Cryptosporidiums are protozoan parasites belonging to the order Sporozoa. One of these (C. hominis) is a human parasite. Also several others may be parasitic in humans in addition to animals (e.g. C. parvum).
Worldwide significance has increased due to epidemics, difficult-to-manage AIDS-related diarrhoea and observations related to nutritional problems in children.
Two other protozoans, Cyclospora cayetanensis and Cystoisospora belli (formerly Isospora belli), can cause cryptosporidium-like infections.
Distribution
Encountered world-wide. C. parvum that causes diarrhoea in calves may infect humans.
The global significance has increased due to epidemics, AIDS-related diarrhoea that is difficult to manage as well as observations regarding nutritional disturbances in children.
Transmission
Transmission occurs through ingestion of cysts in fecally contaminated food or drink or by direct faeces-mediated contact.
Symptoms
The incubation period is around one week (2 to 10 days).
The symptoms start with watery diarrhoea and epigastric cramps. Nausea is common, vomiting less frequent.
One third of the patients have a short (24h) fever period.
Symptoms last on average 12 days, varying from 2 days to 1 month. Symptoms may be violent and prolonged in immunocompromised patients.
Diagnosis
The diagnosis is based on detection of the causative organism through either nucleic acid detection or microscopy.
The most sensitive and hence the primary test is detection of parasitic nucleic acids in faeces.
If nucleic acid detection test is not available, a microscopy-based test is an alternative. Oocysts are excreted most abundantly and are thus best detected in the early phase of the disease. Two stool samples obtained on different days may then be sufficient. After the symptoms have disappeared oocysts continue to be excreted in the faeces for about 1 week.
This test can also detect the oocysts of the diarrhoea-causing protozoans Cyclospora cayetanensis and Cystoisospora belli. Microscopy is thus the primary test when these organisms are suspected.
Treatment and prognosis
In generally healthy individuals the disease is gradually cured spontaneously and the treatment is usually symptomatic. Some of the infected persons remain asymptomatic carriers.
Nitazoxanide (500 mg × 2 for 3 days; in children aged 1-3 years 100 mg × 2 and in children aged 4-11 years 200 mg × 2 for 3 days) can be used for non-immunocompromised patients with severe symptoms. The drug is, however, under special license and effective only in approximately half of the patients. Therefore, it is advisable to centre the drug treatment to specialized care.
In immunocompromised patients (e.g. HIV-infected), the diarrhoea may be extremely profuse and the disease may persist for several months. The infection may spread outside the intestine and may even be fatal.
The evidence on the effectiveness of drug treatment in immunocompromised patients is controversial. Cryptosporidiosis may be treated with oral nitazoxanideTreatment of Cryptosporidiosis in Immunocompromised Patients. More important, however, is to try to reduce immunosuppression. Of the drugs used for HIV infection, protease inhibitors are also slightly effective against Cryptosporidium.
Cyclospora cayetanensis and Cystoisospora belli infections that cause cryptosporidium-like manifestations can be treated with trimethoprim-sulfamethoxazole.
Prevention
Prevention is based on avoiding contamination, which requires identification of the possible sources of infection, i.e. diagnosing Cryptosporidium infections.
Cryptosporidium is easily transmitted and can, therefore, cause epidemics spread by water, food or person-to-person contact.
The oocysts are not destroyed in chlorinated water but remain infective several days. Therefore, swimming must be avoided during the infection, at least in swimming pools.
References
Pönkä A, Kotilainen H, Rimhanen-Finne R et al. A foodborne outbreak due to Cryptosporidium parvum in Helsinki, November 2008. Euro Surveill 2009;14(28):. [PubMed]
Cacciò SM, Chalmers RM. Human cryptosporidiosis in Europe. Clin Microbiol Infect 2016;22(6):471-80. [PubMed]
Checkley W, White AC Jr, Jaganath D et al. A review of the global burden, novel diagnostics, therapeutics, and vaccine targets for cryptosporidium. Lancet Infect Dis 2015;15(1):85-94. [PubMed]