Imminent risk of disease from live animal markets

Imminent risk of disease from live animal markets

Karmele Llano Sanchez, Jakarta

An article published last July in Emerging Infectious Diseases
reports on the significant impact that the wildlife trade and
live animal markets are having on human health worldwide, in
particular Asia.

The large population on this continent arguably increases the
likelihood of a pandemic occurring. It is in this continent also
where the population is at higher risk of contracting animal-
borne diseases due to the encroachment of humans into wildlife
habitats, and the presence of animal markets where animal
products and live animals are on sale.

Presently, an outbreak of H5N1 type A influenza virus (bird
flu) has alerted human health authorities in Indonesia. This
zoonosis (an animal disease capable of being transmitted to
humans) has already cost the lives of dozens of people. However,
the most threatening aspect is the possibility that many other
zoonotic pathogens could be covertly infecting people basically
because they are difficult to diagnose by physicians.

This highlights the question of where these emerging pathogens
are hidden and what causes them to emerge. According to Lonnie
King et al, three-quarters of emerging human diseases over the
past two to three decades have been animal-borne, and the future
will probably bring many more such outbreaks.

In addition, the threat of these diseases spreading quickly
worldwide is reasonably high due to contemporary global transport
patterns: planes, ships, people and animals carry infections in
every direction.

Animal health has broad implications, ranging from the health
of individual animals, human health and global security. Animal
diseases have implications not only for the global food supply
but also for human health directly due to the existence of animal
borne diseases transmissible to humans (zoonoses).

The pool of infectious pathogens shared between animals in a
market will not stay confined to these locations. To the
contrary, these animals and their pathogens will be transported
to other areas, locally and nationally, and even internationally
when animals are smuggled outside of the country.

This not only threatens people but also wildlife, when, for
instance, they are eventually released by the owners because they
are no longer wanted, or when they escape and become a threat to
local wildlife.

The likelihood of disease transmission is also increased when
animals are submitted to unnatural conditions causing high stress
levels.

Wild animals suffer much stress when they are captured and
transported, then forced into a completely unknown environment,
surrounded by their most dangerous predator: humans. They are
also offered for sale in cramped cages with no space to even
stretch their bodies.

At the same time, this stress renders their immune system
less effective, making them more prone to infections for which
they are not a natural host.

Pathogens for which humans become new hosts are more hazardous
while human immunity does not yet posses the ability to fight
them.

Some estimations of the numbers of wild animals traded
annually worldwide includes approximately 40,000 live primates, 4
million live birds, 640,000 live reptiles, and 350 million live
tropical fish. According to one report, in a single market in
North Sulawesi up to 90,000 mammals are sold per year.

Over the last 25 years, more than 35 diseases have emerged. In
a list of 1,415 human pathogens, 61 percent are known to be
zoonotic, and multiple-host pathogens are twice as likely to be
associated with emerging infectious diseases in humans. As much
as 77 percent of pathogens found in livestock are shared with
other host species.

The rash of emerging or reemerging livestock disease outbreaks
around the world since the mid 1990s, including bovine spongiform
encephalopathy, foot-and-mouth disease, avian influenza, swine
fever, and other diseases, has cost the world economy $80
billion.

Efforts to control the spread of avian influenza in Asian
countries since 2003 has required the killing of about 140
million chickens. In order to keep up with an increasing
population and growth in demand for protein, countries such as
Indonesia will have to increase livestock production which will
increase the risk of livestock disease outbreaks. Following
this tendency, it is very likely that these infections will be
linked to wild animals.

In July of this year, studies reported the first case of
simian foamy virus (SFV) infection, a non-human primate-borne
disease, in a person with known exposure to free-ranging
Indonesian macaques in an eco-tourism monkey attraction in Bali.

Alarm warns foreign tourists not to have close contact with
macaques in these kinds of premises. However, no risk awareness
is raised for local people who keep these monkeys as pets, or who
sell them in markets. In all the animal markets of Jakarta and in
other large cities in Java and other islands, macaques are
commonly seen on sale either as pets or for human consumption. No
animal disease control is carried out and no authority warns
people of the risk of transmission of diseases.

The poor hygienic conditions in these markets means a risk for
sellers, buyers, visitors and the entire environment. The close
contact between people and animals and their diseases in the
context of any animal market is, arguably, a potential risk for
zoonoses to emerge.

All these wild animals harboring pathogens would not be a
hazard to human beings at all if they were left alone in their
natural habitats far away from humans. It's only when humans
cross the barrier and stand in the way of these pathogens that
the risk of new disease emerges.

Emerging Infectious Disease reports that some studies have
shown that closing down retail poultry markets in Hong Kong for
one day per month reduced the rate of H9N2 avian influenza virus
in market birds. In the same terms, it seems reasonable to think
that closing down animal markets would have an analogous effect
in the Indonesian context.

The writer is a veterinarian based in Jakarta.