Searching for the source of Ebola: the elusive factors driving its spillover into humans during the West African outbreak of 2013-2016.

The natural ecology of Ebola virus infection remains enigmatic. No clear reservoir species has been confirmed but there is evidence of infection in a wide spectrum of mammals, including humans, non-human primates, domestic and wild ungulates and a variety of bat species, both frugivorous and insectivorous. Humans and most other species examined appear to be spillover hosts and suffer disease. Bats are the exception and are tolerant to infection in some laboratory studies. Some surveys show a low prevalence of antibodies against Zaire Ebola virus (ZEBOV) strains in bats during human outbreaks and inter-epidemic periods, and this order of mammals is considered to be the likely reservoir for the virus. Other putative sources include insects but this hypothesis is unproven in the field or laboratory. Moreover, some potential sources, such as aquatic species, have yet to be investigated. There are a number of environmental, human behavioural and ecological risk factors proposed with respect to spillover and spread. In the West African outbreak, which was unprecedented in scale and geographic spread, the source of the spillover remains unproven, although an association exists between the proposed index case and a colony of insectivorous bats. In all but a few Ebola virus disease events, spillover has only been superficially investigated and this was also the case in the West African epidemic. The authors suggest that, to address risks at the human-animal-environmental interface, using a One Health approach, more effort is needed to investigate spillover factors at the time of a ZEBOV epidemic, in addition to conducting inter-epidemic surveys in peridomestic environments. The true prevalence of ZEBOV infection in any species of bats remains unknown. Large-scale, expensive, non-randomised surveys, with low sampling numbers per species, are unlikely to provide evidence for Ebola virus reservoirs or to improve our epidemiological understanding.

L'écologie naturelle de l'infection par le virus Ebola demeure énigmatique. Si aucune espèce réservoir au sens strict n'a été clairement identifiée, le virus peut infecter un large spectre d'espèces de mammifères, parmi lesquelles l'être humain, des primates non humains, des ongulés domestiques et sauvages ainsi que de très nombreuses espèces de chauves-souris tant frugivores qu'insectivores. Les humains et la plupart des espèces animales étudiées semblent être des hôtes incidents chez qui la maladie se développe. Les chauves-souris constituent l'exception, certaines études de laboratoire ayant prouvé qu'elles sont tolérantes à l'infection. Des enquêtes ayant montré la présence d'anticorps dirigés contre les souches Zaïre du virus Ebola (Ebola-Zaïre) chez les chauves-souris, à un taux faible de prévalence, pendant les périodes d'activité des foyers chez l'homme ou dans les intervalles inter-épidémiques, cet ordre de mammifères est considéré comme un réservoir possible du virus. Les insectes constituent aussi des sources présumées mais cette hypothèse n'est pas encore démontrée sur le terrain ni même au laboratoire. D'autres sources potentielles doivent encore être étudiées, par exemple parmi les espèces aquatiques. Un certain nombre de facteurs de risque environnementaux, anthropiques et écologiques ont été proposés pour expliquer la transmission entre espèces et la propagation du virus. En ce qui concerne le foyer survenu en Afrique de l'Ouest, sans précédent par son ampleur et par son étendue géographique, la source de la transmission demeure inconnue bien qu'une corrélation ait été observée entre le cas index présumé et la présence d'une colonie de chauves-souris insectivores. Dans pratiquement tous les événements dus au virus Ebola (et l'épidémie en Afrique de l'Ouest ne fait pas exception), l'origine de la transmission n'a guère fait l'objet d'investigations approfondies. Pour que les risques à l'interface humains­ animaux­environnement puissent être traités selon la méthode Une seule santé, les auteurs estiment indispensable d'élucider au préalable les facteurs de transmission qui ont pu intervenir lors des épidémies dues au virus Ebola-Zaïre, en plus des enquêtes à effectuer entre deux épidémies et dans un environnement péridomestique. Nous ignorons encore quelle est la prévalence réelle de l'infection par le virus EbolaZaïre chez les chauves-souris, toutes espèces confondues. Il est peu probable que des enquêtes à grande échelle, onéreuses et basées sur des échantillons non aléatoires constitués d'un faible nombre d'individus par espèce parviennent à identifier les réservoirs du virus Ebola ou à améliorer nos connaissances sur son épidémiologie.

La ecología natural de la infección por el virus del Ebola sigue siendo enigmática. No hay especie en la que esté probada una clara función de reservorio, aunque existen datos demostrativos de infección en muy diversos mamíferos, como el ser humano, primates no humanos, ungulados domésticos y silvestres y varias especies de murciélago, tanto frugívoras como insectívoras. El ser humano y la mayoría de las especies estudiadas parecen ser hospedadores no preferentes y padecer la enfermedad, con la única excepción de los murciélagos, que a tenor de ciertos estudios de laboratorio son tolerantes a la infección. En estos animales, algunas investigaciones realizadas sobre el terreno muestran una baja prevalencia de anticuerpos contra cepas de la especie Zaire del virus durante los brotes de infección en el hombre y en los periodos interepidémicos, y se considera probable que este orden de mamíferos sea el reservorio del virus. Se presume que otra fuente podrían ser los insectos, pero ni los datos de laboratorio ni los obtenidos sobre el terreno avalan por ahora tal hipótesis. Además, aún hay otras posibles fuentes por estudiar, como ciertas especies acuáticas. Con respecto a la extensión secundaria y la propagación del virus se han apuntado una serie de posibles factores de riesgo de índole ambiental o ecológica o ligados al comportamiento humano. En el caso del brote habido en África Occidental, que revistió una escala y un alcance geográfico sin precedentes, no se ha demostrado aún cuál fue la fuente de la extensión secundaria, aunque existe una relación entre el caso índice propuesto y una colonia de murciélagos insectívoros. En casi todos los episodios de enfermedad por el virus del Ebola la extensión secundaria se ha investigado solo de forma superficial, como también fue el caso de la epidemia de África Occidental. Los autores sugieren que, para abordar los riesgos existentes en la interfaz del ser humano, los animales y el medio ambiente en clave de Una sola salud, es preciso investigar más a fondo los factores que inducen la extensión secundaria durante una epidemia del virus Zaire del Ebola, además de efectuar estudios del medio peridoméstico en las fases interepidémicas. En ninguna especie de murciélago se conoce aún la verdadera prevalencia de la infección por el virus Zaire. Es poco probable que la realización de onerosos estudios no aleatorizados a gran escala, con la obtención de un pequeño número de muestras por especie, depare indicios sólidos en cuanto a los reservorios del virus del Ebola o nos sirva para entender mejor su epidemiología.

Vertebrate reservoirs and secondary epidemiological cycles of vector-borne diseases.

Vector-borne diseases of importance to human and domestic animal health are listed and the increasing emergence of syndromes, new epidemiological cycles and distributions are highlighted. These diseases involve a multitude of vectors and hosts, frequently for the same pathogen, and involve natural enzootic cycles, wild reservoirs and secondary epidemiological cycles, sometimes affecting humans and domestic animals. On occasions the main reservoir is in the domestic environment. Drivers for secondary cycles are mainly related to human impacts and activities and therefore, for purposes of prevention and control, the focus needs to be on the socioecology of the diseases. Technical and therapeutical solutions exist, and for control there needs to be a clear understanding of the main vertebrate hosts or reservoirs and the main vectors. The targets of interventions are usually the vector and/or secondary epidemiological cycles and, in the case of humans and domestic animals, the spillover or incidental hosts are treated. More attention needs to be given to the importance of the political economy in relation to vector-borne diseases, as many key drivers arise from globalisation, climate change and changes in structural ecologies. Attention to reducing the risk of emergence of new infection cycles through better management of the human-animal-environment interface is urgently needed.

Detection and Genetic Characterization of Lineage IV Peste Des Petits Ruminant Virus in Kazakhstan.

Peste des petits ruminant (PPR) is endemic in many Asian countries with expansion of the range in recent years including across China during 2013-2014 (OIE, 2014). Till the end of 2014, no cases of PPR virus (PPRV) were officially reported to the Office Internationale des Epizooties (OIE) from Kazakhstan. This study describes for the first time clinicopathological, epidemiological and genetic characterization of PPRV in 3 farm level outbreaks reported for the first time in Zhambyl region (oblast), southern Kazakhstan. Phylogenetic analysis based on partial N gene sequence data confirms the lineage IV PPRV circulation, similar to the virus that recently circulated in China. The isolated viruses are 99.5-99.7% identical to the PPRV isolated in 2014 from Heilongjiang Province in China and therefore providing evidence of transboundary spread of PPRV. There is a risk of further maintenance of virus in young stock despite vaccination of adult sheep and goats, along livestock trade and pastoral routes, threatening both small livestock and endangered susceptible wildlife populations throughout Kazakhstan.

Will the damage be done before we feel the heat? Infectious disease emergence and human response.

The global political economy is facing extreme challenges against a backdrop of large-scale expansion of human and domestic animal populations and related impacts on the biosphere. Significant global socio-ecological changes have occurred in the period of a single lifetime, driven by increased technology and access to physical and biological resources through open markets and globalization. Current resource consumption rates are not sustainable and ecological tipping points are being reached and one of the indicators of these may be a changing balance between hosts and pathogens. A period of extraordinary progress in reducing infection risk and disease impact on humans and domestic animals in the 20th Century is reversing in the 21st, but not always and not everywhere. Drivers for this shift are discussed in terms of demographics, agroecology, biodiversity decline and loss of resilience in ecosystems, climate change and increasing interconnectedness between species globally. Causality of disease emergence remains highly speculative, but patterns and data are emerging to commend a precautionary approach, while reassessing our global political, social and economic systems.

The role of wildlife in transboundary animal diseases.

This paper identifies some of the more important diseases at the wildlife-livestock interface and the role wildlife plays in disease transmission. Domestic livestock, wildlife and humans share many similar pathogens. Pathogens of wild or domestic animal origin that can cause infections in humans are known as zoonotic organisms and the converse are termed as anthroponotic organisms. Seventy-seven percent of livestock pathogens and 91% of domestic carnivore pathogens are known to infect multiple hosts, including wildlife. Understanding this group of pathogens is critical to public health safety, because they infect a wide range of hosts and are most likely to emerge as novel causes of infection in humans and domestic animals. Diseases at the wildlife-livestock interface, particularly those that are zoonotic, must be an area of focus for public health programs and surveillance for emerging infectious diseases. Additionally, understanding wildlife and their role is a vital part of understanding the epidemiology and ecology of diseases. To do this, a multi-faceted approach combining capacity building and training, wildlife disease surveillance, wildlife-livestock interface and disease ecology studies, data and information sharing and outbreak investigation are needed.

Disease risks associated with the translocation of wildlife.

Translocation is defined as the human-managed movement of living organisms from one area for free release in another. Throughout the world, increasing numbers of animals are translocated every year. Most of these movements involve native mammals, birds and fish, and are made by private and national wildlife agencies to augment existing populations, usually for sporting purposes. The translocation of endangered species, often to reintroduce them into a part of the historical range from which they have been extirpated, has also become an important conservation technique. The main growth in reintroduction projects over the last decade has involved smaller animals, including amphibians, insects and reptiles. The success of potentially expensive, high-profile wildlife translocation projects depends to a large extent on the care with which wildlife biologists and their veterinary advisers evaluate the suitability of the animals and chosen release site, and on the ability of the translocated animals to colonise the area. The veterinary aspects of reintroduction projects are of extreme importance. There are instances of inadequate disease risk assessment resulting in expensive failures and, worse still, the introduction of destructive pathogens into naïve resident wildlife populations. In this paper, some of the disease risks attending wildlife translocation are described. Risk assessment, involving the examination of founder and recipient populations and their habitats, is now a pre-requisite of managed movements of animals.

Re-infection of wildlife populations with rinderpest virus on the periphery of the Somali ecosystem in East Africa.

We report surveillance for rinderpest virus in wildlife populations in three major ecosystems of East Africa: Great Rift Valley, Somali and Tsavo from 1994 to 2003. Three hundred and eighty wild animals were sampled for detection of rinderpest virus, antigen or genome and 1133 sampled for antibody in sera from Kenya, Uganda, Ethiopia and Tanzania from 20 species. This was done modifying for wildlife the internationally recommended standards for rinderpest investigation and diagnosis in livestock. The animals were selected according to susceptibility and preference given to gregarious species, and populations were selected according to abundance, availability and association with livestock. Rinderpest virus, antigen and/or genome were detected in Kenya; within Tsavo, Nairobi and Meru National Parks. Serological results from 864 animals (of which 65% were buffalo) from the region were selected as unequivocal; showing the temporal and spatial aspects of past epidemics. Recent infection has been only in or peripheral to the Somali ecosystem (in Kenya). Our evidence supports the hypothesis that wildlife is not important in the long-term maintenance of rinderpest and that wildlife are infected sporadically most likely from a cattle source, although this needs to be proven in the Somali ecosystem. Wildlife will continue to be a key to monitoring the remaining virus circulation in Africa.

Infectious animal diseases: the wildlife/livestock interface.

The long-standing conflict between livestock owners and animal health authorities on the one hand, and wildlife conservationists on the other, is largely based on differing attitudes to controlling diseases of livestock which are associated with wildlife. The authors have attempted to highlight the fact that these disease problems are frequently bi-directional at the wildlife/livestock interface. The different categories of diseases involved are presented. A new dimension being faced by veterinary regulatory authorities is the spectre of emerging sylvatic foci of diseases, such as bovine tuberculosis, bovine brucellosis and possibly rinderpest; these diseases threaten to undermine national and international eradication schemes, which have been implemented and executed with significant success, and at great cost. Conversely, wildlife-based ecotourism world-wide has expanded rapidly over the past decade and is the source of lacking foreign revenue for many developing countries. Traditional subsistence farming is still the largest source of much-needed protein on some continents and this, together with the growth and hunger of historically disadvantaged communities for land, is forcing enterprises and communities with markedly different objectives and land-use practices to operate effectively in close proximity. Some land-users rely exclusively on wildlife, others on livestock and/or agronomy, while yet others need to combine these activities. The net result may be an expansion or intensification of the interface between wildlife and domestic livestock, which will require innovative control strategies that permit differing types of wildlife/livestock interaction, and that do not threaten the land-use options of neighbours, or the ability of a country to market animals and animal products profitably.

Scabies in free-ranging mountain gorillas (Gorilla beringei beringei) in Bwindi Impenetrable National Park, Uganda.

Between August and December 1996, there was an outbreak of a debilitating skin disease attributed to Sarcoptes scabiei infection in mountain gorillas (Gorilla beningei beringei) in Bwindi Impenetrable National Park in Uganda. All four members of a gorilla group which had been habituated to tourists were clinically affected; the infant male gorilla was most severely affected and died, the juvenile male showed serious manifestations of the disease and the two adult animals showed milder signs. The three older animals recovered after a single intramuscular dose of ivermectin. S scabiei mites were observed on skin scrapings and biopsies taken while the juvenile was immobilised and in postmortem samples taken from the infant. The clinical signs did not recur during the following year, and no other gorilla groups in the park were observed to be clinically affected.

Rinderpest epidemic in wild ruminants in Kenya 1993-97.

A severe epidemic of rinderpest, affecting mainly wild ruminants, occurred between 1993 and 1997 in East Africa. Buffalo (Syncerus caffer), eland (Taurotragus oryx) and lesser kudu (Tragelaphus imberbis) were highly susceptible. The histopathological changes, notably individual epithelial cell necrosis with syncytia formation, were consistent with an infection with an epitheliotrophic virus. Serology, the polymerase chain reaction, and virus isolation confirmed the diagnosis and provided epidemiological information. The virus was related to a strain which was prevalent in Kenya in the 1960s, of a second lineage (II), and distinct from isolations of rinderpest virus in the region since 1986. The source of the virus was presumed to be infected cattle from the Eastern region of Kenya and Somalia. The pathogenicity of the virus varied during the epidemic. The mortality in buffalo populations was estimated to be up to 80 per cent, and population data suggested that the virus had an adverse effect on a wide range of species. The virus caused only a mild disease in cattle, with minimal mortality. The results confirmed the importance of wildlife as sentinels of the disease, but although wildlife were important in the spread of the virus, they did not appear to act as reservoirs of infection.

Effects of translocation on hematologic parameters of free-ranging black rhinoceros (Diceros bicornis michaeli) in Kenya.

Management of the endangered black rhinoceros (Diceros bicornis michaeli) in Africa frequently involves translocation. These procedures are not without risk, and protocols must be critically examined. Hematologic analyses can be used to evaluate the effects of translocation on animal health. Hematologic data obtained during routine translocation of free ranging black rhinoceros (n = 74) in Kenya between 1991 and 1995 were examined, and subsets of data from rhinoceros (n = 43) that were translocated to different regions of Kenya were compared. All animals showed an increase in total blood protein. Animals transported for longer periods and to lower altitude zones with higher ambient temperatures and trypanosomiasis developed anemia and showed neutrophilia, lymphopenia (males), and eosinopenia. The changes in packed cell volume (PCV), hemaglobin, and neutrophils were more marked in females, and the PCV drop was more significant in subadults. The red cell changes were most probably pathologic, involving the loss of red cells from circulation through sequestration or hemorrhage. The changes in white cell parameters are consistent with the effect of endogenous corticosteroids as a result of stress. Transport and confinement stress might lead to gastric ulceration with hemorrhage. In many animals, exposure to trypanosomes contributes to anemia.

Mycobacterium avium-related epizootic in free-ranging lesser flamingos in Kenya.

An epizootic in free-ranging lesser flamingos (Phoeniconaias minor) in Kenya resulted in more than 18,500 deaths from August through mid-November 1993. Disease was concentrated along the shores of Rift Valley Lakes Bogoria and Nakuru (Kenya) and did not involve any of the other avian or mammalian species frequenting the lakes. Coincidental to the outbreak was a bloom of algae on Lake Bogoria, toxins from which were first suspected to be causative. Discrete necrotic and granulomatous lesions were often noted in spleen and liver, and Mycobacterium avium serovar I was isolated from both organs. Escherichia coli and Pseudomonas aeruginosa also were often recovered in pure culture from liver. Gross and histopathological evaluation of the cases disclosed signs of acute sepsis and also chronic, potentially life-threatening lesions of mycobacteriosis, primarily involving the spleen and liver. Lesions typical for algae toxicosis were not seen in any birds. Deaths were attributed to septicemia complicated in those affected, by mycobacteriosis.

Diploid chromosome number and chromosomal variation in the white rhinoceros (Ceratotherium simum).

Chromosomal studies were conducted on 38 white rhinoceroses representing both the northern and southern subspecies and one subspecies hybrid. Improvements in tissue culture methods and harvesting techniques have made it possible to obtain a highly repeatable diploid number of 82 chromosomes for both subspecies. Comparison of G-banded karyotypes from the two subspecies failed to indicate a difference in banding pattern, but did reveal size polymorphisms involving short arm additions in five individuals. Chromosomal polymorphism, resulting in three individuals with a diploid number of 2n = 81, was noted in northern white rhinoceroses.

Haematological changes in domestic fowl (Gallus gallus) and cranes (Gruiformes) with Mycobacterium avium infection.

Haematological findings in 26 domestic fowl and 17 cranes with confirmed Mycobacterium avium infection were compared with normal values from the species concerned. Heterophils and monocytosis occurred frequently in the infected birds; in many cases very large numbers of these cells were present. Haematological findings were related, where possible, to the results of the intradermal tuberculin test and the haemagglutination test. It was concluded that haematological testing has a useful role in both diagnosis and screening for avian TB infections in the species studied.

Haematology of clinically normal and sick captive reindeer (Rangifer tarandus).

A retrospective analysis of haematological values from clinically normal captive reindeer (Rangifer tarandus) showed that the red cell count, haemoglobin level, packed cell volume and lymphocyte count were higher and the erythrocyte sedimentation rate and eosinophil count were lower in juveniles than in adults. Newborn animals were anaemic compared with juveniles and adults and had high reticulocyte counts. The values from healthy reindeer were used to identify abnormal haematological variations in a number of sick animals. It was shown that reindeer exhibit similar haemopathological responses to those of other artiodactyla, with increases in the erythrocyte sedimentation rate and fibrinogen level being of particular diagnostic significance. Eosinophilia was the only abnormal haematological finding in individuals with subclinical infections of intestinal parasites.

Observations on the treatment of necrobacillosis in wallabies.

Clinical experience of 73 cases of necrobacillosis in red-necked wallabies (Macropus rufogriseus) over a 6-year period is reviewed. Diagnostic methods and the medical and surgical treatment options are detailed. It is suggested that survival curves are necessary to assess the outcome of treatment.

Physiological effects of etorphine, acepromazine and xylazine in the scimitar horned oryx (Oryx dammah).

Scimitar horned oryx (Oryx dammah), kept under confined and unconfined conditions were immobilised with etorphine in combination with acepromazine or xylazine or both, and with xylazine alone. Both groups of animals were successfully sedated with etorphine and xylzine, with or without acepromazine, although hypothermia and mild hypoxaemia and a fall in packed cell volume were frequently noted. Xylazine alone produced a dose dependent degree of sedation in semitame subadult animals kept in confinement, but only slight depression in their wild, unconfined counterparts. If xylazine was not included in the immobilising mixture induction was traumatic and full sedation not achieved. Heart rates and arterial pressures (systemic and pulmonary) were also monitored but no remarkable changes were noted. The only abnormalities in blood biochemistry were raised aspartate transminase and creatine kinase. Ruminal regurgitation could be a major problem if endotracheal intubation was not achieved early in the procedure.