Effect of Culicoides Sonorensis Salivary Proteins on Clinical Disease Outcome in Experimental Bluetongue Virus Serotype 8 Infection of Dorset Sheep

Authors: Drolet, Barbara; Reister-Hendricks, Lindsey; Lehiy, Christopher; VAN RIJN, PIET - Central Veterinary Institute; BOWEN, RICHARD - Colorado State University

Submitted to: Veterinaria Italiana
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2015
Publication Date: 12/31/2015
Publication URL: http://handle.nal.usda.gov/10113/61783
Citation: Drolet, B.S., Reister-Hendricks, L.M., Lehiy, C.J., Van Rijn, P.A., Bowen, R.A. 2015. Effect of Culicoides Sonorensis Salivary Proteins on Clinical Disease Outcome in Experimental Bluetongue Virus Serotype 8 Infection of Dorset Sheep. Veterinaria Italiana. 51(4):379-384.

Interpretive Summary: Bluetongue is a disease of sheep, cattle, deer, and antelope that is transmitted by a biting fly called a Culicoides midge. There are many different types of bluetongue virus (BTV), some of which have been in the U.S. for decades and some that have recently been introduced. The ability to cause disease in animals varies greatly between these virus types. To determine whether a specific virus type will cause disease in a specific animal species or breed of species, experimental infection studies are typically conducted. Unfortunately, injecting virus into the animal rarely results in the types of clinical disease we see in natural, insect bite-transmitted infections. This study examined whether adding midge salivary proteins to the virus injection method would affect the clinical disease outcome. Sheep that received virus mixed with salivary proteins had clinical disease similar to what is seen in nature.

Technical Abstract: Bluetongue is an insect-transmitted disease of domestic and wild ruminants. In the U.S., sheep are the most susceptible livestock species. Severity and form of clinical disease varies greatly depending on the outbreak serotype or specific strain within a serotype. To predict disease risk from any of the 26 serotypes identified to date, experimental infections are typically conducted. The value of such studies are limited, however, because experimental infection of domestic U.S. sheep breeds by inoculation rarely produces clinical disease seen in natural, Culicoides bite-transmitted infections where animals are exposed to both virus and vector saliva. Thus, risk assessments based on experimental infections often underestimate the severity posed by a given virus strain should an outbreak occur. To determine whether Culicoides saliva delivered with virus affects clinical disease outcomes, secreted Culicoides sonorensis salivary proteins were mixed with a BTV-8 viral inoculum. Four sheep were intradermally inoculated with BTV-8 + salivary protein mixture and four sheep received virus alone. Clinical signs were monitored daily. Sheep receiving an the BTV-8 + salivary protein inoculum had more types and more severe clinical disease compared to sheep receiving virus alone and the duration of clinical disease was three times longer. Utilizing Culicoides vector salivary proteins in experimental inoculations resulted in clinical disease which more closely mimics natural BTV infections of sheep in the U.S.