What Makes Emerging Viruses Emerge?

September 30, 2002, BioMedNet

The transformation of two harmless fruit-bat infections into killers of humans has been disturbing enough to trigger an international research effort aimed at figuring out just what is going on. Researchers from Australia, Malaysia, the US, and Britain are poised to embark on a $1.5-million project to study these diseases and their environmental antecedents.

The bat infections are caused by so-called paramyxoviruses, which recently proved themselves far from harmless when they leaped the species barrier. The first, Hendra virus, was identified in Australia in 1994 when it killed two people. The second, Nipah virus, made a more dramatic appearance when it killed 105 people in Malaysia in 1998. The virus appears to need an intermediate host before it passes to humans: Hendra virus initially infected horses; the deadlier Nipah virus was first transmitted to pigs.

The key question, says Peter Daszak, who will be coordinating the multi-centre project from his base at the Consortium for Conservation Medicine (CCM) in Palisades, New York, is what prompted these viruses to suddenly jump from fruit bats - where they've probably co-evolved for a few million years - into humans.

Daszak hopes that the project will lead researchers to understand how environmental changes caused by human activity could drive emergence, eventually informing predictions of the next outbreaks and enabling concrete actions to stop them or prevent them altogether.

Support for the project, "Anthropogenic Change and Emerging Zoonotic Paramyxoviruses," is provided by the US National Institutes of Health's Fogarty International Center. Funds will be distributed among two centres in Australia, three in Malaysia, four in the US and one in the UK. The award was granted in August and work will start in October. Some groups will focus on the disease itself, while others will concentrate on ecological aspects.

Researchers at the International Medical University in Malaysia, for example, will examine possible links between El Niño, fire, fruit-bat migration and virus emergence, while researchers in Malaysia's Veterinary Research Institute will study the serology of Malaysian fruit bats and purify the viruses from their sera.

Research at the CCM under Dazsak will examine how agriculture has changed in Malaysia. Have pig farms, for instance, become more closely associated with bat habitats recently?

In Australia, Alex Hyatt at the Australian Animal Health Laboratory of CSIRO (Commonwealth Scientific and Industrial Research Organisation) is leading a researcher team that will investigate viral pathogenesis in Australian and Malaysian fruit bats and try to determine how they shed the virus. He and his colleagues will study the amount of virus that is needed to infect pigs and they will analyze field scenarios whereby pigs can become infected.

With all this research effort, however, one concern remains. With the emphasis on predicting outbreaks of recently emerged viruses, would other novel emergent viruses be overlooked? His centre aims to investigate virus biodiversity in fruit bats, Daszak says, by gathering funds from several sources.

No official surveillance program for spotting novel emergent viruses exists, says Hyatt, but the network of other surveillance programs would "maybe" pick up any unusual events. "The question is difficult," he added, "because how can one detect emerging viruses unless they have emerged?"

Daszak says the problem is serious, not just for virology but for the whole of microbiology.

"There are a small number of programmes investigating biodiversity of other unknown potentially zoonotic pathogens, but they're difficult to fund," said Daszak. "People [that is, peers who review grants] often see these as stamp-collecting fishing expeditions and not good science, because they don't test hypotheses. But I disagree - it's a key part of predicting future emergence to know the range of pathogens out there."