>I'm not a medical doctor (and I don't even play one on TV), so perhaps I
just don't get it. But couldn't ANY host serve to move the virus? If I'm
>infected and carrying active virus, and I get on a plane and go to
Argentina, or any place, for that matter, and I get off the plane and a
mosquito >bites me, wouldn't that be as effective a source of transmission
as an infected bird flying to Argentina?
In response to Ellen Paul's comment above:
No, not all hosts can infect mosquitoes and not all mosquitoes can become
infected when feeding on an infectious host. The determination of the
ability of a mosquito to become infected with and transmit a disease
pathogen is a measure of vector efficiency. It is generally measured in a
laboratory. A susceptible host animal is infected with a disease pathogen.
The level of the pathogen in the blood is measured over time and known or
suspected arthropod vectors are allowed to feed on the infected host. The
lower the quantity of pathogen ingested by the arthropod that results in an
infected and infectious arthropod vector, the higher the vector
efficiency. For West Nile virus a chicken would probably be used as the
host and the vectors tested would be mosquitoes species in the genus Culex.
Normally, colonized mosquitoes are used which can limit the species tested
as not all mosquitoes have been colonized. Using St. Louis encephalitis
as a model, it is reported that Culex are highly efficient vectors of SLE.
Mosquitoes become infected when then imbibe even minimal levels of virus
circulating in the bloods of chickens. The problem in trying to translate
this to human disease is that no one has or can experimentally determine
the viremia of West Nile virus in a human. I am aware of only one report
of human experiments with a mosquito-borne disease and these were conducted
before they it was possible to measure a transient viremia. West Nile
virus has broken many of the long held tenants in of medical entomology.
It would not surprise me that it may have also violated the one that
states: Humans are a dead end host. They don't circulate enough virus
to....
The opinions expressed are those of the author and should not be viewed as
the official position of the New York State Department of Health.
John J. Howard, MPH, Dr. PH
Research Scientist V
Arthropod-borne Disease Program
Bureau of Communicable Disease Control
New York State Department of Health
Received on Fri Jan 17 11:52:51 2003
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