Confronting emerging infection threat
Humans have been badly affected by epidemics
throughout history. People are more interconnected as they travel
frequently. Changes in society bring more infectious diseases as viruses
can spread very quickly
The lecture Confronting the threat of new emerging infection, one of
a series called Meeting of Minds was organized by the University of Hong
Kong. It is trying to bring scientists from Hong Kong to talk to
students, predominantly those who are beginning their university careers
and high school students; to stimulate them with what research is and
what science is, so that some of them might be motivated to take up
science and research as a career.
Epidemics throughout history have been very frightening. For many
years people thought these were acts from supernatural forces.
The Black Death came to England and wiped out almost one third of the
population and in similar parts of Europe. It was a horrible disease.
“I started life as a microbiologist here in Sri Lanka and the first
major epidemic I confronted was in Sri Lanka. At that time I was working
in Peradeniya University in 1985. A major outbreak of Encephalitis was
recorded in Anuradhapura in October 1985. It is a brain fever; a brain
infection with about 10 percent deaths and even some of those who
recover have paralysis for life”, said Professor Malik Peiris of the
Microbiology Department, University of Hong Kong in his address at the
Normally it is one case in hospital in every three or four months. To
see 500 in three months in one hospital is absolutely incredible.
So we at Peradeniya diagnosed the cause of Japanese Encephalitis. But
then the question came up; why did this thing happen suddenly out of the
blue? Because before this the disease had been present in Sri Lanka
occasionally but never a big outbreak. So how do you tackle such a
“The information available suggested that the virus itself is present
in wild birds and transmitted from mosquitoes from bird to bird and as
long as it stays there then it doesn’t do any harm. Sometimes it gets
transmitted occasionally from mosquitoes to pigs and then pigs to
humans. But why 500 cases in that particular hospital?,” stated Peiris.
What is the trigger? What caused this? Is it a mutation in the Virus?
Could it be a change from mosquito numbers or the type of mosquitoe
spreading the disease? Maybe it is a different animal and not a pig
amplifying this disease.
So those were the possibilities Professor Peiris and his team thought
“We looked at the Virus and it was no different to the virus we found
in the previous years in Sri Lanka. So no real mutation in the virus.
Then we collected mosquitoes and hung mosquito traps in pigpens at
“There were more than 10,000 mosquitoes caught in the trap. So we
tested these mosquitoes and we worked out what mosquitoes were carrying
this. It was the typical mosquito, so there was no difference there,”
pointed out Professor Peiris.
Poor rice farmer
Then the team looked at the pigs, taking blood samples and in the
course of the outbreak they found pigs get infected before the humans
and this is the typical pattern. The virus is going from birds to
mosquitoes to pigs, then pigs and mosquitoes to humans.
They then found out that that the problem lay with the rice farmers.
Rice farmers have a tough life, they don’t have a huge amount of money
and the logical thing was to supplement the income of the poor rice
farmer by providing them with back yard pigs as an additional protein
“What it did was to set the match to the conditions that were perfect
for Japanese Encephalitis transmission.
Rice Paddies, thousand’s of mosquitoes, the birds were there in the
same environment and the pigs were the missing link. That missing link
become a reality and then you have this huge outbreak,” concluded
This shows how a change in an ecological equation, maybe for very
good intentions but can actually lead to many sad outcomes.
“We really have to be conscious of infectious disease because of the
changes in society. We are becoming much more interconnected. There is
much more travel. Any infection that breaks out anywhere can spread
across the world in two weeks,” said Professor Peiris.
So the studies they did with the recent swine flu. Swine flu was
detected in April 2009 in Mexico. By October 2009 from studies we had
done, half of the children in Hong Kong were infected by that time. So
within five months of hearing about this new virus - it had spread so
rapidly all across the world. Around 50 percent of children were
infected but they were very lucky that as a virus it was relatively mild
- it is an influenza virus called Swine Flu H1N1.
“So I think this just shows how quickly a new virus can emerge and
spread very quickly around the world,” said Professor Peiris.
Swine Flu emerged in 2009. How do these pandemics emerge? We
understood this only 30 years ago. When the influenza virus infects
humans it goes on year after year by changing slightly, doing so it can
continue to circulate in the human population. But after 20 or 30 years
it is a completely new virus. And then the human immune system
completely doesn’t see it. So it can spread very rapidly. It was
realized that what was happening is that Alien influenza virus genes are
being picked up by human influenza virus’ becoming hybrid, mixing alien
and human genes giving rise to a complete change in the outer core
leading to a pandemic.