Man and pigs: sharing the same C. difficile

Abstract

Clostridium difficile is an anaerobic spore forming gram-positive bacterium. Infection with C. difficile may lead in humans to symptomless carriership, but may also lead to diarrhea varying in severity from mild to life-threatening pseudomembraneous colitis. C. difficile spores can survive for long periods of time in the environment and are resistant to extreme temperatures, drought, radiation, and chemicals including disinfectants. C. difficile was considered a classical nosocomial pathogen, with a risk group consisting of elderly patients with comorbidities, treated with antimicrobials. However, since the beginning of the 21th century C. difficile infection (CDI) is increasing in incidence and severity, and is also reported in younger patients, not receiving antimicrobials, and in patients in the community. Ribotype 078 is associated with this change in epidemiology and has increased in prevalence, to the 3rd most common isolated type in human patients in Europe. The finding of the same 078 ribotype in diarrheal piglets led to the concern that interspecies transmission could occur. The goal of this PhD research was to investigate the risk of transmission of C. difficile from pigs to humans. C. difficile was commonly found in fecal samples of neonatal piglets with diarrhea. The use of a more sensitive detection method for the bacterium resulted in isolating C. difficile in fecal samples of almost all piglets, regardless their disease status. With this method, samples from sows, piglets and the environment were investigated to determine how piglets become infected with C. difficile. Since C. difficile was found in all piglets within 48 hours after birth, while all sows became positive within 113 hours after parturition, contamination of the environment with C. difficile is the most logical source for infection. Indeed, C. difficile was present in environmental samples in the farm. C. difficile was also found in the air of the farrowing ward. Follow-up research on all pig wards at the same pig farm revealed a widespread dissemination of C. difficile. Furthermore, C. difficile was present in air samples 20 meter outside the farm. Consumption of pork meat is considered a possible infection route, because C. difficile was found in retail pork samples. To determine if the source could be slaughter pigs colonized with the bacterium, rectal samples of slaughter pigs were taken at the abattoir. A prevalence of around 10% was found. However, whether C. difficile can subsequently contaminate the carcass depends on the slaughter hygiene. Human and pig C.difficile ribotype 078 seem to be genetically related because a comparison of C. difficile isolates from humans with CDI and piglets with diarrhea revealed a high similarity in antimicrobial susceptibility patterns. Samples from farmers, employees, family members and the pigs at the same farms were investigated for the presence of C. difficile. Colonization rates of C. difficile in pig farmers and their employees were higher then the colonization rates described in healthy adults. C. difficile isolates from pig farmers and their pigs are highly similar, which indicates that working with pigs is an occupational risk for colonization with C. difficile.