Infection with Cryptosporidium hominis provides incomplete protection of the host against Cryptosporidium parvum.

Cryptosporidium hominis and Cryptosporidium parvum, which infect humans equally, are genetically/antigenically almost identical. It remains unclear, however, whether infection with C. hominis protects against C. parvum. Gnotobiotic piglets were used to investigate cross-protection. After ≥3 days of recovery from C. hominis infection, the piglets were completely protected against subsequent challenge with C. hominis but only partially against challenge with C. parvum, as compared with age-matched control animals challenged with either species. In conclusion, C. hominis-specific immunity was sufficient to completely protect against challenge with the same species but insufficient to provide the same level of protection against C. parvum.