Cell culture adapted bluetongue virus in dogs

Abstract

A cell culture adapted bluetongue virus (BTV), isolated from a contaminated commercial modified-live 4-component canine vaccine, was administered by the intramuscular route to four pregnant bitches in mid gestation. The bitches were monitored and observed for 10 days. Elevated temperatures, vomiting, anorexia, depression, and vaginal discharge were observed. Three of the 4 bitches were observed to have aborted on days 4 to 6 after challenge. The remaining bitch was determined to have aborted when necropsied at the conclusion of the study. One bitch exhibited respiratory distress, another had a rapidly falling temperature after aborting and subsequently died v^thin 24 hours. Bluetongue virus was isolated from blood samples collected on days 1 to 9, with Veterinary Biologies Laboratory, National Veterinary Services Laboratories, Veterinary Services, Animal and Plant Health Inspection Service, USD A, PO Box 844, Ames, lA 50010 ** Pathobiology Laboratory, National Veterinary Services Laboratories, Veterinary Services, Animal and Plant Health Inspection Service, USD A, PO Box 844, Ames, lA 50010 Washington Animal Disease Diagnostic Laboratory, College of Veterinary Medicine, Washington State University, PO Box 2037, College Station, Pullman, WA 99165 ^ Veterinary Medical Research Institute, Iowa State University, Ames, lA 50010. 43 maximum viral titer obtained on days 3 to 5. Bluetongue virus was isolated from tissues from the 4 bitches and from fetuses from 2 of 3 bitches. The most consistent BTV isolation came from lung, spleen, and placenta of the bitches. One of 4 of the bitches seroconverted based on a commercial cELIS A diagnostic kit. The remaining 3 had rising cELIS A inhibition percentages, indicative of the early stages of an immune response. Following the administration of a cell culture adapted BTV, bitches became clinically ill, BTV was recovered during clinical illness, 3 of 4 of the bitches were observed to abort, and BTV was isolated from both maternal and fetal tissues. This study demonstrates that cell culture adapted BTV can cause clinical illness and abortion in pregnant bitches when iatrically administered. Introduction Bluetongue virus (BTV), the prototype virus for the genus Orbivirus^ is naturally transmitted to animals by various Culicoides spp. midges, and has historically infected sheep, cattle, and wild ruminants.^'^ Clinical disease occurs primarily in sheep. Cattle and wild ruminants, although infected, normally remain subclinical. Bluetongue virus has not been reported to be associated with infection and disease in non ruminants. Recently, abortion and death in pregnant bitches following use of a commercial modified live vaccine contaminated with a BTV have been reported.'*'® In those studies, the same serotype BTV was isolated from a multivalent vaccine and from various tissues of both bitches and aborted fetuses. Based on these isolations, an association with the clinical disease in these bitches was made. This study details the experimental infection of pregnant bitches with a cell culture adapted BTV obtained from the contaminated vaccine to show that 44 cell culture adapted BTV iatrically administered can conclusively be demonstrated as the cause of infection, viremia, and abortion in pregnant bitches. Materials and Methods Dogs Foiu* purebred female beagles were used in this study. Two bitches were obtained from a commercial dog colony and had only been vaccinated with a killed rabies product. Bitches were supplied as being in mid to late gestation based on date of last observed breeding. Two bitches were obtained from the National Veterinary Services Laboratories (NVSL) SPF dog colony and had never received any vaccinations. Bitches were housed in a climate controlled enviromnent in separate pens, 2 bitches per room. The floor of the pen was washed twice daily and the bitches were fed a commercial dry dog food supplemented with commercial wet food. Bitches within each room had fence line contact. Bitches from the commercial colony were wormed and treated for fleas upon arrival and a 21-day acclimation period was observed prior to initiation of the experiment. Bitches from the NVSL colony were locally moved and allowed to acclimate for 3 days. The experiment was conducted with the approval of the NVSL Animal Care and Use Committee in accordance with the NIH guidelines and the Animal Welfare Act.