Biology Reference
In-Depth Information
found in urban areas. For example, A. aegypti breeds in stagnant water such
as flower vases, uncovered barrels, buckets, and discarded tires. A dengue
vector study done near Bangkok, Thailand (Strickman and Kittayapong 2002),
demonstrated that mosquito larvae responsible for dengue fever were spa-
tially correlated and predominately concentrated in specific regions of the
study area. In addition, this study showed that the abundance of larvae pre-
vails in wet seasons compared to hot and cool seasons. A longitudinal study
conducted in an endemic area of northern Thailand (Vanwambeke et al. 2006)
showed that the outbreak of dengue in 2002 was correlated with the loca-
tion of the individuals and the type of land cover around the houses, such as
irrigated fields and orchards. On the other hand, this study discovered that,
unlike malaria, temperature and precipitation do not seem to correlate with
the occurrence of dengue fever in Northern Thailand.
3.2.3 West Nile Virus
West Nile virus (WNV) is an infectious disease transmitted by a few species
of mosquitoes, and can infect birds, horses, humans, and other animals. In
humans, WNV can cause inflammation of the brain or its lining, which can
lead to encephalitis or meningitis. In the United States, WNV is transmit-
ted by certain types of Culex and Aedes mosquitoes. Human cases of WNV
in Iowa (USA) between 2002 and 2006 were investigated by De Groote et al.
(2008). They found that human WNV incidents were associated with unique
landscape, and, to some extent, average precipitation, minimum tempera-
ture, and dew points. In a study examining the WNV incidents in California
during the summer of 2003, it was concluded that above average temperature
and rainfall were probably the important causes for WNV outbreaks (Reisen
2004). A landscape-based model was developed to derive avian WNV risk
maps for Mississippi (Cooke 2006)—road density, stream density, slope, and
normalized difference vegetation index (NDVI) were all demonstrated to be
significant factors in the WNV occurrences.
3.2.4 rift Valley Fever
Rift Valley fever (RVF) is a viral infectious disease transmitted by some
species of Aedes mosquitoes. It primarily affects livestock but can also be
transmitted to humans. RVF leads to abortion in pregnant, infected domestic
livestock. As such, it has devastating economic implications and can lead to
meat shortages and scarcities. RVF largely affects some regions in Africa and,
recently, certain parts of the Middle East, including Saudi Arabia and Yemen.
Outbreaks of RVF in Africa are associated with heavy rainfall and flood-
ing (Davies et al. 1985). Studies have also shown associations between
deviations in vegetation growth and RVF outbreaks in Saudi Arabia and
Yemen in 2000; such anomalies in the NDVI measurements were used as
an early warning for possible RVF outbreaks there (Anyamba et al. 2006).
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