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©New
Sunday Times (Used by permission)
by Chai Mei Ling
• The bat way to understand a virus
KUALA LUMPUR: This is the eighth year that Malaysia is free of the Nipah virus
since the 1998-99 outbreak that took more than 100 lives, but the authorities
are not letting their guard down.
Abbatoirs are still being screened, samples from cattle,
strays and pets tested, and clinical surveillance carried out in major
hospitals.
"I won't rule out the possibility of another Nipah outbreak in Malaysia or in
any part of the world," said Professor Dr Tan Chong Tin (right), speaking at
University Malaya's Nipah Virus colloquium last week.
"More and more countries, including Bangladesh, Indonesia, Thailand, Cambodia
and India, have found their bats to have Nipah virus. So the potential of an
outbreak is there," said Dr Tan, a consultant neurologist with UM's department
of medicine.
The movement of labour across borders could pose a threat to Malaysia, which is
home to migrant labour from these countries.
Research in the past 10 years have shown the ability of the virus to evolve and
infect people differently and directly. If it ever does so, it could be in a
strain so different from the virus that struck Malaysia in 1998-99, that we
could find ourselves grappling for answers again.
While the disease then had pigs as the intermediary and amplifying hosts to the
virus with a connection to fruit bats and flying foxes, reports from Bangladesh
now talk of another bat connection.
And in Bangladesh, which continued to experience Nipah virus outbreaks almost
annually in the last seven years, the virus was found to manifest itself a
little differently. For one, it caused more respiratory problems, said Tan.
"We saw Nipah virus as mainly a brain disease, but the Bangladeshis and Indians
saw it with a very strong lung component. Sometimes, it can produce a disease
like SARS where there's a lot of lung infection.
"So, it very well can spread from human to human. It can even spread the whole
world over."
Indeed, person-to-person transmission forms half of the cases in Bangladesh,
unlike in Malaysia, where we had none recorded.
Although statistics showed that each person in Bangladesh infects only half a
person, Dr Dr Steve Luby from the International Centre for Diarrhoeal Disease
Research, Bangladesh, said the outbreak could still be devastating.
"It's not yet a pandemic. It's not going into lots and lots of people and
spreading beyond village areas, but we do have devastating outbreaks.
"My suspicion is that this virus knows no borders and I doubt that the zone of
risk ends at the border."
The Nipah disease also took a new twist in Bangladesh in the form of direct
infection of humans by bats -- there is a high possibility that humans can get
infected by drinking raw, contaminated date palm juice.
Infrared cameras put up at night have caught images of bats visiting palm trees
and licking the cut segment from which the sap drips into a jar.
The next morning, some of the juice would be sold and drunk raw.
The third notable difference in the Bangladeshi case, also a serious cause for
concern, is that although the outbreaks have been small, having only 206
reported cases in seven years, the disease has become almost twice as deadly. It
records a fatality rate of 74 per cent, as opposed to Malaysia's 40 per cent.
However, the marked jump is not solely attributable to the new strain of virus,
as culturally, Bangladeshis' social norm in providing personal care for the sick
is also believed to have given rise to more close contact.
Whatever its ugly manifestation in other parts of the world, the Nipah disease
is never the problem of only that one country.
The very real risk that it could evolve into a pandemic, much like SARS and the
Avian influenza, means that it is a global issue.
Dr Peter Daszak of the Consortium for Conservation Medicine, New York, said that
a review of past literatures showed that zoonoses -- animal diseases that can be
passed on to humans -- are on the rise.
"There are 50,000 vertebrate species on the planet. Let's assume each species
has 20,000 viruses that are endemic, and that's a pretty low estimate
considering that studies have shown that humans, cats and dogs have many more
viruses.
"We've known only 2,000 viruses, so if you work out the math, there are millions
of viruses waiting to be discovered. There are 20,000 in bats alone."
People are at risk, wherever they are, says Dr Daszak.
"Even if it emerges in Bangladesh or Amazon, once it gets into the human
population, it starts to spread.
"Once a virus gets into the pandemic status, it would gravitate to the countries
that have the most people flying around the world."
Many of the speakers at the conference said that international co-operation was
essential to handling the threat posed by new diseases.
"Internationalism is very important. There's no border. The whole world is
sensitised towards these emerging diseases, so it's very useful to keep in
touch," said Emeritus Prof Datuk Dr Lam Sai Kit, who headed the research team in
UM that identified the Nipah virus 10 years ago.
Dr Lam should know; he placed many phone calls to colleagues the world over when
Malaysia was facing that Nipah threat then, and they came over to help.
The experience gained from containing the Nipah virus outbreak has been
important in making Malaysia today a better prepared nation.
"Nipah taught us a lesson. We were ill-equipped," said Prof Sazaly Abu Bakar,
head of UM's department of medical microbiology.
"The ministries didn't work together. But when the outbreak took place, they
were forced to collaborate.
"It forced Malaysia to look into its capacity on whether it can handle this kind
of outbreak in the future."
NIPAH VIRUS: The bat way to understand a virus
WITH a piercing cry, the wounded bat parachuted a few feet down in the sky,
before plunging all the way to the ground.
As it landed in a ditch 50m away from where Dr Sohayati Abdul
Rahman stood, her assistant made a dash for the creature, now wet and barely
alive.
Using a syringe, Sohayati expertly drew a sample of the animal's blood from its
weakening heart.
She then swabbed its mouth for saliva, sliced open the side of its lower trunk
and pulled a kidney out for urine sampling.
Everything was tagged and stored while the bat was placed in a sack.
The technician standing next to Sohayati positioned himself
to target another cloud of bats emerging from its roost in the evening to feed.
One was shot and, plop! it fell in a swirl into a river. Sohayati, an officer
with the veterinary research institute in Ipoh, and her assistants wasted no
time in repeating the process.
"I've to get the bat while it's still alive and the heart is pumping. If the bat
is dead, the blood stops flowing and I can't get a sample.
"My assistants have to be efficient in retrieving the bat. We cannot manipulate
the flesh too much when cutting out the kidney as the technician doesn't want us
to spoil the tissues."
The veterinary research team works fast, devoting only five minutes to process
each animal, so as not to keep the tech waiting for his catch of the night.
The quick action also allows the team to get as many bats sampled as possible. A
three-hour outing would generally get some 30 samples.
Besides tagging along these excursions, Sohayati also does her own bat-trapping
by constructing a net high up on poles.
Bats flying out from their roost would sometimes get tangled in the messy
weaving of the net.
After a sample is taken, they are released back into the wild, or kept captive
in the institute's quarantine station.
For four years now, bat catching has formed a major part of Sohayati's job scope
in understanding the origin of the Nipah virus.
An epidemiologist, Sohayati studies the incidence and prevalence of disease in
large populations and tries to detect the source and cause of epidemics of
infectious disease.
Her study zeroed in on bats in Malaysia after the Nipah virus had been observed
to be genetically similar to the Hendra virus in Australia, which came from
fruit bats.
The local large flying fox (Pteropus vampyrus), which can weigh up to 1kg, and
small flying-fox (Pteropus hypomelanus) has been identified as the natural
reservoir hosts for the Nipah virus.
"This means that the virus is endemic in both the species, it's naturally
there," said Sohayati.
It also means that there's no disease in the bats, even though they harbour the
virus.
Sohayati managed to detect the presence of antibodies in some of the bats,
signalling that they have been exposed to the virus before.
But she has never detected the virus per se in any of the 1,000 bats that she
has sampled -- up until now.
The one time she found the virus present was when a bat in her captivity
secreted urine which tested positive for it.
But something was absolutely baffling.
The bat had been negative for both virus and antibody for the last 11 months.
And it was never exposed to bats from the wild, which could carry the virus.
This led Sohayati to hypothesise that it is possible for the Nipah virus to be
"reactivated" after lying dormant in the body.
The virus could have hidden in the cells, tricking the body into thinking that
it is virus-free and so, reducing the antibody in the body.
Bats which are stressed and have an active reproductive status carry a higher
risk in having the virus, the study showed.
"Since the virus is endemic in bats and I found evidence that it can be
reactivated, the risk of an outbreak occurring again in Malaysia or in other
countries that have Pteropus bats is there."
The overlapping of the Pteropus' home range, which spreads from Australia all
the way up to Pakistan, makes transborder transmission very real, Sohayati
added.
Thus far, however, she has never heard of any cases of local bat hunters being
infected with the virus and go on to develop encephalitis.
While the researcher has no hard evidence on whether thorough cooking can kill
the virus, she said the Nipah, a RNA virus, is sensitive to heat.
"I believe the virus is destroyed after being cooked.
"We have to remember that a virus can only be transmitted when it has a chance
to get contact and that the contact can cause effective transmission.
"You need to get enough viruses to the right organs in order to get infected."
So many questions, she said, have yet to be answered, especially on the
reservoir status of the bats and its immune response to the disease.
BLAME IT ON FLYING FOXES
THE NIPAH virus was identified in 1999 when it caused an outbreak of
neurological and respiratory disease on pig farms in Peninsular Malaysia,
resulting in 105 human deaths and the culling of over a million pigs.In the
early stage of the outbreak, it was mistakenly classified as Japanese
Encephalitis due to the similarity in pigs being infected.
Symptoms of infection from the Malaysian outbreak were primarily encephalitic in
humans and respiratory in pigs.
Patients suffered from a rapid progression of illnesses, including fever,
headache, drowsiness, jerking movements and coma.
Later outbreaks elsewhere have caused respiratory illness in humans, increasing
the likelihood of human-to-human transmission and indicating the existence of
more dangerous strains of the virus.
The primary reservoir for the virus was identified as Pteropid fruit bats,
including Pteropus vampyrus (Malayan flying fox) and Pteropus hypomelanus
(Island flying fox), both of which are present in Malaysia.
The transmission of the virus from flying foxes to pigs is thought to be due to
an increasing overlap between bat habitats and piggeries.
At the index farm, fruit orchards were located within the piggery, allowing the
spillage of urine, faeces and partially eaten fruits onto the pigs.
There is no cure for Nipah encephalitis.
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