West Nile virus surveillance in mosquitoes in New York State, 2000-2004

A West Nile virus (WNV) surveillance system was created and implemented in New York State (NYS) in 2000 and described previously (White et al. 2001). We examine and evaluate the results of mosquito and virus surveillance for 2000 through 2004 exclusive of New York City. Forty-nine counties submitted 1,095,426 mosquitoes in 35,280 pools for WNV assay. Specimens of 47 species were tested, with Culex species accounting for 47.6% of all pools tested. WNV was detected in 814 pools from 10 species, with combined Culex pipiens/Culex restuans pools accounting for 90.8% of all detections. Pools submitted from gravid traps were 5.7 times more likely to be positive than submissions from carbon dioxide-baited light traps. Most human WNV cases resided in counties that conducted mosquito surveillance. Local health departments' use of mosquito surveillance information often led to an enhanced disease prevention response. In NYS, Cx. pipiens/Cx. restuans groups are most likely vectors of WNV. Future efforts to improve system efficacy are discussed.     

West Nile virus infection in birds and mosquitoes, New York State, 2000

West Nile (WN) virus was found throughout New York State in 2000, with the epicenter in New York City and surrounding counties. We tested 3,403 dead birds and 9,954 mosquito pools for WN virus during the transmission season. Sixty-three avian species, representing 30 families and 14 orders, tested positive for WN virus. The highest proportion of dead birds that tested positive for WN virus was in American Crows in the epicenter (67% positive, n=907). Eight mosquito species, representing four genera, were positive for WN virus. The minimum infection rate per 1,000 mosquitoes (MIR) was highest for Culex pipiens in the epicenter: 3.53 for the entire season and 7.49 for the peak week of August 13. Staten Island had the highest MIR (11.42 for Cx. pipiens), which was associated with the highest proportion of dead American Crows that tested positive for WN virus (92%, n=48) and the highest number of human cases (n=10).     

West Nile virus outbreak among horses in New York State, 1999 and 2000

West Nile (WN) virus was identified in the Western Hemisphere in 1999. Along with human encephalitis cases, 20 equine cases of WN virus were detected in 1999 and 23 equine cases in 2000 in New York. During both years, the equine cases occurred after human cases in New York had been identified.     

West Nile virus in New York City

In 1999, a cluster of encephalitis cases was detected in New York City. The city applied larvicide to standing water and aerially sprayed pesticides to control adult mosquitoes. The causative agent was West Nile virus, a type of encephalitis that had never before been transmitted in the western hemisphere. This experience offers many lessons for the practitioners of public health and of public health law. A public health infrastructure that does not lose sight of the old threats must be maintained. The public health and environmental governmental establishments must work together. Law is closely intertwined with policy and programmatic initiatives and can facilitate a better public health outcome.     

Dead crow densities and human cases of West Nile virus, New York State, 2000

In 2000, Staten Island, New York, reported 10 human West Nile virus cases and high densities of dead crows. Surrounding counties with <2 human cases had moderate dead crow densities, and upstate counties with no human cases had low dead crow densities. Monitoring such densities may be helpful because this factor may be determined without the delays associated with specimen collection and testing.     

West Nile virus activity--New York and New Jersey, 2000

In late August 1999, an outbreak of encephalitis caused by West Nile virus (WNV) was detected in New York City and subsequently identified in neighboring counties (1). In response, an extensive mosquito-control and risk-reduction campaign was initiated, including aerial and ground applications of mosquito adulticides throughout the affected areas. No human WNV infections were found in New York City with an onset date after the campaign was completed. Cases continued to occur among humans in surrounding counties that did not undertake mosquito-control efforts until later, suggesting that the campaign may have reduced human risk. In May 2000, CDC issued guidelines to direct national surveillance, prevention, and control efforts (2) and provided funds to support these efforts in 19 state and local health departments where WNV transmission had occurred or where transmission would probably occur based on known bird migration patterns. This report presents the findings of surveillance activities.     

Dead crow density and West Nile virus monitoring, New York

New York State used the health commerce system to monitor the number of West Nile virus (WNV) human disease cases and the density of dead crows. In each year from 2001 to 2003 and for the 3 years combined, persons living in New York counties (excluding New York City) with elevated weekly dead crow densities (above a threshold value of 0.1 dead crows per square mile) had higher risk (2.0-8.6 times) for disease caused by WNV within the next 2 weeks than residents of counties reporting fewer dead crows per square mile. This type of index can offer a real-time, relatively inexpensive window into viral activity in time for prevention and control. Changes in reporting, bird populations, and immunity may require that thresholds other than 0.1 be used in later years or in other areas.     

Enhancing West Nile virus surveillance, United States

We provide a method for constructing a county-level West Nile virus risk map to serve as an early warning system for human cases. We also demonstrate that mosquito surveillance is a more accurate predictor of human risk than monitoring dead and infected wild birds.     

Intrauterine West Nile virus infection--New York, 2002

West Nile virus (WNV), a mosquito-borne flavivirus and human neuropathogen, is epidemic in the United States. In 2002, newly recognized mechanisms of person-to-person WNV transmission were described, including possible transmission from mother to infant through breast milk. WNV has not been previously associated with intrauterine infection or adverse birth outcomes. This report describes a case of transplacental WNV transmission. Pregnant women should take precautions to reduce their risk for WNV or other arboviral infection and should undergo diagnostic testing when clinically appropriate.     

West Nile virus isolates from mosquitoes in New York and New Jersey, 1999

An outbreak of encephalitis due to West Nile (WN) virus occurred in New York City and the surrounding areas during 1999. Mosquitoes were collected as part of a comprehensive surveillance program implemented to monitor the outbreak. More than 32,000 mosquitoes representing 24 species were tested, and 15 WN virus isolates were obtained. Molecular techniques were used to identify the species represented in the WN virus-positive mosquito pools. Most isolates were from pools containing Culex pipiens mosquitoes, but several pools contained two or more Culex species.     

West Nile virus surveillance, Guadeloupe, 2003-2004

We conducted extensive surveillance for West Nile virus infection in equines and chickens in Guadeloupe in 2003-2004. We showed a high seroprevalence in equines in 2003 related to biome, followed by a major decrease in virus circulation in 2004. No human or equine cases were reported during the study.     

Field evaluation of CDC gravid trap attractants to primary West Nile virus vectors, Culex mosquitoes in New York State

A field study was conducted to evaluate two CDC gravid trap attractants available for the West Nile virus surveillance program in New York State (NYS). According to potential attractiveness, a common lawn sod in NYS, Kentucky bluegrass (Poa pratensis) infusion and a rabbit chow infusion were compared for attractiveness to primary West Nile virus vectors, Culex mosquitoes. Attractiveness of each infusion was measured by the number of adult mosquitoes caught in CDC gravid traps and the number of egg rafts laid in ovitraps. Both gravid trap and ovitrap studies demonstrated that lawn sod infusion with a 7-day incubation period had better attractiveness to Culex restuans/Culex pipiens than rabbit chow infusion with the same incubation period. Attractiveness of lawn sod infusions was increased as they became aged within a week's period. Lawn sod infusion also attracted more Ochlerotatus japonicus, a potentially important West Nile virus vector in New York.