Lymphatic filariasis - investigating the effectiveness of insecticide-treated nets for control, Uganda
Situation:
Lymphatic filariasis (LF) is caused by species of nematode parasites—Wuchereria bancrofti, Brugia malayi, and Brugia timori—and is transmitted by mosquitoes. While LF is usually acquired in childhood, its visible manifestations occur in adults where they lead to temporary and permanent disability. As such, the disease has a major social and economic impact on endemic countries. LF is now recognized as a major source of morbidity and physical disability and has been ranked by the World Health Organization as the second major cause of long-term disability after mental illness. Filariae lodge in the lymphatic system where they cause inflammation, dilatation and lymphatic system failure. They are responsible for a variety of clinical manifestations, including lymphoedema of the limbs, genital disease (hydrocele, chylocele and swelling of the scrotum and penis) and acute, recurrent secondary bacterial infections known as "acute attacks".
The majority of infected people are asymptomatic, but virtually all of them have sub clinical lymphatic damage. Epidemiological surveys have shown that LF in Uganda is due to W. bancrofti. The parasite is mainly transmitted by Anopheles gambiae s.l. and An. funestus mosquitoes. W. bancrofti infections seem to be concentrated in a large focus located in the north of the Victoria Nile, covering most districts in the east, north and north-western parts of the country. Particularly high prevalences have been reported to the north of Lake Kyoga and in the northern part of the Albert Nile basin.
The cornerstone of LF control is annual mass drug administration (MDA) with a single dose of ivermectin plus albendazole, provided to the entire ‘at-risk’ population in targeted districts. The first MDA for LF was carried out at the end of 2002 in two districts with a population of one million people, reaching about 75% coverage. MDA continues to be carried out in schools and communities using trained teachers and community drug distributors, respectively, with most districts having reached at least 65% coverage. Reliance on drug-based LF control has its limitations and it should therefore be complemented by vector control.
Interventions that have been effective elsewhere range from larval control to prevention using long-lasting insecticidal nets (LLINs). The type of intervention chosen usually depended on the local LF vector(s). In Uganda, where LF is mainly transmitted by anopheline mosquitoes, the use of LLINs would seem appropriate, but funds for LF-specific vector control are not available. At the same time, LLINs are being rolled out as part of the national malaria control strategy.
Catches of the mosquito vector were conducted with CDC light traps
Response:
To contribute to the evidence base for LF vector control, Malaria Consortium has received funding through the Research Programme Consortium COMDIS for a study to investigate the effectiveness of LLINs against LF in areas where malaria and LF are coendemic and where long-lasting insecticidal nets are being rolled-out as a malaria control intervention. The study is being implemented in an area north of lake Kyoga, known to be highly endemic for LF. A rapid mapping exercise, using immunochromatographic card tests was carried out in May 2007 to identify a suitable sentinel site. A site with LF prevalence > 20% was identified in Dokolo district. In July 2007, Malaria Consortium randomly selected villages from the parish around this site. A household survey was conducted alongside a census of each village. Randomly selected individuals from each household were subsequently examined for clinical signs of LF, as well as infection with the parasite. Analysis of this baseline data will be completed in July 2008.
Preliminary analysis showed that LLIN coverage was much lower than expected. Malaria Consortium therefore applied for a LLIN donation for the whole parish from the Against Malaria Foundation. A donation of 4,000 LLINs was distributed to these highly malaria and LF endemic villages in early 2008. Follow-up entomological surveys and rapid assessments of LLIN retention and usage are planned for July 2008 and 2009, and a follow-up parasitological survey is planned for July 2009. The study is being carried out in close collaboration with the National Filariasis Control Programme, which is part of the Vector Control Division (VCD) of the Ministry of Health. Senior VCD staff were involved in the formulation of the study, and field activities draw on their expertise and the skills of their technicians for data collection.
Registration during night-time parasitological surveys (Above left)
Study subject with hydrocele, one of the possible outcomes of infection with Wuchereria bancrofti (Right)
Points to note:
Study results will be widely distributed within Uganda and will be published in an international, peer-reviewed journal. Depending on the outcome of the study, the results may also be used to formulate guidelines for integrated LF/malaria prevention. This would ensure that the study directly influences implementation in Uganda. It may also be potentially useful to advocate for more resources to be put into integrated vector-control for malaria and LF. We also expect that the results will strengthen the evidence-based for LF control at regional level, as the findings will be relevant to those settings in eastern Africa where LF is mainly transmitted by anopheline mosquitoes.
Publications: