Although known for over a century, cryptosporidiosis was believed to be an extremely rare condition and it only gained attention with the discovery that it can affect humans, especially immune-compromised individuals. It is caused by a single-cell parasite, one of a family known as cryptosporidia. Some cryptosporidia also infect reptiles, where after a sometimes lengthy incubation period they cause gastrointestinal problems even in otherwise healthy individuals. The condition is usually persistent and is presently impossible to cure. It is therefore important to minimize infections and in this regard reliable diagnostic procedures are essential.
Diagnosis is based on the detection of parasites in faeces but is complicated by the fact that snakes in particular excrete parasites that they swallow together with their prey, so the presence of cryptosporidia in faeces does not necessarily mean the animals are infected. For this reason it is essential to be able to distinguish between "prey" cryptosporidia and those that cause infection in the snake. Barbara Richter and colleagues at the Institute of Pathology and Forensic Veterinary Medicine in the University of Veterinary Medicine, Vienna now report a DNA-based procedure able to determine not only whether cryptosporidia are present but also whether they are of mammalian or snake origin.
By means of the test, Richter was able to show that a particular type of cryptosporidium is present in about one in six samples from the popularly kept corn snake and in about one in twelve samples from the attractive leopard gecko, a lizard frequently found in reptile collections. These prevalence figures are far higher than previously suspected, showing the widespread nature of the disease. The corn snake in particular seems highly susceptible to infection. Worryingly, the new tool revealed that a large proportion of captive leopard geckos contain cryptosporidia of one form or another. It is possible that some of the infections do not inconvenience the host geckos but the animals nevertheless represent a source of infection for other reptiles that come into contact with them. Many reptile collections house a number of species together and there is therefore a significant risk of cross-species infection.
The new diagnostic procedure represents a precise method for the early diagnosis of cryptosporidiosis in lizards and snakes, before the animals show symptoms of disease. Nevertheless, Richter still raises a cautionary note. "A further problem is that cryptosporidia are often present in faeces in very low numbers so it is easy to miss them in a single test. We are working to make our method more sensitive but it is very important to test the reptiles repeatedly. A negative result does not necessarily mean that the animal is really free of the parasite."