The method of transmission of LSDV from animal to animal and herd to herd is incompletely understood. There is strong evidence that the virus is spread by biting insects (vectors) such as biting flies (e.g. Stomoxys calcitrans and Biomyia fasciata) and mosquitoes (e.g. Culex mirificens and Aedes natrionus). Direct transmission between animals is believed to occur but the relative importance of this method of spread compared to vector transmission is unknown.