Many protozoa live in the human body. Many of them are pathogenic. Our story is about ten of them, the best. The review is based on both historical and recent publications.
The largest. BalantidiumBalantidium coli
The largest protozoan is a human parasite and the only eyelash in this company. Its dimensions vary from 30 to 150 microns in length and from 25 to 120 microns in width. For comparison: the length of the malarial plasmodium at its largest stage is about 15 microns, and several times less than the balantidium of the intestinal cells between which the infusoria lives. An elephant in a Chinese store.
Scatteredwherever there are pigs - its main carriers. It usually lives in the submucosa of the colon, although in humans it also occurs in the pulmonary epithelium. It feeds on the bacteriaB. coli, food particles, fragments of the host epithelium. In animals, the infection is asymptomatic. People can develop severe diarrhea with bloody, liquid discharge (balantidiasis), sometimes ulcers form in the walls of the colon. It is rare to die of balantidiasis, but it causes chronic fatigue.
People become infected through contaminated water or food containing cysts. The infection rate in humans does not exceed 1%, while pigs can be infected worldwide.
Treatedwith antibiotics, no drug resistance reports have been reported for this eyelash.
Discoveredby Swedish scientist Malstem in 1857. Today, balantidiasis is associated with tropical and subtropical areas, poverty and poor hygiene.
First. Oral amoeba Entamoeba gingivalis
The first parasitic amoeba found in humans. The description of the amoebae was published in 1849 in the oldest scientific journal. Found amoeba on dental plaque, hence the name from the Latin gingivae - gums.
Livesin the mouths of almost all people with toothaches or gums, resides in gum pockets and plaque. It feeds on epithelial cells, leukocytes, microbes and in the case of erythrocytes. Rare in people with a healthy oral cavity.
This small protozoan, 10–35 μm in size, does not protrude into the environment and form cysts; transmitted to another host by kissing, 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 twentieth century,E. gingivaliswas described as the causative agent of periodontal disease, as it is always present in inflamed dental cells. However, its pathogenicity has not been proven.
Drugsthat affect this amoeba are unknown.
Most prevalent. Diesenteria amoebaEntamoeba histolytica
This bloody intestinal parasite penetrates the tissues of the liver, lungs, kidneys, brain, heart, spleen, genitals. Eat what you will get: food particles, bacteria, red blood cells, leukocytes and epithelial cells.
Scatteredeverywhere, especially in the tropics. Usually, people become infected by swallowing a cyst.
In soft places, the amoeba usually remains in the intestinal lumen and the infection is asymptomatic. In the tropics and subtropics, the pathological process often begins:E. histolyticaattack the walls. The reasons for the transition to the pathogenic form are still unclear, but some molecular mechanisms of what is happening have already been described. So it is clear that amoebae secrete lysing substances, penetrate through mucus and destroy cells. Apparently, the amoeba can destroy the host cell in two ways: by causing apoptosis in it or simply by chewing pieces. The first method was considered the only one for a long time. By the way, the mechanism of cellular suicide at a record speed - in minutes - has not been identified. The second method was described quite recently, the authors called trogocytosis from the Greek "three" - to gnaw. It is worth noting that the amoebae that bite the cells abandon their prey as soon as it dies. Others can completely phagocytose dead cells. It is assumed that biting and swallowing cells differ in the pattern of gene expression.
Now the ability of the amoeba to penetrate the bloodstream, liver and other organs is associated with trogocytosis.
Amebiasis is a deadly disease, with about 100, 000 people dying from E. histolytica infection each year.The dysentery amoeba has a non-pathogenic twin,E. dispar, so microscopy is not enough to diagnose the disease.
To curemust be destroyed as removableE. histolyticaand cysts.
DescribedE. histolyticaand determined its pathogenic nature in 1875 in a patient with diarrhea. The Latin name for the amoeba was given in 1903 by the German zoologist Fritz Schaudin.Histolyticameans tissue destroyer. 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 about 300 million people.
Parasites livein the host duodenum and bile ducts, where they float, working with flagella, then attach to the epithelium with the help of an adhesive disc located at the bottom of the cell. At 1 cm2the epithelium sticks to one million lamblias. They damage the villi, which interfere with the absorption of nutrients, causing inflammation of the mucosa and diarrhea. If the disease affects the bile ducts, it is accompanied by jaundice.
Giardiasis is a disease of dirty hands, water and food. The life cycle of the protozoan is simple: in the intestine it has an active form and at the exit with fecal masses there are stable cysts. To become infected, it is enough to swallow a dozen cysts, which in the intestines will again return to an active form.
The main secretof the ubiquity of lamblia in the variability of surface proteins. The human body fights lamblia with antibodies and, in principle, is able to develop immunity. But people who live in the same area and drink the same water get infected again and again by the offspring of their parasites. WhyBecause during the transition from the active phase to the cyst and vice versa, lamblia changes the proteins in which antibodies are produced - the specific surface protein of the variant. There are about 190 variants of these proteins in the genome, but only one is always present on the surface of an individual parasite; the translation of the rest is interrupted by the RNA interference mechanism. And change happens about once in ten generations.
Treatedwith an antiprotozoal agent with antibacterial activity. The disease disappears within a week, but if the bile ducts are infected, relapses are possible for many years. Cysts are fought by iodizing water.
DiscoveredGiardia lambliain 1859 by Czech scientist Vilém Lambl. Since then, the simplest has changed several names and the current one has taken on the honor of French discoverer and parasitologist Alfred Giar, who did not describe lamblia.
And Giardia's first sketch was made by Anthony van Leeuwenhoek, who found him in his creepy chair. It was in 1681.
By the way, Giardia is also very ancient evolutionary, it comes almost directly from the ancestor of all eukaryotes.
The most intimate. Trichomonas vaginalisTrichomonas vaginalis.
The simplest, which is sexually transmitted. Lives in the vagina and in men - in the urethra, epididymis and prostate gland, 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 corrugated membrane; if necessary, it releases pseudopods. The maximum size of Trichomonas is 32 by 12 microns.
Trichomonas is more prevalentthan the causative agents of chlamydia, gonorrhea, and syphilis combined. It affects about 10% of women, and probably more, and 1% of men. The latter figure is unbelievable because it is more difficult to detect the parasite in men.
T. vaginalisfeeds on microorganisms, including lactic acid bacteria of the vaginal microflora, which maintain an acidic environment, and thus create an optimal pH for themselves above 4. 9.
Trichomonas destroys mucosal cells, causing inflammation. About 15% of infected women complain of symptoms.
Treatedwith an antibacterial drug. As a preventive measure, regular washing with diluted vinegar is recommended.
Describedin 1836 by the French bacteriologist Alfred Donne. The scientist did not realize that he had the pathogenic parasite before him, but he determined the size, appearance, and type of movement of the simplest.
Most deadly. The causative agent of sleep sicknessTrypanosoma brucei
The causative agent of African sleep sickness is the most deadly protozoan. An infected person dies without medication. Trypanosoma is an elongated flagella 15-40 μm long. There are two subspecies that are not distinguished from the outside. Disease caused byT. brucei gambiense, lasts 2-4 years.T. brucei rhodesienseis a more virulent, transient pathogen from which they die after months or weeks.
Distributedin Africa, between the 15th parallel of the Southern and Northern Hemispheres, in the natural range of the carrier - blood-sucking insects. Sleep sickness affects the population of 37 countries in sub-Saharan Africa at 9 million km2. Up to 20, 000 people get sick each year. There are now about 500, 000 patients, 60 million living at risk.
From the intestines of fliesT. bruceienters the human bloodstream, from there enters the cerebrospinal fluid and affects the nervous system. The disease begins with fever and inflammation of the lymph glands, followed by apathy, drowsiness, muscle paralysis, fatigue, and irreversible coma.
Mortality of the parasite is associated with its ability to overcome the blood-brain barrier. Molecular mechanisms are not fully understood, but it is known that when it enters the brain, the parasite secretes cysteine protease and also uses some host proteins. In the central nervous system, on the other hand, trypanosome is hosted by immune factors.
The first description of sleep sickness in the upper Niger was made by the Arab scholar Ibn Khaldun (1332-1406). In the early 19th century, Europeans were already aware of the initial sign of the disease - swollen lymph nodes in the back of the neck (a symptom of Winterbottom), and slave traders paid special attention to it.
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 extravagant parasites because they live and reproduce in macrophages - cells created to destroy parasites.L. donovaniis the most dangerous of them. Causes leishmaniasis of the internal organs, dumdum conversational fever, or kala azar, from which almost all patients die without treatment. But survivors gain long-term immunity.
There are three subtypes of the parasite.L. donovani infantum(Mediterranean and Central Asia) mainly affects children and is often a dog tank.L. donovani donovani(India and Bangladesh) is dangerous for adults and the elderly, has no natural reservoirs. American L. donovani chagasi (Central and South America) can live in the blood of dogs.
L. donovani- flagella not more than 6 microns in length. Humans become infected after being bitten by mosquitoes of the genusPhlebotomus, sometimes through sexual contact, infants - passing through the birth canal. Once in the bloodstream, L. donovanipenetrates macrophages, which carry the parasite through internal organs. Reproduction 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, which contribute to a secondary bacterial infection. Every year 500 thousand people get visceral leishmaniasis and about 40 thousand die.
Treatmentsevere - intravenous antimony and blood transfusion.
Taxonomic affiliationL. donovaniwas defined in 1903 by renowned malaria researcher and Nobel laureate Ronald Ross. Its general name is owed to William Leishman and the specific name to Charles Donovan, who in the same 1903 independently discovered protozoan cells in the spleen of patients who died from the azar castle, one in London, the other in Madras.
The most difficult life cycle.Babesia spp.
Babesias, in addition to multiphase asexual reproduction in mammalian erythrocytes and sex mites in the intestines of the genusIxodes, have complicated their development by transovarial transmission. From the intestines of a female mite, protozoan sporozoites penetrate the ovaries and infect the embryos. When the mite larvae hatch, the babysitter passes into their salivary glands and, with the first bite, enters the blood of vertebrates.DistributedBabes in America, Europe and Asia. Their natural reservoir is rodents, dogs and livestock. A person is infected with several types: B. microti, B. divergent, B. duncaniandB. venatorum.
Symptoms of babesiosity are similar to malaria - recurrent fever, hemolytic anemia, enlarged spleen and liver. Most people recover spontaneously, but babysitting is fatal to patients with weakened immune systems.
Treatment methodsare still being developed, while antibiotics and, in severe cases, blood transfusions are prescribed.
Babesia was described by the Romanian microbiologist Victor Babes (1888), who discovered it in sick cows and sheep. He decided it had to do with a pathogenic bacterium he calledHaematococcus bovis. Babesia has long been considered an animal pathogen, until it was discovered in 1957 in a Yugoslav herb that died from B. divergens infection.
Most influential. Toxoplasmosis causative agentToxoplasma gondii
T. gondiiis the most powerful parasite as it controls the behavior of intermediate hosts.
Scatteredeverywhere, unevenly distributed. In France, for example, 84% of the population is infected, in the UK - 22%.
The life cycle of Toxoplasma consists of two stages: asexual occurs in the body of any warm-blooded reproduction, sexual is possible only in the epithelial cells of the feline intestine. For herT. gondiimay terminate development, the cat should eat an infected rodent. 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 he does it is unknown. One of the putative mechanisms of action is a local immune response to infection. It alters cytokine levels, which in turn raises the levels of neuromodulators such as dopamine. Toxoplasma also affects human behavior, which is also manifested at the population level. So in countries with a high level of toxoplasmosis, neuroticism and a desire to avoid insecurity, new situations are more common. It is possible that infection withT. gondiican lead to cultural changes.
Infectionin humans is often asymptomatic, but with weakened immunity, destroys cells of the liver, lungs, brain, retina, causing acute or chronic toxoplasmosis. The course of the infection depends on the virulence of the species, the condition of the host's immune system and its age - older people are less susceptible toT. gondii.
Treat toxoplasmosis with antiprotozoal drugs.
Describedin 1908 in desert rodents. This honor belongs to the staff of the Pasteur Institute in Tunisia Charles Nicolas and Luis Manso.
Most pathogenic. Plasmodium malariaPlasmodium spp.
Plasmodium malaria is the most pathogenic parasite in humans. The number of malaria patients can reach 300-500 million, and the death rate during epidemics - 2 million. The disease still requires three times more lives than armed conflict.Five species of Plasmodium cause malaria in humans:Plasmodium vivax, P. falciparum, P. malariae, P. ovaleandP. knowlesi, which also affects macaques.
Scatteredin the range of vectors - mosquitoesAnopheles, which need a temperature of 16–34 ° C and a relative humidity of more than 60%.
Comparison of the genome of the most virulent plasmodium,P. falciparum, with gorilla plasmodia suggests that humans were infected by its ancestor from these apes. 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.
Plasmodium sexual reproduction occurs in the intestines of mosquitoes and in the human body is a parasite within the cell that lives and reproduces in hepatocytes and erythrocytes until the cells explode. 1 ml of patient blood contains 1 - 50 thousand parasites.
The disease manifests itself as inflammation, recurrent fever and anemia, in case of pregnancy it is dangerous for mother and fetus. Erythrocytes infected withP. falciparumblock capillaries and in severe cases ischemia of internal organs and tissues develops.
Treatmentrequires a combination of several medications and depends on the specific pathogen. Plasmodia becomes drug resistant.