Title

Vector Control - An attainable goal

Creator

P K Das

P Jambulingam

Date

1998

extracted text

VECTOR CONTROL
€>'

An attainable goal

Development has ironically invited the resurgence of many a vector-borne
disease. Finding new drugs is not rhe panacea. P. K. Das and P. Jambulingam
make the case for eco-friendly integrated vector management.
ECTOR-BORNE diseases are caused by a
variety of parasites which are transmitted
by a living carrier. A majority of the vectors
are arthropods.
The important vector-borne diseases prevalent in
India are malaria, filariasis and arboviral diseases
such as Japanese encephalitis, dengue, chikungunya
and dengue haemorrhagic fever (spread by mosqui­
toes), leishmaniasis, dermal & visceral (sandflies),
plague (fleas) and Kyasanur forest disease (ticks).
Statistics indicate that more than five million
children die of vector-borne disease annually
throughout the world. Fragmented data makes it
impossible to estimate the prevalence of vectorborne diseases in India. While the prevalance of
malaria and fiiariasis can be estimated to a certain
extent, data on other vector-borne diseases is negli­
gible. One thing is certain though, we are losing the
battle against most vector-borne diseases. Worse,
some of these diseases are re-emerging as major
problems - the frequent outbreaks of arboviral dis­
eases like Japanese encephalitis, dengue and plague,
to cite an example.
The outbreak of vector-borne diseases is deter­
mined by the complex interaction of three agents,

namely parasite, hose and vector in a particular envi­
ronment (physical, socio-economical and cultural).
The increase or decrease of vector-borne diseases
cannot be attributed to the success or failure of the
control programmes alone.
Population growth

Ecological changes associated with population
growth and development are often responsible for
any outbreak of vector-borne diseases. The growth
in population facilitates host-parasite vector interac­
tion by bringing the two together.
Development activities could broadly be classi­
fied into two groups. One group of activities is
meant for increasing primary production, namely,
agricultural activities, including irrigation projects,
construction of dams and sinking of borewells.
These lead to deforestation, waterlogging, climatic
changes, etc. The second group of activities is relat­
ed to secondary production, which includes indus­
trialisation and consequent urbanisation that trig­
gers large-scale migration.
These activities facilitate the movement of para­
site carriers or non-immune people, creating a new
foci or an epidemic of vector-borne diseases.

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Construction of dams often leads to ar malaria outbreak.
11

Development projects arc initiated to provide basic
amenities in human settlements. In the process,
extensive ecological changes are wrought that are
conducive for not only vector-borne diseases but for
many other new diseases.
Let us examine how we can tackle the problems
of shelter, water, air and food and their impact on
the proliferation of mosquito-borne diseases.
Shelter. The world is inhabited by 5.7 billion
people with 90 million being added every year. We
keep converting fertile agricultural land into housing
plots to accommodate an increasing population.
When horizontal expansion is not possible we con­
struct multi-storied buildings. This way, we induce
permanent changes in an area by replacing the nat­

ply, people store water in a variety of containers.
This also facilitates the breeding of the aedes mos­
quito, increasing the risk of an outbreak of dengue.
Water. Water is essential for our survival; the
demand for it is growing with the increase in popu­
lation. The technology for extracting groundwater is
so advanced that we neglect to harness surface water.
We continue to exploit groundwater resources
desoite realising that it is not unlimited.
inadequate solid waste and waste water manage­
ment are often major causes for the proliferation of
vectors, especially the filariasis vector Culex quinquefasciatus, houseflies, cockroaches and rodent.®
Diseases like filariasis occur due to poor waste water
management, while malaria and dengue are the

Stagnant water: Ideal breeding groundfoi>r mosquitoes.

ural ecosystem with a man-made one. One conse­
quence of such development is the multiplication or
expansion of mosquito breeding habitats.
Haven for vectors

Multi-storied buildings are a haven for mosqui­
toes. Overhead water tanks, ornamental tanks and
cisterns help in the breeding of the malaria vector/
stephensi while modern home—appliances like air­
conditioners, coolers and heaters, etc.,- provide an
ideal condition for rhe breeding of the aedes mos­
quito, which transmits dengue and yellow fever.
Construction in urban areas lead to large-scale
migration of labourers from different parts of the
country and aggregation of non-immune people and
parasite carriers. When there is irregular water sup-

result of improper water storage methods.
Food'. Various technologies have been introduced
in agriculture and animal husbandry to ensure food
security. Irrigation projects can either increase rhe
malariogenic potential in an "area by introducing an
increasing vector population or sometimes reduce
the potential by replacing an efficient vector with an
inefficient vector. However, the problem in water
development-projevts- is^more acu’te’irt'thc time of- ’ ~
construction when migration’ of non-immune peo­
ple creates an epidemic situation - for example,
intense transmission of Falciparum was recorded at
the time of the construction ot the Nagarjuna Sagar
dam in Andhra Pradesh, the Indravati Project in
Orissa, the Upper Krishna project in Karnataka and
the Indira Gandhi Canal in Rajasthan.

Modern agricultural practices depend on piephylactic use of pesticides. This has eliminated many
useful insects and the hymenoptcran parasites that
helped in regulating vector population. For example,
coelomonyces, a fungal infection in mosquitoes was
quite common bur with the extensive use of insecti­
cide. the infection rate drastically reduced due to a
decline in cyclops and other ostracod population
(intermediate host). It also precipitated resistance in
the vector population.
Fallout of deforestation

Deforestation, which is a common factor in any
development activity, causes an imbalance in the
mamanimal ratio, diverting the mosquito vectors
which otherwise feed on animals to humans. The
incidence of malaria is high in the border districts of
Andhra Pradesh and Orissa and in north-eastern
States where labour camps are organised for cutting
bamboo for the paper industry. In time, the forest­
dwelling species disappear with the forest and are

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area depends upon the host-parasite vector inrer.it
tion in that area. It is therefore a local problem ami
varies even within the city. Following a uniform
strategy' for the entire city- is neither cost-effective
nor necessary. However, planners stick to a single
and uniform strategy in the name of simplicity, over­
looking the fact that if control measures arc initiated
according to the local problem, one can not onlysave money but implement it more efficiently.
In the Sixties, insecticide was the panacea and
now the bio-environmental control of vectors and
anti-parasitic drugs have the same status. Instead of
controlling the vectors, drugs are distributed for
controlling diseases like malaria and filariasis.
Suddenly, insecticide has become bad and the use of
drugs good.
We do nor intend to advocate the importance of
insecticides alone. In fact, we arc against depending
on any' particular tool for all types of situations.
Neither vector control nor parasite control in isola-

Advertisements like “Fever? It may be malaria, take chloroquine” mislead
people into believing that a few tablets of the drug will cure malaria.
replaced either by C. quinquefaciatus which breed in
rion can produce the desired results. While there arc
many tools for a particular situation, there is no tool
man-made breeding habitats or by other anophelinc
species like A. culicifacies breeding in wet lands. By­ which can be effective for all situations.
destroying forests man encroaches on the natural
Bottlenecks
ecosystem and renders himself susceptible to many
zoonotic diseases, which in due course of time may .
The present strategy also suffers from some operbecome anthroponotic. The Kyasanur forest disease ~ ational and administrative bottlenecks like inade­
quate funding, lack of quality control of insecticides,
is a good example of this.
absence of flexibility in decision-making, lack of
Until 1940, programmes to control vector-borne
motivation for vector-control staff, unwillingness to
diseases were based on improving sanitation and per­
introduce new concepts, etc.
sonal protection measures. A few examples are the
Inspire of these problems, the control pro­
vellow fever control programme in the Panama canal
grammes in our country did achieve considerable
and the malaria control programmes in Malaysia and
results in the past. After the introduction of DDT
Peshawar, etc. However, these control methods were
residual spray under the National Malaria
considered too expensive for large-scale pro­
Eradication Programme (NMEP), the incidence of
grammes. The control programmes at that time were
meant only for a selected percentage of the popula­
malaria declined from an estimated 75 million cases
tion. With the introduction of DDT, all the mea­ with 0.8 million deaths in 1952 to an all-time low of
0.1 million case with no casualties. Diseases like
sures based on sanitation were completely neglected.
Here, we would like to emphasise that developed
leishmaniasis, dengue, etc., were brought under con­
trol. A four-fold increase in the population testified
countries in the West controlled many of these dis­
to the success of various technological developments
eases mainly by resorting to simple sanitary mea­
in bringing down mortality from vector-borne dissures. They did nor wait for any new vaccine, drugs
- or molecular tools to control these diseases.
___ eases. If the efforts were successful why arc we then
.80.

THE HINDU SURVEY OF THE ENVIRONMENT ‘97

gral part of the strategy and
witnessing the emergence
carried out independently.
or re-emergence of vectorSince there is no substitute
borne diseases? Is it that the
for surveillance, one can­
tools available are not ade­
not dispense with it.
quate to tackle the problem
However, the cost of sur­
or is it the lack of applica­
veillance can be minimised
tion of these tools?
by either utilising existing
The risk of an outbreak
infrastructure or seeking
of disease has increased
the help of NGOs.
over the years. We arc con­
Community involve­
tent with fire-fighting mea­
ment must be ensured
sures to tackle these dis­
from the planning stage
eases. What is required is a
itself and education should
comprehensive plan and
form an integral pan of the
concentrated efforts based
strategy. Educating peop.^
■.on a continuous monitor­
with
half-truths
may
ing of the situation. The
boomerang. The advertise­
tools available are still suffi­
ment in inland letters says
cient to keep the diseases
“Fever? It may be malaria
under control. Since envi­
, | take chloroquine.” Such
ronmental degradation is
,Jre' S advertisements make peo­
the major cause for the
ple believe that a few
increase of vector-borne
tablets of chloroquine will
Itnproper toaste disposal also causes vector-borne diseases.
diseases, must we not
cure malaria. The message
attempt to improve envi­
could instead read “Fever? It can be malaria and may
ronmental conditions?
be fatal if not treated. Take treatment under the
The strategy for controlling vectors varies from
supervision of a physician.”
species to species. Even for the same species, rhe
Vector control can be achieved either by killing
method of control may vary from one area to anoth­
or regulating the_ population of the vectors. Our
er. Therefore, the approach to vector control must
change from an overuse of pesticides to an ecoexperience has shown that using chemicals to kill
insects with a high reproductive potential is a cum­
friendly integrated vector management (IVM).
IVM is essentially an ecological information­
bersome process requiring repeated application
based control programme that utilises artificial or
which are operationally and economically not feasi­
ble in the long run. Secondly, the resurgence of the
natural control tools to be fitted as unobtrusively as
possible into the total environment to effect the supvector population due to rhe elimination of biocenotic regulators by toxic chemicals leads to popu­
, pression o( pest species at the time and place where
lation stabilisation at a higher level.
they escape the repressive elfccr of natural control.
A majority of our programmes suffer due to poor
Community must participate
implementation. Implementing agencies need to be
identified at the design stage. It is not possible for
Information about the vectors - where they live,
vector control agencies alone to tackle the problem.
when they feed, where they breed, etc. - is impor­
tant for any strategy to control them. Gathering
The major responsibility for improving the enviroment must He with rhe people. This needs to be
information on ecology' and epidemiology during a
enforced by a strict Public Health Act. Punishment
lean period is considered unnecessary expenditure.
should be so severe as to thwart any repetition.
However, public health authorities must be vigilant
and try to destroy the vectors during the lean period
itself. This Is easier said than done as maintaining a huge infrastructure for surveillance may be beyond
Dr. P. K. Das is Director and Dr. P. Jambulingam is
many disease control agencies. Since we are dealing
Assistant Director of the Vector Control Research Centre,
with a dynamic system which changes rapidly due to
Pondicherry.
human interference, surveillance should be an inte-

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