Age and episode-associated occurrence of Cryptosporidium species and subtypes in a birth-cohort of dairy calves.

The role of species-specific immunity in infection patterns of Cryptosporidium spp. in humans and farm animals is not well understood. In the present study, the dynamics of Cryptosporidium infections in a natural cryptosporidiosis model was examined using genotyping, subtyping and whole genome sequencing tools. In a cross-sectional survey of Cryptosporidium spp. in 934 dairy cattle on one farm, marked age-associated differences in the distribution of Cryptosporidium species and C. bovis subtypes were observed. In a closely followed longitudinal birth cohort study of 81 calves over a 9-month period, shedding of C. parvum oocysts by the IIdA19G1 subtype started at 4 days, peaked at 2 weeks and ended mostly by 4 weeks. In contrast, the shedding of C. bovis oocysts started at 2 weeks, peaked initially at 6 weeks and had a second wave during 15th to 23rd weeks. For C. ryanae, calves had mostly only one episode of infection by one subtype, with accumulative infection increasing much slower than C. parvum and C. bovis. Overall, the accumulative infection rates and mean duration of oocyst shedding for calves in the cohort were 97.4% (76/78) and 2.3 weeks, 100.0% (80/80) and 3.9 weeks, and 78.7% (63/80) and 3.2 weeks for C. parvum, C. bovis and C. ryanae, respectively. The oocyst shedding intensity was much lower in C. bovis and C. ryanae infections compared with C. parvum infection, and in the second episode of C. bovis infection compared with the first episode. The two episodes of C. bovis infections were caused by different genome types that differed mostly in nine genes. Cryptosporidium parvum infection was associated with the occurrence of watery diarrhoea. Data from the natural history study of cryptosporidiosis indicate that despite the existence of acquired immunity against homologous pathogens, neonatal animals experience waves of Cryptosporidium infections by different species and genome types.

Cryptosporidiosis outbreak caused by Cryptosporidium parvum subtype IIdA20G1 in neonatal calves.

Cryptosporidium parvum is a major zoonotic pathogen responsible for outbreaks of severe diarrhoea in humans and calves. Almost all investigations of cryptosporidiosis outbreaks caused by C. parvum have focused on its IIa subtype family in industrialized nations. From December 2018 to April 2019, approximately 200 neonatal calves on a large cattle farm in Hebei Province, China, were diagnosed with watery diarrhoea and over 40 died. To investigate the cause of the outbreak, faecal samples were taken during and after the outbreak from neonatal calves of ≤4 weeks of age (n = 40 and n = 56) and older calves of 4-24 weeks of age (n = 79 and n = 38). A total of 18 faecal samples collected from ill calves at the peak of the outbreak were analysed for four common enteric pathogens using an enzymatic immunoassay (EIA). In addition, 75 samples from neonatal calves were tested for rotavirus by EIA. All samples were analysed for Cryptosporidium spp. using PCR and sequencing techniques. Of the initial 18 samples from sick calves, ten were positive for C. parvum, five for rotavirus, and one for coronavirus. The overall prevalence of rotavirus in neonatal calves was 20.0% (15/75), with no significant differences during and after the outbreak. In contrast, Cryptosporidium parvum infections were significantly higher during the outbreak (60.0%, 24/40) than after the outbreak (30.4%, 17/56; p = .004). Cryptosporidium parvum infection was associated with the presence of watery diarrhoea in neonatal calves (OR = 11.19), while no association was observed between C. bovis infection and diarrhoea. All C. parvum isolates were identified as subtype IIdA20G1. This is one of the few reports of outbreaks of severe diarrhoea caused by C. parvum IId subtypes in calves. More attention should be directed towards the dissemination of C. parvum in China.