Ebola in animals - our knowledge to date: assessing human exposure risks

Abstract

Purpose: Many unknowns remain concerning the role of animal species in the epidemiology of ebolavirus (EBOV) and transmission risk to humans. The 2018 Ebola outbreak led the Food and Agriculture Organization of the United Nations (FAO) to update its qualitative risk assessment on EBOV release from animals or their products and human exposure. Methods & Materials: A literature review identified recent publications (since January 2015, when FAO's last EBOV risk assessment was published). International scientists provided information from ongoing research, both laboratory and field studies. FAO colleagues from affected and at risk countries contributed field knowledge. Utilizing the information collected from various sources, the likelihood for human exposure to EBOV was assessed considering close contact, handling and consumption of (i) wild animal species or (ii) domestic animal species in areas where EBOV is present, as well as (iii) the likelihood of EBOV introduction into non-infected countries through trade, handling or consumption of meat from susceptible wild animals originating from affected areas. Results: The likelihood for human exposure from susceptible wild animals, such as fruit bats, non-human primates and duikers, in areas where EBOV is present was assessed as low. For domestic animals in these areas, such as pigs and dogs, the likelihood was assessed as very low. The likelihood of EBOV introduction into non-infected countries through trade, handling and consumption of wild meat was also assessed as very low. Given limited availability of surveillance or field study data, the level of uncertainty in the assessment remains high. Conclusion: Investigations of historic human outbreaks suggest that EBOV is initially introduced into human populations through contact with infected wild mammals or their meat. However, in line with the assessed low likelihood, this is considered a rare event. The public health impact of spillover, when occurring, is however devastating due to the huge consequences that human outbreaks entail. The risk assessment helped consolidating current knowledge on EBOV in animals and highlighted outstanding knowledge gaps, including EBOV survival in the environment, susceptibility of animal species in field settings, and information on wild meat trade movements.