Cryptosporidia are very small, unicellular parasites of the gastrointestinal tract. They are classified as coccidia. Different species are described with very similar morphology. Some of these are host-specific; others (e.g. Cryptosporidium parvum) can infect various animal species and humans (zoonosis).
Infections occur after intake of sporulated oocysts. The infectious dose is very low (approx. 100 oocysts). Subsequently the liberated sporozoites infect the intestinal epithelial cells, followed by a development cycle over trophozoites, meronts, merozoites, gamonts, zygotes and in the end again oocysts are formed. The oocysts excreted in the faeces show a high tenacity, are resistant to many disinfectants and can remain infectious for months. Therefore, e.g. contaminated pens or terrariums are frequent sources of infection.
In cattle cryptosporidiosis is a very common endoparasitosis. A large proportion of calves go through an infection with C. parvum. Clinically apparent courses with enteritis and diarrhoea occur especially in calves up to 3 weeks of life, often related to co-infections. Quite often lambs, piglets and foals are also affected.
A much lower prevalence is seen in dogs and cats, with usually asymptomatic infections. However, oocysts are excreted in the faeces here, too, for about 2 weeks. Manifest infections can be seen in puppies or immunocompromised animals (e.g. FeLV, FIV, distemper, neoplasia, etc.).
In reptiles, cryptosporidiosis is a serious disease that can cause severe losses, especially in snake and lizard stocks. C. serpentis is an important parasite in snakes and infects the gastric mucosa. Due to the chronic inflammation a subsequent swelling and hardening of the connective tissue in the gastric area can occur. A typical sign is the regurgitation of food days after digestion. C. saurophilum (also called C. varanii) destroys the lining of the intestinal walls of affected lizards and snakes. Clinically malabsorption with excretion of undigested food, profound weight and fluid loss are observed. Both pathogens are not pathogenic to humans. Quite often, C. muris and C. parvum are found in reptile faeces as intestinal passengers (origin: infected feeder animals). Therefore, further differentiation is absolutely necessary if the result is positive.
In laboratory diagnostics, several methods are available for detection. Already during the microscopic examination after specific enrichment (SAFC) oocysts can be found. As with all parasitological faecal examinations, sensitivity is relatively limited at approximately 60%.
In cattle, ELISA testing, which detects C. parvum, is recommended. The immunofluorescence test includes a wider range of Cryptosporidium species and is therefore suitable for dogs, cats, but also small rodents (guinea pig: C. wrairi).
In case of positive test results in reptiles, differentiation between pathogenic agents and intestinal passengers is of interest. For this, PCR with subsequent differentiation is recommended. In addition to PCR, detection by IFAT and microscopy are also available. Yet, these methods do not allow for a differentiation of the individual species. If reptile faeces are examined microscopically, the preparations will be stained additionally (modified Ziehl-Neelsen stain) to increase the detection rate.
It should be noted that a single negative result does not completely rule out a Cryptosporidia infection, as the pathogen can be excreted intermittently. So far, no successful treatment is available.The emphasis in the control of cryptosporidiosis is on symptomatic treatment and hygiene management.