Botswana, Namibia and Swaziland the project target current hot spots of transmission for demonstration projects. Winter larviciding is part of the countries national vector control strategy for malaria elimination but is currently not used extensively. Study locations were tentatively selected during the national inception meetings with the help of the countries’ NMCPs, WHO representatives, and malaria research organizations active in the country to maximize feasibility and availability of baseline data. The study locations are rural communities in which traditional homes, which are usually targeted for DDT spaying, dominate to put the demonstration in the contexts in which DDT is still used as a matter of priority. It was proposed to implement winter larviciding in addition to IRS which is implemented by the NMCPs to achieve maximum coverage in the demonstration areas.
Botswana lies along the southern endemic margin of transmission in sub-Saharan Africa and has experienced a substantial decline in malaria. The country reported over 101,000 cases in 1997 and just 326 confirmed cases in 2015. Botswana has a population of about 2.26 million people, approximately a third are at risk of malaria. Malaria transmission is unstable and largely occurs during Botswana’s rainy season, between November and April, with peaks from February to mid-April. Intensity of transmission fluctuates with the country’s varying rainfall each year, resulting in sporadic malaria epidemics. Transmission is highest in the northern districts of Chobe, Ngami, and Okavango, all which neighbour the highly endemic Zambezi region and account for more than 85 percent of the country’s malaria cases. North central districts experience focal transmission and are at high risk for outbreaks after heavy rains; the southern part of Botswana is considered non-endemic and at low risk for sporadic cases (UCSF, 2015). Botswana began reorienting its programmatic focus from control to elimination in 2009 (Chihanga et al., 2016). Anopheles arabiensis is the major vector in all malaria prone districts, however a range of species of the An. funestus complex have recently been recorded in Botswana highlighting the need for appropriate surveillance. IRS has been the primary vector control intervention in Botswana for decades. The use of DDT for malaria control in Botswana goes back to the mid-1950s as a small-scale intervention. However, in 1998, there were challenges in obtaining good quality DDT and as a result Botswana introduced the use of pyrethroids for malaria vector control. Vector susceptibility tests undertaken in 2006 and 2007 revealed a reduced vector susceptibility level to pyrethroids. In 2009, Botswana re-introduced DDT as part of its malaria elimination strategy. The country sprays most parts of at-risk areas using both DDT and pyrethroids, protecting about 600,000 people. LLINs are used as a complementary measure to IRS.
Namibia has a total population of 2.46 million, with approximately 1.9 million at risk of contracting malaria (WHO, 2016). Malaria transmission is unstable and seasonal in all malaria endemic regions of Namibia. Malaria vectors are An. arabiensis, An. gambiae and An. funestus, with An. arabiensis currently considered the most important. IRS is the main malaria vector control strategy in Namibia and has been applied in all malaria prone areas of the country since 1965. After independence (1990) a change was made by introducing pyrethroids in addition to DDT. DDT continues to be used in traditional structures while pyrethroids are used to spray modern houses in 22 districts in 9 regions protecting >700,000 people. The WHO has worked closely with the National Vector borne Diseases Control programme (NVDCP) to address the persistent problems associated with quality and timeliness in relation to transmission season observed in the late 1990s and early 2000s. The program has shown progressive changes and improved operational coverage and quality of IRS over the years since 2005 up to date. LLINs are distributed to selected communities however, overall LLIN usage is low.
Swaziland’s malaria transmission is seasonal and unstable and confined to the northern and eastern border areas. Of the 1,3 million population 28% are at risk. In 2015 a total of 157 cases were confirmed at health facilities (WHO, 2016). The country has a well-managed and successful malaria control program with IRS at the centre of the strategy. Anopheles arabiensis is the principal vector prevailing in the country. An. funestus used to play a role in the past. It has not been detected in the country for many years even in areas bordering with Mozambique where the species is still a very important vector. Indoor spraying of almost all malarious areas using DDT was already achieved by 1950. Since the early 2000s, however, spraying in traditional structures is being done with DDT while in urban centres pyrethroids are used. Due to many years of IRS and other malaria control interventions, malaria burden has decreased to a very low level. Nonetheless, the country is continuing IRS campaigns due to inadequate capacity for effective surveillance to guide decision and implementation at local level targeting only transmission foci and put in place alternative strategies to prevent re-introduction in areas freed from malaria.