West Nile Virus in Host-Seeking Mosquitoes within a Residential Neighborhood in Grand Forks, North Dakota

Abstract

West Nile virus (WNV) was first recovered in North Dakota near the city of Grand Forks in June 2002. During 2002, 2003, and 2004, we collected mosquitoes from Grand Forks using Mosquito Magnet traps and tested them for WNV. The seasonal abundance, species composition, and reproductive status of female mosquitoes were correlated with local environmental temperature and state surveillance data on WNV to determine the factors affecting local transmission of WNV. Over 90% of the mosquitoes collected were Aedes vexans, Ochlerotatus dorsalis, and Culex tarsalis, but WNV was detected only in Cx. tarsalis. Average summertime temperatures and relative abundance of mosquitoes were highest in 2002 but no WNV-positive mosquitoes were detected until the following summer. In 2003, nulliparous Cx. tarsalis appeared in mid-June (first summer brood), and parous Cx. tarsalis appeared in mid-July. The first WNV-positive pool occurred 21 July, and minimum daily infections rates increased thereafter until 27 August. The minimum infection rate (MIR) for Cx. tarsalis during the season was 5.7 infected mosquitoes per 1,000 tested, with the highest infection rates occurring at the end of the season as Cx. tarsalis populations started to decline. Mid-to-late August was identified as the period of highest risk for being bitten by a WNV-infected mosquito in Grand Forks during 2003. In 2004, viral activity in Grand Forks was low, due to very cool temperatures throughout the summer. To examine the genetic diversity of the 2003 WNV isolates from Grand Forks, we sequenced a 366-nucleotide region of the capsid and premembrane gene. Thirteen (46%) of the 28 WNV isolates contained at least one nucleotide substitution when compared to the homologous region of the progenitor WN NY-99 strain, and seven of these 13 substitutions coded for amino acid changes. Thus, WNV is established in North Dakota, it appears to be evolving and it is vectored primarily by Cx. tarsalis.

Arboviruses in North Dakota, 2003–2006

“…tarsalis as one of the most important vectors in western United States, [22][23][24][25] including North Dakota. 26 Our current investigations confirm this conclusion, but we also documented Ae. vexans to be an important vector.…”

“…36 It was relatively abundant in North Dakota from the end of June through the end of August, had a relatively high IR during the summer, is efficient in transmitting this virus horizontally, 22,24,25,37 and is relatively efficient in transmitting this virus vertically. 24,38,39 Culex tarsalis was collected during the weeks of June 2 to October 6, similar to collections made in Grand Forks, North Dakota, 26 Figure 4). These data were similar to those reported in Grand Forks, ND.…”

“…tarsalis in North Dakota. 26,27 Unlike studies elsewhere in the United States where Ae. vexans was not as abundant, [28][29][30] numbers per trap-night in North Dakota averaged 1,890 from June 2 through the week of August 4 and averaged as high as 9,393 per trap-night during the week of July 7 ( Figure 2B).…”

“…These data were similar to those reported in Grand Forks, ND. 26,27 The IR was near or greater than three per thousand specimens, and populations were relatively abundant (Figure 2A). The IR increased in early September, but populations were drastically reduced and risk of transmission reduced.…”

West Nile Virus in American White Pelican Chicks: Transmission, Immunity, and Survival

“…The Culex tarsalis mosquito has been identified as the primary vector of WNV in the northern plains of the United States 4 and, specifically in the region of our study, no other mosquito species has proven to be a major vector. [5][6][7] The high incidence of WNV in these colonies, its rapid spread within the colonies, and the behaviors of pelican chicks 2 warrant exploring the potential for bird-to-bird transmission rather than just mosquito-to-bird transmission. Direct bird-to-bird transmission has been documented in captive populations of chickens, 8 crows, 9 and geese, 10,11 and there is compelling evidence of bird-to-bird transmission in wild populations of American Crows (Corvus brachyrhynchos).…”