Integrated vector control
From 1945 on, DDT, lindane, and other residual insecticides provided a single, highly
effective method of vector control that eclipsed all other methods until about 1970. Since
then, the development of resistance, concerns about environmental contamination and human
safety, and the high cost of alternative insecticides have led to a revival of interest in other
methods of vector control.
Some of these methods were already known, but were neglected during the DDT era:
personal protection (e.g., screens and repellents), source reduction (e.g., draining or removing
artificial breeding sites), the use of fish to prey on mosquito larvae, and community-based
health education.
Other methods, such as genetic control, synthetic attractants, insect growth regulators, and the
use of remote sensing by satellite to detect vector habitats have also been attempted
experimentally and in endemic situations.
Integrated vector control has been defined as "the utilization of all appropriate
technological and management techniques to bring about an effective degree of vector
suppression in a cost-effective manner" (WHO 1983).
Integrated vector management (IVM) is a rational decision-making process to optimize the
use of resources for vector control. The aim of the IVM approach is to contribute to
achievement of the global targets set for vector-borne disease control, by making vector
control more efficient, cost effective, ecologically sound and sustainable. Use of IVM helps
vector control programmes to find and use more local evidence, to integrate interventions
where appropriate and to collaborate within the health sector and with other sectors, as well
as with households and communities.
It demands an adequate knowledge of the biology, ecology, and behaviour of the vector, non-
target organisms, and the human population to ensure not only effective control of the vector,
but also human safety and prevention of other unacceptable side effects, including
environmental damage.
Although there are many integrated approaches to vector control, only some of the more
promising ones are described here, with emphasis on those that could be used in community
programs to achieve greater sustainability.
1. Pesticides
Although DDT and other organochlorines have been banned in many countries and replaced
in others because of vector resistance or adverse effects, many other synthetic insecticides are
still available. WHO listed 37 compounds in common use for the control of vectors and pests
of public-health importance. In some places, such as vast amounts of insecticides are still
used each year for mosquito control.
DDT was replaced initially by organophosphates, such as malathion, and more recently by
synthetic pyrethroids, such as permethrin, which are costly but effective at very low doses.
Unfortunately, there are already many reports of mosquito and biting-fly resistance to
pyrethroids, some of them also because of cross-resistance to DDT.
2. Biological Control
a. Pathogens
Some effective microbial pesticides are now available for vector control especially
spore/crystal preparations of Bacillus thuringiensis serotype H-14 var. israelensis (Bti) and B.
sphaericus. These microbials are highly toxic and specific to the targeted larvae of
mosquitoes and blackflies. However, they are relatively expensive and difficult to formulate
because the toxic crystals sink and become inaccessible to most larvae, although floating,
slow-release formulations of Bti are now available.
Bti is widely used in the Onchocerciasis/River blindness (Onchocerca volvulus) control
program in West Africa and, increasingly, for mosquito control. Because these microbial
pesticides are virtually nontoxic to mammals, they can be applied by community volunteers.
b. Plant extracts
Endod, an extract of seeds of the Ethiopian plant Phytolacca dodecandra, and damsissa, a
product of Ambrosia maritima in Egypt, are effective against the snail intermediate hosts of
Schistosoma.
Other local natural products could be developed for vector control. For example, fruit pods of
the tree Swartzia madagascarensis, widely used in Africa as a fish poison, were also found to
be toxic to Anopheles larvae and Bulinus snails; Alpha T from the marigold flower
(Tagetes) is toxic to mosquito larvae.
c. Predators
Larvivorous fish such as Cambusia affinis have been used for controlling mosquito larvae for
many years. Among the more promising recent developments is the use of young Chinese
catfish (Clarias fuscus) to control Aedes aegypti in household water containers in China and a
community-based malaria-control scheme in India, which paid for itself by selling carp and
prawns that were reared in the same group of ponds as the guppy fish used for controlling
mosquitoes.
Many other organisms have been tested for the biological control of vectors. Candidates for
controlling larvae of Aedes aegypti and other mosquitoes that develop in small containers are
dragonfly larvae, the copepod crustacean Mesocyclops aspericornis, and the predatory
mosquito species, Toxorhynchitis.
3. Personal protection
Personal protection includes all measures taken at the individual or the household level to
prevent biting by vectors. Anklets impregnated with repellents significantly reduced biting
rates of mosquitoes.
Washing with soap containing a repellent (diethyl toluamide, DEET) or an insecticide
(permethrin) reduced mosquito biting rates.
Bed netting has been used for centuries to give personal protection against biting insects.
When impregnated with insecticides, the netting provides community protection as well;
mosquitoes rest on the treated fabric and are killed. In numerous large-scale trials in various
parts of the world, malaria transmission appears to have been reduced by the systematic use
of nets impregnated with permethrin or deltamethrin.
House improvements such as screening, insecticidal paints, and filling in cracks in the walls
could provide definitive measures against some house hold insects.
4. Trapping
Mechanical and other types of traps have been used to reduce populations of tsetse flies.
Several designs have been developed, some of them incorporating chemical attractants and
insecticides. In Uganda, an effective tsetse trap has been made from old tires and locally
available plant materials.
Light traps, installed in pig sites, have been tested for the control of Culex tritoeniorhynchus
in Japan.
5. Environmental management
Changing the environment to prevent vector breeding or to minimize contact between vectors
and people can be an effective control mechanism. Environmental management methods
include:
a. Environmental modification, i.e., any permanent or long-lasting change in land, water, or
vegetation, such as filling, draining, or forest clearance;
b. Environmental manipulation, e.g., flushing streams, changing water salinity, and
removing shade plants; and
c. Modifying human habitation or behaviour, e.g., locating new settlements away from
vector populations, modifying house design, and changing water supply and waste disposal.
Intermittent irrigation was used to prevent the development of mosquito larvae in rice fields
and layers of expanded polystyrene beads prevented Culex quinquefasciatus from laying their
eggs in wet pit latrines. Much environmental management work can be done by community
volunteers with guidance in the initial stages from vector-control specialists.
6. Training and education
Integrated control strategies require more people trained in vector biology. In addition to the
usual sources of health education, such as schools and clinics, information can reach the
public through billboards, newspapers, radio, and television.
The role of the community
Many problems and failures in vector control have been due, not only to technical difficulties,
poor management, and lack of continuity, but also to the fact that not enough attention had
been paid to the beliefs and attitudes of the affected communities. For example, many Aedes
aegypti control campaigns in the past 20 years have relied too heavily on ultra-low-volume
spraying, which is not always effective. The use of this method has given people a false sense
of security, reinforced their belief that Ae. aegypti control is the government's responsibility,
and taken away the pressure to get rid of larval habitats in their own backyards.
A recent WHO report, explores the ways in which more responsibility for vector control can
be transferred from the national to the district level and ways of getting people more involved
in protecting themselves against vector-borne diseases because "community participation
makes people more aware of their ill-health and general underdevelopment and of how they
can overcome these problems." Vector control at the community level has to compete with
more basic needs, such as food, shelter, and employment, and the need for it may not be
appreciated during periods of little or no disease.
Nevertheless, examples of successful community participation include: setting tsetse traps;
draining, filling, or clearing weeds from mosquito breeding sites; rearing larvivorous fish;
source reduction of Aedes aegypti; and distribution of nylon filters to keep Cyclops out of
drinking water. Vector-control campaigns should work closely with primary health-care
programs to achieve greater effectiveness and sustainable results.
Despite promising results, long-term community participation in vector control must be
secured, because operations, such as the control of container-breeding mosquitoes, may have
to be continued indefinitely. Little is known about extending pilot projects into permanent
national programs. Community volunteers may become victims of political struggles or
professional rivalries if their work is not given proper recognition. The best chance of
maintaining community support seems to lie in integrating vector control into the primary
health-care system, which is now established in many countries. More research is also needed
on how to coordinate vector control with work in agriculture, forest and water management,
and on the role of migrant workers in disease ecology and control. Community-based vector
control is not a way to reduce government spending. Although local initiatives should be
encouraged, each country will still need teams of professional vector-control workers, using
well-established methods, to meet its obligations under international health regulations.
Research on community strategies for vector control
Building research capacity, producing new knowledge, and creating linkages among
researchers are perceived as essential components of development by the International
Development Research Centre (IDRC). However, IDRC-supported projects must contribute
to improving the welfare and standard of living, particularly of the poor and disadvantaged
who are to be the ultimate beneficiaries of the research. IDRC tries to ensure that the
activities it supports meet the long-term goals of development as viewed from the perspective
of these beneficiaries: sustainable growth, equity, and participation.
Article on Highly Hazardous Pesticides (HHPs) in Kenya:
https://ke.boell.org/en/2023/09/14/data-and-facts-highly-hazardous-pesticides-hhps-kenya
https://cejadkenya.org/wp-content/uploads/2021/07/
final_report_of_hhps_and_alternatives_in_kenya_sept_2019-1.pdf
