[afro-nets] Insecticide Treated Mosquito Nets Project (3)

[Odiere, Maurice <MOdiere@ke.cdc.gov>]

Insecticide Treated Mosquito Nets Project (3)
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Sergio's idea/initiative on efforts towards increasing ITN-use (allow me
to add - "among other interventions") towards malaria control in Africa
is good and needs to be encouraged. 

The World Health Organization/Roll Back Malaria program has placed
emphasis on the use of Insecticide Treated Nets (ITNs) as a vector
control tool in fighting malaria. However, It is surprising that by the
end of 2005, just one (Eritrea) of the 44 countries that signed the Roll
Back Malaria declaration (Abuja 2000) met the Abuja goals. One of the
goals was ensuring that at least 60 percent of those at risk of malaria
- particularly children under five years of age and pregnant women -
benefit from the most suitable combination of personal and community
protective measures, such as insecticide-treated mosquito nets and other
interventions that are accessible and affordable to prevent infection
and suffering. Dr.Shu's survey in Cameroon only serves to confirm this
Roll Back Malaria off-target picture.

However, I would wish to share the following with regards to the Use,
Impact and Efficasy of ITNs:

The long-term impact of ITN-use has been a matter of debate mainly
because there has not been a major sustained national program in
operation outside China (Luo et al., 1994), and because in the areas of
holoendemic infection where most trials have been carried out, these
trials have been of short duration, lasting at the most 5 years. This
picture I believe is rapidly changing.

To argue FOR ITNs; ITNs have been shown to significantly reduce the
numbers of vectors in houses with ITNs as well as to reduce the overall
anopheline population size, in areas where there has been a sustained
intervention. Original trials in The Gambia (D'Alessandro et al., 1995)
and Tanzania (Magesa et al., 1991) also showed a decline in the number
of infective mosquitoes and an improvement in indicators of both malaria
infection and morbidity in the control area.
 
One school of thought AGAINST ITNs holds the view that the reduced level
of exposure through ITN-intervention is likely to have an adverse effect
on the acquisition of immunity. If this is true, then it would imply
that any beneficial outcome is likely to be transitory in endemic areas.
Acquired immunity against clinical malaria is thought to develop
gradually with time and to be a function of the frequency of infections.
The concern here is that the period during which a child is at risk from
clinical malaria might increase in ITN-intervention areas. If a child
was protected by an ITN but later this was withdrawn, there might be a
rebound effect of clinical disease when the child is exposed to
infectious mosquitoes. Therefore, ITNs might reduce exposure and
consequently the multiplicity of infections but with a corresponding
delay of acquired immunity. However, a study in Tanzania (compared
children sleeping under and those sleeping without ITNs) found out that
the development of acquired immunity was not compromised by the ITNs in
the two epidemiological condditions. 

Secondly, it has also been noted that ITNs may not reduce the overall
population of crepuscular (twilight-loving) forms and many culicine (not
malaria vectors) species are not always reduced in number.

There is also evidence that mosquitoes can adapt to some extent to
vector control applications and ITNs can lead to exophagy and earlier
biting. In the event of a shift to earlier biting, personal protection
measures may be required in the early evening, to supplement ITN-use. 

Even when vector population size or longevity is not affected, or when
behaviour changes are induced, consistent use of ITN can still be
expected to reduce human-vector contact. With high ITN coverage the
sporozoite rate, and hence the Entomological Inoculation Rate (EIR),
will decrease as a result of fewer mosquitoes picking up gametocytes.
All in all, an ITN program that will reduce the life expectancy of
vector mosquitoes will consequently go a long way in vector control. 

Efficacy of ITNs borders on aspects of adherence, time since treatment,
number of ITNs per house, type of chemical used on the net, maintenance
& care of the ITNs, degree of insecticide resistance by the
vector/vector species susceptibilty among other things. 

As for the local population (who unfortunately may not understand some
of the arguments above), challenges have arisen from adherence, net
retreatment and maintenance. Recent studies have shown that Culicine
mosquitoes (though not malaria vectors), positively and negatively
influence adherence to ITNs. Positive adherence - use of ITNs is
encouraged by their nuisance biting, and Negative adherence -use of ITNs
is discouraged by perceived ineffectiveness of pyrethroid-treated nets
in reducing nuisance biting, as evidenced by the inabilty of ITNs to
reduce Culicine densities. The findings concluded that therefore that
reductions in culicine densities may have implications for community
perceptions of ITN effectiveness.

Dr. Shu, I share in your concern that 11% of ITN-use by children is poor
indeed. The issue of cost of ITNs definitely has a negative impact on
ITN intervention. It is unfortunate that the levels of Poverty are high
in Africa, where again most of the diseases including malaria are
endemic. I imagine that it was expected that the free distribution of
ITNs under 5 children (through the Global Fund grant for the fight
against malaria) would try to safeguard this. It is sad to note that it
is the same high levels of poverty that are making people to sell ITNs
distributed freely to them so as to purchase food. Some of the people
purchasing the ITNs from these poverty-stricken people are not using
them for the rightful purposes or on the target groups. For instance, a
local daily here in Kenya carried a report on how some people were
selling ITNs that had been distributed to them freely or at subsidised
rates. These ITNs were being sold across the border to a neighboring
country where their rates are high (no subsidies). The nets would be
sold to them at Kshs 50 per unit and would fetch 10 times on resale.
There were also issues of corruption levelled against some agencies
tasked with the responsibilty of distributing the ITNs.

The main problem to be addressed is the process of implementing and
sustaining ITN-use programs, which are dependent on community support.
ITN-intervention programs must include health education/awareness e.g.
through information on maintenance, proper use and benefits of ITN-use.

It is essential that concerted efforts be made to ensure that people
understand that the nets must be retreated regularly. Probably, there is
need to seriously consider the use of Long-lasting Nets (LLNs) to reduce
ineffectiveness of ITNs caused by lack of retreatment. It is also
important that governments in Africa strive to reduce poverty levels and
improve quality of living for their citizens. 

Again, ITNs have to be incorprated with other malaria control
interventions for optimum results.

Sorry for my lengthy views.

Maurice.

--
Maurice R. Odiere
CDC-Entomology section
P.0.Box 1578
Kisumu. 40100
Kenya.
Tel (Office): +254-572022902
Cell: +254-721-845-777
mailto:modiere@ke.cdc.gov