Dynamics of excretion and molecular characterization of Cryptosporidium isolates in pre-weaned French beef calves.

Studies on excretion and molecular characterization of Cryptosporidium have been mostly conducted in dairy calves, both diarrhoeic and non-diarrhoeic. Little is known about Cryptosporidium in beef calves, especially in non-diarrhoeic ones. This study was conducted in a herd of Parthenais beef cattle (France) with no history of clinical cryptosporidiosis. Twenty-five calves were sampled once a week from birth to one month of age (age range: 5-34 days). At each sampling date, presence of clinical signs of cryptosporidiosis (diarrhoea) was recorded. Oocyst excretion was assessed using the Heine staining method and a direct immunofluorescence method (Merifluor(®) C/G) which allowed quantification (oocysts per gram of faeces, opg). All samples were subjected to a two-step nested PCR protocol to amplify the 18S rRNA gene and amplification products were sequenced. None of the calves presented diarrhoea. Twenty-three of them excreted oocysts at least one sampling date. Prevalence of excretion was maximal when calves were 27-34 days old, with a percentage of excretion of 85% in this age category [95% CI: 70; 100]. Mean excretion was maximal when calves were 20 to 26 days old, with a mean excretion of 7.6×10(5) opg (range: 0-8×10(6) opg). 32 isolates were successfully identified: 27 as Cryptosporidium bovis, 4 as Cryptosporidium ryanae and 1 as Cryptosporidium parvum. C. bovis was isolated from samples of calves between 11 and 33 days old. C. ryanae was isolated from samples of calves between 17 and 34 days old. C. parvum was isolated from one calf aged 13 days. This survey demonstrated the high infection rate of non-diarrhoeic beef calves by Cryptosporidium species other than C. parvum.