Temporal and Spatial Patterns of West Nile Virus Transmission in Saginaw County, Michigan, 2003–2006

Abstract

The dynamics of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) infection in mosquitoes, sentinel pheasants, and wild dead birds were evaluated during 2003-2006 in Saginaw Co., MI. Mosquitoes were collected by New Jersey Light Traps at 22 sites during May-September, pooled by species and sample location, and tested for presence of WNV RNA by using a real-time reverse transcription-polymerase chain reaction assay. Oral swabs from wild dead birds submitted by the public were tested by Vec-Test assay. Sentinel pheasants were bled weekly, and serum was tested for antibodies with an inhibition enzyme immunoassay. In total, 37,225 mosquitoes [Aedes vexans (Meigen), Culex pipiens L., and Culex restuans Theobald] were tested in 5,429 pools, of which 59 (1.1%) were positive. Ae. vexans was most abundant but had a comparatively low infection rate (0.06-2.11) compared with Cx. pipiens (1.75-4.59) and Cx. restuans (1.22-15.67). Mosquito abundances were temporally related to variations in 2-wk average weather variables. Infected dead crows appeared earlier each transmission season than blue jays, but infection prevalence for both peaked approximately mid-August. Space-time clusters were found in different locations each year. Sentinel pheasant seroprevalence was 19.3% (16/83), 12.7% (10/79), and 7.7% (5/65) during 2003-2005, respectively. We demonstrated temporal patterns of WNV activity in corvid birds and Culex spp. mosquitoes during the study period, suggesting virus transmission within an enzootic cycle. Despite the absence of human case reports nearby, this surveillance system demonstrated WNV transmission and possible human risk. Maintained surveillance using more appropriate gravid traps and CDC CO2 light traps could improve sensitivity of vector collection and virus detection.

Meteorological Conditions Associated with Increased Incidence of West Nile Virus Disease in the United States, 2004–2012

“…Other epidemiologic investigations have found similar associations between warmer than normal temperatures in the months before a WNV season and increased human disease cases using a variety of meteorological measures including fewer cold winter days, 25 warmer mean minimum temperature in January, 26 warmer winter temperatures, 27 and monthly temperature anomalies from the 30-year average. 28 Higher temperature favors greater larval 29 and adult mosquito abundance, [30][31][32][33] likely caused by the acceleration of larval emergence, development and adult reproduction, and more successful overwintering of adults or eggs. 34,35 The rate of WNV replication in adult mosquitoes is also positively associated with temperature, which reduces the time interval between a blood meal to when an adult mosquito can transmit the virus to another host 36 and results in an augmented mosquito infection rate.…”

Epidemiological Characteristics and Space-Time Analysis of the 2015 Dengue Outbreak in the Metropolitan Region of Tainan City, Taiwan

“…The p -value is generated using the Monte Carlo hypothesis testing method with 999 times simulation, and the cut-off point is set at 0.05 [ 28 ]. This approach has been applied to dengue and other infectious diseases in our previous work [ 17 , 29 ]. The space-time permutation model was carried out by SaTScan V9.4 software ( , Boston, MA, USA).…”

Environmental Forcing Shapes Regional House Mosquito Synchrony in a Warming Temperate Island

“…Insect vectors of disease are among the species raising major concerns, given their potential to extend the geographical range of vector-borne disease transmission to areas where disease transmission maybe limited by low temperature constraints on vector abundance and competence to transmit pathogens, or by altering the impact of exogenous environmental factors on vector population dynamics (Koenraadt et al 2006, Chaves andKoenraadt 2010). For example, in temperate areas, West Nile Virus transmission season length is extremely sensitive to temperature changes, becoming longer at high temperatures (Ruiz et al 2010;Chuang et al 2011Chuang et al , 2012. Moreover, other weather factors, such as rainfall, where recent changes have been associated with global warming (Zhou et al 2001), can also inßuence changes in both vector abundance and infection (Chaves et al 2011a).…”