Biology Reference
In-Depth Information
In other helminthiases, namely filariasis and schistosomiasis,
individual-based stochastic models have been developed as stand-alone
computer simulation models (ONCHOSIM for onchocerciais,
233
LYMFASIM for lymphatic filariasis
234
and SCHISTOSIM
235
for schisto-
somiasis) and have been used for answering very applied questions on
the effectiveness of helminth control strategies
236
and the feasibility of
elimination.
237
Although such models offer the potential to include
much more complexity and realism compared to their deterministic
counterparts, adequate parameterization can be difficult unless
extremely detailed, community-specific epidemiological information is
available. This renders such models rather location specific and makes
their applicability to the broader epidemiological context
rather
uncertain.
CONCLUSIONS
Ascariasis, like other helminthiases, is currently being targeted by
MDA of anthelmintics on an unprecedented scale. To guide, enhance and
ensure the ongoing effectiveness of MDA-based control it is imperative
that the epidemiology and population biology of A. lumbricoides continues
to be elucidated by applying and developing mathematical and statistical
analytical approaches. Those applying these disciplines in research,
development and data analysis should endeavor to communicate and
collaborate with those involved with policy making, planning and
application to maximize benefits to public health. To substantiate this
ideal, we conclude by revisiting some of the parasite's epidemiology
which has particular relevance to the effective implementation of
MDA-based control.
Monitoring and evaluation of the effectiveness of MDA
which when
undertaken is generally based on the direct smear Kato-Katz method for
detecting eggs in feces
e
must take into account diagnostic performance
under changing endemicities. In particular, because diagnostic sensi-
tivity declines with decreasing infection intensity, egg count-based
estimates of intensity and prevalence will become increasingly under-
estimated. Premature cessation of adequate control could result if
strategic decisions on when MDA can safely be halted or reduced in
intensity (treatment frequency) are based on absolute pre-defined
thresholds levels of infection which do not account for variable diag-
nostic sensitivity. Stopping treatments too early will not only lead to
recrudescence of infection but also
e
e
if alleles conferring anthelmintic
resistance have been spreading through the parasite population
to
widespread and catastrophic treatment failure following recommence-
ment of control.
238
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