Photo by Chi Liu
For many infectious disease watchers, Nipah virus (NIV) holds a certain fascination. Identified only 14 years ago, this bat-borne virus produces deadly, albeit small, outbreaks of disease each year between December and May in Bangladesh.
The primary route of infection in Bangladesh is linked to the consumption of of raw (uncooked) date palm juice - which is `tapped’ from cuts in trees much in the same way as maple trees are for their syrup.
But human-to-human transmission has been reported as well, along with infection from intermediate hosts.
In 1999, hundreds of abattoir workers in Malaysia and Singapore were infected from pigs carrying the virus (see MMWR Update: Outbreak of Nipah Virus -- Malaysia and Singapore, 1999) killing more than 100.
And once infected, humans can transmit the virus on to others, albeit not terribly efficiently (see EID Journal Person-to-Person Transmission of Nipah Virus in a Bangladeshi Community).
Nipah (and its Australian cousin Hendra, discovered in 1994) are sufficiently different from other members of the Paramyxoviridae family to have led to the creation of a new genus; Henipavirus.
As you will see, victims are predominantly male, and the CFR (Case Fatality Ratio) is nearly 90%.
Nipah Infection in 2013
12 March 2013: 19 Nipah cases were identified among them 17died (mortality rate 89%);. These cases are from 13 districts (Gaibandha, Natore, Rajshahi, Naogaon, Rajbari, Pabna, Jhenaidah, Mymensingh, Nilphamari, Chittagong, Kurigram, Kustia). Age distribution of cases are 8 months to 55 years among them 13 are male and 6 are Female.
Human Nipah virus (NiV) infection, an emerging zoonotic disease, was first recognized in a large outbreak of 276 reported cases in Malaysia and Singapore from September 1998 through May 1999.
NiV is a highly pathogenic paramyxovirus belonging to genus Henipavirus. It is an enveloped RNA virus.
The median incubation period of the secondary cases who had a single exposure to Nipah case was nine days (range 6–11 days) but exposure to onset of illness varies from 6-16 days. The median incubation period following single intake of raw date palm sap to onset of illness is 7 days (range: 2-12 days) in Bangladesh.
- Drinking of raw date palm sap (kancha khejurer rosh) contaminated with NiV
- Close physical contact with Nipah infected patients
Nipah surveillance began in 2006, Institute of Epidemiology, Disease Control and Research (IEDCR) in collaboration with ICDDR,B established Nipah surveillance in 10 District level Government hospitals of the country where Nipah outbreaks had been identified. Presently surveillance system is functioning in five hospitals of Nipah Belt.
While as many as half of all Nipah infections reported in Bangladesh appear to be secondary infections (due to close contact with someone already infected) the virus has not managed to spark an epidemic.
The caveat being that viruses – particularly singled-stranded RNA viruses like Nipah (along with influenzas, hantaviruses, filoviruses, and others) -are known for their ability to mutate.
When Steven Soderbergh made his pandemic thriller `Contagion’ a couple of years ago, technical advisor Professor Ian Lipkin created fictional MEV-1 virus based on a mutated Nipah virus (see The Scientific Plausibility of `Contagion’).
While the Nipah virus continues to produce only small, limited outbreaks, we watch these developments closely each year for any signs of change.