Animals and birds have long been our friends, foes or food.
They became ill and the viruses and bacteria they carry can also
infect human beings and endanger our lives.
According to scientists, as many as 75 per cent of all emerging
infectious diseases are zoonotic. That is, they can be transmitted
from animals and birds to humans.
Since last year, we have had encounters with severe acute
respiratory syndrome (SARS), West Nile encephalitis, Legionnaires'
disease, monkeypox, and now bird flu, all with origins in the
animal world.
As Zhao Guoping, a researcher with the Chinese National Human
Genome Centre in Shanghai, said at a press conference last week,
vigilance and early monitoring and control of coronavirus
infections among animals is the key to preventing the outbreak of
diseases such as SARS among people.
Zhao and his colleagues from home and abroad, have tracked
genetic adaptations of the SARS virus between November 2002 and
February of last year. They have just published their findings in
the latest issue of Science magazine, which came out last Thursday,
under the title, "Evolution of SARS."
In their paper, they included their very recent findings from
the first confirmed SARS patient in Guangzhou in late December,
after a six-month hibernation of the virulent respiratory
disease.
The SARS coronavirus they collected and analyzed from the swab
sample showed that it "is much closer to the SARS-like coronavirus
of the palm civet than any other human SARS coronavirus detected in
the previous epidemic."
Likewise, the genetic codes of the coronavirus from the early
patients of the 2002-2003 SARS epidemic were also genetically very
similar to those seen in civets, weasel-like animals whose meat has
long been considered a delicacy at the dinner table. Until
recently, civets were raised and sold in farmers' markets, mostly
in southern parts of the country.
The researchers note that seven of the first 11 SARS patients
"had documented contact with wild animals."
Zhong Nanshan, a leading Chinese respiratory disease expert,
said the same vigilance is also in order with the current avian
influenza, which is affecting farms and villages in some areas in
China, Viet Nam, Cambodia, Thailand, Laos, Indonesia, Japan and
South Korea.
There is no evidence of transmission to humans of the pathogenic
strain from the bird flu known as "H5N1," according to World Health
Organization (WHO).
In the words of Dr Zhong Nanshan, such evidence is, at least,
"not apparent."
However, the WHO states that the virus does cause severe disease
in humans.
Up to this week, 12 people have died of H5N1 virus -- nine in
Viet Nam and three in Thailand.
Reasons for concern
Jia Youling, the chief veterinarian of the Ministry of
Agriculture, said in an interview with China Central Television
that China has followed the codes established by the World
Organization for Animal Health on the control and prevention of
severe infectious diseases among animals.
Poultry are "culled" and destroyed within a 3-kilometre radius
around infected areas. Enforced vaccination is carried out within a
5-kilometre radius.
It is an essential measure to ensure the health of both the
poultry industry and people.
Public health officials have also been alerted. The Ministry of
Health last week issued a circular stating that medical workers
must go through a training programme to deal with the unprecedented
outbreaks of bird flu among poultry and for the possible diseases
caused by the H5N1 pathogenic strain.
They must be made aware of the dangers, WHO warned.
First of all, "there is mounting evidence that this strain has a
unique capacity to jump the species barrier and cause severe
disease, with high mortality, among humans," the WHO circular on
avian influenza states.
"A second and even greater concern is the possibility that the
present situation could give rise to another influenza pandemic in
humans," it adds.
Cai Yuxiang, a professor of zoology and veterinary science at
Nanjing Agriculture University, has devoted about half a century to
the study of animal diseases.
In a telephone interview with China Daily, Prof Cai said
researchers worldwide have found numerous diseases in avian
populations.
He himself has studied fowl cholera, New Castle disease and a
few other common ailments that infect chickens in the country.
He has also identified a few types of avian influenza, such as
the H9 type, which "is not as virulent as the 'highly pathogenic
avian influenza' with H5N1 virus," he said.
Avian influenza was first discovered in 1878 in Italy. So far
researchers have identified more than a dozen strains of the bird
flu. But the "highly pathogenic avian influenza" is considered
almost the most contagious and deadly.
And it is new to the Chinese mainland, even though an outbreak
occurred in Hong Kong in 1997, Cai said.
The origin of the virus in Hong Kong is still unknown, Cai said,
as it could have originated in and been carried by wild birds.
But avian influenza viruses mutate easily, Cai said.
Researchers have also found that "avian and human influenza
viruses can exchange genes when a person is simultaneously infected
with viruses from both species.
"This process of gene swapping inside the human body can give
rise to a completely new subtype of the influenza virus to which
few, if any, humans would have natural immunity," the WHO
warns.
Each year, scientists develop vaccines against flus by matching
currently-spreading strains to protect humans during seasonal
epidemics. However, the vaccines are often powerless in battling a
completely new influenza virus.
When the new virus contains sufficient human genes,
"transmission directly from one person to another (instead of from
birds to humans only) can occur," WHO warns.
This would be the right conditions for the start of a new
influenza pandemic, according to WHO. "Most alarming would be a
situation in which person-to-person transmission resulted in
successive generations of severe disease with high mortality," the
WHO circular states.
The WHO cited the great influenza pandemic of 1918-1919, when a
completely new influenza virus subtype emerged and spread around
the globe, in around four to six months.
There were several waves of infection spanning two years,
killing an estimated 40-50 million people around the world.
Veterinary public health
Human tragedies offer us lessons to learn and prevent future
tragedies.
Since the 1950s, veterinary public health has been a focal issue
for the WHO, which is now collaborating with the United Nations'
Food and Agricultural Organization and the World Organization for
Animal Health to help Asian countries fight the bird flu.
Experts from the three world organizations and representatives
from many countries are convening in Italy this week to explore
ways for further co-operation.
In a lengthy report titled "Future Trends in Veterinary Public
Health," published two years ago, the WHO study group pointed out
that human society has embraced "emerging and re-emerging zoonotic
diseases" in the past two decades, as human travel and trade
increase.
The group of the researchers listed Salmonella enteritidis in
poultry, an illness that results in fever, abdominal cramps and
diarrhea in humans after eating eggs contaminated with the
Salmonella bacterium, ebola viral haemorrhagic fevers in Africa,
rift valley fever in east Africa, the Arabian Peninsula and Egypt,
the New World screw worm (Cochliomyia hominivorax) in north Africa
and new rabies-like viruses in bats in Australia and Europe.
There has also been the unexpected link between bovine
spongiform encephalopathy (BSE) and its variant Creutzfeldt-Jakob
disease (vCJD), hantaviruses -- the deadly disease transmitted by
infected rodents, and the West Nile virus in the Americas.
Above all, the researchers say that there is still the threat of
"a global influenza pandemic" and as a result, a lot of research is
being done in efforts to clarify mammalian and avian
reservoirs.
All of the diseases discussed above are "examples of zoonotic
agents that can cause human illness and death, and that require
rapid responses from, and teamwork between, physicians,
veterinarians and biologists," their report states.
All this calls for global attention to veterinary public health,
and, hopefully, the international conference this week will not
only result in more effective actions and measures in the global
battle against the current bird flu but also in future work for the
prevention and control of zoonotic diseases.
(China Daily February 2, 2004)