Emerging outbreaks associated with equine coronavirus in adult horses

Abstract

Equine proliferative enteropathy (EPE) is an emerging enteric disease of foals caused by Lawsonia intracellularis. Affected foals, generally less than one year of age, display lethargy, anorexia, fever, weight loss, peripheral edema, diarrhea and colic. Transmission of L. intracellularis is thought to occur through the ingestion of feed or water contaminated with L. intracellularis-infected feces from free-living or domestic animals. Lawsonia intracellularis has been detected by PCR in the feces of a variety of domestic and wild animals. Recently, the authors found that 7.5% of fecal samples and 27% of serum samples from cottontail rabbits from a farm with endemic occurrence of EPE tested positive for L. intracellularis by PCR and serology, respectively. Of interest was that on this farm, a large population of rabbits lived in the hay barn and directly contaminated hay fed to the horses. The goal of this study was to determine if feces from rabbits experimentally infected with L. intracellularis could be the source of infection for naive weanling foals. Two 9-week-old New Zealand white rabbits were experimentally infected with 2.5 x 109 L. intracellularis of equine origin via nasogastric intubation, while two rabbits served as uninfected controls. Eight weanling foals randomly assigned to one of two groups (infected and control) received daily feces from the infected or control rabbits mixed with feed or water. All rabbits and foals were monitored daily for the development of clinical abnormalities and were weighed once weekly for the duration of the study. Feceswere collected every day to every other day for the quantitative molecular detection of L. intracellularis via real-time PCR. Blood was collected weekly for the measurement of concentrations of total solids and serologic analysis. None of the infected rabbits or foals developed any clinical signs or hypoproteinemia compatible with PE. Onset of fecal shedding of L. intracellularis was detected by PCR on days 3 and 9 post-challenge in the 2 infected rabbits. The duration of fecal shedding was 6 and 9 days for the 2 infected rabbits. All infected foals began to shed L. intracellularis between days 10 and 14 post-infection, and fecal shedding lasted between 4 and 10 days. Feces and rectal swabs indicated that control rabbits and control foals, respectively, remained PCR negative for L. intracellularis throughout the entire study period. A humoral immune response was detected in all infected rabbits and foals. This study represents the first report documenting the successful feco-oral transmission of L. intracellularis using infectious fecal material from rabbits. Lagomorphs may represent an effective reservoir/amplifier host for L. intracellularis due to their large population, their close contact to horses, their short reproductive cycle and their world-wide distribution.