Cecilia Cortes-Crispin
Biology Lab 1615
August 01, 2013
West Nile Virus Epidemic in North America Are Driven by shifts in Mosquito Feeding Behavior
General Purpose: Why does the shift in the feeding of mosquitoes play an important factor in
the epidemics of human West Nile Virus?
According to Kilpatrick three quarters of human infectious diseases are caused by
animals. The West Nile Virus (WNV) is a zoonotic pathogen that is transmitted from viremic
birds and Ornithophilic bird biting mosquitoes. The mosquito feeding behaviors play an
important role in determining the force of the infection (Kilpatrick). It was believed that
mosquitoes that bite birds infected with the West Nile Virus are most likely transmitting it to
the humans. According to Kilpatrick because the mosquitoes feed on birds in the summer they
are most likely to feed on humans in the fall. His model showed that there were higher risks of
transmission to humans by the Cx. Pipiens from July to August. This was tested in several areas
and the infections in those areas were very similar (Kilpatrick). This might explain why there is a
high epidemic in the summer in birds and mosquitoes and then why it was later found in
humans. Watching the shifts in mosquito feeding behaviors would help determine if their
hypothesis was accurate. Before the West Nile Virus was found on humans, the mosquitoes
were not feeding on humans. This is why it was suspected that it was through the mosquitoes
that they were getting infected with the West Nile Virus. The West Nile Virus was first detected
in New York City in 1999. There has been over 20,000 thousand reported cases. Also, there
have been 770 deaths and 215,000 illnesses during the past seven years (Kilpatrick).
There were three experiments done in order to analyze and point the mosquitos as the
main cause as to why and how the virus was being spread. There were three hypotheses made.
One; The West Nile Virus was highly infective to the American crows (corvus brachyrhynchos)
than the old strain in the old world. Second; the birds in North America had no previous
exposure to the West Nile Virus. Third; The Culexpipiens mosquitos appear to be hybrid of the
bird-biting”pipiens” form human human-feeding “molestus” form of the Old World Cx. Pipiens.
The scientist focuses on a fourth hypothesis, which was, that the West Nile Virus epidemic was
driven by the shifts in mosquito feeding behavior (Kilpatrick). First, during the mosquito season,
mosquitoes feed on humans (mammals) and the probability of mosquito feeding on avian hosts
declined. Second, during the early summer the mosquito’s shifted the preference to avian
hosts. Third, the abundance of their preferred host (Robins) shifted the interest back to
humans. Due to change in feeding preference to humans is what leads to the increase in cases
of humans found to be infected with the West Nile Virus.
The data collected by the scientist on feeding behavior, population, and epidemiology of
mosquitoes and birds lead to conclude that the shifts of feeding behaviors of mosquitoes was a
main cause on why the humans were now being infected with the West Nile Virus. According to
the results, the West Nile Virus epidemic in North America was driven by the changes or eating
behaviors of the mosquitoes. It proves the hypothesis.
Works Cited: Kilpatrick AM, Kramer LD, Jones MJ, Marra PP, Daszak P (2006) West Nile virus
epidemics in North America are driven by shifts in mosquito feeding behavior. PLoSBiol 4(4):
e82.