Emergence of West Nile Virus in Mosquito (Diptera: Culicidae) Communities of the New Mexico Rio Grande Valley

Abstract

The first appearances of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in New Mexico were reported in late summer to early fall 2002. Several dead birds tested positive for WNV, and 78 equine cases were confirmed. All mosquito pools tested (n = 268) were negative. A statewide surveillance program was launched in May 2003 to study the emergence and spread of this new arbovirus in mosquitoes from the Rio Grande valley. Mosquitoes were trapped at 32 sites along a 750-km stretch of the Rio Grande valley. Sites were trapped for one night either weekly or biweekly, by using CO2-baited CDC light traps and gravid traps. Pools of captured mosquitoes were tested for WNV by reverse transcription-polymerase chain reaction. By mid-July 2003, WNV levels in the mosquito population had reached levels that were detectable by the surveillance program. Positive pools of mosquitoes were found in the Rio Grande valley from mid-July through late September. In total, 75 positive pools were found, from sites throughout the study area. The predominant species infected with WNV in this region were Culex tarsalis (Coquillett) in rural areas, and Culex salinarius (Coquillett) and Culex pipiens quinquefasciatus (Say) in urban areas. There were 202 human cases and 438 equine cases of WNV in New Mexico in 2003, which corresponded well in time with the positive mosquitoes. Our results seemed to be consistent with introduction of WNV in late summer 2002, followed by a period of transmission and amplification cycles between local avian hosts and mosquito vectors.

Regional Differences in the Association Between Land Cover and West Nile Virus Disease Incidence in Humans in the United States

“…tarsalis in Western regions. 5,6,10,11,[31][32][33][34][35][36][37][38] Supplemental Figure S2 has a range map of these species. 24 A few studies have reported results that were contradictory to our findings.…”

“…In the Southwest, higher infection rates of primary mosquito vectors were found in urban areas. 11 However, high mosquito infection rates do not necessarily lead to high human disease infection rates, especially if high densities of other appealing hosts are also present in urban areas and therefore, mosquitoes are not feeding on humans (the dilution effect). 13 Another possible explanation is that increased mosquito infection rates are masked by even larger increases in the human population.…”

“…Numerous studies have reported associations between different land cover types and WNV disease incidence in humans, [3][4][5][6] seroprevalence or infection rates in birds 7 and wild and domesticated mammals, [8][9][10] and infection rates in mosquitoes. 11,12 However, the strength and direction of these correlations have varied considerably. For instance, both positive 6 and negative 9 associations with crop land cover were reported in the South Central state of Texas.…”

Horizontal and Vertical Transmission of West Nile Virus Genotype NY99 by Culex salinarius and Genotypes NY99 and WN02 by Culex tarsalis

“…salinarius may be the important vectors in urban ecosystems. 6,7,12 Culex tarsalis has been reported to have a relatively short WNV extrinsic incubation period, 12 to vertically transmit WNV, 13,14 and, along with Cx. pipiens , 15 to transmit the relatively newly recognized WN02 genotype more quickly than the original NY99 genotype.…”

Entomologic Investigations during an Outbreak of West Nile Virus Disease in Maricopa County, Arizona, 2010

“…quinquefasciatus is the predominant vector in urban areas. 30,31 The detection of WNV in three pools of Ps. columbiae is of interest, in light of research identifying WNV in nine pools of this species in New Mexico, 31 and in two pools captured at alligator farms in Louisiana.…”