The last three decades have seen an alarming number of high-profile outbreaks of new viruses and other pathogens, many of them emerging from wildlife. Recent outbreaks of SARS, avian influenza, and others highlight emerging zoonotic diseases as one of the key threats to global health. Similar emerging diseases have been reported in wildlife populations, resulting in mass mortalities, population declines, and even extinctions. In this paper, we highlight three examples of emerging pathogens: Nipah and Hendra virus, which emerged in Malaysia and Australia in the 1990s respectively, with recent outbreaks caused by similar viruses in India in 2000 and Bangladesh in 2004; West Nile virus, which emerged in the New World in 1999; and amphibian chytridiomycosis, which has emerged globally as a threat to amphibian populations and a major cause of amphibian population declines. We discuss a new, conservation medicine approach to emerging diseases that integrates veterinary, medical, ecologic, and other sciences in interdisciplinary teams. These teams investigate the causes of emergence, analyze the underlying drivers, and attempt to define common rules governing emergence for human, wildlife, and plant EIDs. The ultimate goal is a risk analysis that allows us to predict future emergence of known and unknown pathogens.
The Nipah virus was discovered twenty years ago, and there is considerable information available regarding the specificities surrounding this virus such as transmission, pathogenesis and genome. Belonging to the Henipavirus genus, this virus can cause fever, encephalitis and respiratory disorders. The first cases were reported in Malaysia and Singapore in 1998, when affected individuals presented with severe febrile encephalitis. Since then, much has been identified about this virus. These single-stranded RNA viruses gain entry into target cells via a process known as macropinocytosis. The viral genome is released into the cell cytoplasm via a cascade of processes that involves conformational changes in G and F proteins which allow for attachment of the viral membrane to the cell membrane. In addition to this, the natural reservoirs of this virus have been identified to be fruit bats from the genus Pteropus. Five of the 14 species of bats in Malaysia have been identified as carriers, and this virus affects horses, cats, dogs, pigs and humans. Various mechanisms of transmission have been proposed such as contamination of date palm saps by bat feces and saliva, nosocomial and human-to-human transmissions. Physical contact was identified as the strongest risk factor for developing an infection in the 2004 Faridpur outbreak. Geographically, the virus seems to favor the Indian sub-continent, Indonesia, Southeast Asia, Pakistan, southern China, northern Australia and the Philippines, as demonstrated by the multiple outbreaks in 2001, 2004, 2007, 2012 in Bangladesh, India and Pakistan as well as the initial outbreaks in Malaysia and Singapore. Multiple routes of the viremic spread in the human body have been identified such as the central nervous system (CNS) and respiratory system, while virus levels in the body remain low, detection in the cerebrospinal fluid is comparatively high. The virus follows an incubation period of 4 days to 2 weeks which is followed by the development of symptoms. The primary clinical signs include fever, headache, vomiting and dizziness, while the characteristic symptoms consist of segmental myoclonus, tachycardia, areflexia, hypotonia, abnormal pupillary reflexes and hypertension. The serum neutralization test (SNT) is the gold standard of diagnosis followed by ELISA if SNT cannot be carried out. On the other hand, treatment is supportive since there a lack of effective pharmacological therapy and only one equine vaccine is currently licensed for use. Prevention of outbreaks seems to be a more viable approach until specific therapeutic strategies are devised.