Tuesday, January 05, 2016

Study: Hotspots For Bat To Human Disease Transmission

WHO Nipah Virus (NiV) Infection GAR page
Photo by Chi Liu 


The past two decades have been an exceptionally good ones for Chiroptologists (scientists that study bats) worldwide, as each year we seem to learn of new (and potentially zoonotic) diseases carried by these ubiquitous flying mammals.

In the late 1990s an outbreak of a previously unrecognized paramyxovirus - similar to a recently discovered Hendra virus in Australia - sickened 250 people, and killed more than 100, in Malaysia and Singapore.  It was eventually named Nipah. 

While initially linked to pigs, it was discovered the virus was carried by bats, and pigs were only an intermediate host. 

Every winter we continue to see small outbreaks of Nipah in Bangladesh, and Northern India. Of particular concern, 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).

We now know that SARS was likely a bat-borne virus, and there are strong indications that bats may be the original host for MERS-CoV as well. Ebola,  Marburg, and a growing array of coronaviruses have been similarly linked to bats, although intermediate hosts may often play a major role in their jump to man.

And in the past four years, bats have even been found to harbor several unique influenza viruses (see CDC: Bat Flu Q&A).

When Steven Soderbergh made his pandemic thriller `Contagion’ a few years ago, technical advisor Professor Ian Lipkin created fictional MEV-1 virus based on a mutated Nipah virus (see The Scientific Plausibility of `Contagion’) simply because of the potential of someday seeing a bat-borne pandemic virus. 

All of which makes the study of bat viruses - and the conditions under which they are most likely to jump into the human population - of great importance.

Which brings us to a study, published today in the The American Naturalist, that looks to quantify the risks of zoonotic transmission of a wide variety of bat viruses to humans.

Quantifying Global Drivers of Zoonotic Bat Viruses: A Process-Based Perspective
Liam Brierley1,2*, Maarten J. Vonhof3, Kevin J. Olival4, Peter Daszak4, and Kate E. Jones1
*. Corresponding author; e-mail: l.brierley@sms.ed.ac.uk.

SUBMITTED: Jan 29, 2015  ACCEPTED: July 22, 2015 ONLINE: Jan 5, 2016


Emerging infectious diseases (EIDs), particularly zoonoses, represent a significant threat to global health. Emergence is often driven by anthropogenic activity (e.g., travel, land use change). Although disease emergence frameworks suggest multiple steps from initial zoonotic transmission to human-to-human spread, there have been few attempts to empirically model specific steps. We create a process-based framework to separate out components of individual emergence steps. We focus on early emergence and expand the first step, zoonotic transmission, into processes of generation of pathogen richness, transmission opportunity, and establishment, each with its own hypothesized drivers. Using this structure, we build a spatial empirical model of these drivers, taking bat viruses shared with humans as a case study.
We show that drivers of both viral richness (host diversity and climatic variability) and transmission opportunity (human population density, bushmeat hunting, and livestock production) are associated with virus sharing between humans and bats. We also show spatial heterogeneity between the global patterns of these two processes, suggesting that high-priority locations for pathogen discovery and surveillance in wildlife may not necessarily coincide with those for public health intervention. Finally, we offer direction for future studies of zoonotic EIDs by highlighting the importance of the processes underlying their emergence.

Although the full study is behind a pay wall we've got a press release from University College London that fleshes out the details a bit, and provides a map of the global hot spots.

Map shows hotspots for bat-human virus transmission risk

5 January 2016

West Africa, sub-Saharan Africa and South East Asia are most at risk from bat viruses ‘spilling over’ into humans resulting in new emerging diseases, according to a new global map compiled by scientists at UCL, the Zoological Society of London (ZSL) and the University of Edinburgh.

The map shows risk levels due to a variety of factors including large numbers of different bat viruses found locally, increasing population pressure, and hunting bats for bushmeat.

Approximately 60-75% of reported human emerging infectious diseases (EIDs) are ‘zoonotic’, where infectious diseases in animals are naturally transmitted to humans. The researchers chose to study bats in particular as they are known to carry multiple zoonotic viruses and are the suspected origin of rabies, Ebola and SARS (severe acute respiratory syndrome).

Lead researcher, Professor Kate Jones, Chair of Ecology and Biodiversity at UCL Biosciences and ZSL, said: “We’ve identified the factors contributing to the transmission of zoonotic diseases, allowing us to create risk maps for each. For example, mapping for potential human-bat contact, we found Sub-Saharan Africa to be a hotspot. Whereas for diversity of bat viruses, we found South America was at most risk. By combining the separate maps, we’ve created the first global picture of the overall risks of bat viruses infecting humans in different regions.”

The research, using data published between 1900 and 2013, identified West Africa as the highest risk hotspot for zoonotic bat viruses. This area was outside the endemic range proposed by previous studies but has since experienced the largest scale outbreak of Ebola virus disease seen yet.
(Continue . . .)

No comments: