Tracking viral infection in wild animals could help prevent disease transmission to humans
Grace Chua Straits Times 26 Oct 11;
IF BIRD droppings that land on your shirt are a sign of good fortune, Dr Ian Mendenhall must be Singapore's luckiest man.
The infectious diseases researcher at the Duke-National University Singapore (NUS) Graduate Medical School has been well-decorated in the line of duty.
At one of his many field sites in Singapore, he spreads a plastic sheet underneath a tree where hundreds of Javan mynas roost, braving a spatter of droppings and an ear-splitting cacophony.
The 35-year-old parasitologist collects an array of samples using swabs which go into plastic vials, and hauls a small cooler of the vials back to the lab to study them.
He studies bird and bat droppings to find out what viruses are present in the animal populations.
Dr Mendenhall, an American post-doctoral researcher who has been based here since last December, has been doing this twice a week, every week, for most of this year.
Duke-NUS this year began its virus surveillance work in Singapore, to find out what the 'normal' rate of viral infection is in local, wild animal populations, explained Associate Professor Gavin Smith, who leads the project.
This is important because urbanisation puts pressure on wild animal populations and increases their possible contact with humans. And certain groups of people may be exposed more often to animals that carry viruses.
For example, abattoir workers here contracted the Nipah virus from pigs in 1999, while in the past, hunters in Africa may have contracted HIV, or the human immunodeficiency virus, from chimpanzees they killed.
Also being studied are bats, rodents and mosquitoes. Singapore has some 25 species of bats, but little is known about bat viruses in an urban setting.
So far, the team has not found any viruses in the Javan mynas it studied. It has found some viruses in bats, but they are not known to affect humans.
The research is at a very early stage, Dr Mendenhall said. Its purpose is to find out what normal levels are, so public health workers know how to spot an unusual event.
So, if this is an early warning system, what would trigger an alert?
Prof Smith listed possible warning signs such as a massive rise in the number of animals infected, or in the diversity of the viruses they carry.
'There are some markers in the virus' genetic code that signal that it is more likely to cause illness, or be able to adapt to a new host species,' he said.
Scientists can figure out roughly when the animal was infected, and where the virus has been.
But they do not know for certain what factors affect inter-species transmission, Prof Smith said, adding: 'If anybody tells you they do, they're lying!'
Associate Professor Leo Yee Sin, who heads the Communicable Disease Centre at Tan Tock Seng Hospital, said it is important to monitor animal viruses.
'Surveillance of the environment, including other living things sharing the same sphere as humans, should run in parallel to the surveillance of human pathogens,' she said in an e-mail.
She cited cases of disease transmission from animals to humans - such as the H1N1 pandemic influenza of 2009, which contained genetic sequences from bird, pig and human viruses - as a reason to carry out such surveillance.
Lest anyone suggest cutting down trees or culling wild animals, Dr Mendenhall said: 'People tend to rush to judgment and say 'kill them all' - but it's not about killing all the birds or bats so they don't transmit diseases.'
After all, he said, some bats eat insect pests while others help to pollinate fruit trees. He added: 'We want healthy landscapes, healthy ecosystems. It's about improving ecological conditions so that the risk of disease transmission is reduced.'
