In epidemiology, a vector is an organism that
does not cause disease itself but which transmits infection by conveying
pathogens from one host to another. There are two types of vector that convey
infectious organisms to a host: mechanical and biological. Microbes do not
multiply within mechanical vectors - mechanical vectors only physically
transport microbes from host to host. In contrast, microbes must propagate
within a biological vector before the biological vector can transmit the
The transmission of vector-borne diseases to
humans depends on three different factors: the pathologic agent; the arthropod
vector; and the human host.
The majority of vector-borne diseases survive in nature by utilising animals as
their vertebrate hosts (zoonoses). For a small number of zoonoses, such as
malaria (and dengue fever), humans are the major host, with no significant
animal reservoirs. Intermediary animal hosts often serve as a reservoir for the
pathogens until susceptible human populations are exposed.
Key components that determine the occurrence of vector-borne
diseases are: (i) the availability of vectors and intermediate and reservoir
hosts; (ii) the prevalence of disease-causing pathogens suitably adapted to the
vectors and the human or animal host; (iii) the local environmental conditions,
especially temperature and humidity; and (iv) the susceptibility of the host.
Although this disk concentrates primarily on the vectors
of disease, it also covers some pests of public health interest.
A pest is an organism which has characteristics that are can be injurious or
unwanted. They can it cause damage to agriculture through feeding on crops or
being parasites on livestock, such as codling moth on apples, or boll weevil on
cotton. An animal can also be a pest when it causes damage to a wild ecosystem
or carries germs within human habitats. Examples of these include those
organisms which vector human disease, such as rats and fleas which carry the
plague, or mosquitoes which vector malaria.
It is almost safe to presume that people will always have to live with
vector-borne diseases, and that it would be folly to try to eradicate vectors
and pests as some of them are beneficial to humans and the environment. Time has
also shown that maintaining a strong public health infrastructure and
undertaking research activities directed at improved means of control, —possibly
utilizing biological and genetic-based strategies, combined with the development
of new or improved vaccines for diseases such as malaria, dengue and Lyme
disease—should lessen the threat to human health.
This project was undertaken by the following:
The knowledge gained would not
have been possible had it not been for the magnanimous financial contribution
made by the Danish Government to whom we owe a sincere gratitude.
- Mr M Kgware : Durban University of
- Mr J Maniram : Environmental Health
Component, KwaZulu-Natal Department of Health
- Mr PP Maharaj : CDC, eThekwini Municipality
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