How severe and prevalent are Ebola and Marburg viruses? A systematic review and meta-analysis of the case fatality rates and seroprevalence.

Luke Nyakarahuka,Julius Lutwama,Randi Krontveit,Frank N Mwiine,Benjamin Mayer,Eystein Skjerve,Clovice Kankya

doi:10.1186/s12879-016-2045-6

Abstract

BackgroundEbola and Marburg virus diseases are said to occur at a low prevalence, but are very severe diseases with high lethalities. The fatality rates reported in different outbreaks ranged from 24–100%. In addition, sero-surveys conducted have shown different seropositivity for both Ebola and Marburg viruses. We aimed to use a meta-analysis approach to estimate the case fatality and seroprevalence rates of these filoviruses, providing vital information for epidemic response and preparedness in countries affected by these diseases.MethodsPublished literature was retrieved through a search of databases. Articles were included if they reported number of deaths, cases, and seropositivity. We further cross-referenced with ministries of health, WHO and CDC databases. The effect size was proportion represented by case fatality rate (CFR) and seroprevalence. Analysis was done using the metaprop command in STATA.ResultsThe weighted average CFR of Ebola virus disease was estimated to be 65.0% [95% CI (54.0–76.0%), I2 = 97.98%] whereas that of Marburg virus disease was 53.8% (26.5–80.0%, I2 = 88.6%). The overall seroprevalence of Ebola virus was 8.0% (5.0%–11.0%, I2 = 98.7%), whereas that for Marburg virus was 1.2% (0.5–2.0%, I2 = 94.8%). The most severe species of ebolavirus was Zaire ebolavirus while Bundibugyo Ebolavirus was the least severe.ConclusionsThe pooled CFR and seroprevalence for Ebola and Marburg viruses were found to be lower than usually reported, with species differences despite high heterogeneity between studies. Countries with an improved health surveillance and epidemic response have lower CFR, thereby indicating need for improving early detection and epidemic response in filovirus outbreaks.

Highlights

Ebola and Marburg virus diseases are said to occur at a low prevalence, but are very severe diseases with high lethalities
While there have been some reports of Ebola virus disease (EVD) being associated with a case fatality rates (CFR) of 100%, this CFR is attributed to only a single case fatality that did not result into transmission of the virus to other individuals [7, 8]
Of those included in the study, 23 reported outbreaks of EVD (Table 1) [3, 8, 27,28,29,30,31,32,33,34,35,36,37,38,39,40,41, 7, 42, 43], 12 reported outbreaks of Marburg virus disease (MVD) (Table 2) [10, 11, 42, 44,45,46,47,48,49,50,51], 26 reported seroprevalence of Ebola virus (Table 3) [8, 12,13,14, 28, 31, 52,53,54, 29, 55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70] and 11 reported sero-prevalence of Marburg virus (Table 4) [14, 15, 57, 61,62,63,64, 67, 71,72,73]

Summary

Introduction

Ebola and Marburg virus diseases are said to occur at a low prevalence, but are very severe diseases with high lethalities. Ebola virus disease (EVD) and Marburg virus disease (MVD) are caused by filoviruses in the family Filoviridae and are both associated with high case fatality rates (CFR). While there have been some reports of EVD being associated with a CFR of 100%, this CFR is attributed to only a single case fatality that did not result into transmission of the virus to other individuals [7, 8]. It seems that CFR differs from species to species, both Ebola Sudan and Ebola Zaire have shown a CFR of 100% [1]. The largest MVD outbreak was in Angola in 2004 with CFR of 90% [10] and in Democratic Republic of Congo (DRC) in 1998 with CFR of 83% [11]

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