The control programme adopted has been in two phases.
-
In 1999 there was a mass culling of pigs in infected
areas and severe restrictions on movement of pigs.
-
This has been successful in preventing disease spreading
to Singapore where many pigs from Malaysia were
slaughtered.
-
The second phase is the identification of carrier herds
and their depopulation.
NIPAH VIRUS
Nipah virus is a newly recognized zoonotic virus. The
virus was discovered in 1999. It has caused disease both
in animals and in humans, through contact with
infectious animals. The virus is named after the
location where it was first detected in Malaysia. Nipah
is closely related to another newly recognized zoonotic
virus (1994), called Hendra virus, named after the town
where it first appeared in Australia. Both Nipah and
Hendra are members of the virus family
Paramyxoviridae. Although members of this group of
viruses have only caused a few focal outbreaks, the
biologic property of these viruses to infect a wide
range of hosts and to produce a disease causing
significant mortality in humans has made this emerging
viral infection a public heath concern.
Natural host
It is currently believed that certain species of fruit
bats are the natural hosts of both Nipah and Hendra
viruses. They are distributed across an area
encompassing northern, eastern and south-eastern areas
of Australia, Indonesia, Malaysia, the Philippines and
some of the Pacific Islands. The bats appear to be
susceptible to infection with these viruses, but do not
themselves become ill. It is not known how the virus is
transmitted from bats to animals.
Transmission
The mode of transmission from animal to animal, and from
animal to human is uncertain, but appears to require
close contact with contaminated tissue or body fluids
from infected animals. Nipah antibodies have been
detected in pigs, other domestic and wild animals. The
role of species other than pigs in transmitting
infection to other animals has not yet been determined.
It is unlikely that Nipah virus is easily transmitted to
man although previous outbreak reports suggest that
Nipah virus is transmitted from animals to humans more
readily than Hendra virus. Despite frequent contact
between fruit bats and humans there is no serological
evidence of human infection among bat carers. Pigs were
the apparent source of infection among most human cases
in the Malaysian outbreak of Nipah, but other sources,
such as infected dogs and cats, cannot be excluded.
Human-to-human transmission of Nipah virus has not been
reported.
Clinical features
The incubation period is between 4 and 18 days. In many
cases, the infection is mild or inapparent
(sub-clinical). In symptomatic cases, the onset is
usually with influenza like symptoms, with high fever
and muscle pains (myalgia). The disease may progress to
inflammation of the brain (encephalitis) with
drowsiness, disorientation, convulsions and coma. Fifty
percent of clinically apparent cases die.
Treatment
No drug therapies have yet been proven to be effective
in treating Nipah infection. Treatment relies on
providing intensive supportive care. There is some
evidence that early treatment with the antiviral drug,
ribavirin, can reduce both the duration of feverish
illness and the severity of disease. However, the
efficacy of this treatment in curing disease or
improving survival is still uncertain.
Protection of health care professionals
The risk of transmission of Nipah virus from sick
animals to humans is thought to be low, and transmission
from person-to- person has not yet been documented, even
in the context of a large outbreak. Therefore, the risk
of transmission of Nipah virus to health care workers is
thought to be low. However, transmission without
percutaneous exposure (through a break in the skin
barrier) is theoretically possible, as respiratory
secretions contain the virus. This is why it has been
categorized as a biohazardous agent that should be
managed in a high-level biosecurity laboratory. It is
recommended that close contact with body fluids and
infected tissues be avoided if Nipah infection is
suspected.
Outbreaks of Nipah and Hendra viruses
From September 1998 to April 1999, there was a large
outbreak of encephalitis in Malaysia. During the
investigation of this outbreak, Nipah virus, a
previously unrecognized virus, was identified as the
causal agent. A total of 265 people were infected, of
whom 105 died. Ninety-three percent of cases had
occupational exposure to pigs. An associated outbreak
among abattoir workers in Singapore during March 1999
led to 11 cases, with one death. These workers had been
handling pigs that had been imported from the outbreak
areas in Malaysia.
There have been three recognized outbreaks of Hendra
virus in Australia in 1994 and 1999. Three human cases,
leading to two deaths, were recorded in the 1994 and
1995 outbreaks. In 1995 a horse was infected, with
associated human cases. The precise mode of virus
transmission to the three Australian patients is not
fully understood. All three individuals appear to have
acquired their infection as a result of close contact
with horses which were ill and later died.
Nipah As a Biological Weapon
Nipah virus is important as a potential biological weapon
(targeted to animals, humans, or both) for the following
reasons:
-
Even
a small outbreak in pigs could result in mass
culling of affected herds, thereby causing
substantial economic loss to the industry or to the
national economy of the affected country.
-
Nipah
virus can infect humans and the case-fatality rate
may be as high as 50%.
-
There
is no effective treatment or vaccine for the disease
in either pigs or humans (although ribavirin may
reduce mortality in humans with encephalitis).
-
Little is known about Nipah virus, so an outbreak in
animals or humans could cause substantial fear and
social disruption.
The Centers for Disease Control and Prevention (CDC) has
listed Nipah virus as a critical biological agent, Category
C. Category C agents are emerging pathogens that could be
engineered for mass dissemination in the future because of:
Nipah Virus probe team honoured with Merdeka Award
PETALING JAYA: The courage shown by the investigation team
dealing with the highly infectious Nipah Virus, an unknown
disease in 1999 with no known cure and rapidly fatal, was
exemplary, said Universiti Malaya Medicine Faculty’s Prof
C.T. Tan. Prof Tan, who headed the Nipah Virus Investigating
Team in 1999, after the outbreak started in 1998, said it
was “the entire team’s effort” which led to their success in
identifying the virus and bringing it under control.
“Initially, the virus was thought to be the Japanese
encephalitis (JE) carried by mosquitoes. “But we found
that it was not JE, and that this virus spread directly from
pigs to humans, the solution was to cull the infected pigs
to stop the spread of the virus. And then the infection came
under control,” he said. Prof Tan and his team, consisting
of specialists and researchers from the fields of virology,
neurology, pathology, radiology, infectious diseases and
intensive care, were joint recipients of the Merdeka Award
under the Health, Science and Technology Category. The
Star is the official media of the Merdeka Awards. “I’m
very, very pleased. This award is very meaningful for our
team and an affirmation of the good work that we have done,”
Prof Tan said in an interview last Wednesday. They were
honoured for their “contribution in the understanding of the
causes, effects and control of the Nipah encephalitis
viral infection”, which had infected 350 people, and killed
105 persons.
The other recipient of the award in the same category was
Prof Datuk Dr Khalid Kadir. Both teams received a
certificate, a trophy and one half of the RM500,000 cash
prize. Prof Tan, a neurologist whose main work is on
epilepsy, said the team had also worked out the management
strategy and treatments of the infection. In the scientific
world, the team has received international recognition with
their journals published in the New England Journal of
Medicine, Lancet, Annals of Neurology, American Journal of
Pathology and Journal of Virology. They have
also been made World Health Organisation (WHO) consultants,
and were in Bangladesh in 2004 during a Nipah
encephalitis outbreak there. Asked what his team
planned to do with the RM250,000 award money, Prof Tan said
the money could be used for projects that they have problems
getting funding for. “This is our recognition outside the
scientific world. It’s a great morale boost for good
science,” he said.
Nipah Virus, Malaysia, May 1999
Emerging Disease Notice
Summary
-
Nipah
virus is a previously unknown virus of the family
Paramyxoviridae that has been identified in the northern
peninsula of Malaysia. The virus has caused illness and
death in humans and pigs.
-
The
apparent source of infection for humans is direct
contact with pigs. Transmission of virus is thought to
be from body fluids of infected pigs. Human-to-human
transmission has not been documented.
-
In pigs,
the disease is not well documented. Clinical signs in
pigs appear to include rapid and labored breathing; an
explosive and nonproductive cough; and neurologic
changes, including lethargy or aggressive behavior.
-
The
natural reservoir of the virus is not yet unknown.
Virus has been isolated from humans, pigs, and one dog.
Bats, two horses, dogs, and at least one cat have
reportedly shown serologic evidence of Nipah virus
infection.
-
Malaysia
exported over one million live pigs in 1997, mostly if
not entirely to Singapore.
-
The U.S.
imported no live pigs from Malaysia or Singapore in 1998
or 1999, but did import some swine leather and other
products that may have come from pigs. In 1997, the
U.S. imported some mammalian wildlife from both Malaysia
and Singapore.
-
About 330
thousand airline passengers arrived in the U.S. on
direct flights from Malaysia and Singapore in 1997.
-
It seems
prudent for U.S. pork producers to stay aware of the
situation and to maintain adequate biosecurity.
Background
Nipah virus is a previously unknown virus of the family
Paramyxoviridae that has been identified primarily in humans
and pigs in Malaysia. In humans, the virus causes fever,
severe headache, myalgia, and signs of encephalitis or
meningitis. The case fatality rate has been about 40%. The
first human cases of disease attributed to Nipah virus
occurred in late September 1998 in the northern city of
Ipoh. The cases were first attributed to the Japanese
encephalitis (JE) virus; however, the epidemiology of the
disease was not consistent with JE. Most of the cases were
in adult males who had direct contact with pigs. In March
1999, Malaysian researchers identified the virus as a
previously unknown paramyxovirus. This was confirmed by the
CDC. The virus was first called Hendra-like virus because
it is similar to the Hendra virus, first identified in
horses in Australia in 1994. The virus is now named after
the village near Kuala Lumpur from where it was first
isolated. As of late April 1999, 257 cases of febrile
encephalitis had been reported in Malaysia, including 100
deaths. Malaysian states in which these cases have occurred
are Perak, Negri Sembilan, and Selangor (map not to scale).
Nipah virus was also confirmed in abattoir workers in
Singapore, where many hogs from Malaysia are slaughtered.
The degree of involvement of the Nipah virus and the JE
virus in causing human disease was initially in question.
However, scientists now conclude that the role of JE in the
outbreak was insignificant, and that most of the cases were
due to Nipah virus. According to Malaysian authorities, of
the 146 cases where tests were available, 116 tested
positive for Nipah virus, 18 tested positive for both Nipah
and JE virus, and 12 tested positive for JE.
In pigs, the Nipah virus is associated with clinical signs
and death, although the morbidity and mortality rates are
not yet known. Clinical signs in pigs appear to include
rapid and labored breathing; an explosive and nonproductive
cough; and neurologic changes, including lethargy or
aggressive behavior.
Source: Promed; NY Times, May 4, 1999; Science Apr 16,
1999; MMWR, Apr 30, 1999; MMWR, Apr 9, 1999
Transmission and reservoir of the Nipah virus
The apparent source of infection for humans is close contact
with pigs. The specific routes of infection have yet to be
determined, however the prevailing thought is that
transmission of the virus is through direct contact with
body fluids. Another theory is that humans may become
infected via aerosol transmission from respiratory or
urinary secretions.
There appear to have been no cases of human-to-human
transmission of the virus. Family members of case patients
have remained uninfected. Further, a survey of physicians,
nurses, and pathologists who had direct contact with
infected persons found none with encephalitic illness or
with serologic evidence of Nipah virus infection.
The natural reservoir of the virus is unknown at this time.
Virus has been isolated from humans, pigs, and one dog.
Nucleotide sequence studies of the virus isolates from the
dog, pigs, and humans suggest all three isolates are
identical. Reportedly, serologic evidence of Nipah virus
infection has been found in bats, two horses, dogs, and at
least one cat. Studies of wildlife are currently ongoing in
an attempt to identify the natural reservoir.
With Hendra virus, it is thought that the 3 humans were
infected through exposure to blood or other body fluids or
excretions from infected horses. Evidence suggests that
fruit bats are the natural host of the Hendra virus. It has
been shown that both bat urine and part of the bat placenta
can contain the virus. In the case of Hendra virus, one of
the human victims died 14 months after he was infected. (A
factsheet on Hendra virus, previously called equine
morbillivirus, is available on the APHIS web site. For a
brief review of other paramyxoviruses and details of the
Menangle virus, identified in pigs in Australia in 1997,
see Emerging disease notice - New virus of animals and
humans emerges in Australia , CEI, November 1998.)
Source: Promed; NY Times, May 4, 1999; Science, Apr 16,
1999; MMWR, Apr 30, 1999; MMWR, Apr 9, 1999.
Control measures in Malaysia
The primary control measure has been culling of pigs. In
the 3 affected states, almost 900,000 pigs have been
killed. Transport of pigs within the country has been
banned. Other control measures include educational efforts
and national surveillance to detect any additional infected
herds.
Source: MMWR, Apr 30, 1999
What is the country's production and trade in
affected animals and animal products?
Malaysia
Pigs are the primary livestock industry in Malaysia. In
1998, estimated inventories of pigs were 3.3 million head,
representing 0.34% of world stocks. Also in 1998, Malaysia
produced an estimated 241,124 metric tons of pig meat.
The two Malaysian states in which most of the human deaths
have occurred (Negri Sembilan and Perak) together account
for half the swine population in Malaysia. Inventories in
Negri Sembilan, the largest swine-producing state, are
normally about 620,000 pigs.
Self-sufficient in the swine industry, Malaysia also exports
to other countries in the region. In 1997, Malaysia was the
principal source of swine imports to Singapore. Malaysia
exported 1,046,000 live pigs in 1997, as well as 2,760
metric tons of pig meat.
Malaysia imported 440 live swine and 3,863 metric tons of
pig meat in 1997.
Singapore
The swine herd in Singapore
totals only 190,000 animals. This herd is supplemented with
the importation of live pigs, principally from Malaysia. In
1997, a total of 1,046,648 pigs were imported into
Singapore, making Singapore the 4th largest importer of live
pigs in the world.
Singapore produced a total of 83,900 metric tons of pig meat
in 1998. Singapore's production accounted for less than 1
percent of worldwide production. Domestic pig meat
production is supplemented with imports. In 1997, pig meat
imports totaled 23,006 metric tons (less than 1 percent of
worldwide imports).
In 1997, Singapore exported only 348 live pigs and 2,328
metric tons of pig meat. Exports go principally to other
southeastern Asian countries.
Source: United Nations FAO; USDA
Foreign Agricultural Service
What are
the U.S. imports of affected animals or animal products from
the country?
The U.S. imported no live pigs from Malaysia or Singapore in
1998 or in January-February 1999. The only potentially
relevant products that the U.S. imported from Malaysia in
1998 were 56,441 kg of soups, broths, and preparations
thereof. From Singapore, the U.S. imported 7,323 square
meters of swine leather, 28,605 kg of soups, broths, and
preparations thereof, and an unknown amount of preparations
used in animal feed (valued at $739 thousand). In
January-February 1999, the U.S. imported 9,746 kg and 1,050
kg of soups, broths, and preparations thereof from Malaysia
and Singapore, respectively.
Because of the potential connection between Nipah virus and
wildlife, wildlife import statistics were checked.
According to data form the US Fish and Wildlife Service, 8
unspecified mammals were imported into the US from Malaysia
in 1997. From Singapore, 2 leopards, 50 mongooses, and 2
tigers were imported. These numbers do not represent all
mammals imported from Malaysia or Singapore, as CEI does not
have access to the complete wildlife import database.
Source: World Trade Atlas; LEMIS
database, US FWS
What is the level of passenger traffic arriving in the
United States from the affected country?
There are 5 daily direct flights from Singapore to the U.S.
west coast, and 1 daily direct flight from Kuala Lumpur to
the west coast. U.S. Department of Transportation data show
that, in 1997, 52,375 passengers arrived in the US on direct
flights from Malaysia, and 282,375 arrived on direct flights
from Singapore. In addition, there are numerous other
routes from Malaysia to the U.S., including via cities in
the far east or in Europe. The World Tourism Organization
reports that 80,066 tourists from Malaysia and 114,713
tourists from Singapore arrived in the U.S. in 1996. Of the
240 passengers from Malaysia that were sampled as part of
PPQ's agricultural quarantine inspections in fiscal 1998, 73
reported California as the final destination in the U.S.
Other frequent destinations included PA (16), TX (15), WA
(15), MA (12), and VA (12). In all, 33 states were reported
as destinations. Only 1 passenger, whose destination was
MN, reported going to visit or work on a farm or ranch while
in the U.S. Eight of the passengers were carrying relevant
products, including pork, salami, and unspecified meat.
These numbers are an indication of the amount of animal
product illegally entering the U.S. via airline passengers.
From the same data, 692 passengers from Singapore reported a
total of 41 states as final destinations in the U.S.
California again was the top destination, with 242
passengers. Other main destinations were NY (98), WA (28),
NJ (28), MA (26), TX (23), and FL (23). One passenger with
destination TX reported going to visit or work on a farm or
ranch in the U.S. Six passengers were carrying meat
products, including pork, sausage, and soup mixes with meat.
Source: www.flifo.com; World Tourism Organization; PPQ -
Agricultural Quarantine Inspections database
CEI's interpretation:
Direct contact with infected pigs is thought to be the most
likely route of virus transmission to humans. However,
routes of transmission between pigs or from humans to pigs
are not known. Given that human-to-human transmission does
not appear to occur, it is unlikely, though possible, that
humans can transmit the virus to pigs. The survival of the
virus outside of the host is unknown; therefore, the role
that mechanical transmission might play in spread of the
disease is also unknown. It seems prudent for U.S. pork
producers to stay aware of the situation and to maintain
adequate biosecurity. The amount of live pigs and pig
products imported into the U.S. from Malaysia and Singapore
since 1998 has been minimal. However, until more
information is available regarding what animal products may
play a role in disease transmission,
the risk these products
present is unknown.
