Cryptosporidiosis - Overview

Cryptosporidiosis is a saprozoonotic protozoan disease characterized by lesions primarily of the digestive tract and dehydration of the body, affecting all groups of vertebrates and humans and characterized by acute diarrhea and spontaneous recovery; in immunosuppressed individuals it becomes chronic (chronic diarrhea) and can be fatal. The route of transmission is fecal-oral.

Code by MB 10

A07.2. Cryptosporidiosis.

Epidemiology of cryptosporidiosis

The natural source of invasion for humans is various mammals, mainly livestock (calves, lambs), as well as animals living in places where people live (rodents, etc.).

Cryptosporidiosis can be transmitted from person to person. This is evidenced by cases of infection of children in child care institutions, hospital outbreaks and accidental infections of laboratory personnel. There are known cases of intrafamilial infection, when adults were infected from children.

The mechanism of transmission of cryptosporidiosis is mainly fecal-oral (through food, water, milk). Transmission by contact-household means is possible, there is a possibility of transmission of cryptosporidia sexually in homosexuals.

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

In more than 80% of cases, cryptosporidiosis is sporadic, the remaining 20% involve group diseases, including waterborne outbreaks. Water is currently considered to be the main route of transmission.

Oocysts are isolated from tap and river water, from wastewater in irrigation fields, from ice obtained from the surface of open water sources. Large waterborne outbreaks of cryptosporidiosis have been described in various areas.

The infectious dose is very small. In an experiment on primates, it was shown that cryptosporidiosis develops when 10 oocysts enter the gastrointestinal tract, and mathematical modeling showed that the disease can be caused by even one oocyst. In healthy volunteers, the clinical picture of the disease developed when 1,000 oocysts entered in 100% of cases and 30 oocysts in 20%.

The natural susceptibility of people is low. Children under 2 years of age are more susceptible to the disease, as well as people with immunodeficiency states (patients receiving chemotherapy, patients with cancer, diabetes, bone marrow and organ transplant recipients) and especially patients with HIV infection in the late stages of the disease. The risk group also includes veterinarians, livestock breeders, and workers at slaughterhouses. Cryptosporidiosis is widespread almost everywhere, on all continents.

Cumulative incidence is about 1-3% in industrialized countries and 5-10% in developing countries. Results of serological studies indicate a wider distribution of cryptosporidiosis. Antibodies to cryptosporidia are found in 25-35% of the population in industrialized countries and in 65% in developing countries. According to some authors, cryptosporidiosis is characterized by seasonality with a peak in the warm season.

Cryptosporidium oocysts are highly resistant to most disinfectants used in homes, hospitals, laboratories, and water treatment systems, making complete removal or eradication of oocysts difficult.

Since there is no completely effective specific therapy for cryptosporidiosis, it is necessary to limit contacts of patients suffering from immunodeficiency conditions with possible reservoirs of the pathogen as much as possible, i.e. avoid their contact with cattle, swimming in natural and artificial reservoirs and drinking raw water. Persons with a normal immune system do not require any special preventive measures. When using medical equipment that is subject to possible contamination 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.

Due to the waterborne spread of cryptosporidium, many countries are tightening requirements for tap water treatment, mainly through improved filtration technology.

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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 C. parvum is pathogenic for humans. Cryptosporidia are obligate parasites that infect the microvilli of the mucous membranes of the gastrointestinal tract and respiratory tract of animals and humans.

The life cycle of cryptosporidia occurs in the body of one host, includes the stages of schizogony, merogony, gametogony and sporogony. Cryptosporidia are localized in a parasitiform vacuole formed by intestinal microvilli, therefore the parasite is located intracellularly, but extraplasmically. First-generation merozoites are capable of proliferating in two directions: into first-generation schizonts or second-generation schizonts, therefore the number of parasites increases. Two types of oocysts are formed in the host's body: thick-walled - leaving the host's body with feces. and thin-walled - releasing sporozoites in the intestine, as a result of which autoinfection is possible.

Pathogenesis of cryptosporidiosis

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

What are the symptoms of cryptosporidiosis?

The main symptoms of cryptosporidiosis are diarrhea syndrome, which occurs as acute enteritis or gastroenteritis and develops 2-14 days after infection. For 7-10 (from 2 to 26) days, patients without immunodeficiency experience 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 abdominal pain, nausea and vomiting (50%), a slight increase in body temperature (not higher than 38 ° C in 30-60% of patients during epidemic outbreaks), loss of appetite, headache. Recovery usually occurs, but in weakened children the disease can last more than 3 weeks and end in death. Very rarely, cryptosporidiosis takes on the character of colitis with the appearance of blood and mucus in the stool.

How is cryptosporidiosis diagnosed?

No specific changes are observed in laboratory tests. Cryptosporidiosis has a severe course with severe immunodeficiency (the number of CD4 lymphocytes is below 0.1x10 ⁹ /l), therefore, changes characteristic of its manifestations are recorded in the tests (for example, leukopenia and erythrocytopenia).

Methods for detecting cryptosporidium oocysts in feces have been developed. For this purpose, the Ziehl-Neelsen staining method, the Koester safranin staining method, and the Romanovsky-Giemsa azure-eosin staining method, as well as negative staining methods, are used. Flotation or sedimentation methods are used (if the material contains a small number of oocysts); when using appropriate preservatives, oocysts can be detected in native material stored in the refrigerator for 1 year.

How is cryptosporidiosis treated?

In mild or moderate cases and in the absence of immune system disorders, cryptosporidiosis can be cured with a sufficiently complete diet (table no. 4) and adequate fluid intake (saline solutions for oral rehydration). In severe cases, it is advisable to perform intravenous rehydration in accordance with the degree of dehydration.