THE ROLE OF DIPTEROUS INSECTS IN THE MECHANICAL TRANSMISSION OF ANIMAL VIRUSES

Animal viruses may be transmitted by arthropods in two ways, either bi ologically or mechanically. Many different species of Diptera are impl icated in mechanical transmission, but haematophagous species are the most important. The insects become contaminated with virus during norm al feeding behaviour, and virus persists on their mouthparts or body u ntil the next feed. Some viruses are inactivated rapidly on mouthparts , whereas others survive for many days or weeks, prolonging the potent ial period of transmission. Some viruses produce high titles in the sk in of the infected vertebrate host, which facilitates transmission, wh ereas other viruses are transmitted even during relatively low levels of viraemia. Mechanical transmission by arthropods is important in the epidemiology of many animal diseases, and may be the major mode of ho rizontal transmission. In other instances vector spread is merely inci dental.