Department of Defense West Nile Virus Surveillance in 2002

Military Medicine, Jun 2004 by Witt, Clara Josting, Brundage, Mary, Cannon, Charles, Cox, Kenneth, Et al

The Department of Defense (DoD) has engaged in West Nile virus (WNV) surveillance and response since 1999. In 2002, the three Services continued their cooperative, multidisciplinary approach to the WNV outbreak. Activities included a doubling of mosquito surveillance and vector control responses, extension of and doubling of bird and nonhuman mammal surveillance to all four continental United States regions, expanded diagnostic testing by DoD laboratories, and installation environmental clean up and personnel protection campaigns. Medical treatment facilities conducted passive surveillance and reported possible cases in DoD health care beneficiaries. Efforts were coordinated through active communication within installations, with commands, and with surrounding communities. Undertaken activities complemented each other to maximize surveillance coverage. The surveillance detected WNV on 44 DoD installations. It led directly to vector control and prevention activities, and there were no confirmed cases of WNV reported in the DoD force. This multi-Service effort is a surveillance template for future outbreaks that threaten DoD force health.

Introduction

West Nile virus (WNV] is a mosquito-borne virus (genus Flavivirus, family Flaviviridae) and the cause of West Nile fever and West Nile encephalitis and meningitis. In the 1950s, investigators at the U.S. Naval Medical Research Unit No. 3 in Cairo, Egypt, described much of what is known of the natural behavior of the virus, including an understanding that WNV was geographically limited to the eastern hemisphere.1 Since its North American introduction in 1999, WNV has explosively spread across 44 states, the District of Columbia, and six Canadian provinces.2,3 As of December 2002 in the United States, WNV has been found in 37 mosquito species, 138 bird species, and 13 nonhuman mammal species.4 Table I shows the reported numbers of mosquito pool detections and bird, equine, and human cases reported to U.S. civilian authorities since 1999. WNV is now the leading single cause of human arboviral encephalitis in the United States.5

To meet the challenge of the WNV outbreak and in compliance with the Department of Defense (DoD) health affairs policy, the Services have conducted a multidisciplinary WNV surveillance and response effort to protect the DoD force health and readiness.6 Components include mosquito, bird, nonhuman mammal, and human surveillance. Using centrally developed guidelines, DoD installations and medical treatment facilities designed and implemented activities to characterize WNV exposure and transmission risk and to prevent WNV infection in DoD personnel. Activities were coordinated through active communication and, where needed, task sharing. all surveillance findings were reported to Service and DoD commands, as well as to civilian state and federal public health officials for local, regional, and national prevention and control decision making.

Materials and Methods

Mosquito Surveillance

To assess the WNV exposure threat to DoD forces and dependents, installations conducted active mosquito surveillance to determine vector composition, abundance, and spatial distribution and, if possible, to detect WNV presence. Surveillance primarily relied on the use of used gravid mosquito traps to collect postprandial Culex spp. mosquitoes (considered most likely to harbor WNV), light traps to collect other potentially infective mosquitoes, and oviposition traps to monitor for epizootic mosquitoes.7"10 Personnel identified mosquitoes to at least the genus level and pooled them (maximum 25 mosquitoes/pool) for testing. The U.S. Army Center for Health Promotion and Preventive Medicine (CHPPM)-North used reverse transcriptase-polymerase chain reaction (RT-PCR) to detect WNV viral RNA and they characterized positive mosquito pools to the species level. ' ' The Air Force Institute for Environment, Safety and Occupational Health Risk Assessment identified mosquitoes by species, and then tested pools using the VecTest (Medial Analysis Systems, Camarillo, CA).12 all positive VecTest results were confirmed by RT-PCR at CHPPM-North. CHPPM compiled all mosquito collection and testing data and provided summarized results back to installations, higher commands, and DoD-Global Emerging Infections Surveillance and Response Systems (GEIS) on a weekly basis. Installations used surveillance results to direct mosquito control activities.

Avian Surveillance

Avian surveillance comprised two forms, sentinel chicken surveillance and passive surveillance of wild dead birds brought into or reported to U.S. Army Veterinary Treatment Facilities (VTF) or installation veterinary or environmental health staff by the DoD community. The VTFs and staffs Waged the wild birds for submission and sent suitable birds to the U.S. Geologic Survey National Wildlife Health Center or to state health department laboratories that in turn performed RT-PCR to detect virus presence as per Centers for Disease Control and Prevention (CDC) guidance.13"15 The laboratories reported positive and negative test results back to submitters. Results were then communicated to installation pest management, preventive medicine, public and environmental health officials, and higher commands for appropriate control responses. Results were also reported to surrounding communities to aid in their WNV efforts. Commands reported aggregated wild bird surveillance results to DoD-GEIS on a monthly basis.