Date Palm Sap Collection – Credit FAO
# 6904
The history of emerging infectious diseases in recent decades has increasingly implicated bats as significant reservoirs of potentially dangerous zoonotic pathogens.
While long known for carrying the most dreaded of viruses – rabies – during the 1990s we learned that certain types of bats were also natural hosts of both Nipah and Hendra, henipaviruses in the family Paramyxoviridae.
In recent years Marburg virus has been isolated in Egyptian Fruit bats in Kenya, and antibodies to Ebola viruses have been found in bats in both Africa and Asia (see EID Journal: Ebola Virus Antibodies From Bats In Bangladesh.
In 2003 the SARS epidemic – caused by a novel coronavirus which was initially linked to Civits, but later linked to bats, emerged (see EID Journal Review of Bats and SARS).
In 2012, for the first time a `bat influenza virus’ was discovered (see A New Flu Comes Up To Bat), and the newly detected novel coronavirus from the Middle East - EMC/2012 – has been tentatively linked to bats as well (see EID Journal: EMC/2012–related Coronaviruses in Bats).
Bats are abundant, geographically widespread, and able to move over long distances – and according to the Bat Conservation Trust - there are more than 1,000 types of bats, which make up roughly 1/5th of all mammalian species.
All things considered, Chiroptology (the study of bats) among infectious disease investigators has never been more in vogue.
Since we’ve already seen one major epidemic spring from bats – bat coronaviruses are closely monitored - but the Nipah virus, which has demonstrated a limited ability to transmit from human-to-human, keeps a lot of researchers up at night as well.
Since it was first identified in Malaysia in 1998, most of the outbreaks have been centered around Bangladesh.
Epidemiological investigations have fingered the consumption 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 – as the virus’s primary route into the human population.
Fruit bats of the Pteropodidae family are the reservoir host for the virus, and usually carry it asymptomatically. Roosting in trees rather than caves, they can easily contaminate the date juice collection jars with their virus laden urine and feces.
From there the virus can jump into unwary imbibers of the beverage. But it isn’t necessarily a dead end infection for Nipah, as humans can spread the virus amongst themselves as well (see EID Journal Person-to-Person Transmission of Nipah Virus in a Bangladeshi Community).
Collection of date palm juice is a seasonal activity (December - May) in Bangladesh, so that time period also defines their Nipah season as well.
Last Sunday, in Bangladesh: Nipah Returns, we looked at a fresh outbreak that had infected 8, and killed 6 in recent weeks.
Today, an update from Bangladesh’s Institute of Epidemiology Diseases Control and Research (IEDCR) which raises the total number of infections (as of Jan 30th) to 11, with 8 deaths.
Situation Update:
30th January 2013: 11 Nipah cases were identified among them 8 died (mortality rate 73%); 3 cases are still under treatment. These cases are from 8 districts (Gaibandha, Natore, Rajshahi, Naogaon, Rajbari, Pabna, Jhenaidah, Mymensingh). Age distribution of cases are 8 months to 43 years among them 8 are male.
Till January 30, 2013, a total of 176 human cases of Nipah infection in Bangladesh were recognized from outbreak among them 136 (77%) died.
Nipah
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.
Agent
NiV is a highly pathogenic paramyxovirus belonging
to genus Henipavirus. It is an enveloped RNA virus.
Incubation period
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.
Transmission:
- Drinking of raw date palm sap (kancha khejurer rosh) contaminated with NiV
- Close physical contact with Nipah infected patients
Surveillance
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.
So far, while roughly half of all Nipah infections in Bangladesh appear to be secondary infections (due to close contact with someone already infected) the virus has not managed to spark an epidemic.
But viruses – particularly singled-stranded RNA viruses like Nipah (along with influenzas, hantaviruses, filoviruses, and others) can mutate at exceptionally high rates, and so what we can say is true about them today may not hold true tomorrow.
For more on bats, and bat-hosted viruses, you may wish to revisit:
Disease Transmission At The Human-Animal Interface
