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)