Dynamics of Plasmodium falciparium and Plasmodium vivaxin a micro-ecological setting, Southwest Ethiopia: effects of altitude and proximity to a dam

Abstract

BackgroundRefining the spatial and temporal data on malaria transmissions at a defined ecological setting has practical implications for targeted malaria control and enhancing efficient allocation of resources. Spatial and temporal distribution of P. falciparium and P. vivax were explored around the Gilgel Gibe Hydroelectric Dam (GGHD) in southwest Ethiopia.MethodsA review of confirmed malaria episodes recorded over eight years at primary health services was conducted. Using individual identifiers and village names malaria records were cross-linked to location and individual records of Gilgel Gibe Health and Demographic Surveillance System (HDSS) data, which had already been geo-referenced. The study setting was categorized in to buffer zones with distance interval of one kilometer. Similarly, altitude of the area was categorized considering 100 meters height intervals. Incidence rate ratios were estimated using Poisson model for the buffer zones and for the altitudinal levels by adjusting for the underlying population density as an offset variable. Yearly temporal variations of all confirmed malaria cases were also evaluated based on the Poisson model using STATA statistical software version 12.ResultsA considerable proportion (45.0%) of the P. falciparium episodes were registered within one kilometer radius of the GGHD. P. falciparium showed increment with distance from the GGHD up to five kilometers and with altitude above 1900 meters while P. vivax exhibited the increase with distance but, decrease with the altitude. Both species showed significantly higher infection among males than females (P <0.01). Temporally, malaria episodes manifested significant increments in the years between 2006/7 to 2009/10 while reduction of the malaria episodes was indicated during 2004/5, 2005/6 and 2010/11 compared to 2003/4 (P <0.01). On average, P. vivax was 52% less than P. falciparium over the time period considered. P. vivax was significantly higher in the years 2004/5 to 2007/8 and 2010/11 (P <0.001).ConclusionsSpatial and temporal variations of malaria were observed. The spatial and temporal variations of malaria episodes were also different for the two main malaria species in the area.

Identification of different malaria patterns due to Plasmodium falciparum and Plasmodium vivax in Ethiopian children: a prospective cohort study

“…The shape model parameter value below one confirmed that malaria incidence rates for both species decreased with time during the study period. A similar decreasing malaria incidence trend has been reported in southwest Ethiopia [ 29 ] and may be explained by positive effects of control interventions in the area. Indeed, the government re-started indoor residual spraying with deltamethrin in 2009 and replaced old long-lasting insecticidal nets (LLINs) in 2010 [ 30 ].…”

Proximity to vector breeding site and risk of Plasmodium vivax infection: a prospective cohort study in rural Ethiopia

“…The study did not find evidence that gender, household wealth or education of head of household were associated with P. vivax infection, which contrasts conclusions from other studies [ 28 , 31 , 37 , 40 , 41 ]. Part of this discrepancy might be because the present study lacked power to detect these associations (versus Siri [ 41 ]); categorized variables differently (versus Graves et al and Khaireh et al [ 28 , 31 ]; or required objective/subjective fever in addition to a positive RDT and microscopy reading to meet P. vivax case definition (versus most other studies which did not require clinical signs or symptoms [ 28 , 31 , 37 , 41 ].…”

“…Various risk factors for P. vivax infection have been investigated around the Horn of Africa, including climatic parameters, bed net use, indoor residual spraying, household characteristics and demographic factors [ 23 , 28 – 41 ]. A few studies have investigated household proximity to vector breeding site as a risk factor, though the evidence from these studies is mixed: three studies found an enhanced risk [ 29 , 30 , 33 ], one found no difference [ 28 ], and one found a reduction in risk with increasing proximity [ 40 ]. A separate study concluded that the association between proximity to breeding site and P. vivax infection is modified by age, with proximity a much stronger risk factor in children compared to adults [ 38 ].…”

Malaria epidemiology and interventions in Ethiopia from 2001 to 2016

“…These areas may have scattered seasonal micro-geographic local transmissions due to local environmental suitability [ 10 , 34 ]. For example, construction of dams might increase malaria transmission in the valleys of highland areas where overall malaria transmission was very low [ 35 ]. These dams create transmission hot spots along valleys where irrigation is important for farming [ 36 ].…”