Really bad news.
Nipah emerged as a recognizable zoonotic threat in Malaysia in 1998 when it spread from bat to pigs – and then from pigs to humans – eventually infecting at least 265 people, and killing 105 (see Lessons from the Nipah virus outbreak in Malaysia).
Since then, we’ve seen a few dozen outbreaks in India, Pakistan, and most commonly, Bangladesh, but it is likely that additional individual infections and/or outbreaks have gone undetected.
As the CDC map above indicates, the range of fruit bats of the Pteropodidae family – the natural host of Henipaviruses (Nipah & Hendra) – extends from Australia, to China, and across the Indian Ocean to Africa.
While old world fruit bats have been pegged as the natural host for Nipah (and for its less well known Australian cousin Hendra), that family encompasses scores of species, and other types of bats may also be carriers.
In addition to bats and humans – other mammals have been infected in the wild (horses, pigs, and dogs) – and many others have been experimentally infected in the lab (including guinea pigs, hamsters, ferrets, squirrel monkeys, and African green monkeys).
In the 2013 paper The pandemic potential of Nipah virus by Stephen P. Luby, the author wrote (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.
All of which means that the more we can learn about the host range, ecology, and pathogenicity of these Henipaviruses, the more likely we are to be able to prevent, or at least contain, larger outbreaks in the future.
To this end, the January 2020 issue of the CDC’s EID Journal provides us with detailed look at Nipah Virus (NiV) isolate collected in 2003 from Cambodia; a country that has yet to report human infection.
This is a lengthy, detailed, report and so I’ve only post the abstract and some excerpts from the discussion. Follow the link to read it in its entirety. I’ll have a postscript when you return.
High Pathogenicity of Nipah Virus from Pteropus lylei Fruit Bats, Cambodia
Maria Gaudino, Noémie Aurine, Claire Dumont, Julien Fouret, Marion Ferren, Cyrille Mathieu, Olivier Reynard, Viktor E. Volchkov, Catherine Legras-Lachuer, Marie-Claude Georges-Courbot, and Branka Horvat
We conducted an in-depth characterization of the Nipah virus (NiV) isolate previously obtained from a Pteropus lylei bat in Cambodia in 2003 (CSUR381). We performed full-genome sequencing and phylogenetic analyses and confirmed CSUR381 is part of the NiV-Malaysia genotype.
In vitro studies revealed similar cell permissiveness and replication of CSUR381 (compared with 2 other NiV isolates) in both bat and human cell lines. Sequence alignments indicated conservation of the ephrin-B2 and ephrin-B3 receptor binding sites, the glycosylation site on the G attachment protein, as well as the editing site in phosphoprotein, suggesting production of nonstructural proteins V and W, known to counteract the host innate immunity. In the hamster animal model, CSUR381 induced lethal infections.
Altogether, these data suggest that the Cambodia bat-derived NiV isolate has high pathogenic potential and, thus, provide insight for further studies and better risk assessment for future NiV outbreaks in Southeast Asia.
Although NiV has been shown to circulate in Cambodia (20,21), Thailand (39), and Vietnam (40), transmission to humans or domestic animals has not been reported in these countries. According to our results, the absence of detected outbreaks in this region cannot be attributed to lower pathogenicity of the circulating NiVs; our results suggest that other factors probably contribute. However, the NiV isolate presented in this report has been the only live NiV isolated in this region, and the existence of other NiVs with different pathogenic potentials cannot be excluded.
In Cambodia, P. lylei bats were found to often forage in residential areas and visit palm trees used in the region as a source of date palm sap; thus, opportunities abound for bats to interaction with humans and livestock in this country (41). Bat colony migration toward urban sites is further enhanced by the presence of hunters in rural areas (42) and deforestation (causing consequent damage to roosting trees and food sources) (43). Contamination of palm sap, which is consumed raw by persons in the region, with bat urine, saliva, or feces was found to be a major route of NiV transmission to humans during annual outbreaks in Bangladesh (10).
Diverse agricultural practices in Southeast Asia could also play a role in NiV regional ecodynamics, potentially favoring easier NiV spillover in some countries over others. High intensity pig farming was recognized as a major risk factor for outbreaks in Malaysia during 1998–1999; because of the low-scale pig production ongoing in Cambodia (44), the risk for NiV transmission from Pteropus spp. to domestic animals and humans in this country might be reduced.
Unrecognized NiV outbreaks might have occurred in Cambodia and neighboring countries; hospital-based surveillance in Bangladesh was shown to have missed nearly half of the NiV outbreaks in that country since the first reported virus emergence (45). Interdisciplinary approaches are certainly required to identify these outbreaks and the drivers of NiV emergence (46), and regular testing of patients with encephalitis in Cambodia and neighboring countries could provide additional insight.
Our study contributes to the assessment of the risk for NiV outbreaks in Asia. Our findings can be used to help target adequate preventive measures, which could ultimately help reduce the risk for NiV emergence.
(Continue . . . )
While novel influenza remains the world’s biggest pandemic threat, over the past couple of decades Nipah, SARS, MERS-CoV, and other suspected bat-borne viruses have become increasingly viewed as having some pandemic potential.
- In Steven Soderbergh’s 2011 pandemic thriller `Contagion’, technical advisor Ian Lipkin – director of Columbia University’s Center for Infection and Immunity in New York – painstakingly created a fictional MEV-1 pandemic virus based on a mutated Nipah virus.
- In May of 2018, in the Johns Hopkins Clade X exercise, a genetically altered Nipah virus (spliced onto a parainfluenza backbone) was the cause of their fictional pandemic.
In 2017 EcoHealth Alliance published a letter in Nature (Host and viral traits predict zoonotic spillover from mammals) providing the first comprehensive analysis of viruses known to infect mammals.
From their website summary:
The study shows that bats carry a significantly higher proportion of viruses able to infect people than any other group of mammals; and it identifies the species and geographic regions on the planet with the highest number of yet-to-be discovered, or ‘missing’, viruses likely to infect people. This work provides a new way to predict where and how we should work to identify and pre-empt the next potential viral pandemic before it emerges.
Bats are the most abundant and geographically dispersed vertebrates on earth. Their ability to carry and vector dangerous diseases without ill-effect (i.e. Rabies, Nipah, Hendra, etc.) is increasingly viewed as a potential public health threat.
None of this is meant to demonize bats, as they are an important part of our environment, but it does make them very much worth studying.
Some other bat-related blog posts include:
PLoS NTDS: Prioritizing Surveillance of Nipah Virus in India
Potential For Zoonotic Emergence Of Coronavirus In Latin America
Nature: Fatal Swine Acute Diarrhoea Syndrome Caused By An HKU2-related Coronavirus Of Bat Origin
Emerg. Microbes & Infect.: Novel Coronaviruses In Least Horseshoe Bats In Southwestern China
PNAS: SARS-like WIV1-CoV Poised For Human Emergence
Sci Rpts: Avian & Human Influenza Compatible Receptor Cells In Little Brown Bats