Population-level estimates of the proportion of Plasmodium vivax blood-stage infections attributable to relapses among febrile patients attending Adama Malaria Diagnostic Centre, East Shoa Zone, Oromia, Ethiopia

Abstract

BackgroundMalaria is ranked as the leading communicable disease in Ethiopia, where Plasmodium falciparum and Plasmodium vivax are co-endemic. The incidence of P. vivax is usually considered to be less seasonal than P. falciparum. Clinical cases of symptomatic P. falciparum exhibit notable seasonal variation, driven by rainfall-dependent variation in the abundance of Anopheles mosquitoes. A similar peak of clinical cases of P. vivax is usually observed during the rainy season. However, the ability of P. vivax to relapse causing new blood-stage infections weeks to months after an infectious mosquito bite can lead to substantial differences in seasonal patterns of clinical cases. These cannot be detected with currently available diagnostic tools and are not cleared upon treatment with routinely administered anti-malarial drugs.MethodsA health- facility based cross-sectional study was conducted in Adama malaria diagnostic centre from May 2015 to April 2016. Finger-prick blood samples were collected for thin and thick blood film preparation from participants seeking treatment for suspected cases of febrile malaria. Informed consent was obtained from each study participant or their guardians. Seasonal patterns in malaria cases were analysed using statistical models, identifying the peaks in cases, and the seasonally varying proportion of P. vivax cases attributable to relapses.ResultsThe proportion of patients with malaria detectable by light microscopy was 36.1% (1141/3161) of which P. vivax, P. falciparum, and mixed infections accounted for 71.4, 25.8 and 2.8%, respectively. Of the febrile patients diagnosed, 2134 (67.5%) were males and 1919 (60.7%) were urban residents. The model identified a primary peak in P. falciparum and P. vivax cases from August to October, as well as a secondary peak of P. vivax cases from February to April attributable to cases arising from relapses. During the secondary peak of P. vivax cases approximately 77% (95% CrI 68, 84%) of cases are estimated to be attributable to relapses. During the primary peak from August to October, approximately 40% (95% CrI 29, 57%) of cases are estimated to be attributable to relapses.DiscussionIt is not possible to diagnose whether a P. vivax case has been caused by blood-stage infection from a mosquito bite or a relapse. However, differences in seasonal patterns of P. falciparum and P. vivax cases can be used to estimate the population-level proportion of P. vivax cases attributable to relapses. These observations have important implications for the epidemiological assessment of vivax malaria, and initiating therapy that is effective against both blood stages and relapses.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-017-1944-3) contains supplementary material, which is available to authorized users.

A preliminary study on urban malaria during the minor transmission season: The case of Adama City, Oromia, Ethiopia

“…In agreement with this finding, the recent retrospective study conducted by File et al (2019) from 2013 to 2018 also confirmed the same. The present study also revealed male individuals are proportionally more affected (64%) compared to female which agrees with the report of Golassa and White (2017) , where they reported that, males are proportionally more affected by malaria in Adama City. This is due to sex related occupation in Ethiopian tradition, where males are commonly engaged in outdoor activities which when accompanied by warmer climate of the city that favors malaria transmission by increasing human vector contact ( Golassa and White, 2017 ).…”

“…Similarly, variation in malaria cases as a function of frequency of respondents' previous malaria history was again found to be significantly related for the same reason. This strongly support the previous study done in Adama City in 2015 by Golassa and White (2017) , where they concluded 70% of P. vivax infections are suggested to have arisen from relapse during February to April, and 40% from August to October 2015. The epidemiological shift towards P. vivax dominance in the city could be partly due to relapse cases, the emerging trend of the parasite clone to infect Duffy negative individuals ( Mendis et al, 2001 ), and highest genetic diversity of P. vivax over P. falciparum that shows the relative evolutionary advantage of fitness to the environmental challenges.…”

“…The rainfall pattern is heavy from mid-June to mid-September and shorter rainy season in March. Most of the seasons are having the environmental temperature of 16--32°c that is favorable for the breeding of Anopheles arabiensis (a predominant malaria vector in the region) ( Golassa and White, 2017 ). In addition, plenty of bushy gorges, ditches, shanty and slum dwelling, poor tidiness, vegetation covered residential areas are some of the common epidemiological factors that favor mosquito breeding in Adama City ( File et al, 2019 ).…”

A pilot randomized controlled trial to compare the effectiveness of two 14-day primaquine regimens for the radical cure of vivax malaria in South India

“…In the transmission season P. vivax cases are presumed to be arising both from new mosquito infections and relaps. [25]. The interval to relapse ranged between 80 and 105 days in this study which is longer than usual in East Asia, but is consistent with some studies from India which suggest an intermediate duration of latency [26–28].…”

Spatial and genetic clustering of Plasmodium falciparum and Plasmodium vivax infections in a low-transmission area of Ethiopia

“…No spatial clustering was observed for P. vivax. The loss of relatedness and household level clustering may reflect differences in the biology of these two Plasmodium species where the majority of clinical P. vivax cases are attributable to relapsing episodes and do not necessarily reflect an active circulating infection that involves www.nature.com/scientificreports/ mosquito bites 43,44 . This would contribute to considerable variation in the time between the original inoculation by mosquito bite and parasite detection in the bloodstream, and thus diffuse any genomic signal.…”