Tuesday, July 17, 2018

Nipah Transmission In Kerala Outbreak

Credit CDC


The Nipah virus, first identified in 1999 after hundreds of abattoir workers in Malaysia and Singapore were infected by pigs carrying the virus (see MMWR Update: Outbreak of Nipah Virus -- Malaysia and Singapore, 1999), has been on our watch list for nearly two decades.
Carried asymptomatically by fruit bats that range across South East Asia and the Indian Ocean region - Nipah, (and its Australian cousin Hendra) - can occasionally spill over into humans, horses, pigs, and presumably other mammals. 

While outbreaks of Nipah since 1999 have been relatively small, widely scattered, and mostly reported out of Bangladesh - last May the Indian Government announced their third NiV outbreak since 2001, with the last one in 2007.
Human-to-human transmission - primarily in households and in hospital settings - has been frequently reported with the Nipah virus, but is generally described as `limited'.
Last night CIDRAP News carried a brief report (see Nipah outbreak report details hospital transmission patterns) on the apparently robust human-to-human transmission of the virus in this 19-person outbreak. 
News Scan for Jul 16, 2018

Nipah outbreak report details hospital transmission patterns

A report summing up all the investigation findings in India's Nipah virus outbreak says 17 of 19 patients appear to have contracted the virus from the index patient, a 26-year-old man, Press Trust of India (PTI) reported yesterday, citing findings released by health officials from Kerala state.

The people exposed to the first patient included 3 family members, 4 people at the first hospital that treated him, and 10 at a medical college hospital where he was taken for a computed tomography scan. One patient was infected by another patient at the first hospital.

People infected at the first hospital included the man's sister, who helped care for him. Though the man was at the second hospital for only 1 day, he passed the virus to 10 people.
(Continue . . . )

The good news in all of this is that most of the H-2-H transmission appears to be from the index patient to others, while only one secondary transmission (patient to patient) was documented.
As we've discussed previously (see Two MERS-CoV Hospital Super Spreading Studies), some patients shed more virus than others, and are therefore more able to infect others. 
Additionally, the index patient in an outbreak isn't usually identified as being highly infectious right away, so initial infection control procedures may be lax.  Once additional cases show up, they tend to be isolated more quickly, limiting their ability to further spread the virus.

The concern is, that the Nipah virus already has two of the three qualities we look for in an emerging pandemic threat.  It can jump fairly easily to humans, and it has a very high (75%) mortality rate. 
All it lacks is the ability to transmit H-2-H efficiently, and in a sustained manner.  And like MERS-CoV, and Ebola, and (to a lesser extent) Avian flu, it is part way there.
In the 2013 paper The pandemic potential of Nipah virus by Stephen P. Luby, the author writes (bolding mine):
Characteristics of Nipah virus that increase its risk of becoming a global pandemic include: humans are already susceptible; many strains are capable of limited person-to-person transmission; as an RNA virus, it has an exceptionally high rate of mutation: and that if a human-adapted strain were to infect communities in South Asia, high population densities and global interconnectedness would rapidly spread the infection.
Two weeks ago, in IJID: Enhancing Preparation For Large Nipah Outbreaks Beyond Bangladesh, we looked at a new open-access article that appeared in the International Journal of Infectious Diseases, that discussed the potential of the Nipah virus producing a large urban epidemic, similar to what we saw in West Africa with Ebola in 2014.

And the Nipah virus is on the short list of select agents considered to have significant bio-terrorism applications (see National Academy Of Sciences: Biodefense in the Age of Synthetic Biology).

While novel influenza - because of its mutability, transmissibility, and impressive track record  - remains the pandemic threat that keeps most scientists up at night, it is far from the only threat.
The next pandemic could also come from a bat coronavirus, a mutation in the Monkeypox virus, an exotic hemorrhagic fever, or from something completely out of left field. 
All reasons why pandemic preparedness needs to become a year-round national priority, not just something we think about during severe flu seasons or during the centenary of a particularly bad global epidemic.

For more on the challenges posed by the next pandemic, you may wish to revisit:

The Challenge Of Promoting Pandemic Preparedness

Pandemic Unpreparedness Revisited
Smithsonian Livestream: “The Next Pandemic: Are We Prepared?"
World Bank: World Ill-Prepared For A Pandemic

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