Salmonella serotype shift during an endemic dairy infection

Authors: Van Kessel, Jo Ann; Karns, Jeffrey

Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/23/2009
Publication Date: 7/14/2009
Citation: Van Kessel, J.S., Karns, J.S. Salmonella serotype shift during an endemic dairy infection. Joint Abstracts of the American Dairy Science and Society of Animal Science. J. Anim. Sci. Vol. 87, E-Suppl. 2/J. Dairy Sci. Vol. 92, E-Suppl. 1 221

Interpretive Summary:

Technical Abstract: Dairy farms are known reservoirs for Salmonella spp. and control of this organism is challenging. Salmonellae have been shown to be endemic in herds in part because they are easily spread between animals and throughout the farm environment. The impact of the infection on the herd is variable and dependent, in part, on the serotype. More than 2500 serotypes are known and animal carriers can be difficult to identify because they are often asymptomatic. As part of a multi-herd study, a dairy herd with an endemic, asymptomatic Salmonella infection was monitored extensively for 4 years. Bulk milk and in-line milk filters were collected weekly, and individual fecal samples were collected from all adult animals every 6 to 8 weeks. Salmonella detection was based on traditional culture methods. Prevalence of fecal Salmonella shedding in the 105 cow herd averaged 56 percent (range 10-95 percent) during this time. Although several Salmonella serotypes were identified over the course of the study, the initial dominant (>99 percent of isolates) serotype was Cerro. After 1.5 years into the outbreak, the serotype Kentucky began to gradually increase in prevalence, and at 2 years 39 percent of the fecal isolates were Kentucky. Over the next six months Kentucky became the dominant serotype representing >85 percent of fecal isolates. The serotype conversion from Cerro to Kentucky was first detected via analysis of the weekly milk filters. However, while monitoring of the milk filters was useful for detecting major shifts in serotype dominance, serotype prevalence in the individual milk filters was not predictive of the concurrent fecal serotype prevalence. This is the first detailed description of an endemic Salmonella infection in a dairy herd that undergoes a gradual shift from one serotype to another.