Quelle des Ebolafieber-Ausbruchs in Westafrika eingegrenzt

[Robert Koch-Institut - 30.12.2014] Quelle des Ebolafieber-Ausbruchs in Westafrika eingegrenzt
Ein Team von Wissenschaftlern unter Federführung des Robert Koch-Instituts hat die Wildtier-Quelle des Ebolafieber-Ausbruchs in Westafrika eingegrenzt und bisherige Vermutungen zum Reservoir des Virus in Wildtieren bestätigt. Die Arbeiten sind in der Fachzeitschrift EMBO Molecular Medicine erschienen, in der Januarausgabe 2015, die am 30.12.2014 veröffentlicht wurde. Beteiligt an dem internationalen interdisziplinären Team waren das Max-Planck-Institut für Evolutionäre Anthropologie in Leipzig, die Wild Chimpanzee Foundation in Guinea, die Phillips Universität Marburg, das Institut für Tropenmedizin und internationale Gesundheit an der Charité Universitätsmedizin Berlin und die McGill University, Montreal, Canada ("Investigating the zoonotic origin of the West African Ebola epidemic, EMBO Molecular Medicine Januar 2015).
Das Team war im April 2014 in Guinea, um zu untersuchen, ob im Rahmen des aktuellen Ausbruchgeschehens auch Wildtiere von Ebola betroffen sind. Frühere Krankheitsausbrüche bei Menschen waren mit erheblichen Todesfällen unter Wildtieren assoziiert, vor allem Menschenaffen und kleine, im Wald lebende Antilopen (Ducker); bei der Verarbeitung des Fleischs tot aufgefundener Tiere kann das Virus auf den Menschen überspringen. In Guinea fanden die Forscher keine Hinweise auf eine erhöhte Sterblichkeit unter Wildtieren, die Populationen scheinen sich nicht verändert zu haben.
Das Team untersuchte auch die Umgebung des Indexpatienten, mit dem der Ausbruch begonnen hat, ein zweijähriger Junge in der Ortschaft Meliandou in Guinea. Die Umgebung dieser Ortschaft ist stark durch den Menschen geprägt, es gibt dort keinen tropischen Urwald wie bei den Orten in Zentralafrika, wo frühere Ebolafieberausbrüche begonnen hatten. Bisher ist das Reservoir des Ebolavirus nicht eindeutig geklärt. Flughunde (die wahrscheinlich selbst nicht an Ebolafieber erkranken) werden seit einiger Zeit als Tier-Reservoir angesehen. Die Wissenschaftler fanden fünfzig Meter vom Wohnort des Jungen entfernt einen einzelnen hohlen Baum, in dem die Kinder vor Ort oft gespielt haben. Obwohl der Baum kurz vor dem Eintreffen der Wissenschafter gebrannt hatte, konnte das Team die Erbsubstanz der Flughunde-Art nachweisen, die vor dem Brand auf dem Baum gelebt hatte. Gefunden wurde die Erbsubstanz in Boden und Ascheproben. Es handelte sich um Mops condylurus, eine Art (Spezies), die schon bei früheren Ebolaausbrüchen als mögliches Reservoir diskutiert worden ist und von der bekannt ist, dass sie Ebolavirus-Infektionen überlebt und in der Antikörper gegen Ebolaviren gefunden worden waren. Die EMBO-Arbeit ist vermutlich der bestmögliche Einblick, der in die Ursprünge des aktuellen Ausbruchs zu gewinnen ist.
Nachfolgend eine ausführliche Darstellung der Studienergebnisse in englischer Sprache. Die Veröffentlichung in der Fachzeitschrift EMBO Molecular Medicine kann auf Anfrage mit Embargo zur Verfügung gestellt werden.
Wildlife origins of West African Ebola virus disease outbreak narrowed down
In April 2014, shortly after the World Health Organization announced that the Zaire Ebolavirus was responsible for a number of deaths in southeastern Guinea, an international team began the search for the animal origins of the current Ebola virus disease epidemic. The team wanted to know whether there was a larger Ebola virus outbreak happening in wildlife in the region and how the index case, a two-year-old boy in Meliandou, Guinea, might have gotten infected and sparked the epidemic that has since spread into other areas of Guinea and then Sierra Leone, Liberia, Nigeria, Senegal, USA, Spain and Mali, representing the largest ever recorded outbreak.
To address these questions, Fabian Leendertz, head of the group "Epidemiology of Highly Pathogenic Microorganisms at the Robert Koch Institute, Berlin, assembled a large international interdisciplinary team consisting of virologists, veterinarians, ecologists, epidemiologists and an anthropologist stemming from various institutions; the Robert Koch-Institute, Berlin, Germany, the Max-Planck-Institute for Evolutionary Anthropology, Leipzig, Germany, the Wild Chimpanzee Foundation, Guinea, the Phillips University of Marburg, Germany, the Institute of Tropical Medicine and International Health, Charité, Berlin, Germany, and the McGill University, Montreal, Canada. The manuscript reporting their findings is published Dec 30th 2014 in EMBO Molecular Medicine (Issue January 2015).
The team first investigated whether there were signs of a recent decline in wildlife populations in the two largest protected areas in southeastern Guinea. During past Ebola virus disease outbreaks, particularly in Central Africa, the virus has caused major die offs in wildlife, particularly in great apes and duikers, where up to 90% population declines have been reported and this sometimes led to hunters contracting the virus by handling and consuming carcasses found in the forest. The monitoring team did not encounter any wildlife carcasses in their surveys, nor did they document a recent decline in wildlife densities in the region. This suggests that there was likely not an "amplifying epidemic in wildlife in the region, which could have enabled the virus to jump into the human population.
While the team was monitoring wildlife densities, it was announced by local health authorities that the first human case was a two-year-old boy from the small village of Meliandou. The landscape in that region is heavily human-modified, with Meliandou surrounded by plantations and bushland rather than tropical rainforests, as was the case for index villages in many previous Zaire Ebolavirus outbreaks. The team then set about to investigate how that two-year-old boy might have come into contact with the virus.
People, including children, were questioned about their hunting practices and contact to bushmeat. As in many other parts of Africa, both adults and children in the region hunt bats rather opportunistically. Children however tend to focus on small insectivorous bats, which they hunt under the roofs of houses or in other hides around the village. Once caught and killed, the bats are put on a stick and roasted over a fire. Even though this hunting practice is common throughout the region, special features in Meliandou might have been involved in enabling the transmission of the Ebola virus to a two-year-old boy. The team discovered a large burnt tree about 50 meters from the home of the index case, near a path used by women to reach their washing place at a small river. Children reported that they used to play regularly in and around this hollow tree, but that it had burned accidentally on March 24th, shortly before the research team arrived. Luckily the team was able to identify the species of bats that had inhabited this tree by identifying its DNA in soil and ash samples and deep-sequencing them. The bat species was identified as Mops condylurus, a species that has been discussed as a possible reservoir in early Ebola virus disease outbreaks in central Africa, it has then been shown to survive experimental infections and has been found with antibodies against Ebola viruses in the wild. Since the tree was burned, this species of bat was not found any more in Meliandou, but other fruit- and insect-eating bats were caught and subsequently analyzed for Ebola virus infection. As in many outbreaks before, no virus could be found.
The work presented by Leendertz and colleagues likely provides the best insight we will get into the origins of the current epidemic, but further in-depth ecological and experimental studies are urgently needed to understand the role of these and other bat species in Ebola viruses transmission and the circulation of these viruses in nature, to ultimately allow us to prevent future outbreaks.
In line with the "One Health concept, (a worldwide strategy for expanding interdisciplinary collaborations and communications in all aspects of health care for humans, animals and the environment) the researchers emphasize that culling or eviction attempts targeting bat colonies aimed at mitigating human-wildlife conflicts or reducing disease transmission risk are frequently unsuccessful; in some cases even producing effects opposite to those desired by the initiative. Health education initiatives should inform the public about potential disease risks posed by bats, recommend minimizing contact with bats, and advice against the consumption of bats. Education programs should further teach about the crucial roles bats play in the ecosystem, including pollination, seed dispersal and insect reduction. These ecosystem services provide invaluable benefits to people directly and indirectly, thereby supporting local livelihoods and healthy ecosystems. Similarly, while the village of Meliandou had the misfortune to be where this epidemic began, care needs to be taken to avoid retribution attacks and stigmatization of the region.
Further information
- EMBO Molecular Medicine January 2015 http://onlinelibrary.wiley.com/journal/10.1002/%28ISSN%291757-4684
- Ebola, RKI activities and recommendations: www.rki.de/ebola-en (in English. In German see www.rki.de/ebola)
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