Cryptosporidiosis: an overview

Cryptosporidiosis (Cryptosporidiosis) is a saprozonotic protozoal disease characterized by the defeat of the predominantly digestive tract and dehydration of the body, affecting all vertebrate and human groups and characterized by acute diarrhea and spontaneous recovery; in immunosuppressive individuals is chronic (chronic diarrhea) and can lead to death. The transmission route is fecal-oral.

MB code 10

A07.2. Cryptosporidiosis.

Epidemiology of cryptosporidiosis

A natural source of infestation for humans is various mammals, mainly livestock (calves, lambs), as well as animals living in human settlements (rodents, etc.).

Cryptosporidiosis can be transmitted from person to person. This is evidenced by cases of infection of children in children's institutions, nosocomial outbreaks and accidental contamination of laboratory personnel. There are cases of intrafamily infection, when adults were infected from children.

The mechanism of transmission of cryptosporidiosis is mainly fecal-oral (through food, water, milk). Possible transmission by contact-household way, there is a possibility of sexual transmission of cryptosporidia in homosexuals.

From the epidemiological point of view, it is important that oocysts in the invasive stages can survive in the feces of patients for 2 weeks after cessation of diarrhea. The importance of sanitary and hygienic conditions (changes in the nature of nutrition, physico-chemical properties of water, climatic conditions) is evidenced by the fact that cryptosporidium is one of the etiological factors of travelers' diarrhea. In this regard, the second mechanism of the onset of the disease is likely - the activation of invasion in healthy carriers.

More than 80% of cases of cryptosporidiosis are sporadic, the remaining 20% include group diseases, including water outbreaks. Currently, it is believed that the waterway is the main way of transmission of infection.

Oocysts are isolated from tap and river water, from sewage on irrigation fields, from ice obtained from the surface of open water sources. Large water flashes of cryptosporidiosis in various territories are described.

The infectious dose is very small. In the primacy experiment it was shown that cryptosporidiosis develops when 10 oocysts enter the gastrointestinal tract, and by mathematical modeling it is established that even one oocyst causes the disease. In healthy volunteers, the clinical picture of the disease developed when 1000 oocysts hit in 100% of cases and 30 oocysts in 20%.

The natural susceptibility of people is low. The disease is more likely to affect children under 2 years. As well as persons with immunodeficiency states (patients receiving chemotherapy, patients with oncological diseases, diabetes mellitus, recipients of bone marrow and organs) and especially those with HIV infection in the late stages of the disease. Veterinarians, livestock breeders, and slaughter workers are also classed as risk groups. Cryptosporidiosis is widespread almost everywhere, on all continents.

The cumulative incidence is about 1-3% in industrialized and 5-10% in developing countries. The results of serological studies indicate a wider distribution of cryptosporidiosis. Antibodies to cryptosporidia were found in 25-35% of the population in industrially developed countries and in 65% in developing countries. According to some authors, seasonality with a peak in the warm season is typical for cryptosporidiosis.

Oocysts of cryptosporidia are highly resistant to most disinfectants used at home, hospitals, laboratories and water treatment systems, so it is difficult to achieve complete elimination or destruction of oocysts.

Since there is no effective specific therapy for cryptosporidiosis, it is necessary to limit the contacts of patients suffering from immunodeficiency states as much as possible to the possible reservoirs of the pathogen, i.e. Avoid their contact with cattle, bathing in natural and artificial ponds and drinking raw water. Persons with a normal immune system do not need any special prevention measures. When using medical equipment that is exposed to possible infection with cryptosporidia, autoclaving is recommended. Endoscopic instruments should be treated with a 2% solution of glutaraldehyde with a pH of 7-8.5 for 30 minutes.

In connection with the waterway spreading cryptosporidium in many countries, the requirements for purification of tap water are tightened, mainly due to the improvement of filtration technology.

[1], [2], [3], [4]

What causes cryptosporidiosis?

Cryptosporidiosis is caused by coccidia of the genus Cryptosporidium, family Cryptosporidiae, class Sporozoasida, subclass Coccidiasina. The genus Cryptosporidium includes 6 species, of which P. Pervum is pathogenic for humans . Cryptosporidia are obligate parasites that infect microvilli of the mucous membranes of the gastrointestinal tract and respiratory tract of animals and humans.

The life cycle of cryptosporidium passes in the body of one host, includes the stages of schizogony, megohonia. Gametogony and sporogony. Localized cryptosporidia in a parasitiform vacuole formed by intestinal microvilli, therefore the parasite is located intracellularly, but extraplasmatically. Merozoites of the first generation are capable of proliferating in two directions: to the schizonts of the first or to the schizonts of the second generation, so the number of parasites increases. In the host organism, two types of oocysts are formed: thick-walled - leaving the host with faeces. And thin-walled - releasing sporozoites in the intestine, resulting in possible autoinfection.

Pathogenesis of cryptosporidiosis

The pathogenesis of cryptosporidiosis is not well understood. The predominance of cholera-like profuse watery diarrhea in the clinical picture of cryptosporidiosis suggests the production of enterotoxin, but despite numerous searches, the toxin in cryptosporidia has not been detected. Some studies have shown the presence of a gene responsible for the production of a protein with hemolytic activity similar to that of E. Coli 0157 H7 in cryptosporidia . The most typical localization of the process is the distal parts of the small intestine. After the oocyst enters the intestine, the increased multiplication of the parasite begins; the resulting merozoites spread and affect a large number of enterocytes, causing degenerative changes in them (atrophy of the villi). This is accompanied by hypertrophy of crypts, mono- and polymorphonuclear infiltration of the basal membrane and leads to the appearance of craterial depressions on the surface of the epithelium. In severe forms of cryptosporidiosis, total microvilli damage occurs.

What are the symptoms of cryptosporidiosis?

Cryptosporidiosis has the main symptoms - diarrhea syndrome, which proceeds according to the type of acute enteritis or gastroenteritis and develops 2-14 days after infection. During 7-10 (from 2 to 26) days in patients without immunodeficiency there is an abundant watery (cholera-like) stool with a very unpleasant odor, with an average frequency of up to 20 times a day. The patient loses from 1 to 15-17 liters of fluid per day. Profuse diarrhea is accompanied by moderate spastic pain in the abdomen, nausea and vomiting (50%), a slight increase in body temperature (no higher than 38 ° C in 30-60% of patients during epidemic outbreaks), lack of appetite, headache. Usually recovery occurs, but in weakened children the disease can last more than 3 weeks and end with a fatal outcome. Very rarely cryptosporidiosis acquires the character of colitis with the appearance of blood and mucus in the feces.

How is cryptosporidiosis diagnosed?

In laboratory analyzes, no specific changes are observed. Cryptosporidiosis has a severe course with a pronounced immunodeficiency (the number of CD4-lymphocytes is below 0.1x10 ⁹ / l), therefore, changes typical of its manifestations (eg, leukopenia and erythrocytopenia) are recorded in the analyzes.

At present, methods have been developed for the detection of oocysts of cryptosporidia in feces. To do this, apply methods of painting according to Tsiol-Nielsen, safranin Kester and azur-eosin by Romanovsky-Giemsa, as well as methods of negative staining. Flotation or sedimentation methods are used (if the material contains a small amount of oocysts), with the use of appropriate preservatives, oocysts can be found in the native material stored in the refrigerator for 1 year.

How is cryptosporidiosis treated?

In case of mild or moderate disease progression and in the absence of disturbances in the immune system, cryptosporidiosis can be cured under the condition of a sufficiently high-grade diet (table No. 4) and the intake of an adequate amount of liquid (saline solutions for oral rehydration). In severe cases, it is advisable to carry out intravenous rehydration in accordance with the degree of dehydration.