Effectiveness of mass drug administration for reducing seasonal malaria transmission towards its elimination in hotspot areas in Zanzibar

Abstract: Background: Following the increase of international funding for implementation of the combined effective malaria control strategies for prevention, diagnosis and treatment in the past decades, a significant reduction with 30% of malaria attributed morbidity and mortality has been achieved. At present, declining transmission intensities, in areas of successful malaria control, have resulted in a relative increase of asymptomatic low parasite density infections that fall below the detection level of rapid diagnostic tests and microscopy. Mass drug administration (MDA) is a treatment of the entire population in a geographic area with antimalarial drugs irrespective of the presence of symptoms and without diagnostic testing, with the purpose of targeting asymptomatic malarial infections.   Aim: The overall purpose of this study is to determine the effectiveness of two rounds of MDA for reducing malaria transmission on Unguja island in Zanzibar.   Methods: A cluster-randomised controlled study with two arms was performed: an arm with two rounds of MDA, and a control arm without MDA. A total of 7941 field samples from the first MDA round and 9853 samples four months after the second round of MDA were screened. Two different sets of qPCRs, 18Sq-PCR and cytb-qPCR were used to detect the positivity of Plasmodium infection. The species were further identified using restriction fragment length polymorphism (RFLP).   Results: Cytb-qPCR detected more positive samples compared to 18S-qPCR. The qPCR determined malaria prevalence six months after the second MDA round was 1.7%. P. falciparum was the predominant species accounting for 64.6% and 63.3% from first MDA round and four month after second round of MDA respectively. From the first MDA round, the prevalence of P. malariae and P. vivax was 15.4% with 0.6% respectively. The parasite prevalence in the second round of MDA was: 10.8 % in P. malariae, 7.2 % in P. ovale and 0.6 % in P. vivax.   Conclusion: There is still a presence of asymptomatic low-density parasite carriers and the parasite prevalence remains relatively low in Zanzibar. MDA can be effective in low endemic settings when the goal is elimination.