Submitted to: Keystone Symposia
Publication Type: Abstract Only
Publication Acceptance Date: 12/1/2004
Publication Date: 2/3/2004
Citation: Campbell, C.L., Vandyke, K.A., Mummey, D.L., Wilson, W.C. 2004. Functional genomics of vector competence in the arbovirus vector, culicoides spp.. Keystone Symposia.
Interpretive Summary: Culicoides sonorensis is a biting midge that transmits virus (bluetongue and epizootic hemorrhagic disease virus) diseases to animals, such as cows and deer. The only time that these viruses are transmitted to animals is through an insect bite. Thus the insects are referred to as disease vectors. The insects pick up the virus by biting an infected host animal. Before the virus can be transferred to a new host animal, the virus must first successfully infect the vector insect and move from the initial infection site, the gut, to the salivary glands for a subsequent bite. For this reason, we are especially interested in learning how the virus infects the insect gut. Some scientists postulate that variations in the insect's ability to be infected with a virus and then transmit it to another animal host may be caused by either differences in the environment or genetic differences between individual insects. It is also possible that a combination of these two factors play a part in whether an individual insect can successfully transmit the virus. Increased knowledge about the insect gut and how the virus invades and grows in it will make it possible to devise ways to prevent virus spread to the salivary glands. If successful, this would interrupt the virus disease cycle and prevent further spread of the disease to uninfected animals. Knowledge of the specific kinds of bacteria that inhabit the gut of the biting midge may also enable us to design novel insect control measures. For these reasons, several approaches were undertaken: 1) To identify insect genes that respond to a virus infection, we detected differences in levels of expressed genes during an orbivirus infection; 2) To determine if midgut bacteria community members vary between geographically separated Culicoides spp. expected to differ in the ability to transmit orbiviruses, we assessed bacterial genes and made preliminary identification of those community members; 3) A gene discovery project is also underway. This project allows us to identify genes that may be useful for future experiments to characterize the factors that allow this insect to spread virus disease pathogens to livestock.
Technical Abstract: The biting midge, Culicoides spp., transmits a variety of agriculturally important disease pathogens throughout the world. In North America, Culicoides spp. are responsible for transmitting arboviral pathogens of the Orbivirus family, bluetongue (BTV) and epizootic hemorrhagic disease viruses (EHDV) to domestic and wild ruminants. Successful propagation and dissemination of the arbovirus within the insect vector may be due to environmental or genetic factors, or a combination thereof, and is dependent on the establishment of a productive infection in the initial target tissue, the insect midgut. For these reasons, several approaches have been undertaken: 1) To identify insect genes that respond to a virus infection, we used real-time quantitative PCR to detect differential transcript levels during an orbivirus infection; 2) To determine if midgut microbial community members vary between geographically separated wild Culicoides spp. expected to differ in the ability to transmit orbiviruses, we assessed 16S rDNA for preliminary characterization of microbiota; 3) An EST gene discovery project of midgut and salivary gland-specific cDNAs is underway.