Isosporiasis is an anthroponotic protozoal infection with a fecal–oral transmission mechanism, characterized by damage to the gastrointestinal tract and the development of exicosis. There is the appearance of symptoms of gastroenterocolitis, possibly hemocolitis. The main method of diagnosis is the detection of oocysts in the fecal smears of patients. Additionally, serological methods for detecting infection are used. Symptomatic and pathogenetic therapy aimed at restoring the functions of the body is carried out. As a specific treatment, co-trimoxazole, pyrimethamine, metronidazole are used.
Isolated cases of isosporiasis are recorded everywhere, but the greatest frequency of occurrence is noted in countries of subtropical and tropical climatic zones, such as the states of South Africa, South and Central America, Southeast Asia and the Mediterranean. The entire population is susceptible to infection, but this pathology is characteristic of children under 5 years of age, people living in poor sanitary and hygienic conditions, as well as HIV-infected patients. Seasonality is not expressed. Outbreaks of isosporiasis are recorded mainly in children’s groups.
The causative agent of the disease is Isospora belli (I. hominis) and I. natalensis. The mechanism of infection is fecal-oral, implemented by food, water and household ways. The life cycle of isospores is characterized by the presence of endogenous and exogenous stages. The endogenous stage takes place in the human intestine, the exogenous stage takes place in the environment. The parasite is characterized by sexual (in the host body) and asexual (both in the host body and in the natural environment) reproduction.
A person becomes infected by ingesting mature oocysts with contaminated food and water. Sporozoites come out of the oocyst in the intestine. They penetrate into the cells of the digestive tract, as it is believed – the ileum. Sporozoites are located near the nuclei of epithelial cells, forming trophozoites. After multiple divisions, meronts (schizonts) develop from trophozoites. A section of cytoplasm separates around each daughter nucleus of the schizont – the stage of merozoites begins.
Then the schizont disintegrates, the epithelial cell is destroyed, merozoites penetrate into the intestinal lumen and infect new cells. Thus, the cycle of asexual reproduction (schizogony) repeats many times. After several cycles of schizogony, asexual reproduction is replaced by sexual reproduction. Merozoites from the last generation, hitting epithelial cells, turn into macro- and microgametocytes. Mobile microgametes with two flagella are formed from microgametocytes, and fixed macrogametes are formed from macrogametocytes.
After fertilization, a zygote is formed, which, being covered with a shell, becomes an immature oocyst. Oocysts with feces enter the environment. In the external environment, an exogenous phase of development occurs – sporogony. The zygote inside the cyst divides, forming two sporoblasts. After the formation of the shells, the sporoblasts become sporocysts. After a cycle of division, four sporozoites are formed in each sporocyst, which must enter the host body for further development.
Maturation outside the host body at a temperature of 20 ° C is 2-3 days, in a tropical climate – about a day. Oocysts are quite stable. At low temperatures, sporulation slows down, but when favorable conditions occur, the process resumes. At -21 ° C, sporocysts are able to survive up to a month. According to some reports, cysts are insensitive to the effects of many disinfectants.
It is believed that I. hominis oocysts are pathogenic only for pigs and cattle, forming tissue forms in their bodies. A person becomes infected when eating insufficiently heat-treated meat. Such an infection usually proceeds asymptomatically, however, cases of the disease with symptoms of damage to the digestive system have been described, which were stopped independently without specific therapy.
Getting into the gastrointestinal tract, isospores penetrate into enterocytes. During the development of the parasite form, the mechanism of pinocytosis consumes the cytoplasm of enterocytes, causing their destruction. There is atrophy of the villous epithelium, hypertrophy of crypts occurs, leukocyte exudate and areas of capillary bleeding are formed at the site of inflammation. Such zones contribute to the penetration of virulent pathogens into the human body. As a result of these changes, parietal digestion and absorption of nutrients are disrupted.
The host body begins to lose proteins, fats, vitamin B12, malabsorption syndrome develops and the clinical picture of enterocolitis. It has been proven that some of the sporoziotes newly formed in the human body are able to move to the lymph nodes and there go into a state of rest. Such forms exist for a long time, and with the development of immunodeficiency, in particular, HIV infection, they can be reactivated, forming trophozoites and provoking reactivation of the pathological process.
The incubation period of the disease is about 6-7 days. The disease begins acutely. The appearance of feelings of malaise, weakness, headaches, nausea, vomiting is characteristic. In some cases, there is an increase in body temperature up to 39 ° C. There is pain all over the abdomen. The pain syndrome is both permanent and cramping in nature before the urge to defecate. Patients are concerned about bloating.
The main sign of this nosology is the appearance of diarrhea. The stool becomes liquid, mushy, sometimes watery. There may be impurities in the form of mucus, blood veins. In patients with preserved immunity, isosporiasis occurs in a mild or moderate form and is cured independently after 10-18 days. When the functions of the cells of the immune system are impaired, the phenomena of hemocolitis and severe dehydration are more often recorded.
Due to the difficulties of diagnosis in immunocompetent individuals, this pathology is rarely registered and passes independently without special treatment. Complications and deaths are not described. There are only mentions of isolated cases of cholera-like course. Isosporiasis is considered an opportunistic infection, with immunodeficiency it acquires a prolonged chronic character with a duration of diarrhea up to several months or proceeds in severe form with exicosis of the 3rd degree.
Against the background of a pronounced lack of nutrients, patients lose up to 25% of their body weight. Pronounced electrolyte disturbances and metabolic acidosis are formed. Severe dehydration can cause hypovolemic shock. When the parasite enters the blood, a disseminated process develops with a possible fatal outcome.
When symptoms of gastroenterocolitis appear, patients are hospitalized in an infectious diseases hospital. During the examination, the infectious disease doctor pays attention to the severity of the symptoms of dehydration. Severe exicosis is characterized by lethargy, decreased elasticity of the skin, dryness of the mucous membranes, the appearance of a “white spot” symptom. There is a deafness of heart tones, a decrease in diuresis. The following laboratory methods are used for diagnosis:
- General research. A feature of isosporiasis is the increasing eosinophilia in the general blood test, which can reach 60%. The concentration of hematocrit and hemoglobin increases. In the biochemical analysis of blood with severe dehydration, electrolyte shifts are possible. The coprogram determines mucus, steatorrhea, leukocytes, bacteria, but such changes are not strictly specific to this pathology.
- Identification of the pathogen. To make a diagnosis, microscopy of stool smears is performed. Oocysts from the human body begin to stand out about 10 days after the onset of the disease, when the stage of sexual reproduction begins and clinical manifestations subside, which should be taken into account when prescribing the study. After the onset of clinical recovery, oocysts can be detected in human feces for up to 1-2 months, on average up to 20 days. Additionally, the ELISA method is used.
Differential diagnosis is carried out with diseases provoked by various bacterial pathogens that can cause similar stool disorders: salmonella, klebsiella, clostridium, as well as viral infections – rotavirus and adenovirus. Taking into account abdominal pain, diarrhea, fever, it is necessary to distinguish isosporiasis from surgical diseases with the clinic of “acute abdomen”, for example, appendicitis and pancreatitis.
Pathogenetic and symptomatic therapy is carried out to normalize the stool. Oral rehydration with glucose-salt solutions, infusion therapy with polyionic crystalloids, enterosorbents are prescribed. These measures are aimed at restoring the pathological and physiological losses of the body. When the body temperature rises, antipyretics are used, for example, paracetamol, a mixture of analgin with diphenhydramine.
In people with immunodeficiency, isosporiasis becomes severe. In the initial stages, broad-spectrum antibiotics, such as ciprofloxacin, can be used 15-20 times a day with stool. After determining the pathogen, trimethoprim, metronidazole, pyrimethamine are prescribed. Additionally, biologics containing live lyophilized bacteria are used. Lacto- and bifidobacteria are more suitable for the intestinal microflora.
Prognosis and prevention
In the absence of immune disorders, the outcome is favorable. Symptoms disappear without a trace after 10-20 days, oocysts can be excreted with feces from the host body for up to 2 months. With immunodeficiency, the prognosis is serious. The infection becomes chronic, may result in the death of the patient. Dispensary observation is carried out only in HIV-infected patients. Measures of non-specific prevention include compliance with the rules of personal hygiene and prevention of environmental pollution. To prevent relapses, AIDS patients take co-trimoxazole and pyrimethamine for up to 3-4 weeks.