Evaluation of a genetically attenuated Cryptosporidium parvum strain in the calf clinical model of cryptosporidiosis.

Abstract

The protozoan parasite Cryptosporidium parvum is a leading cause of diarrhea and mortality in young children and neonatal calves. There are no effective drugs to treat cryptosporidiosis, and no vaccines are available to prevent infection or reduce transmission. The substantial global public health burden of cryptosporidiosis calls for urgent efforts to develop effective treatments and prevention strategies. This includes identifying and functionally characterizing new parasite targets and evaluating vaccine candidates in relevant animal models. Recently, we identified the important role of C. parvum calcium-dependent protein kinase 5 (CDPK5) in the parasite's sexual cycle and found that genetic deletion of this kinase reduced virulence and oocyst shedding in immunocompromised mice. In this study, we evaluated the genetically attenuated C. parvum CDPK5-knockout (CDPK5-KO) strain in a natural and clinically relevant calf model of cryptosporidiosis. We compared clinical health, diarrhea, dehydration, and oocyst shedding in calves infected with the CDPK5-KO strain to those infected with the control strain expressing a functional kinase (CDPK5-HA). We observed a significant improvement in overall clinical outcome, with less diarrhea and dehydration in calves infected with the CDPK5-KO strain compared with those infected with CDPK5-HA strain. Although total fecal oocyst shedding was lower in CDPK5-KO-infected calves than in the control group, diarrhea and oocyst shedding did not fully resolve during the trial. These findings show the effectiveness of a neonatal calf model for evaluating genetically attenuated C. parvum strains and for guiding future challenge studies to better understand their role in reducing diarrheal disease.