Post weaning diarrhea in pigs: preventing colistin use
Colistin is a last resort antibiotic used by doctors to treat severe infections caused by multi-drug resistant bacteria called “superbugs”. Unfortunately, in 2015 colistin-resistant bacteria were discovered and these newly developed colistin-resistance genes can be transferred to other bacterial species. These bacteria were found to use farm animals including pigs as reservoirs, which is defined as the place an infectious agent normally lives and multiplies. A group of bacteria called enterotoxigenic Escherichia coli (ETEC) are responsible for most cases of post-weaning diarrhea (PWD) in pigs, a disease that causes major losses in the porcine industry. Despite its efficacy in treating PWD, colistin is not approved for use in Canadian production animals. However, due to the general increase in multidrug resistant bacteria, colistin is occasionally administered under the supervision of a veterinarian to treat intestinal infections in pigs.
Over the past few decades at the Swine and Poultry Infectious Diseases Research Center (CRIPA),
several researchers have been studying PWD. To help farmers and veterinarians make informed decisions when it comes to the prevention and treatment of PWD, Drs John Fairbrother, Francis Beaudry, Ann Letellier and Mohamed Rhouma reviewed the available scientific literature (271 articles). The impact and limitations (cost, work required) of different herd management strategies, including selective breeding of infection-resistant pigs, biosafety measures, vaccine strategies, nutrition and alternative therapeutic options were investigated. The findings of this systemic review were published in Acta Vet Scand (2017) 59:31.
Preventative strategies involving herd management and vaccination were the most effective at controlling PWD. Furthermore, alternatives to antibiotics such as feed additives (organic acids, prebiotics, probiotics, etc) are promising, but have yet to be validated as prophylaxis or treatment in industrial farms.
To minimize the need for antibiotic use, the researchers recommend following strict herd management guidelines, before, during and after treating a sick animal. These guidelines are summarized as follow:
Quarantine sick animals to ensure they are the only ones to receive treatment;
Use diagnostic tests to confirm that the causative (etiologic) agent is a bacterium. PWD can be caused by viruses and antibiotics do not work on viral infections;
Only ETEC strains that produce toxins (LT and/or STa or STb) and specific adhesins (F4 and occasionally F18) cause PWD. As a result, the presence of E. coli is not enough to confirm that PWD is caused by bacteria. Researchers recommend using sensitive molecular diagnostic tests to confirm the presence of ETEC:F4 in the feces of infected pigs and to monitor the disappearance of the F4 marker to determine antimicrobial treatment efficacy. BMC Microbiology (2017).
