Texas A&M Research Unlocks Mystery Of Salmonella Infection

Salmonella infection, or salmonellosis is a major public health burden that carries a significant economic price tag. Recent news stories about outbreaks of salmonellosis have led to detrimental effects on impacted industries. Historically, pigs and the consumption of salmonella contaminated pork have been a major source for the transmission of this disease to humans. To better control exposure to and infection by this pathogen in humans, it is important to gain a better understanding of the swine host-pathogen relationship that will lead to better detection measures.

Scientists at Texas A&M College of Veterinary Medicine & Biomedical Science working in collaboration with researchers from the Swedish National Veterinary Institute and the Swedish University of Agricultural Sciences, examined the intermittent pattern in which pigs shed salmonella bacteria in their feces and discovered that salmonella may lay dormant in the host at an undetectable level as a survival strategy that prolongs the host's infection. Furthermore, different salmonella serotypes are shed and go dormant in different frequencies, making detection difficult at best. The results of this study were recently published in PLoS ONE.

This "off and on" pattern of pathogen excretion can lead to a host being misdiagnosed as clear of bacteria when indeed it is still infected. In the either stage, pigs typically do not show physical signs of being infected. In the "on stage," the host sheds the bacteria in fecal material, while in the "off stage," the pathogen is still present in the host but is not shed. Therefore, the leading method of detecting infection, fecal shedding, becomes difficult.

"Because of the important role that pigs have played in salmonellosis outbreaks in other pigs and humans, reliable detection measures and models are critical in developing efficient salmonella control efforts," said Dr. Renata Ivanek-Miojevic, assistant professor of epidemiology at the Veterinary Integrative Biosciences Department.

While this early study has documented the ability of salmonella bacteria to lay dormant thereby extending its presence in the infected host, future research will investigate if the same association between the cyclic behavior and the length of infection holds true in other host-pathogen models.

"With this study, we were able to observe the relationship between shedding pattern and length of infection in several serotypes of salmonella in the swine host," noted Ivanek-Miojevic. "From here, we will need to use what we learned and the models that we were able to develop to see if the same behavior is observed in other host-pathogen systems.

"If so, the relationship may be useful not only in improving detection methods but also in understanding evolutionary ecology of this and similar infectious diseases with 'off and on' pattern of pathogen excretion, and consequently adopting better control measures."

This study, funded by the National Science Foundation, will become a model for future studies aimed at furthering the detection capabilities and effective control for salmonella and similar infectious agents in their animal and human host populations.