Biology Reference
In-Depth Information
the second most devastating disease after malaria globally. The distribution
of Schistosomiasis species is geographically dependent. With approximately
90% of all the cases in the world, Africa bears the majority of the burden of
this disease.
Human transmission of schistosomiasis is through the intermediate hosts
of certain species of freshwater snails. Larvae can be released daily from
snails, depending on ambient temperature and light; these then can attach to
and penetrate human skin. Farm animals may be infected by some species
of
Schistosoma
as well. Swimming, playing, or working in infected water
bodies can lead to infection. Eggs of schistosomes may also be present in
an infected person's stool or urine. In the poorest communities where there
is inadequate hygiene and waste management, eggs may recontaminate or
cross-contaminate bodies and/or sources of water, completing the transmis-
sion cycle.
The ecology of the snail (as the intermediate host) provides insight on how
remote sensing can be used for the detection, control, and prevention of
schistosomiasis (Yang et al. 2005). Temperature, type of vegetation/ground
cover, bodies of water, precipitation, flood, irrigation, and water transport
projects and farms have all been related to the presence and movement of
these snails. Because remote sensing is a practical tool for monitoring and
measuring these environmental and socioeconomic factors, it is possible to
use this method as a tool for risk assessment and control.
3.2.9 avian influenza (ai)
Since 1996, when the highly pathogenic avian influenza (HPAI) H5N1 virus
was isolated in China, the disease has spread across Asia to Europe and
Africa. As of June 2009, there have been 432 human cases worldwide with
262 deaths. Indonesia has been the country hardest hit with 141 human cases
and 115 deaths.
AI, which is caused by influenza Type A viruses, is a common infec-
tious disease among many species of wild birds. The Type A viruses are
normally of low pathogenicity to wild birds as well as to domestic poultry
(when initially infected). In a dense poultry population, however, the virus
can mutate very efficiently and may become highly pathogenic in the
course of several months (Kida and Sakoda 2006). Infection in poultry with
an HPAI virus such as H5N1 results in severe mortality. Globally, approxi-
mately 250 million poultry have been lost in recent years due to H5N1 and
massive culling.
Fortunately, the H5N1 virus has not yet mutated into a form that is easily
transmittable to humans. So far, human-to-human transmission is limited
to prolonged, close contact with infected humans. However, coinfection of
HPAI and human influenza viruses in humans or pigs may produce, through
genetic reassortment or adaptation, deadly strains of an influenza virus that
could be H5N1 or another highly pathogenic subtype. The worry among the
