Evidence of 'Cryptosporidium' transmission between cattle and humans in northern New South Wales

'Cryptosporidium' is an enteric parasite of public health significance that causes diarrhoeal illness through faecal oral contamination and via water. Zoonotic transmission is difficult to determine as most species of 'Cryptosporidium' are morphologically identical and can only be differentiated by molecular means. Transmission dynamics of 'Cryptosporidium' in rural populations were investigated through the collection of 196 faecal samples from diarrheic (scouring) calves on 20 farms and 63 faecal samples from humans on 14 of these farms. The overall prevalence of 'Cryptosporidium' in cattle and humans by PCR and sequence analysis of the 18S rRNA was 73.5% (144/196) and 23.8% (15/63), respectively. Three species were identified in cattle; 'Cryptosporidium parvum', 'Cryptosporidium bovis' and 'Cryptosporidium ryanae', and from humans, 'C. parvum' and 'C. bovis'. This is only the second report of 'C. bovis' in humans. Subtype analysis at the gp60 locus identified 'C. parvum' subtype IIaA18G3R1 as the most common subtype in calves. Of the seven human 'C. parvum' isolates successfully subtyped, five were IIaA18G3R1, one was IIdA18G2 and one isolate had a mix of IIaA18G3R1 and IIdA19G2. These findings suggest that zoonotic transmission may have occurred but more studies involving extensive sampling of both calves and farm workers are needed for a better understanding of the sources of 'Cryptosporidium' infections in humans from rural areas of Australia.