Malaria, Lymphatic Filariasis and Insecticide-treated Nets

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Throughout Africa one of the main vectors that carry Lymphatic Filariasis (LF) is the Anopheles mosquito, which also carries the malaria parasite. The Carter Center has been promoting use of insecticide treated nets (ITNs) for many years as part of its LF control efforts, but others may not have gotten the message.

The global community is targeting LF for elimination in 2020. The primary strategy is mass drug administration annually with ivermectin and albendazole. The plan is that up to seven annual rounds of drug distribution in endemic communities where 90% of population coverage is achieved is necessary to stop LF transmission. The Carter Center explains that distribution of long-lasting insecticidal bed nets (LLINs) protects pregnant women and children who cannot take drug treatment.

The LF strategy often builds on and integrates with onchocerciasis control efforts where these diseases overlap. The community directed treatment with ivermectin (CDTI) model pioneered by the African Program for Onchocerciasis Control  (APOC), wherein communities or villages plan together the distribution process including selecting their own community directed distributors (CDDs). This model has also been used to distribute ITNs.

20160818_100110-1A second component of the LF strategy is morbidity management which focuses on enhanced personal hygiene or cleaning of the parts of the body that experience lymphedema. Another aspect uses surgery to address some of the worst effects, hydrocele.  While this component does not ‘control’ LF, it is a necessary effort to reduce suffering and the negative stigma from the disease.

To judge whether transmission has stopped and elimination has been achieved Transmission Assessment Surveys (TAS) are conducted with rapid diagnostic tests on young children after at least 5 years of MDA in a community.  Specifically WHO recommends an implementation unit must have completed five effective rounds of annual MDA defined as achieving rates of drug coverage exceeding 65% in the total population.

For example the Carter Center in Support of the Nigerian Federal Ministry of Health worked in Plateau and Nasarawa States through community health education, delivery of long lasting insecticide-treated nets (LLINs) and 33 million drug treatments for lymphatic filariasis and river blindness between 2000 and 2011. “In 2012, it was confirmed (through TAS) that lymphatic filariasis transmission had stopped. Post-treatment surveillance is currently underway to assure that the parasite is not reintroduced into the area.”

Another component of the assessment process is yet to be fully realized. That is the testing of mosquitoes for the presence of microfilariae. This indirectly implies an important role in preventing human-vector contact as would be achieved through the use of ITNs as well as indoor residual spray (IRS).

Vector control can benefit more than one disease. Integrated vector management is seen as a key tool to prevent reintroduction of LF in areas where anopheles mosquitoes carry the disease and where ITN campaigns are successful.

Ultimately the key to benefiting from the disease control synergies provided by insecticide-treated nets is an understanding what if any effect nets have on transmission. This poses a challenge in terms of separating it from the effect of MDAs as well as the fact that MDAs are time-limited. As MDAs are still underway in many places it is incumbent on program managers to monitor and evaluate the impact of all activities, treatment and vector control, over the next decade to determine the success of eliminating LF and hopefully malaria, too.

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