Outbreak investigation

Transcription

1 Outline Mosquito-borne Zoonoses CMED/EPI 526 Spring Quarter 2008 WNV Outbreak NYC Cases Descriptive Epidemiology time, place Vectors-Hosts Descriptive Epidemiology person Viral persistence Surveillance Prevention Outbreak investigation Background Aug 99 - Chief of infectious diseases at Flushing Hospital calls the Dept of Health in NYC regarding increase in encephalitis cases. Thinks it is botulism Sample collection Samples collected from the hospital and sent to the Diagnostic lab and CDC Results - St. Louis Encephalitis (9/3) Sept 99 - NYC health dept hears about large numbers of dead birds 1

2 Animal investigation Mid-June 99- Bayside Veterinary Clinic finds crows with nervous system disorders, treats and releases survivors Aug 99 - Many reports of dead crows - samples sent to NYS Dept of Environmental Conservation Continued 8/16 - ProMED posting of crows being poisoned in NYC 8/23 - Birds sent to NVSL (Ames, IA) 8/25 - Bird deaths at Bronx Zoo Veterinary pathologist notes similar lesions in exotic zoo birds and crows Is there a connection? Crow Chilean Flamingo 9/21 - Virus isolated from crow and mosquito same virus isolated from humans 9/25 - News breaks of West Nile Virus Closing remarks on NYC outbreak 2

3 Cases of Mosquito-borne Zoonoses by Year United States, Year EEE WEE SLE CE Surveillance for West Nile Virus, United States, Year States Humans Horses Birds * 26* 44* 46* 41* ,156 9,862 2,470 2,942 4, ,038 15,745 6,033 5,145 1,386 1,143 1,121? 4,305 7,338 11,597 7,847 7,331 5,266 4,106 Mosquitoes ,371 11,386 11,898 Humans & Horses cases Birds Dead birds positive for virus Mosquitoes mosquito pools positive for virus *Includes D.C. 3

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5 Reported Cases of Mosquito-borne Disease, WA San Juan Clallam Island Jefferson Grays Mason Harbor Wahkiakum Kitsap Skagit Snohomish King Thurston Pierce Cowlitz Lewis Clark Whatcom Skamania Chelan Kittitas Yakima 6 WEE; 1 SLE Klickitat Okanogan Douglas Grant Benton Ferry Lincoln Adams Western Equine Encephalitis N=10 St. Louis Encephalitis N= 2 Stevens Pend Oreille Spokane Whitman Franklin Garfield Columbia Walla Walla Asotin Host and environmental factors to be considered in transmission of viruses by arthropod vectors Vector/reservoir host factors: Contact with critical host Population indices of vector and hosts Diurnal feeding habits of the vector Susceptibility of and ability of the virus to replicate in the host (Intrinsic incubation period point from inoculation of virus by mosquito to point when there is sufficient titer of virus in blood to infect other mosquitoes) Host feeding preferences and longevity (influenced by season) Vector/environmental factors: Precipitation increased (flooding) and decreased (drought) Temperature Vector competence (ability of vector to become infected with and transmit virus). (Extrinsic incubation period point from ingestion of blood meal to point when salivary glands have sufficient titer of virus to enable efficient transmission by mosquito) (influenced by temperature) Proximity of vectors/reservoirs to human populations (range of mosquitoes) 5

6 Mosquitoes and Birds 284 different Birds Corvids (crows, jays, magpies) are over represented House sparrow Clinically found dead 59 types of Mosquitoes Culex most often identified C. pipiens most often Vectors and reservoir hosts of arboviruses Vectors Disease Reservoir Reservoir hosts Humans EEE Birds Culiseta melanura Aedes sollicitans Aedes vexans WEE Birds Culex tarsalis Culex tarsalis SLE Rural Birds Culex tarsalis Culex tarsalis Culex pipiens Culex pipiens Urban Birds Culex pipiens Culex pipiens Culex nigripalpis Culex nigripalpis C. quinquefasciatus C. quinquefasciatus WNV Birds Culex pipiens Culex pipiens Culex tarsalis Culex tarsalis C. quinquefasciatus C. quinquefasciatus Culex restuans CE Rodents Aedes triseriatus Aedes triseriatus Pathogenicity of arboviruses in horses and humans Disease Horses Humans EEE WEE ++ + WNV SLE silent + CE silent ++ +=mild, ++=moderate, +++=marked 6

7 Strategies of viral persistence in nature Chronic infection of vertebrate hosts (birds) Reintroduction of the virus by migratory birds Persistence in hibernating adult mosquitoes Vertical transmission in mosquitoes Alternate arthropod vectors (ticks) Surveillance Activities Monitor weather conditions temperature, humidity, precipitation Wild-bird population: Moribund/death birds test for virus Healthy birds test for antibodies Sentinel chicken flocks test for antibodies Mosquito collections test for virus Horses encephalitis Strategies to prevent infections with arboviruses Environment: Reduce habitats of mosquito production Screen windows/doors Mosquitoes: Larvicide applications Aerial spraying (adulticide) Mosquito fish Humans: Mosquito-avoidance behaviors Restrict outdoor activity at dawn and dusk Wear long-length clothing when outdoors Use mosquito repellant 7