Transmission of arboviruses without involvement of arthropod vectors

Transmission of arboviruses (arthropod-borne viruses belonging to various v irus families) without involvement of arthropod vectors has been documented for years, but the reports have not been reviewed systematically. The rece nt report of West Nile (WIN) virus isolation from a hawk in mid-winter in N ew York (Garmendia et al., J. Clin. Microbiol. 38, 3110-3111, 2000) generat ed a considerable interest in this mode of arbovirus transmission. In this article, the data available worldwide are analyzed according to the factors involved in such a transmission under natural conditions, mode of infectio n, virus entry mechanism, administration and efficacy evaluation of vaccine s, and significance in agricultural trade and public health. Analysis of nu merous reports compiled for this review revealed that peroral and intranasa l/aerosol transmissions are very common among arboviruses. The mechanism of virus infections in animals was most extensively studied for intranasal/ae rosol infection, confirming two routes of virus spread to central nervous s ystem (CNS), olfactory and hematogenous. To rule out the possibility of asy mptomatic, cryptic infection the efficacy evaluation of candidates for vacc ines against neurotropic arboviruses should include virus isolation from ti ssues of not only symptomatic but also of asymptomatic animals that survive intranasal virus challenge. Human activities, such as feeding livestock an imals with food containing virus-contaminated meat and assembling a large n umber of livestock from many geographically-separated locations, have been identified as a cause of spread of some arboviral diseases. Despite numerou s laboratory reports, the significance of this mode of transmission of arbo viruses under natural conditions was rarely investigated, except for a few viruses important for veterinary medicine.