Transmissibility and dynamics of P. vivax and P. falciparum infections in Ethiopia | New Voices in Infection Biology

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Talk abstract:

Located in the Horn of Africa, Ethiopia recorded substantial decline in malaria burden in the last two decades. The epidemiology of malaria is unique in Ethiopia compared to endemic settings in Africa; the major one being the very high prevalence of P. vivax infections. P. vivax contributes to ~40% of reported cases in the country which is 9% of the global burden.

In our studies, we have been investigating the contribution to the infectious reservoir and dynamics of symptomatic and asymptomatic Plasmodium infections in different settings. We have found that asymptomatic Plasmodium infections were widely distributed throughout the country (Hailemeskel2021MalJ), cluster around index cases (Tessema2021SciRep), and contribute substantially to the infectious reservoir compared to clinical cases (Tadesse2018CID). In a longitudinal study that involves sampling twice weekly and membrane feeding on 14 days interval upon infection detection by PCR, we have observed varying trends in temporal fluctuations in parasite densities and infectivity to mosquitoes.

In a parallel assessment of factors modulating infectivity of clinical cases to mosquitoes, it was rare for P. falciparum clinical cases to infect mosquitoes in our studies whilst 60-70% of P. vivax infected patients were infectious at presentation. Although gametocyte density is the most important determinant of transmissibility to mosquitoes, human, parasite, mosquito, and environmental factors modulate transmission. In matched membrane feeding experiments using patients’ own and naïve European serum, we have identified serum samples that block heterologous transmission of P. vivax. In a monthly follow up, we have observed high rate of relapses in patients infected with P. vivax and persistent transmission to mosquitoes.

Using our field setting in Adama (Ethiopia) we have recently demonstrated the very high competency of An. stephensi to transmit local Plasmodium strains (Tadesse2021Emerg Infect Dis). An. stephensi is a metropolitan Indian malaria transmitting mosquito that recently invaded the Horn of Africa.