This study provides a broad overview of vector control activities in the 17 African countries that are yet to start, or have only recently started MDA implementation for LF elimination. Overall, the significant scale up of ITNs, and to a lesser extent IRS, is promising, and it is likely that these interventions that reduce malaria transmission [21, 22, 42–44], have also already impacted on the transmission of W. bancrofti in many co-endemic areas. However, monitoring their impact will be critical, and it may be more efficient and cost effective for the new LF Programmes to develop formal links with national malaria control programmes and include IVM as one of their key intervention strategies . A recent review has highlighted several examples of IVM carried out in a range of ecological settings , which suggests that this integrated approach could be successful in Africa where the main vectors of malaria and LF are similar Anopheles species, and transmission may coincide [10, 11, 45–48]. In order to achieve this, it is critical that countries take advantage of the current funding available for malaria, as resources may be declining and the window of opportunity for vector control may be closing in the near future.
The reason for the variation in vector control coverage across the different countries may be due to a number of factors including the geographical size (e.g. São Tomé and Príncipe - small islands), and the relative wealth and political stability of a country (e.g. DRC, Guinea, Angola, Zimbabwe - post conflict) . It may also be related to whether a country has an established and active malaria control programme (e.g. The Gambia - traditional high net coverage, Eritrea - high bed net coverage) [49–53], or has received substantial funding for malaria control from the government and international donors and particularly the Global Fund (e.g. Zambia - significant support from World Bank) [35, 36]. These factors are complex and interacting, and how the GPELF can use this information to take full advantage of the increasing scale up of ITN and IRS activities, needs to be considered in the context of the LF endemicity and programmatic capacity of each country, as it can vary considerably [1, 13].
It is possible that a number countries such as The Gambia, Eritrea and São Tomé and Príncipe may not need to develop a LF Elimination Programme or implement MDA at all, as they are small, politically stable, have established active malaria control programmes, relatively high bed net coverage and shown limited or no evidence of LF transmission in the past decade. While The Gambia has historical evidence of high LF transmission [54–56], it also has a long history of large scale bed net distribution [52, 53], and recent reports suggest that LF is no longer a public health problem (unpublished data). Eritrea has little historical evidence [8, 56], has no current data on LF, as programmatic mapping has not started , but has a successful vector control programme [49–51]. In São Tomé and Príncipe, historical reports indicate disease presence , and recent IVM activities are likely to have impacted transmission [35–41, 49]. Therefore, it may be more appropriate to assess these countries for the interruption of transmission using the new Transmission Assessment Survey (TAS) developed by WHO [57, 58]. Recently, WHO reassessed nine other countries and compiled sufficient evidence to reclassify them as non-endemic, thereby reducing the global number of endemic countries to 73 . A similar assessment using TAS as a tool to verify the lack of transmission in The Gambia, Eritrea and São Tomé and Príncipe may help ‘shrink the map’, as well as contribute to considerable cost savings. Similarly, on Bioko Island, Equatorial Guinea the use of ivermectin in onchocerciasis control together with a high net and IRS use will have been likely to have an additive impact .
Zambia is another country with a well established vector control programme with relatively high bed net coverage, and some IRS activities, which also could have impacted on LF transmission [37, 41, 49, 61, 62]. However, in Zambia the LF Programme recently finalised baseline mapping and found two thirds of the population at risk of LF. Overall antigen prevalence rates were low ≤10%, except in a few selected regions of the country (unpublished data). The first MDA is due to start in early 2013 and together with the ongoing vector control activities, the LF Programme could see a significant reduction in transmission in most regions of the country within a few years. The only concern to note is that there is already widespread insecticide resistance found in several Anopheles species across the country and different strategies to overcome this are currently being developed [41, 63].
The extent to which insecticide resistance prevents ITNs and IRS from being effective is not known, especially in relation to LF transmission. However, given the increasing geographical spread of resistance to multiple classes of insecticide across Africa [64–68], there seems to be another small window of opportunity to maximise the full potential of these alternative strategies. Alarmingly, almost all of the 17 countries have already reported some degree of insecticide resistance to one of the main classes of insecticides, in one of the main Anopheles species responsible for malaria transmission. The scope of this problem is yet to be fully determined, however, resistance monitoring is becoming increasingly important among international stakeholders such as PMI , and the development of publicly accessible up-to-date databases and maps, including the new IR Mapper [67, 68], will help to assess the situation over time and space along with other programmatic activities [69–71]. This is particularly important given the limited availability of vector control tools and the fact that new products will not be available for some years . It is also not know what effect insecticide resistance will have on filarial worm development in Anopheles mosquitoes, as in Culex, highly elevated esterases involved in insecticide resistance were found to inhibit development of microfilariae of W.bancrofti in a study in Sri Lanka .
The countries facing the greatest challenges are those that have endured conflict and civil unrest, and have among the lowest coverage of vector control interventions such as Congo, Guinea, and DRC [15, 35–41]. New LF programmes in these countries are establishing themselves, with significant barriers related to the lack of public infrastructure, transport networks and trained health personnel. Malaria control programmes face similar constraints despite significantly more funding available for vector control [35, 36, 40, 41]. In large countries such as DRC, significant geographical factors have been found to contribute to low bed net coverage in remote, rural areas , which suggests that alternative distribution methods are needed, especially where LF may be co-endemic with L. loa and ITNs are one of the main recommended strategies by WHO . Increased efforts to boost vector control coverage in high risk L. loa co-endemic areas is critical, especially as potential alternative strategies such as twice a year albendazole have to go to scale whilst the use of doxycycline an anti-Wolbachia macrofilaricide or adult sterilising agent [74–76], has yet to be recommended or available for distribution without medical supervision.
The use of the established and extensive network of community drug distributors working for the African Programme for Onchocerciasis Control (APOC) in eight of the 17 countries may be an entry point to increase ITN distributions as has been demonstrated in Nigeria [77, 78]. This will benefit both the LF and malaria programmes, and provide new opportunities for onchocerciasis programmes which may be scaling down due to their success as they move towards the elimination of transmission of Onchocerca volvulus[79, 80]. Already many LF Elimination Programmes across Africa use the community-directed treatment with ivermectin (CDTi) strategy developed by APOC, as a platform to distribute MDA . It seems sensible to extend this to include ITNs and other interventions in the remote hard-to-reach, co-endemic areas where CDTi already operates [78, 81]. Finer scale mapping, using the micro-stratification overlap mapping (MOM) approach, could be used to identify the populations most at risk, so that ITNs distributions can be specifically targeted . However, more collaboration, communication and coordination between the various NTD and malaria vector-borne disease control programmes is important and becoming an international priority.