New findings on fruit bats as vectors for Ebola

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EBOLA HEMORRHAGIC FEVER, FRUIT BAT - DEMOCRATIC REPUBLIC OF CONGO, 2007 *********************************************************************** A ProMED-mail post <http://www.promedmail.org> ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>  Date: Fri 29 May 2009 Source: allAfrica.com, ex SciDev.Net [edited] <http://allafrica.com/stories/200905290730.html>   Central Africa: scientists find more signs of bats' role in Ebola ----------------------------------------------------------------- Ebolavirus, a filovirus, causes fever, vomiting, diarrhoea, and sometimes  bleeding. There is no treatment or vaccine and 25-90 per cent of infected  people die. The virus is transmitted by direct contact with infected blood,  body fluids, and tissues. The new findings have emerged from data collected  in the remote Kasai-Occidental and Kasai provinces of the Democratic  Republic of Congo (DRC) which experienced a large Ebola [hemorrhagic fever]  outbreak in 2007 in which 186 people died. Some members of the research  team helped discover in 2005 that fruit bats are a natural reservoir of the  ebolavirus.  For the new study, researchers led by Eric Leroy from the International  Centre for Medical Research in Franceville, Gabon, interviewed locals about  the background of the ebolavirus infection cases. They were told that the  annual migration of the fruit bat _Hypsignathus monstrosus_ was  particularly large in 2007. Bats are an important source of protein in the  area as wild animals are in short supply. They are often shot and then sold  covered in blood.  The researchers believe the source of the 2007 outbreak was a man who  bought bats at market. He survived, experiencing only a low fever, but his  4 year old daughter died after developing a sudden fever accompanied by  vomiting. A family friend who prepared the girl's body for burial was  subsequently infected and went on to infect 11 members of her family, all  of whom died. Researchers say their study suggests infection is only  transmitted after prolonged contact with an infected person, meaning it may  be easier to contain an outbreak than was previously believed.  Jean-Jacques Muyembe, epidemiologist at the DRC's National Biomedical  Research Instituteand co-author of the study, told SciDev.Net that the team  will continue to retrace events around outbreaks and carry out ecological  studies on bats "to definitely prove that these bats are the direct vectors  of Ebola [hemorrhagic fever] to humans." Vital Mondonge, a co-author from  the infectious disease section of DRC's health ministry, says that the bat  migration should be a focus of efforts to prevent ebolavirus infection.  Chimpanzees and gorillas are also known ebolavirus vectors. Bats, however,  appear not to die from ebolavirus [infection], suggesting they play a role  in maintaining the virus in tropical forests. The research was published in  March in Vector-borne and Zoonotic diseases: Vector-Borne and Zoonotic  Diseases doi 10.1089=vbz.2008.0167 (2009).  [byline: Esther Tola and Christina Scott]  
--  Communicated by: ProMED-mail rapporteur Susan Baekeland  [This report is based on the following publication: EM Leroy, A Epelboin, V  Mondonge, X Pourrut, J-P Gonzalez, J-J Muyembe-Tamfum, et al. Human Ebola  outbreak resulting from direct exposure to fruit bats in Luebo, Democratic  Republic of Congo, 2007. Vector-borne and Zoonotic Diseases, 28 Mar 2009  <http://www.liebertonline.com/doi/abs/10.1089/vbz.2008.0167>.  Abstract: "Twelve years after the Kikwit Ebola outbreak in 1995, ebolavirus  reemerged in the Occidental Kasai province of the Democratic Republic of  Congo (DRC) between May and November 2007, affecting more than 260 humans  and causing 186 deaths. During this latter outbreak we conducted several  epidemiological investigations to identify the underlying ecological  conditions and animal sources. Qualitative social and environmental data  were collected through interviews with villagers and by direct observation.  The local populations reported no unusual morbidity or mortality among wild  or domestic animals, but they described a massive annual fruit bat  migration toward the southeast, up the Lulua River. Migrating bats settled  in the outbreak area for several weeks, between April and May, nestling in  the numerous fruit trees in Ndongo and Koumelele islands as well as in palm  trees of a largely abandoned plantation. They were massively hunted by  villagers, for whom they represented a major source of protein. By tracing  back the initial human-human transmission events, we were able to show  that, in May, the putative 1st human victim bought freshly killed bats from  hunters to eat. We were able to reconstruct the likely initial human-human  transmission events that preceded the outbreak. This study provides the  most likely sequence of events linking a human Ebola [hemorrhagic fever]  outbreak to exposure to fruit bats, a putative virus reservoir. These  findings support the suspected role of bats in the natural cycle of  ebolavirus and indicate that the massive seasonal fruit bat migrations  should be taken into account in operational Ebola [hemorrhagic fever] risk  maps and seasonal alerts in the DRC."  In their discussion the authors point out that these findings strongly  suggest that ebolavirus can be contracted by humans through direct exposure  to fruit bats, and the massive fruit bat migrations should therefore be  taken into account in operational Ebola [hemorrhagic fver] risk maps and  seasonal alerts. Specific studies of the routes and dates of fruit bat  migration are needed. However, in the short term, it may be difficult or  even impossible to halt human consumption of fruit bats, which represent a  readily available and abundant source of protein, especially as many game  species are protected or becoming rare.  The authors point out in addition that these observations raise several  questions. Firstly, why was there only one bat-to-human transmission event?  The outbreak only really started after the 3rd human case had occurred.  Transmission from the father to his daughter, then from the girl's corpse  to another person, took place in very particular circumstances and went  unnoticed. In fact, it is highly likely that several other persons were  infected by bats but the circumstances required for subsequent  human-to-human transmission were not present.  Secondly, why was only one secondary case observed among all the people who  came into contact with patient? The mild illness (isolated fever) in the  primary case suggests a low viral load. This would imply a low risk of  transmission to another person, except in certain conditions (such as,  close and long-lasting contact, with a young child, for example).  Thirdly, why was the first secondary case so rapidly fatal (4 days)? The  answer is probably that this patient, being a young child, succumbed  rapidly to untreated dehydration due to vomiting and diarrhoea.  The full text of the paper contains a map of the location of the outbreak  and an image of the fruit bat _Hypsignathus monstrosus_ identified as the  carrier of the virus:  <http://www.liebertonline.com/doi/abs/10.1089/vbz.2008.0167>. - Mod.CP]