Many protozoa live in the human body. Many of them are pathogens. Our story is about ten of them, most of them. The review is based on historical and recent publications.
Larger. BalantidiumBalantidium coli
The largest protozoan is a human parasite and the only ciliated one in this company. Their dimensions vary from 30 to 150 microns long and 25 to 120 microns wide. For comparison: the length of the malaria plasmodia in the largest stage is about 15 microns, and several times less than the balantidium of intestinal cells, among which the ciliates live. An elephant in a china shop.
Distributedwherever there are pigs, their main carriers. It usually lives in the submucosal layer of the colon, although in humans it also occurs in the lung epithelium. It feeds onB. colibacteria, food particles and fragments of the host's epithelium. In animals, the infection is asymptomatic. People can develop severe diarrhea with a slimy and bloody discharge (balantidiasis), sometimes ulcers form on the walls of the colon. It is rare to die of balantidiasis, but it causes chronic exhaustion.
People become infected through dirty water or food containing cysts. The infection rate in humans does not exceed 1%, while pigs can be infected throughout the world.
Treatedwith antibiotics, no reports of drug resistance of this cilium have yet been reported.
Discoveredby the Swedish scientist Malstem in 1857. Today, balantidiasis is associated with tropical and subtropical areas, poverty and poor hygiene.
The first. Oral amoebaEntamoeba gingivalis
The first parasitic amoeba found in humans. The description of amoebas was published in 1849 in the oldest scientific journal. Amoeba found in dental plaque, hence the Latin name gingivae - gums.
Livesin the mouth of almost all people with toothache or gum pain, inhabits gum pockets and plaque. It feeds on epithelial cells, leukocytes, microbes and in the case of erythrocytes. It is rare in people with a healthy oral cavity.
This small protozoan, 10 to 35 µm in size, does not go out into the environment and does not form cysts, it is transmitted to another host through kisses, through dirty dishes or contaminated food.E. gingivalisis considered an exclusively human parasite, but is sometimes found in captive cats, dogs, horses, and monkeys.
In the early 20th century,E. gingivaliswas described as the causative agent of periodontal disease, as it is always present in inflamed tooth cells. However, its pathogenicity has not been proven.
The drugsthat affect this amoeba are unknown.
The most ubiquitous. Dysentery amoebaEntamoeba histolytica
This bloody intestinal parasite penetrates the tissues of the liver, lungs, kidneys, brain, heart, spleen, genitals. You eat what you get: food particles, bacteria, red blood cells, leukocytes, and epithelial cells.
Distributedeverywhere, especially in the tropics. Generally, people become infected by swallowing a cyst.
In temperate countries, the amoeba usually remains in the intestinal lumen and the infection is asymptomatic. In the tropics and subtropics, the disease process often begins:E. histolyticaattacks the walls. The reasons for the transition to the pathogenic form are not yet clear, but various molecular mechanisms of what is happening have already been described. Therefore, it is clear that amoebae secrete lysis substances, pass through mucus and kill cells. Apparently, the amoeba can destroy the host cell in two ways: by triggering apoptosis in it, or by simply chewing on pieces. The first method was considered the only one for a long time. By the way, the mechanism of cell suicide has not been identified with a record speed, in minutes. The second method was recently described, the authors called it trogocytosis from the Greek "three" - gnaw. Notably, cell-biting amoebae abandon their prey as soon as it dies. Others can engulf the dead cells completely. Cells that bite and eat are supposed to differ in gene expression pattern.
Now, the amoeba's ability to penetrate the bloodstream, liver, and other organs is associated with trogocytosis.
Amebiasis is a deadly disease, around 100, 000 people die from infection withE. histolyticaeach year.
The dysentery amoeba has a non-pathogenic twin,E. dispar, so microscopy is not sufficient to diagnose the disease.
To curemust be destroyed as mobileE. histolyticaand cysts.
DescribedE. histolyticaand determined its pathogenic nature in 1875 in a patient with diarrhea. The Latin name amoeba was given in 1903 by the German zoologist Fritz Schaudin.Histolyticameans tissue destruction. In 1906, the scientist died of an amoebic intestinal abscess.
The most common. Intestinal lambliaGiardia lamblia (G. intestinalis)
Giardia, the most common intestinal parasite, is ubiquitous. 3-7% of people in developed countries and 20-30% in developing countries are infected. That is around 300 million people.
Parasites livein the duodenum and bile ducts of the host, where they float, working with flagella, then adhere to the epithelium with the help of a sticky disc located at the bottom of the cell. For 1 cm2, the epithelium adheres to one million lamblia. They damage the villi, which interferes with the absorption of nutrients, causing inflammation of the mucous membranes and diarrhea. If the disease affects the bile ducts, it is accompanied by jaundice.
Giardiasis is a disease of unclean hands, water, and food. The life cycle of a protozoan is simple: in the intestine there is an active form, and at the exit - with fecal masses - stable cysts. To become infected, it is enough to swallow a dozen cysts, which in the intestines will revert to an active form.
The main secretof the ubiquity of lamblia in surface protein variability. The human body fights against lamblia with antibodies and, in principle, is capable of developing immunity. But people who live in the same area and drink the same water become infected over and over again by the descendants of their own parasites. Why? Because during the transition from the active phase to the cyst and vice versa, lamblia changes the proteins for which the antibodies are produced: variant-specific surface proteins. There are about 190 variants of these proteins in the genome, but only one is ever present on the surface of an individual parasite, the translation of the rest is disrupted by the RNA interference mechanism. And the change happens about once every ten generations.
It is treatedwith an antiprotozoal agent with antibacterial activity. The disease clears up within a week, but if the bile ducts are infected, relapses may occur for many years. Cysts are fought by iodizing the water.
DiscoveredGiardia lambliain 1859 by the Czech scientist Vilém Lambl. Since then, the simplest has changed several names and the current one has been received in honor of the French discoverer and parasitologist Alfred Giar, who did not describe lamblia.
And the first sketch of Giardia was done by Anthony van Leeuwenhoek, who found it in his own deranged chair. It was in 1681.
By the way, Giardia is also very old from an evolutionary point of view, it comes almost directly from the ancestor of all eukaryotes.
The most intimate. Trichomonas vaginalisTrichomonas vaginalis.
The simplest, which is transmitted sexually. It lives in the vagina and in men; In the urethra, epididymis, and prostate, it is transmitted sexually or through wet cloths. Babies can become infected by passing through the birth canal.T. vaginalishas 4 flagella at the anterior end and a relatively short wavy membrane; if necessary, release pseudopods. The maximum size of Trichomonas is 32 by 12 microns.
Trichomonas is morewidespreadthan the causative agents of chlamydia, gonorrhea, and syphilis combined. It affects approximately 10% of women, and possibly more, and 1% of men. This last figure is not reliable because it is more difficult to detect the parasite in men.
T. vaginalisfeeds on microorganisms, including lactic acid bacteria from the vaginal microflora, which maintain an acidic environment and therefore create an optimal pH for itself above4. 9.
Trichomonas kills mucosal cells and causes inflammation. About 15% of infected women complain of symptoms.
It is treatedwith an antibacterial drug. As a preventive measure, a regular douche with diluted vinegar is recommended.
Describedin 1836 by the French bacteriologist Alfred Donne. The scientist did not understand that there was a pathogenic parasite in front of him, but he determined the size, appearance and type of movement of the simplest.
The deadliest. The causative agent of sleeping sicknessTrypanosoma brucei
The causative agent of African sleeping sickness is the deadliest protozoan. An infected person dies without treatment. The trypanosome is an elongated flagellate 15–40 µm in length. Two subspecies are known that are apparently indistinguishable. Disease caused byT. brucei gambiense, lasts from 2 to 4 years.T. brucei rhodesienseis a more virulent transient pathogen from which they die after a few months or weeks.
Distributedin Africa, between the 15 parallels of the southern and northern hemispheres, in the natural range of the carrier: blood-sucking insects of the genusGlossina(tsetse fly). Of the 31 species of flies, 11 are dangerous to humans. Sleeping sickness affects the population of 37 countries south of the Sahara at 9 million km2. Up to 20 thousand people fall ill each year. Now there are about 500 thousand patients, 60 million live at risk.
From the intestine of the flyT. bruceiit enters the human bloodstream, from there it enters the cerebrospinal fluid and affects the nervous system. The disease begins with fever and swollen lymph nodes, followed by lethargy, drowsiness, muscle paralysis, exhaustion, and irreversible coma.
The lethality of the parasite is associated with its ability to cross the blood-brain barrier. The molecular mechanisms are not fully understood, but it is known that when it enters the brain, the parasite secretes cysteine proteases and also uses some host proteins. In the central nervous system, on the other hand, the trypanosome takes refuge from immune factors.
The first description of sleeping sickness in upper Niger was left by the Arab scholar Ibn Khaldun (1332-1406). At the beginning of the 19th century, Europeans were already well aware of the initial sign of the disease - swelling of the lymph nodes in the back of the neck (a symptom of Winterbottom), and the slave traders paid special attention to it.
DiscoveredT. bruceiThe Scottish microbiologist David Bruce, after whom he is named, and in 1903 first established the connection between the trypanosome, the tsetse fly andsleeping sickness.
Treatmentdepends on the stage of the disease, and medications cause serious side effects. The parasite has a high antigenic variability, so it is impossible to create a vaccine.
The most extravagant. LeishmaniaLeishmania donovani
Leishmanias have earned the title of the most outlandish parasites because they live and reproduce in macrophages, cells designed to destroy parasites.L. donovaniis the most dangerous of them. It causes visceral leishmaniasis, colloquially dumdum fever or kala azar, from which almost all patients die without treatment. But the survivors acquire long-term immunity.
There are three subspecies of the parasite.L. donovani infantum(Mediterranean and Central Asia) mainly affects children, dogs are usually its reservoir.L. donovani donovani(India and Bangladesh) is dangerous for adults and the elderly, it has no natural reservoirs. TheL. donovani chagasiAmerican (Central and South America) can live in the blood of dogs.
L. donovani- flagellate no more than 6 microns in length. People become infected after being bitten by mosquitoes of the genusPhlebotomus, sometimes through sexual contact, babies, who pass through the birth canal. Once in the blood,L. donovanipenetrates macrophages, which transport the parasite through internal organs. By reproducing in macrophages, the parasite destroys them. The molecular mechanism of survival in macrophages is quite complex.
Symptoms of the disease: fever, enlarged liver and spleen, anemia, and leukopenia, all contributing to secondary bacterial infection. Every year 500, 000 people become ill with visceral leishmaniasis and about 40, 000 die.
Treatmentheavy: intravenous antimony and blood transfusion.
The taxonomic affiliationL. donovaniwas determined in 1903 by the famous malaria researcher and Nobel laureate Ronald Ross. It owes its generic name to William Leishman, and the specific name to Charles Donovan, who in the same 1903 independently discovered protozoal cells in the spleen of patients who died from kala azar, one in London, the other in Madras.
The most difficult life cycle.Babesia spp.
Babesias, in addition to multi-stage asexual reproduction in erythrocytes of mammals and sex mites in the intestines of the genusIxodes, complicated their development by transovarian transmission. From the intestines of a female mite, protozoan sporozoites enter the ovaries and infect the embryos. When the mite larvae hatch, the babesia passes into their salivary glands and, with the first bite, enters the vertebrate's blood.
DistributedBabesia in America, Europe and Asia. Its natural reservoir are rodents, dogs and livestock. A person is infected with several types: B. microti, B. divergens, B. duncaniandB. venatorum.
The symptoms of babesiosis are similar to those of malaria: relapsing fever, hemolytic anemia, enlarged spleen and liver. Most people recover spontaneously, but babesiosis is fatal for patients with weakened immune systems.
Treatment methodsare still under development, while antibiotics and, in severe cases, blood transfusions are prescribed.
Babesia was described by the Romanian microbiologist Victor Babes (1888), who discovered it in diseased cows and sheep. He decided that he was dealing with a pathogenic bacterium that he namedHaematococcus bovis. Babesia was long considered an animal pathogen until it was discovered in 1957 in a Yugoslav shepherd who died of a B. divergens infection.
The most influential. The causative agent of toxoplasmosisToxoplasma gondii
T. gondiiis the most powerful parasite as it controls the behavior of intermediate hosts.
Distributedeverywhere, unevenly distributed. In France, for example, 84% of the population is infected, in the United Kingdom, 22%.
The life cycle of Toxoplasma consists of two stages: asexual occurs in the body of any warm blood, sexual reproduction is possible only in the epithelial cells of the cat's intestine. TOT. gondiicould complete development, the cat must eat an infected rodent. By increasing the likelihood of this event,T. gondiiblocks the rodents' natural fear of the smell of cat urine and makes it attractive by targeting a group of neurons in the amygdala. How it does it is unknown. One of the putative mechanisms of action is a local immune response to infection. Alters cytokine levels, which in turn raises levels of neuromodulators such as dopamine. Toxoplasma also affects human behavior, which is manifested even at the population level. So in countries with a high level of toxoplasmosis, neuroticism and the desire to avoid uncertainty, new situations are more common. It is possible thatT. gondiiinfection can cause cultural changes.
Infectionin humans is usually asymptomatic, but with weakened immunity it destroys cells in the liver, lungs, brain, and retina, causing acute or chronic toxoplasmosis. The course of infection depends on the virulence of the strain, the state of the host's immune system, and its age; older people are less susceptible toT. gondii.
Treattoxoplasmosis with antiprotozoal medications.
Describedin 1908 in desert rodents. This honor belongs to the staff of the Pasteur Institute of Tunis, Charles Nicolas and Luis Manso.
More pathogen. Plasmodium malariaPlasmodium spp.
Plasmodium malaria is the most pathogenic parasite in humans. The number of patients with malaria can reach 300-500 million, and the death rate during epidemics - 2 million. The disease still claims three times more lives than armed conflict.
Five types of Plasmodium cause malaria in humans:Plasmodium vivax, P. falciparum, P. malariae, P. ovaleandP. knowlesi, which also affectsmacaques.
Distributedin the vector range: mosquitoesAnopheles, which require a temperature of 16–34 ° C and a relative humidity of more than 60%.
Comparison of the genome of the most virulent plasmodia,P. falciparum, with the gorilla plasmodia suggests that humans were infected by their ancestor of these monkeys. The emergence of this form of Plasmodium is associated with the emergence of agriculture in Africa, which led to an increase in population density and the development of irrigation systems.
Sexual reproduction of plasmodia occurs in the intestines of mosquitoes, and in the human body it is an intracellular parasite that lives and reproduces in hepatocytes and erythrocytes until the cells burst. 1 ml of the patient's blood contains 1 - 50 thousand parasites.
The disease manifests as inflammation, recurrent fever and anemia, in case of pregnancy it is dangerous for the mother and the fetus. Red blood cells infected withP. falciparumobstruct capillaries and, in severe cases, internal organ and tissue ischemia develops.
Treatmentrequires a combination of several drugs and depends on the specific pathogen. Plasmodia become resistant to drugs.