WNV Spread to Humans

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WNV Spread to Humans
Birds WNV Cycle Culex Culex
mosquitoes mosquitoes Birds
Humans Horses Other mammals
Trans ovarial transmission
Migrating Birds
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WNV Spread.Vertebratesin the USAVectors in
the USA
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WNV Spread to Humans

• Cases Neuro- Deaths Case
• STATE(S) Invasive Fatality
• New York 1999 62 59 7 12
• 4 New England States 2000 21 19 2 11
• and Caribbean
• 21 East Central States
• and Canada 2001
• 17 Midwest States 2002 4156 2964 284 10
• 11 Central Plains States, California
• Western Canada 2003 9863 2866 264 10
• 2 Western States 2004 2538 1142 100 9
• 2005 3000 1295 119 9
• 2006 4261 1455 194 12

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WNV Spread via migration of wild birds
Puzzle How do sick birds migrate and carry the
virus?
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Puzzle How do sick birds migrate and carry the
virus?

• The majority of the migrating birds have high
  virus loads, but do not get sick
• Studies show that WNV virus has no effect on
  migration behavior
• Nor does migration behavior have any effect on
  WNV load

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Puzzle 2 There is virtually no neuroinvasive
disease in the Caribbean despite widespread human
infection

• Theories
• Birds infected with a more virulent epidemic
  strain do not migrate No
• There is human immunity due to other related
  Flaviviruses Probably
• Dengue, SLE, YF, Ilheus, Roccio, Cacipacore,
  Aroa, Naranjal, Bussuguara
• Intrinsic or extrinsic factors associated with
  the host or environment temperature, mosquito
  vectors, secondary hosts and ?? ???

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Puzzle 3 Why has WNV recently caused so much
disease when after discovery in Uganda in 1937 it
did not?

• Investigation of other WNV disease outbreaks in
  Romania, Senegal, Italy and Volgograd has now
  shown that a particular strain carries virulence

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World Wide Picture of WNV
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World Wide Picture of WNV