ABSTRACT
Fifty years after narrowly missing the opportunity to eliminate malaria from Sri Lanka in the 1960s, the country has now interrupted malaria transmission and sustained this interruption for more than 12 months – no indigenous malaria cases have been reported since October 2012. This was achieved through a period overlapping with a 30-year separatist war in areas that were endemic for malaria. The challenge now, of sustaining a malaria-free country and preventing the reintroduction of malaria to Sri Lanka, is examined here in the context of rapid postwar developments in the country. Increased travel to and from the country to expand development projects, businesses and a booming tourist industry, and the influx of labour and refugees from neighbouring malarious countries combine with the continued presence of malaria vectors in formerly endemic areas, to make the country both receptive and vulnerable to the reintroduction of malaria. The absence of indigenous malaria has led to a loss of awareness among the medical profession, resulting in delayed diagnosis of malaria despite the availability of an extensive malaria diagnosis service. Highly prevalent vector-borne diseases such as dengue are competing for health-service resources. Interventions that are necessary at this critical time include sustaining a state-of-the-art surveillance and response system for malaria, and advocacy to maintain awareness among the medical profession and at high levels of government, sustained funding for the Anti-Malaria Campaign and for implementation research and technical guidance on elimination. The malaria-elimination effort should be supported by rigorous analyses to demonstrate the clear economic and health benefits of eliminating malaria, which exceed the cost of a surveillance and response system. An annual World Health Organization review of the programme may also be required.
ABSTRACT
Malaria transmission-blocking immunity has been studied in natural malaria infections in man, during infections in animals and following artificial immunization of animals with sexual stage malaria parasites. Effective immunity, which prevents infectivity of a malarial infection to mosquitoes, has been observed under all of these circumstances. Two general types of effector mechanism have been identified. One is an antibody mediated mechanism which acts against the extracellular sexual stages of the parasite within the midgut of a blood feeding mosquito. The other is a cytokine mediated mechanism which inactivates the gametocytes of the parasites while in the circulation of the vertebrate host. Both effects have been observed during natural infections and following artificial immunization. The basis of induction of transmission-blocking immunity, including the nature of the memory for such immunity, however, may be very different in different host/parasite systems and during natural infection of following artificial immunization. Following artificial immunization a strong immune memory for transmission blocking immunity has been observed in animal systems. By contrast, following natural infections in man immune memory for transmission blocking immunity has been found to be weak and short lived if it occurs at all. It is suggested that the immunogens which induce natural transmission blocking immunity may be CD4+ independent