Togaviridae: genus Alphavirus Viruses

Public Health Significance of Urban Pests Birds 245 244

8.2.1. Viruses

8.2.1.1. Togaviridae: genus Alphavirus

8.2.1.1.1. Eastern and Western equine encephalitis viruses In North America, birds are the principal hosts in the natural transmission of mosquito- borne Eastern and Western equine encephalitis viruses EEEV and WEEV, respectively. These mosquito-borne viruses have also been isolated from synanthropic birds mostly passerines and feral pigeons, but mainly during epidemics and epizootic episodes Holden, 1955; Dardiri et al., 1957; Holden et al., 1973; Beran, 1981; Soler, Portales Del Barrio, 1985. Some wild birds develop a relatively high-level, long-term viraemia after inoculation with WEEV and EEEV and can even maintain persistent virus infection, with viraemia lasting up to 10 months for WEEV Hammon, Reeves Sather, 1951; Kissling et al., 1954, 1957a,b; Reeves et al., 1958. Birds serve as a source of infectious blood to mosquito vectors and latently infected birds can be regarded as a virus reservoir. WEEV affects a wide range of wild birds, but it occurs less often than EEEV in epizoo- tic episodes. For instance, mortality in Agelaius spp. blackbirds was observed after expe- rimental infection with WEEV Hardy, 1987. However, no EEEV or WEEV infections of people have been reported as attributable to, or directly associated with, urban birds. 8.2.1.1.2. Sindbis virus Birds are the principal hosts and disseminators of Sindbis virus SINV; Scandinavian sub- type: Ockelbo, while the vectors are largely ornithophilic mosquitoes. SINV was isola- ted from synanthropic species: carrion crows Corvus corone in Egypt Taylor et al., 1955 and European starlings Sturnus vulgaris in Slovakia Ernek et al., 1977. It causes ence- phalitis and occasional death in experimentally infected chickens and pigeons. The chro- nic course of the infection in pigeons has been ascertained experimentally Semenov et al., 1973. However, no SINV infections of people have been reported as attributable to, or directly associated with, urban birds.

8.2.1.2. Flaviviridae: genus Flavivirus