West Nile virus (WNV) is a widely distributed mosquito-borne flavivirus. WNV strains are classified into several genetic lineages on the basis of phylogenetic differences. Whereas lineage 1 viruses are distributed worldwide, lineage 2 WNV was first detected outside of Africa in Hungary in 2004. Since then, WNV-associated disease and mortality in animal and human hosts have been documented periodically in Hungary. After the first detection of WNV from a pool of Culex pipiens mosquitoes in 2010, samples were collated from several sources and tested in a 2-year monitoring program. Collection areas were located in the Southern Transdanubium, in northeastern Hungary, in eastern Hungary, and in southeastern Hungary. During the 2 years, 23,193 mosquitoes in 645 pools were screened for WNV virus presence with RT-PCR. Three pools were found positive for WNV in 2011 (one pool of Ochlerotatus annulipes collected in Fényeslitke in June, one pool of Coquillettidia richiardii collected in Debrecen, Fancsika-tó, in July, and one pool of Cx. pipiens captured near Red-Footed Falcon colonies at Kardoskút in September). The minimal infection rate (MIR=proportion of infected mosquitoes per 1000 mosquitoes) of all mosquito pools was 0.25, whereas the MIR of infected species was 2.03 for O. annulipes, 0.63 for C. richiardii, and 2.70 for C.x pipiens. Molecular data have demonstrated that the same lineage 2 WNV strain has circulated in wild birds, horses, humans, and mosquitoes in Hungary since 2004. Mosquito-based surveillance successfully complemented the ongoing, long-term passive surveillance system and it was useful for the early detection of WNV circulation.
Keywords: Coquillettidia richiardii; Culex pipiens; Hungary; Minimal infection rate; Mosquito; Ochlerotatus annulipes; West Nile virus.