The disease
transmitted from one individual to another by a vector. Vector may be vertebrate like dogs, birds or
invertebrate like mosquitoes, sand flies, flies and cockroaches. The major
requirements those should be fulfilled for transmission of vector borne disease
are presence of parasite, vector and host. But in some diseases reservoir host
is also involved. Ex: Pigs for Japanese Encephalitis.
What are the factors
those accelerate the transmission of vector borne diseases?
Urbanization: Unplanned and
uncontrolled urbanization in urbanize areas in developing countries, it causes
serve health problems. As a result of higher consumption, waste generation is
also increased. Therefore it creates the
habitats for vectors. Derange which is blocked with waste are ideal place for Culex
mosquito breeding. Water accumulated containers like coconut cells, plastic
cans, tins, discard tires and flower vases are preferable breeding place for Aedes
mosquitoes. Dirty and unclean condition
in house prepares the habitats for rats. As a result of high population density,
there is high probability to transmit disease from one individual to another rapidly.
Migration of people from emerge area to none emerge areas also transmits the
diseases because people in non emerge areas have no immunity for such diseases
come from outside.
Climate change: As a result of global
warming, climate and whether patterns are changed. So the world experiences
long period of rainy seasons and long period of dry seasons. During dry season,
eggs of mosquitoes hatch rapidly and larva emerges into adults rapidly. Adults
are died within a short time period. Therefore life cycle of the mosquitoes is
shortened. Biting frequencies of
mosquitoes also increase. During wet
season, density of the vegetation is increased. So it offers more resting sites
for vectors. Continuous rain also supports to improve the both quality and
quantity of the breeding sites.
Agriculture: forested areas are
converted into agricultural areas. People tend to spend their most of the time
in their agricultural lands. So they are exposure vectors easily. Rice fields
are ideal breeding sites for the Culex mosquitoes due to high organic
matte content. As a result of wells for agriculture and dam construction,
moving water is converted into non moving water stagnant water. It is ideal
place for Anophline mosquitoes breeding.
Since most of farmers in developing countries have lower income and less
immunity for diseases, they are more prone to vector borne diseases.
Deforestation and forest related activities-
The conversion of forested area into human settlement, agriculture lands, and
the vectors are persuaded to migrate into urbanize areas. Deforested areas offer breeding places for
vector with low salinity and low acidity compare to those in forested areas.
People who worked with forest related activities like mining, collecting
medicine and extracting woods are exposure vectors easily. Ex: Vectors of
Yellow fever and Malaria. The first person who suffered from coetaneous
Leishmaniasis was reported in Sri Lanka worked in a forest logging.
Excess usage of insecticides: As a result of excess use of insecticides,
mosquitoes become resistant. So application of insecticides for controlling
vector borne diseases is less effective. As an example, emerge of malaria in
mid 1900 centaury in Sri Lank caused serve loss of population. So DDT was
applied to kill Anophiline mosquitoes. Then reported cases were dropped down to
near zero. But after few years, reemergence of Malaria was taken place due to
less considering of the government to control and surveillance. So DDT was
applied again to kill Anophline mosquitoes but it was not
effective because mosquitoes become more resistant to DDT due to the excess
usage. Then Malathine was introduced to kill Anophilne mosquitoes.
Same thing was happen. Mosquitoes became resistant to Malathine.
Animal husbandry: It offers addition feeding
for mosquitoes. Therefore mosquitoes population is rapidly increased which may
result in increase feeding frequencies on the human. Those animals also act as
the reservoir host for some disease. Ex: Pigs for Japanese Encephalitis.
What are the impacts
of the vector borne diseases?
1) Emergence of vector borne diseases in
developing countries, the government has to be pumped more money on the health
to control and treatment for the diseases. So it has to be spending money
health rather than development. It cause economic drop down in country.
2) As a result of serve vector borne
diseases work flow of a country is reduced.
Beside the economic, thousand of human lives are lost once. If the
householder suffers form a disease, he has to rest in home without going to his
job for long time period. It causes the falling down of economic level of a
family. Since most of people are low income in the developing countries, they
are pushed into further poverty because they have to spend most of their money
on health rather their other requirements.
3) Outbreaks of vector borne disease
among animal husbandry causes serve lose of economic burden. It causes loss of
life of animals. It reduces meat yield, eggs and milk yields.
How to control prevent the
reemergence of vector borne diseases?
1) Biological control: It is always considered as the best method for controlling vectors
among other methods. The cost is less compare to the chemical control. Ex: Cats
can be used for controlling of rats. Larvivorus fishes are used for controlling
mosquito’s larvae.
2) Maintenance of the environmental hygiene: It helps to prevent or minimize the
mosquitoes breeding. Maintenance of cleaning condition in households helps to
avoid offering breeding places for rats. Proper waste management prevents the
formation of breeding places for mosquitoes breeding. The prevention of
rainwater accumulation in discard materials also dis-encourages the mosquitoes
breeding.
3) Mass chemotherapy: Use of chemical treatment for killing parasite is easier than the
killing vector because parasites live in the human body. But vectors live in
the all over the environment. So it is difficult to apply insecticides to each
and every vector. It is important to finish entire chemotherapy course until
the end unless some stages of parasite remain in the body become resistant.
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