While infectious disease headlines are rightly focusing attention on the current Ebola outbreak in the DRC, those with an eye to how pandemics unfold are watching a less prominent one unfold in India. A Nipah virus outbreak, centered in the Indian state of Kerala, was first reported last month and has killed 17 of the 18 people it has infected -- a horrific fatality rate that hovers around 75%.
Nipah is not an unknown virus as it has been responsible for sporadic deadly outbreaks since the 1990s in countries such as Singapore, Malaysia and Bangladesh. It has also appeared in India before. It is actually a priority virus when it comes to vaccine development. The virus is zoonotic and spills from fruit bats (the natural host) to pigs and humans. Humans can be infected by direct contact with bats, by consuming date palm sap contaminated with bat urine, by pigs, and by other humans. The virus causes flu like symptoms that can progress to a fulminant infection of the brain (encephalitis). There are no standard treatments for it though the antiviral ribavirin may have some positive impact.
When it comes to pandemic pathogens, as my colleagues and I argued in our recently released report, RNA viruses (because of their mutability) and respiratory-borne microbes rise to the top of the list. Nipah is a paramyxovirus and, as such, has an RNA genome. Though early outbreaks of the disease did not revolve around respiratory transmission between humans, subsequent outbreaks have been augmented by human-to-human transmission, especially to those caring for patients who were likely exposed to oral and respiratory secretions known to harbor the virus. It appears that the current Indian outbreak has been enhanced by human-to-human transmission after originating from exposure to bats.
The major fear is that Nipah might become more efficient at transmitting from human-to-human and cause a large outbreak that spreads to multiple countries (the fictional virus in the movie Contagion was a Nipah-like agent). Such a scenario would rapidly become difficult to contain as there is no vaccine and no standard antiviral regimen. Currently, Nipah transmits only inefficiently between humans (about 1 in 12 pass it on to another human).
While the not-so-contagious Ebola may grab headlines like no other infectious disease, and this NIpah outbreak has not been deemed a global threat, ultimately, it is viruses with the potential for respiratory spread that merit the most attention. While this outbreak will likely be contained, it underscores the danger of this class of microorganisms, the need to understand their evolution, track their transmission, and to be prepared for their appearance with robust countermeasures.
