Issue 52 | May 2009

Managing diseases borne by bats

Bats virus

In 1996, a new virus was

discovered in Australia that

later killed two humans. The

virus was identified as a

member of the lyssavirus group,

and a close relative to classical

rabies found overseas. This

transmission electron

micrograph shows a section

from a bat brain infected with

Australian bat lyssavirus.

Bats can carry a number of diseases that are transmittable to humans, such as Australian bat lyssavirus, Nipah virus, SARS and potentially even the Ebola virus. Yet the bats carry these viruses with very little, if any ill effects.

 

Windows Media Player Listen to the podcast
[Windows Media audio 6m:25s]

 

Dr Linfa Wang is the Project Leader for the Molecular Detection group at the Australian Animal Health Laboratory and heads research projects at the Australian Biosecurity Cooperative Research Centre for emerging infectious disease and has been investigating this interaction between bats and viruses.

In this podcast Dr Wang explains why bats, as the only mammals naturally capable of sustained flight, are favourable hosts for disease. He also explains how many of the bat borne viruses, such as Hendra, would need to pass through an intermediate host before human infection could occur.

Dr Wang also describes how by studying the bat population, scientists will eventually be able to forecast an outbreak of disease and minimise its potential impact on humans.

 

Transcript

Glen Paul:

G'day and welcome to CSIROpod, I'm Glen Paul.

It's been known for some time that bats carry diseases that may be transmitted to people, such as the Australian Bat Lissa Virus which is a close relative of the Rabies virus; the Hendra virus; Nipah virus; SARS and potentially even Ebola virus. Yet the bats carry these viruses with very little, if any, ill effects.

Dr Linfa Wang is the Project Leader for the Molecular Detection Group at the Australian Animal Health Laboratory and heads research projects at the Australian Biosecurity Cooperative Research Centre for Emerging Infectious Disease, and he's been investigating this interaction between bats and viruses.

Dr Wang joins me on the line. Now, Dr, can you tell me why bats are such favourable hosts for diseases that can get into humans and other animals?

 

Linfa Wang:

We don't have the exact answer to that question yet, but we believe that there might be two reasons for that. One is that the bat is a very Asian mammal, if you like, it is a mammal but different from other mammals because bats are the only mammal which can fly. So we believe that in very early stages they have diverged from other mammals, so maybe they have a long history of co-evolving with viruses, so they can handle the virus better and they have symbiotic advantages of habouring the virus without it affecting them. So, that's number one.

Number two is that bats have a different habitat if you like, and they have less interaction with land animals and for that reason, this virus has been happily maintained in the bat population without causing disease to bats.

 

Glen Paul:

Then how did the viruses get into bats in the first place?

 

Dr Wang:

Oh, all living organisms from bacteria to fungus, yeast to humans, all carry viruses. So this was just a natural phenomenon. In the history of evolution any animals or plants carry a virus so that's nothing unique about bats.

 

Glen Paul:

So, do some of the viruses such as the Hendra virus, which went from bat to horse to human, do they kind of mutate when they go via another animal before they get to us? Or would it be just as easy for us to catch the virus straight from a bat?

 

Dr Wang:

There's two different scenarios at least that we know about now. The first scenario is that, such as Hendra viruses for them to jump from bats to horse and to human they don't need any significant mutation actually, so the limiting factor is actually the virus level, if you like and in bats the virus maintains at very low levels so they don't have enough to spread around in the environment and cause infection.

So, so far, we don't have any evidence of direct transmission from bat to human for the Hendra virus in Australia. The role that horses play is the intermediate implant via the host. They don't change the virus as somebody would have thought, what they do is actually amplify the virus so they get it to a much higher level and then when a human comes in contact with a horse they get transmitted and infected.

 

Glen Paul:

I see.

 

Dr Wang:

That's the first scenario. But, we do have virus such as the SARS virus now, which is different and is highly mutatable, meaning it's highly changeable. We have evidence that when the SARS virus passes from one animal to another, an eventually to a human host, there's a rapid mutation in certain of the key viral genes which makes them more adaptable to human infection. So they are two different scenarios.

 

Glen Paul:

Would SARS perhaps fall into one of the bat-borne viruses that you feel has the potential to spread significantly to humans?

 

Dr Wang:

First the virus has the potential to spread significantly to humans. As I've already described, the first scenario is the level so you need an implant via host, the second group needs an adapting host to change the virus. So fortunately, actually none of these mechanisms are easy, so that's why we don't have as frequent outbreaks as we're observing; but the threat is certainly there.

 

Glen Paul:

Ok. Well, without sounding alarmist, do you think there is any one particular disease that could pose a serious threat if it did get into the population?

 

Linfa Wang:

The virus most people currently worry about is the Avian Influenza virus, but to me we know so little about this diversity of the virus families, you know, in bats or in birds for that matter, and so what as a scientist in the field we don't want to scare people but the potential is certainly there. What we are studying is only the viruses which have already jumped from bat to human. What I think the worry is the most is the unknown viruses which have the potential to jump. So in this one has a better ability to spread from human to human. So, in that regard, SARS is more dangerous than Hendra or Nipah because the Hendra virus so far we don't have any evidence of human to human spread so the impact is limited.

 

Glen Paul:

So, what do we do? Try and keep the bats away?

 

Linfa Wang:

No, I don't think so. Because as I always said, it's not the bats fault because the bats had the virus for a long time. I think the solutions are several. One is education, really awareness to try not to have direct contact with bats. The other is really scientific research, you know. Eventually, I think our dream is to be able to forecast potential outbreaks, it's just like weather forecasts. If we do enough research in the bat population to see what sort of viruses they carry, and if there's any seasonality, and what risk factors trigger the speed of the circle of jumping from bats to humans, if we have this sort of information then I am confident that we can minimise the outbreak in humans. So, that's sort of the first line of defense, if you like, is to study indepth in bats before they jump over. The second is to grow better diagnosis for those animals in the human. Then third line of defense is to develop drugs. If a human got a potential exposure to this lethal virus, we hope that we can treat them and reduce the mortality.

 

Glen Paul:

Rightio, well thank you very much Dr Wang for taking time out to talk to us today on what is a very interesting topic.

 

Dr Wang:

Yeah, thank you Glen.

 

Glen Paul:

Dr Linfa Wang, Project Leader for the Molecular Detection Group at CSIRO's Australian Animal Health Laboratory.

For more information, visit www.csiro.au

 

[End of Recording]