APPENDIX II-BL:á WNV Decline Due to Human Immunity-Fankhauser.


This appendix is copied from:




ęDavid B. Fankhauser, Ph.D.,
Professor of Biology and Chemistry
of Cincinnati Clermont College,
Batavia OH 45103

Aedes albopictus
recently emerged 
(Enlarge: Those are its eggs to 
the L in the enlarged picture.

.File "Aedes_albopictus.html" was last modified on 13 Dec 2004.

This page has been accessed  Countertimes since 4 May 2001.

12 Nov 1999, modified 24 Nov 99, 1 Dec 99, 4 May 01 

Aedes albopictus
recently emerged



Electron Micrograph
of West Nile Virus:
Electron Micrograph of West Nive Virus
( Image from the
 CDC site on WNV )

WEST NILE VIRUS UPDATE:  The current epidemic in the United States of West Nile Virus (WNV) has focused attention on mosquitoes as vectors of this disease.  WNV first made its appearance in the U.S. in 1999, and during the Summer of 2000, numerous cases arose in and around New York City.  Deaths of  a number of patients in Greater New York raised concern about the disease, leading to wide-spread spraying of that area with insecticide.  WNV has now (August 2002) been detected in mosquitoes and/or birds throughout all of the Eastern U.S., and has caused documented illness in approximately 200 humans with the deaths of around 20. Members of the mosquito genus Culex are most frequently associated with its transmission, but Asian Tiger Mosquitoes have also been found carrying the virus. Although Aedes albopictus has not been demonstrated to transmit WNV to humans so far, we expect that it may be implicated with further study.  The rapid spread of  the Asian Tiger Mosquito and its proliferating numbers increase the likelihood of it transmitting the disease.
West Nile Fever Transmission:   Like other examples of arthropod borne viral (arboviral) encephalitis, West Nile Fever is caused by an enveloped "+" single stranded RNA virus, a member of the flavivirus group.  The preferred host for this virus is birds, especially members of the family Corvidae (Crows, Bluejays, etc) which presumably constitute the reservoir for the virus.  (Dead Crows are often the first sign of the virus' presense in a community.)  The virus is transmitted by female mosquitoes when, after picking up the virus from an infected bird, they take another blood meal and transmit the virus to incidental species such as horses and less frequently, humans.  Transmission of the virus from one human to another by a mosquito has never been demonstrated.  (The human is a "dead end" host.)  It is impossible for one person to catch it directly from an infected person.
Symptoms of West Nile Fever:  The vast majority of human cases (perhaps as many as 99%) are subclinical, demonstrating no signs or symptoms.  A small minority may notice "flu-like" symptoms of  fever, achiness, fatigue, etc.  In a much smaller fraction of  persons, especially those with weakened immune systems (the elderly, very young, immunosuppressed, etc) the disease can progress to inflammation and swelling of the brain, a life threatening condition termed encephalitis. 
Symptoms of encephalitis include high fever, neck stiffness, muscle weakness, disorientation, tremors, convulsions, and worse.  Anyone who has these symptoms should see a physician immediately.  As for viral diseases in general, there is no cure, and supportive measures are the best that can be offered at this time.  There is an excellent review of the topic at the CDC site on West Nile Virus .
The frequency of cases of West Nile Fever should decline with time.   As more individuals are infected and become immune to the virus, the number of  acute cases will decline in proportion to those as of yet uninfected.  (In parts of Africa, the number of immune individuals in the population approaches 100%.)  Thus in a few years, West Nile Fever, although endemic, is expected to decline in frequency.