds, as well as the ability of the pathogen to parasitize in tissue cells of virtually all organs. According to the apt definition of T.V. Beir and A. Ya, Lysenko (1984), Toxoplasma is a unique parasite characterized by ubiquity, polyxeness and pantropism.
The circulation of Toxoplasma in nature is provided by two hosts - the final and the intermediate.
The final owners - guardians of the pathogen in nature, in which the sexual development process (intestinal phase) is underway, are representatives of the feline family (Felidae), in the wild they are a wild cat, snow leopard, lynx, jaguar, ocelot, Bengal tiger, in a synanthropic focus - a domestic cat, which, in terms of epidemiological significance, has become the center of the problem, as an important source of infection for humans.
Asexual development of Toxoplasma (extraintestinal, tissue phase) takes place in the organs of intermediate hosts: domestic animals and wild mammals, birds and humans.
In natural foci, the range of intermediate hosts includes almost all surveyed species of mammals and birds, in conditions of synanthropic foci - domestic, farm animals, birds, and rodents.
In the process of implementing the life cycle (two phases), the pathogen passes through the following main stages of development: endozoite (tachyzoite), pseudocyst, tissue cyst and oocyst (zygocyst).
The endozoite is shaped like an orange slice, a crescent moon with one pointed and the other rounded end. Its dimensions vary from 4 - 7 microns in length and 2 - 4 microns in width. When stained according to Romanovsky - Giemsa, the cytoplasm is stained in blue tones, the nucleus - in ruby red. Endozoites are mobile, capable of actively penetrating into the tissue cell of any organ. Inside the invaded cell, the parasite multiplies rapidly through longitudinal division or internal budding (endodiogony). Such an affected cell with an accumulation of endozoites in its cytoplasm is called a pseudocyst.
In the endozoic stage, Toxoplasma die when heated to 55 ° C for 5-10 minutes, when exposed to 50% alcohol, 1% phenol, 2% chloramine. They do not grow on simple media. They can be cultured on chicken embryos, tissue culture, and laboratory animals (white mice, hamsters, etc.).
The tissue cyst reaches sizes from 50 to 100 microns. It has its own shell, impermeable to antibodies, it also undergoes the process of endodiogeny with the formation of bradyzoites. Tissue cysts remain viable for many years, possibly throughout the life of the host.
The oocyst is the final stage in the development of toxoplasma in the intestine of a cat, which is excreted with feces into the external environment. A mature oocyst is 10 - 12 µm in diameter; it contains 2 sporocysts with 4 sporozoites in each.
All of these stages of development of Toxoplasma are invasive, but oocysts and tissue cysts are more active.
Intestinal phase. Cats become infected by the oral route when they eat the tissues of the intermediate host, which contain any stage of Toxoplasma (endozoites, pseudocysts, tissue cysts), as well as by swallowing oocysts isolated on the soil with the feces of a cat infected with Toxoplasma.
In the epithelial cells of the intestinal mucosa of the animal, the process of schizogony with the formation of merozoites takes place, and later - gametogony with the formation of macro- and microgametes. When they merge, oocysts are formed, excreted with feces into the external environment. In 2 - 5 days, the oocyst in the soil matures, becomes invasive and remains viable for up to 18 months.
In a cat, the final host, in each case of infection, asexual development also takes place in parallel with the sexual phase, as in the intermediate host, the tissue, or extraintestinal, phase.
Infection of humans or animals - intermediate hosts - occurs mainly through the oral route when oocysts are swallowed or when the meat of infested animals is eaten. With the destruction of oocysts, tissue cysts in the human digestive canal, the released endozoites penetrate into the cells of the intestinal mucosa and through the lymphatic and blood pathways spread to other organs and tissues, continuing to develop until the formation of pseudocysts.
The duration of development of one generation of endozoites is 5 hours. During this time, 12-32 daughter individuals are formed from one.
When the acute process subsides, with chronic toxoplasmosis against the background of developing immunity, tissue cysts are formed, covered with their own membrane, impermeable to antibodies. Having formed inside the cell, after its death, tissue cysts are located extracellularly, most often in the brain, membranes of the eye, skeletal muscles, heart muscle, uterus. Over time, they will calcify.
At the same time, with long-term preservation, when conditions change (immunosuppression), it is possible to excist and release bradyzoites, which penetrate into cells, multiply and cause a relapse of the disease.
The life cycle of toxoplasma is carried out in three ways (A. Ya. Lysenko), which can pass independently of each other:
- cat - external environment - cat;
- cat - external environment - warm-blooded animal - cat;
- warm-blooded animal - warm-blooded animal.
The optimal way for the development and preservation of the pathogen in nature is the second, in which both phases are involved - intestinal (sexual) in the final host - a cat, and tissue (asexual) in intermediate hosts.
Main clinical signs
Distinguish between congenital and acquired toxoplasmosis. With congenital toxoplasmosis, the clinical picture depends on the period of the disease in which the birth occurred. When a fetus is infected in the early period of its development, when its organs are formed, various congenital deformities are characteristic. In other cases, the generalization of the process occurs in utero and the child is born with symptoms of encephalomyelitis, damage to the liver, spleen, heart. When the fetus is infected, shortly before birth, it develops an acute form of the disease in the womb or shortly after birth: there is a high temperature, convulsions, paralysis, symptoms of damage to the meninges.
Acquired toxoplasmosis in adults often occurs in a latent form. The acute form can have a typhoid (exanthemic) or encephalitic course (as well as with eye damage). The most common is the chronic form of the disease with prolonged low-grade fever, headaches, swollen lymph nodes, liver, spleen, symptoms of myositis, arthralgia.
General information about toxoplasmosis research
Toxoplasma gondii is a unicellular parasitic microorganism that is found in the ground and in the body of some animals and can cause the infectious disease toxoplasmosis.
Toxoplasmosis in humans. Toxoplasma is very common all over the world. The infection rate of the population in some countries is 95%. This parasite is capable of infecting mammals, rodents and birds. This is one of the so-called TORCH infections (translation of the first letters of the Latin names of toxoplasma, rubella, cytomegalovirus, herpes), which are dangerous to the fetus.
The route of Toxoplasma infection is usually oral. The microorganism enters the human body with water and food contaminated with parasites, especially with raw or insufficiently cooked meat. Since cats are a common carrier of infection, infection is possible when cleaning the cat litter of an infected animal and lack of personal hygiene.
The transplacental route of transmission of infection is likely - from mother to child. A person can also become infected through blood transfusions and organ donations.
The life cycle of a microorganism takes place with a change of hosts. The domestic cat, as the final owner, becomes infected by eating rodents and birds. In the intestines of cats, Toxoplasma divides and forms oocysts. With active infection, millions of microscopic oocysts are excreted in cat feces over several weeks. Oocysts become infectious after 2-3 days and remain viable for several months. In the body of other hosts, including humans, Toxoplasma passes through a limited period of its life cycle and forms inactive cysts in the muscles, brain and eyes.
The host's immune system is able to keep cysts dormant and protect the body from infection. The resting stage can last a lifetime until immunodeficiency occurs. For most healthy people, the ingestion of Toxoplasma into their body can be asymptomatic or disguised as a mild cold.
Toxoplasma infection plays a role in the development of mental illnesses such as schizophrenia and psychosis. With toxoplasma damage to the organs of vision, chorioretinitis occurs.
Newly-onset or reactivated Toxoplasma infection can be severe and cause complications in patients with weakened immune systems: patients with HIV, primary immunodeficiencies, patients receiving chemotherapy or immunosuppressive therapy after organ transplantation.
Signs of toxoplasmosis: prolonged fever, headache, swollen lymph nodes, muscle pain, enlarged liver, hepatitis. Intrauterine infection leads to blindness, encephalomyelitis, growth retardation, and even death of newborns. In immunocompromised patients, the infection causes meningitis and encephalitis (inflammation of the brain with impaired consciousness, headache, fever). Early diagnosis is critical to the effectiveness of treatment. It is very difficult to get rid of a parasite in a chronic infection.
If infected during pregnancy, the risk of transmitting Toxoplasma to the fetus is 30-40%. Early infection leads to miscarriage, stillbirth, or serious neurological impairment in the newborn.
Most babies infected late in pregnancy do not develop symptoms of toxoplasmosis until a few years after birth: hearing loss, severe eye problems, and neurological deficits.
There are several ways to detect toxoplasmosis. The choice of technique and material depends on the clinical picture of the disease. To detect primary or secondary toxoplasma infection and determine its activity, the level of IgM and IgG antibodies in serum is measured (serological method) and the DNA of the microorganism is recognized (PCR). The molecular genetic method is highly sensitive and species-specific - with an active infection, Toxoplasma DNA can be determined with great accuracy.
The presence of DNA from the so-called gondia in blood and urine indicates an active infectious process.
Find out more:
- Intracellular parasites: types, diagnosis and treatment
- Toxoplasmosis - causes, symptoms, diagnosis and treatment