outline mosquito-borne zoonoses cmed/epi 526 spring
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Mosquito-borne ZoonosesCMED/EPI 526
Spring Quarter 2008
Outline
• 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 atFlushing Hospital calls the Dept of Health inNYC regarding increase in encephalitiscases.
– Thinks it is botulism
Sample collection
• Samples collected from the hospital andsent to the Diagnostic lab and CDC
• Results - St. Louis Encephalitis (9/3)
• Sept 99 - NYChealth dept hearsabout large numbersof dead birds
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Animal investigation
• Mid-June 99- BaysideVeterinary Clinic findscrows with nervoussystem disorders, treatsand releases survivors
• Aug 99 - Many reports ofdead crows - samplessent to NYS Dept ofEnvironmentalConservation
Continued
• 8/16 - ProMED posting of crows beingpoisoned in NYC
• 8/23 - Birds sent to NVSL (Ames, IA)• 8/25 - Bird deaths at Bronx Zoo
– Veterinary pathologist notes similar lesionsin exotic zoo birds and crows
Chilean Flamingo
Crow
Is there a connection?
• 9/21 - Virus isolatedfrom crow and mosquitosame virus isolated fromhumans
• 9/25 - News breaks ofWest Nile Virus
Closing remarks on NYCoutbreak
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Year EEE WEE SLE CE2000 3 0 2 1122001 9 0 79 1342002 9 0 28 1672003 15 0 43 1132004 6 0 12 1122005 21 0 7 732006 8 0 7 64
Cases of Mosquito-borne Zoonoses by YearUnited States, 2000-2006
Surveillance for West Nile Virus, United States, 1999-2006
11,8984,1061,1214,2682006
11,3865,2661,1432,942422005
8,3717,3311,3862,47041*2004
7,84711,5975,1459,86246*20036,03315,74512,0384,15644*20029187,3387316626*20015154,305632111*200016?256241999MosquitoesBirdsHorsesHumansStatesYear
Humans & Horses – casesBirds – Dead birds positive for virusMosquitoes – mosquito pools positive for virus*Includes D.C.
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Spokane
San JuanIsland
Pierce
King
Snohomish
Skagit
Whatcom
Clallam
Jefferson
GraysHarbor
Thurston
Kitsap
Clark
Cowlitz
Lewis
Skamania
Wahkiakum
Mason
Yakima 6 WEE; 1 SLE
Chelan
Okanogan FerryStevens
PendOreille
Lincoln
Kittitas Whitman
Klickitat
BentonWallaWalla
ColumbiaGarfield
Asotin
Franklin
Adams
Grant
Douglas
Pacif ic
Reported Cases of Mosquito-borne Disease, WA1970-1982
Western Equine Encephalitis N=10St. Louis Encephalitis N= 2
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 whenthere 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 topoint when salivary glands have sufficient titer of virus to enable efficienttransmission by mosquito) (influenced by temperature)
• Proximity of vectors/reservoirs to human populations (range of mosquitoes)
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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 arbovirusesVectors
Disease Reservoir Reservoir hosts HumansEEE 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 pipiensCulex nigripalpis Culex nigripalpisC. quinquefasciatus C. quinquefasciatus
WNV Birds Culex pipiens Culex pipiensCulex tarsalis Culex tarsalisC. quinquefasciatus C. quinquefasciatus
Culex restuans
CE Rodents Aedes triseriatus Aedes triseriatus
Pathogenicity of arboviruses in horses andhumans
Disease Horses HumansEEE +++ ++WEE ++ +WNV +++ ++SLE silent +CE silent ++
+=mild, ++=moderate, +++=marked
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Strategies of viral persistence innature
• 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)
• 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
Surveillance Activities
Strategies to prevent infectionswith arboviruses
Environment:Reduce habitats of mosquito productionScreen windows/doors
Mosquitoes:Larvicide applicationsAerial spraying (adulticide)Mosquito fish
Humans:Mosquito-avoidance behaviorsRestrict outdoor activity at dawn and duskWear long-length clothing when outdoorsUse mosquito repellant
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