Cryptosporidium chipmunk genotype I – An emerging cause of human cryptosporidiosis in Sweden

Most cases of cryptosporidiosis in humans are caused by Cryptosporidium parvum or Cryptosporidium hominis. However, more uncommon species are increasingly being recognised to cause infection in humans. Here we report that Cryptosporidium chipmunk genotype I, which has various rodents as its natural host, is the third most common source of human cryptosporidiosis in Sweden. We also describe the first small outbreak of cryptosporidiosis caused by Cryptosporidium chipmunk genotype I and report the first case of zoonotic transmission of Cryptosporidium chipmunk genotype I from a red squirrel to a human. Cryptosporidium chipmunk genotype I was identified in 20 human cases, including 16 sporadic cases, three outbreak-related cases, and one zoonotic case, as well as in two squirrel samples. Gp60 subtyping which was successful for 19 human cases and two squirrel samples showed that all samples harboured the same subtype, XIVaA20G2T1. The work presented here suggests that red squirrel is a natural host of Cryptosporidium chipmunk genotype I and that infection with Cryptosporidium chipmunk genotype I is an emerging cause of domestic cryptosporidiosis in Sweden and a potential source of outbreaks. [Display omitted] •Cryptosporidium chipmunk genotype I is an emerging cause of domestic cryptosporidiosis in Sweden.•A small outbreak caused by Cryptosporidium chipmunk genotype I is described for the first time in humans.•A zoonotic transmission of Cryptosporidium chipmunk genotype I from red squirrel to human is reported for the first time.•All Cryptosporidium chipmunk genotype I isolates (both human and squirrel) subtyped herein showed gp60 subtype XIVaA20G2T1.