Cryptosporidiosis

　　Cryptosporidiosis is an infectious disease caused by a Cryptosporidium called Cryptosporidium parvum, and its specific etiology and mechanism of action are described as follows.

　　1. Etiology

　　Cryptosporidium is a parasitic protozoan that grows intracellularly, belonging to the class Sporozoa, subclass Eucoccidia, order Eimeriida, suborder Eimeriina, family Cryptosporidiidae, genus Cryptosporidium. The body is spherical, with a diameter of 2-4 μm. Its life cycle is similar to that of other protozoa in the class Sporozoa, including asexual schizogamy, sexual reproduction, and sporogony, all of which occur within the same host. The oocysts are oval, with a diameter of 2-6 μm, with smooth walls. The mature oocysts contain 4 crescent-shaped sporozoites. When ingested by humans or animals, the oocysts are released in the small intestine, and the sporozoites escape from the cracks in the oocyst wall and attach to the microvillus brush along the intestinal epithelial cells, being enclosed in parasitophorous vacuoles for development into trophozoites for asexual reproduction. Initially, they develop into trophozoites containing 8 small nuclei, and then further develop into the 1st type schizonts containing 8 schizonts. After the schizonts mature and rupture, the schizonts re-infect other intestinal epithelial cells, continuing the 1st type schizogamy or developing into the 2nd type schizonts containing only 4 schizonts. The schizonts of the mature 2nd type release schizonts that differentiate and develop into female (large) and male (small) gametocytes, which then produce female and male gametes, respectively. Finally, the male and female gametes combine to form zygotes, which develop into oocysts.

　　Oocysts have thin-walled and thick-walled types, with the former accounting for about 20%, which have weak resistance to the external environment. After the sporozoites escape, they directly侵入 new host cells to continue asexual reproduction, causing repeated infections in the host body. The thick-walled oocysts sporulate within the host, with a double-layered wall that is highly resistant to the external environment. After being excreted out of the body with feces, they become infectious. They can be inactivated with 10% formalin solution or 5% ammonia water, and their infectivity can also be lost after being treated at 65°C for 30 minutes.

　　It is currently believed that there are at least 6 species of Cryptosporidium, and infections in humans and mammals are almost always caused by Cryptosporidium parvum.

　　2. Pathogenesis

　　The exact pathogenesis of this disease is not yet fully understood. Most people believe that it may be due to widespread damage to the intestinal mucosal epithelial cells and villous atrophy, leading to malabsorption.

　　Cryptosporidium causes pathogenic changes in humans and animals that are basically similar, with lesions mainly occurring in the small intestine and colon, while the stomach and esophagus may also be involved. The villi in the lesion sites of the small intestine atrophy and become shorter, even disappearing, while the crypt epithelial cells proliferate and the crypts become significantly deeper. The epithelial cells on the mucosal surface are short columnar, with irregularly arranged nuclei. Mononuclear cells and multinucleated inflammatory cells can be seen in the villous epithelium and lamina propria. The pathological changes in the colon mucosa are similar to those in the small intestine. After recovery, the above lesions can return to normal. When the infection extends to the gallbladder, it can cause acute and necrotizing cholecystitis, with thickening and hardening of the gallbladder wall, flattening of the mucosal surface, and the possibility of ulcers. Under the microscope, necrosis of the gallbladder wall and infiltration by multinucleated cells can be observed. In the lung biopsy samples of patients with Cryptosporidium infection in the lungs, lesions such as active bronchitis and focal interstitial pneumonia can be seen.

　　Cryptosporidiosis is often accompanied by abdominal pain, prone to dehydration, acidosis, hypokalemia, and vitamin deficiency. Cryptosporidiosis can also complicate cholecystitis and pulmonary infection. Reactive arthritis is occasionally seen; infants and young children may have dehydration and electrolyte disturbances.

　　The incubation period of cryptosporidiosis is 4 to 14 days, divided into acute gastroenteritis type and chronic diarrhea type, with specific clinical manifestations as described below.

　　1. Acute gastroenteritis type:Infected individuals with normal immune function often manifest as acute gastroenteritis. Diarrhea, 4 to 10 times a day, paste-like or watery stools, occasionally with a small amount of pus and blood, may have a foul odor. Often accompanied by upper abdominal discomfort, pain, and even nausea and vomiting. Some have fever, the course is self-limiting, and most resolve naturally within 2 weeks. No recurrence, good prognosis.

　　2. Chronic diarrhea type:It is mainly seen in individuals with impaired immune function, especially AIDS patients. The onset is gradual, diarrhea persists for a long time, watery stools, with a large amount, varying from 1 to more than 10 liters per day, about 10 times per day. Occasional bloody stools, often accompanied by abdominal pain, prone to dehydration, acidosis, hypokalemia, and vitamin deficiency. The course of the disease can last from 3 to 4 months to even more than a year, and can recur.

　　Diagnosis is made based on epidemiological data, clinical presentation, and laboratory tests. Any disease that causes acute or chronic diarrhea should be differentiated from it, especially bacterial infectious enteritis.

　　The feces of patients with cryptosporidiosis and animals should be managed more strictly to prevent fecal contamination of food and drinking water, and attention should be paid to personal hygiene. Oocysts are highly resistant to external factors, and common disinfectants cannot kill them. 10% formaldehyde, heated to 65-70°C for 30 minutes, can kill the oocysts. Equipment such as colonoscopes used by patients, and basins, should be soaked in 3% calcium hypochlorite solution for 15 minutes before cleaning. Patients should be appropriately isolated. Pay attention to personal hygiene and do a good job of personal protection.

　　The examination of cryptosporidiosis includes feces, pathogens, immunology, and small intestinal mucosal biopsy, with specific examination methods as described below.

　　1. Feces examination:Microscopic examination of feces can show white blood cells or pus cells, but no red blood cells, and rarely phagocytes. If oocysts are found in the feces, gold amine-phenol staining method is generally used for screening, and modified acid-fast staining method can be used when suspicious parasites are found. The combination of both methods is most ideal.

　　2. Pathogen examination:Collecting the patient's feces or vomit, and examining for cryptosporidium oocysts is the main detection method. Direct smears or concentration methods can be used, with special staining for detection.

　　3. Immunological examination:Enzyme-linked immunosorbent assay (ELISA) is used to detect specific antibodies. IgM antibodies appear early but disappear quickly, making them difficult to detect; IgG antibodies appear about two months after infection and can last for more than a year, making them suitable for epidemiological investigation. Immunofluorescence assay (IFA) and monoclonal antibody assays have both sensitivity and specificity of 100%.

　　4. Small intestinal mucosal biopsy can be used when necessary.

　　When cryptosporidiosis patients have acute diarrhea, they should temporarily avoid eating; after the diarrhea symptoms subside, they should avoid eating foods high in fat and lactose, which helps alleviate symptoms. Symptomatic treatment should also be provided for malnourished and hypoproteinemia patients. It is advisable to eat easily digestible, vitamin-rich light foods, which are beneficial for the recovery of intestinal function. At the same time, attention should be paid to dietary hygiene, rest, and maintaining a good mental state.

　　The treatment of cryptosporidiosis includes supportive treatment, pathogen treatment, and immunotherapy. The specific treatment methods and prognosis are described as follows.

　　I. Treatment of Cryptosporidiosis

　　1. Supportive Treatment:Isolate according to intestinal infectious diseases. Severe cases should be hospitalized for treatment, while mild cases can be treated with oral rehydration. Patients with severe diarrhea may cause water and electrolyte imbalances, which must be corrected. Supportive treatment should be strengthened for patients with low immune function. During the onset, avoid eating foods high in fat and lactose, which helps alleviate symptoms. Symptomatic treatment should also be provided for malnourished and hypoproteinemia patients.

　　2. Pathogen Treatment:To date, there are no drugs with proven efficacy against cryptosporidiosis. Drugs considered to have some efficacy include spiramycin, clindamycin, azithromycin, allicin, and others. Some have used spiramycin to treat severe patients, which can alleviate the condition and relieve diarrhea, but cannot prevent recurrence. The adult dosage is 2-4g/d, and the pediatric dosage is 50-100mg/kg per day, with a course of 7-10 days. Allicin for children is 20mg per dose, taken three times a day; for adults, 40mg per dose, taken four times a day, with a course of 7-10 days.

　　3. Immunotherapy:For patients with cryptosporidiosis and immune function damage, it is the key to treatment success to restore their immune function as much as possible. Some have used high-titer colostrum from immune cows to treat AIDS patients with concurrent cryptosporidiosis, and symptoms have been somewhat relieved, but the efficacy has not been confirmed.

　　II. Prognosis of Cryptosporidiosis

　　The prognosis of cryptosporidiosis is closely related to the immune function status of patients. Patients with normal immune function have self-limiting courses and good prognoses. Patients with defective immune function have more severe conditions, prolonged courses, and it is difficult to completely eliminate the parasites. In AIDS patients, cryptosporidiosis is often difficult to control and can eventually lead to patient death.