I’ve been really interested in Nipah over this past quarter and over Thanksgiving Dr. Luby was kind enough to entertain my questions. Steve Luby is cited in virtually every single paper on Nipah in Bangladesh and I’m really glad I got the chance to talk with him.
One question I had about Nipah is how to best understand the differences between the Malaysian and Bangladesh outbreaks. Nipah first came to the world’s attention in an outbreak in commercial pig farmers in Malaysia in 1998. The disease spread from there to Singapore. Nipah outbreaks have occurred every year in Bangladesh beginning in 2001. The Nipah in Bangladesh and neighboring West Bengal have been characterized by higher rates of respiratory disease, higher mortality rates, and human-to-human transmission. Date palm sap has been implicated as an important route of virus transmission from Pteropus fruit bats to humans.
Dr. Luby had a number of really insightful things to say about the disease. He said that it’s possible that the Malaysian outbreak was just a more mild strain. However, he thought that the differences more likely have to do with differences in supportive care and the viral dose. Bangladesh has a much poorer health care system than Malaysia. Only one or two patients have been intubated in Bangladesh despite the severity of the disease. This could easily explain the higher mortality rates in Bangladesh. Additionally, in animal studies, animals given a larger dose are more likely to develop pneumonia. People drinking date palm sap contaminated with bat feces or saliva may have been exposed to higher doses of virus.
Interestingly despite human-to-human transmission of Nipah in Bangladesh, there haven’t been any nosocomial cases. Dr. Luby highlighted how crowded government hospitals are and that family members usually do most of the care, which would explain why health workers aren’t getting sick. Ironically, hospitals are a place where disease can easily spread.
I also wondered why Nipah has just recently become a problem. Rather than attribute the disease outbreak to a change in bat ecology, Dr. Luby thought that this was more likely a reporting issue. For example, people in Faridpur previously thought that Nipah was an outbreak of avian influenza. Bangladesh has just put in good surveillance for outbreak and response and there still isn’t surveillance in place in West Bengal, India. Luby thinks that it is likely that this zoonotic spillover has been happening for centuries. We just recently have the diagnostic tools and the surveillance in place to find it.