Animal viral diseases and global change: bluetongue and West Nile fever as paradigms

Jiménez-Clavero, Miguel Á

As noted above, though primarily pathogenic in sheep (particularly in some selected breeds) BTV can infect a variety of ruminants, where the disease often remains asymptomatic. For the transmission to occur the virus must replicate in the host to reach a minimum level of viremia which enables it to be ingested in sufficient amount in a blood feed of a Culicoides vector to be able to replicate in it. Camels also seem to act as reservoirs , possibly playing a role in the spread of the disease by facilitating the virus to get through the "sand barrier" represented by the Sahara desert, which stands between the tropics and subtropics (where BTV is endemic), and North Africa and Europe where it causes epizootics periodically. This role for camels not only for BT, but also for other epizootic arboviral diseases is supported by recent serological evidence Touil et al., 2012) . South American camelids are susceptible to the infection, but develop only a mild form of the disease (Schulz et al., 2012) . A wide range of wild ruminant species are susceptible to BTV infection, but only a few suffer from severe disease, including white-tailed deer (Falconi et al., 2011) and mouflon (Fernandez-Pacheco et al., 2008; Lopez-Olvera et al., 2010) . The role of wild ruminants in the eco-epidemiology of BTV is less known.