A more diverse bird population can help lower the incidence of West
Nile virus in the surrounding human population, in a process called the
"dilution effect," according to an article released in the open access
journal PLoS ONE on June 25, 2008.
West Nile Virus, usually infecting birds but also affecting humans, is
often passed through mosquitoes. Part of the Japanese encephalitis
family of viruses, it's symptoms have three phases, but include fever,
chills, and diaphoresis.
In the dilution effect, an increased level of biodiversity in wildlife
results in a lower risk for humans to be infected by animal diseases.
This was first reported in Lyme disease, but this new study, it has
been demonstrated in a vector with an avian host. This effect, relating
biodiversity of birds to West Nile Virus, is the largest application
thusfar of the dilution effect, and may also apply to other infectious
diseases such as avian flu or bubonic plague, according to the authors.
John P. Swaddle and Stavros E. Calos worked with the National Center
for Ecological Analysis and Synthesis (NCEAS) at the Univeristy of
California, Santa Barbara, synthesizing existing data to make
inferences for management and policy applications. "We don't yet know
the precise mechanism that drives this pattern, but
it's likely to be due to diverse areas having relatively few of the
bird species that are particularly competent hosts and reservoirs for
the virus," Swaddle said.A set of qualities that makes a species best
able to contract a particular disease is known as host competence. The
highest levels of host competence for West Nile Virus are found in
rows, jays, thrushes and sparrows, which also happen to thrive when
avian biodiversity is lowest.
This research has many implications, according to Swaddlepoints: by
attracting more land species, land management policies could increase
biodiversity and thus decrease the number of human infection rates in
an outbreak of West Nile Virus. "Biodiversity is giving us a public
health service that people have rarely considered and the value of this
service should be considered when developing land and managing bird
populations in the future," Swaddle said.
About the National Center for Ecological Analysis and Synthesis:
The National Center for Ecological Analysis and Synthesis (NCEAS) was
established in 1995. The organization has hosted more than 3,500
scientists from
over 50 countries, and supported more than 430 collaborative projects
in ecology and related fields. NCEAS scientists develop new
techniques in
informatics, and apply general knowledge of ecological systems to
specific issues such as the loss of biotic diversity, global change, and
sustainability of marine ecosystems. NCEAS is among the top 1 % of
38,000 institutions evaluated for scientific impact in environmental
research.
NCEAS is funded by the National Science Foundation, the State of
California, the University of California, and numerous other donors.
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Increased Avian Diversity Is Associated with Lower Incidence
of Human West Nile Infection: Observation of the Dilution Effect.
Swaddle JP, Calos SE
PLoS ONE 3(6): e2488.
doi:10.1371/journal.pone.0002488
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Written by Anna Sophia McKenney
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