Clostridium difficile is a complex organism with a complex ecology. The extent of illness depends in part on the infecting strain and animal species infected. C difficile infection and disease in various animals and its zoonotic potential are highlighted in this study. 

In horses, C difficile infection frequently results in diarrhea, dehydration, toxemia, abdominal pain, and sometimes death, and healthy foals and adult horses have been documented to shed toxigenic strains. It is not fully understood why only some horses develop illness. The zoonotic risk from horses with C difficile is not well-established, despite horses and humans sharing many strains.

In pigs, C difficile is primarily a disease of younger animals. Clinical presentation is variable, and infection in piglets can result in sudden death with few clinical signs, which may include diarrhea, poor growth, distended abdomen, and decreased appetite. Shedding is much more common in younger pigs, and zoonotic transmission remains possible.

In cattle, shedding of C difficile can occur in adults—in which infection does not appear to cause disease—but is more common in calves, in which infection can cause diarrhea. Issues such as changes in diet, mastitis, and antimicrobial exposure appear to be associated with a higher risk for shedding. The zoonotic risk from cattle with C difficile is unclear, despite the same strains having been found in cattle and humans. 

In dogs, it can be difficult to determine the extent of enteric disease attributed to C difficile because of inconsistencies in finding C difficile toxin in the feces, as well as lack of information on best methods of diagnosis and interpretation of results. Finding C difficile in the feces of healthy and sick dogs and cats complicates the understanding of this pathogen in disease in these animals. C difficile infection in various animals, particularly dogs and cats, can be associated with sharing the same environment as humans, making the direction of transmission challenging to determine. Shedding of C difficile by dogs has been associated with antimicrobial therapy, immunosuppressive medications, visits to human healthcare facilities, exposure to children, and exposure to humans at high risk for C difficile infection.

Key pearls to put into practice:

C difficile can cause disease in some animals yet remains a harmless commensal in others.

Solidifying the role of C difficile disease in dogs and cats is challenging, in part because of the shedding of C difficile in the feces of healthy animals not showing clinical signs.

The zoonotic risk from most animal species remains unclear but possible. It is vital to implement proper infection prevention protocols in the clinic and to educate pet owners about zoonosis and prevention.

Humans infected with C difficile can readily infect dogs and cats, making awareness about transmission important for owners and the community.