The occurrence and zoonotic potential of Cryptosporidium species in freshwater biota.

Background: Protozoan pathogens from the genus Cryptosporidium cause the diarrhoeal disease cryptosporidiosis in humans and animals globally. Freshwater biota could act as potential reservoirs or zoonotic sources of Cryptosporidium infections for livestock and people, but Cryptosporidium occurrence in aquatic biota is largely unexplored. The aim of this study was to investigate the occurrence of Cryptosporidium in a range of freshwater organisms in upland rivers across England and Wales.

Methods: Fish were sampled by electrofishing, invertebrate larvae by kick sampling and the otter Lutra lutra and mink Mustela vison through faecal samples collected opportunistically as part of a nation-wide study. PCR targeting the small subunit ribosomal RNA gene was used to detect Cryptosporidium species.

Results: Cryptosporidium occurred in just 0.8% of all the samples and in none of 73 samples from nine invertebrate genera. Cryptosporidium was detected in two of 2/74 fish samples (2.7%), both salmonids, and in 2/92 otter faecal samples (2.17%), but there were no positive samples in mink (0/24) or the bullhead Cottus gobio (0/16).

Conclusions: Low detection rate of human-infective Cryptosporidium species in aquatic fauna indicates they may present a low risk of contamination of some upland freshwaters.