Biology Reference
In-Depth Information
In this context of limited resources, the population is more vulnerable
to the damage caused by the STH and the need to protect them through
periodical de-worming is greater. However, achieving control is more
difficult and the results are less dramatic.
EPIDEMIO
LOGICAL BASIS OF THE WHO S
TRATEGY
The comprehension of some epidemiological characteristics of STH is
important to select the most appropriate control measures and to evaluate
correctly their public health impact (see also Chapters 7 and 9).
1. Children and women harbor peak worm burdens.
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In addition these
population groups are characterized by intense metabolic and physical
growth, resulting in increased nutritional needs. This explains why
pre-school children, school-aged children and women of child-bearing
age are particularly vulnerable to the nutritional deficits related to the
infections and are considered the population groups at greater risk of
morbidity due to STH.
2. Heavy-intensity infections are the major source of morbidity:
Morbidity is directly related to worm burden.
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The greater the number
of worms in the infected person, the greater the morbidity caused by
these worms will be. For example, in the case of hookworms, the
amount of blood lost in the feces (as an indicator of morbidity) is
directly associated with hookworm egg count (as a measure of worm
burden).
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3. Until environmental and/or behavioral conditions have changed, the
prevalence of infection will tend to return to original pre-treatment
levels. Reinfection occurs because the worm's infective stages will
continue to contaminate the environment. However, repeated treatments
will periodically decrease the worm burden of infected individuals, in
spite of continuing reinfection episodes. Harboring fewer worms will
thus significantly reduce the health damage caused by these parasites.
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Based on the points mentioned above, an appropriate and cost-effective
control strategy can be designed, which would ensure as a priority the
reduction of morbidity in high-risk population groups. This is done by
reducing to minimal levels the proportion of heavily infected individuals
and can be achieved with periodic distribution of de-worming drugs, an
approach that is nowadays referred to as “preventive chemotherapy.” At
the same time, according to available resources, other complementary
control measures such as health education, social mobilization, informa-
tion, education and communication, as well as improvement of sanitation
should be promoted in order to sustain the benefits of periodic treatment
and to achieve long lasting control of transmission of infection.
