Impact of programme to control elephantiasis levels off

22 Jun 2010

Paul Chinnock

Source: PLoS Neglected Tropical Diseases (see original article or PDF)

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Citation: Simonsen PE, Pedersen EM, Rwegoshora RT, Malecela MN, Derua YA, et al. (2010) Lymphatic Filariasis Control in Tanzania: Effect of Repeated Mass Drug Administration with Ivermectin and Albendazole on Infection and Transmission. PLoS Negl Trop Dis 4(6): e696.

Wuchereria bancrofti: the filarial worm that causes lymphatic filariasis. [Credit: WHO/TDR/Stammers.]

Lymphatic filariasis (LF) is a disfiguring and disabling disease, caused by microscopic filarial worms and transmitted by mosquitoes. Around a third of the one billion people at risk of LF live in Africa. One country in which it is common is Tanzania, where a study has demonstrated the need to closely monitor the impact of current control strategies, as their impact may be less than expected.

The main control strategy in endemic areas is mass administration of a combination of two drugs. Although this treatment rarely completely clears individuals of infection, it is believed that the reduction in the number of worms in the population as a whole will lead to a reduction, or even elimination, of LF transmission. In most cases the drugs used are diethylcarbamazine (DEC) and albendazole. However, in areas where another filarial disease – onchocerciasis – is also present, albendazole is combined instead with ivermectin. (This drug an effective treatment for onchocerciasis, whereas people with this disease often suffer severe reactions if they are given DEC.)

Researchers collected data from the Tanga region in August 2004 – prior to the launch of a programme of annual mass drug administration (MDA) – and at intervals over the following four years, during which three rounds of MDA were completed as part of the Tanzanian National Lymphatic Filariasis Elimination Programme.

The baseline data showed this population to be at high risk of LF; a quarter of the 1112 children and adults examined tested positive for the parasite, 4.1% of adults had elephantiasis of the leg, and 32.8% of adult males had hydrocoele.

After the first two MDA rounds, according to surveys conducted in February 2006 and May 2007, infection rates with the blood-stage larva of the parasite (microfilaria) decreased considerably; prevalence was reduced by 40% and mean intensity by over 70%. This led to a reduction in transmission.

After this, however, the effects began to level off. As percentages of the baseline values, levels of infection and intensity were the same in November 2008 as they were one year earlier.

To quote the authors: “The study highlights the importance of monitoring and regular evaluation in order to make evidence based programme adjustments, and it points to a need for further assessment of the long-term effect of repeated ivermectin/albendazole MDAs (including the importance of application intervals and treatment coverage), in order to optimize efforts to control LF in sub-Saharan Africa”.

Even when there is good evidence to support a disease control intervention, the performance of the intervention in practice (and in specific locations) must always be monitored. The combination of ivermectin and albendazole seems, from this study, not to be as effective against LF as that of DEC/albendazole. It may be necessary to conduct MDA activities more frequently than once per year.

2010 Simonsen et al

Source

Title:
Lymphatic filariasis control in Tanzania: effect of repeated mass drug administration with ivermectin and albendazole on infection and transmission.

Authors:
Simonsen PE, Pedersen EM, Rwegoshora RT, Malecela MN, Derua YA, Magesa SM

References:
PLoS Negl Trop Dis 2010: Vol. 4 no. 6, pp. e696

Abstract:
In most countries of sub-Saharan Africa the control of lymphatic filariasis (LF) is based on annual mass drug administration (MDA) with a combination of ivermectin and albendazole, in order to interrupt transmission. Here we present the first detailed study on the effect of 3 repeated MDAs with this drug combination, as implemented by the Tanzanian National Lymphatic Filariasis Elimination Programme (NLFEP).Infection and transmission was monitored during a five-year period (one pre-intervention and four post-intervention years) in a highly endemic community (Kirare village) in north-eastern Tanzania. The vectors were Anopheles gambiae, An. funestus and Cx. quinquefasciatus. After start of intervention, human microfilaraemia initially decreased rapidly and statistically significant (prevalence by 21.2% and 40.4%, and mean intensity by 48.4% and 73.7%, compared to pre-treatment values after the first and second MDA, respectively), but thereafter the effect levelled off. The initial decrease in microfilaraemia led to significant decreases in vector infection and vector infectivity rates and thus to a considerable reduction in transmission (by 74.3% and 91.3% compared to pre-treatment level after first and second MDA, respectively). However, the decrease in infection and infectivity rates subsequently also levelled off, and low-level transmission was still noted after the third MDA. The MDAs had limited effect on circulating filarial antigens and antibody response to Bm14.Critical issues that may potentially explain the observed waning effect of the MDAs in the later study period include the long intervals between MDAs and a lower than optimal treatment coverage. The findings highlight the importance of ongoing surveillance for monitoring the progress of LF control programmes, and it calls for more research into the long-term effect of repeated ivermectin/albendazole MDAs (including the significance of treatment intervals and compliance), in order to optimize efforts to control LF in sub-Saharan Africa.

PMID: 20532226
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