ASTMH 2017, Fitsum Tadesse: “The contribution of symptomatic and asymptomatic infections to the infectious reservoir of Plasmodium falciparum and Plasmodium vivax in Ethiopia”

In collaboration with ASTMH, Image Audiovisuals, and session presenters, MESA brings you this webcast from the 66th ASTMH annual meeting in Baltimore, November 2017

Title: “The contribution of symptomatic and asymptomatic infections to the infectious reservoir of Plasmodium falciparum and Plasmodium vivax in Ethiopia”

Speaker: Fitsum Tadesse, Armauer Hansen Research Institute, Addis Ababa, Ethiopia

Session information: 

Symposium 0175: “Malaria: Mosquito Transmission and Interruption”

Thursday, 9 November, 8:00 – 9:45 AM, Convention Center – Ballroom II (Level 400)

Abstract:

The level of asymptomatic malaria infections is considerably higher than previously thought. Whether these infections need to be targeted to further strengthen control efforts/accelerate malaria elimination needs detailed investigation. In this study we performed detailed assessments of parasite carriage and transmissibility to mosquitoes to investigate the relative contribution to malaria transmission of clinical and asymptomatic malaria. We successfully performed mosquito feeding assays using locally reared A. arabiensis mosquitoes on clinical malaria episodes detected by the routine health system (n=41) and asymptomatic malaria infections detected by microscopy (n=41) and PCR (n=88) in Adama, central Ethiopia. Membrane feeding experiments yielded 5,000 mosquito observations. Mosquito infection was investigated using CSP based ELISA on 20-30 mosquitoes per experiment that were sacrificed 12 days post feeding; infection was confirmed with 18S gene based qPCR. Microscopy and PCR revealed 8.4%(41/487) and 26.5%(129/487) asymptomatic infections, respectively. Most of the infections were attributed to Pv 60.0%(98/164), while only 31.7%(52/164) were due to Pf. Among the feeding experiments analyzed so far, 2 out of 8 asymptomatic Pf carriers were infectious to mosquitoes (5 & 30% infected mosquitoes) but none of the clinical patients (0/8) were found infectious. Among 13 Pv carriers, 2/5 asymptomatic individuals were infectious to mosquitoes (5.5 & 25% infected mosquitoes) while 7/8 symptomatic individuals were infectious to mosquitoes and infected on average 57% of mosquitoes. Transmission data on an additional 4000 mosquitoes from 140 individuals will be completed in the coming months. Preliminary results from this study demonstrate that asymptomatic Pf infections play significant role in the maintenance of the infectious reservoir whereas clinical malaria cases are particularly relevant for Pv transmission. The findings fill an important knowledge gap on the relative contribution of symptomatic and asymptomatic individuals in an area of moderate-low transmission of vivax and falciparum malaria.