Protecting Yourself from Mosquito-borne Infections: West Nile Virus

1. Protecting Yourself from Mosquito-borne Infections: West Nile Virus Dr. Richard M. Houseman Department of Entomology University of Missouri

2. “When unable to defend herself by the sword, Rome could defend herself by means of the fever.” Godfrey of Viterbo, 1167

4. Mosquito-Borne Infections • Filaria • Heartworm • Elephantiasis • Protozoa • Malaria • Virus • Yellow Fever • Dengue • SLE, WEE, WNV

5. West Nile Virus • Encephalitis-type virus identified in Uganda (1937) • Commonly found in humans and birds throughout much of the world • Historically Europe, Africa, Middle East. • Has been in North America since 1999 • First found in New York City • Now permanently established in Western Hemisphere

10. Human WNV Reports in 2003

12. West Nile Virus Symptoms • Most human infections have none or mild symptoms (West Nile Fever) • Recovery in >99% of cases • No long-term effects • <1% with symptoms develop encephalitis • Disorientation, weakness, paralysis, coma • Hospitalization for support therapy • Intravenous fluids, ventilator, monitoring

13. West Nile Virus Transmission • Birds are primary hosts, others are incidental • Human infections are rare • In temperate areas (24º-66º latitude) virus transmission is seasonal • Summer to early fall • Cases appear 3-4 weeks following infection

14. 20 species 140 species Dogs, cats, bats, squirrels, skunks, chipmunks, rabbits

15. Mosquito Vectors of WNV • Of the ~20 known vector species… • 14 have been collected in Missouri • 12 are found in all areas of the state • 8 are common or abundant • 7 inhabit temporary/human-created water • 7 inhabit permanent water • 7 bite at dawn/dusk • 5 overwinter as fertilized females

16. All mosquitoes are not created equal • Different habitat preferences • Water conditions • Activity periods • Different movement patterns • Different host preferences • Warm-blooded • Different groups

17. ‘Urban’ Mosquitoes • Breeding occurs and hosts available in human-dominated environments • Important urban species Culex pipiens (common house) Aedes aegypti (yellow fever) Aedes albopictus (Asian tiger)

18. ‘Suburban’ Mosquitoes • Breed in non-human-dominated environments and move to locate hosts • Highly vagile adults (ie. up to 17 miles) • Important urban ‘invading’ species Culex tarsalis (western encephalitis) Aedes vexans (inland floodwater)

19. ‘Rural’ Mosquitoes • Breed in non-human-dominated environments and feed to a lesser extent on man. • Less vagile (ie. <1 mile) • Important rural species • Anopheles quadrimaculatus (eastern malaria)

20. adult egg pupa larva Life Cycle of Mosquitoes • Water • Eggs, larvae, pupae • Landscape • Adults • Host • Adults • Back to Water • Adults

21. In the Water • Standing water • Pollution • Decaying organic matter • Emergent vegetation (intersection line) • Containers, puddles, drains, etc. • Small or large amounts of water • Decaying organic matter for hatching/feeding

23. In the Water • Eggs (2d) • Oviposition, hatching, breathing system • Larvae (10d) • Feed actively, breathing, mobility • Pupae (2d) • Non-feeding, breathing, mobility

25. In the Water • Feeding on microbes and small nematodes • High mortality rates • No fish in temporary and/or filthy water • Cannibalistic mosquitoes • (Toxorhynchites) • Predaceous insects • (Gyrinidae, Dytiscidae, Gerridae, Notonectidae)

26. In the Landscape • Protected locations that minimize drying • Vertical surfaces used frequently • Landmarks • Near water • Often used by multiple generations, year after year

28. In the Landscape • Development continues (2d) • Cuticle hardening, sexual development • Feeding • plant nectars and honeydew • Blood • Resting and digesting

29. In the Landscape • Mating • Swarming and copulation • Avoiding predators • dragonflies, ants, lizards, and bats

30. On the Host • Mostly warm-blooded vertebrates • Host preferences vary • Carbon dioxide, lactic acid, body heat signals • Activity/biting period varies • Sleeping or active host

32. On the Host • Locating a host • movement, chemical/temperature stimuli • Feeding • Probing for arterioles, venules • Salivating and sucking • Getting away

33. Back to the Water • Resting and Digesting • Humid, protected locations • Predator avoidance • Excretion • Peritrophic membrane surrounds meal • Elimination of liquid portion of blood

34. Back to the Water • Survival to reproduction almost a miracle • Locating oviposition sites • Visual and olfactory • Fermenting stimuli of nutrient-rich water • One clutch of eggs most common • Two, or even three rarely • Death from various causes

35. “If you would see all of nature gathered up at one point, in all her loveliness, and her skill, and her deadliness, and her sex, where would you find a more exquisite symbol than the mosquito?” Havelock Ellis, 1920

36. 2002 Reports 169 human cases in 29 counties Age ranged from 4-92 years Attack rate of 3 per 100,000 (0. 003%) 5 human fatalities Age ranged from 61-88 years 819 horses in 103 counties 277 birds in 82 counties 2003 Reports 61 human cases in 25 counties Age ranged from 6-85 years Attack rate of ~1 per 100,000 (0. 001%) 6 human fatalities Age ranged from 69-83 years 130 horses in 53 counties 144 birds in 54 counties Missouri WNV Update

37. Human WNV in Missouri

40. NE IA MO IL KS OK TN KY AR

41. Avian WNV in U.S. 2002 2003

42. Minimizing the Risk of WNV • Avoid mosquito bites • Reduce mosquito populations • Personal Protective measures

43. Minimizing the Risk of WNV • Reducing Mosquito Populations • Eliminate temporary mosquito breeding habitats • Regular surveillance • Empty containers and clutter • Monitor permanent breeding habitats • ‘dip’ counts • rising and receding water • Insecticide or oil application when present

44. Minimizing the Risk of WNV • Personal Protective Measures • Limit outdoor activity during peak bite times • Dawn, dusk • Prevent mosquitoes from coming indoors • Wear long-sleeved shirts, long pants • Permethrin or DEET may be applied • Apply insect repellent containing DEET • Possible vaccine

45. MU Extension Resources