Rotaviruses associated with neonatal lamb diarrhea in two Wyoming shed-lambing operations.

Abstract

White scours was first recognized in 1927 as an important cause of newborn lamb loss in shed-lambing operations in the western United States. 4 This disease was thought to be caused by bacteria, but no specific pathogen was identified. Lamb scours remains an important disease in the United States, 3 and several bacteria are now considered etiologic agents, including Bacteroides fragilis 5 and K99 piliated, enteropathogenic Escherichia coli. 11 Moreover, the coccidian parasite Cryptosporidium also has been associated with diarrhea in young lambs. 1 Viruses associated with neonatal lamb diarrhea were not reported in the United States until very recently. 7 In this instance, group B rotavirus was detected during an outbreak of diarrhea in newborn confinement-reared lambs in Ohio. Each spring during the past 5 years, several large shedlambing operations in eastern Wyoming have experienced severe outbreaks of neonatal diarrhea associated with high morbidity and mortality. The purpose of this study was to determine if any potentially pathogenic enteric viruses could be detected by negative-stain electron microscopic (EM) examination of specimens collected from neonatal diarrheic lambs in 2 of these operations. In early April 1994, specimens were collected from affected lambs in 2 eastern Wyoming shed-lambing operations situated about 40 km apart. Ranch A routinely shed-lambs over 1,300 lambs within a 30-day period commencing in early March. In some years the first scouring lambs were observed during the first week of shed-lambing, whereas in other years they occurred later. Clinical signs were observed when the lambs were 12-16 hours old and consisted of frothy salivation, inappetence, and scours. Some affected lambs died within 4-5 hours following the onset of signs; surviving lambs, however, often gained weight slowly and were prone to other infectious diseases. Once the outbreak was under way, morbidity approached 100%, and about 10% of the affected lambs died. Ranch B routinely shed-lambs between 3,000 and 5,000 lambs within a 30-day period starting in early March. Affected lambs were not ordinarily observed during the first week, but sometime afterward a lamb would become ill while still in the lambing pen. Within 4-5 days after the first case, many lambs were affected, and thereafter the majority of the lambs kept in the shed area became ill. Initial clinical signs