Prospects for the Future:

1
Prospects for the Future Lessons Learned and
Future Research
Field Biology of WN Virus
Roger S. Nasci, Ph.D. Division of Vector-Borne
Infectious Diseases National Center for
Infectious Disease Centers for Disease Control
and Prevention
2
Factors Determining Rates of Transmission
Reeves, W.C., 1967. Factors that influence the
probability of epidemics of western equine, St.
Louis, and California encephalitis in California.
Calif. Vector Views 1413-18. Monath, T.P.,
1980. Epidemiology. in T.P. Monath, ed. St. Louis
Encephalitis. Washington DC. American Public
Health Assn. 239-312.
3
West Nile Virus Transmission Cycle
4
Virus

• Zoonotic Flavivirus using avian amplifier hosts,
  ornithophilic vectors.
• Strain highly infectious for North American
  birds, causing mortality and high viremia.
• Overwinters in hibernating Cx. pipiens
  mosquitoes.
• Vertical transmission efficiency?
• Overwintering in other species?

5
Vectors

• Avian enzootic-epizootic vectors
• Cx. pipiens, Cx. restuans
• Mammalian epizootic, human epidemic vectors
• Cx. pipiens, Cx. restuans?
• Other species as accessory vectors?

6
Host-Use Patterns of WNV-positive species
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Vectors

• Vector competence of potential accessory vectors?
• Host-use patterns?
• Influence of local ecology on risk?
• Value of various species as indicators of
  transmission activity human risk?

8
Avian Amplifiers

• Susceptibility to WN virus widespread.
• Valuable as surveillance indicators.
• Primary amplifier hosts?
• Identification of species for use as sentinels?
• Evaluate and modify sentinel chicken system?

9
Avian Amplifiers

• Bird-to-bird transmission?
• Relevance to transmission dynamics?
• Relevance to surveillance?

10
Mammals

• Infected with WN virus.
• Mortality (big brown bat, little brown bat,
  rabbit, chipmunk, gray squirrel, horse, cat)
• Seropositive dog
• Valuable as surveillance indicators.
• Identification of species for use as sentinels?
• Role as amplifier hosts?

11
Humans

• Behaviors and habitat structures associated with
  risk of infection?
• Socioeconomic status, occupation, housing
  standards, travel, habits?
• Impact of residential vector production on risk?

12
Vector Management

• Efficacy of control mechanisms?
• Source reduction
• Larvicide
• Adulticide routine and emergency intervention
• Resistance baseline data and resistance
  management practices?

13
West Nile Virus Transmission Cycle