Beating 'bird flu' against the odds

Nations hit hardest by 'bird flu' have pledged to develop vaccines to prevent a human-to-human epidemic, but as one reporter discovers, combating the virus is an uphill task.

When chickens from a farm in the Thai district of Nong Bua suddenly began dying back in November 2003, farmers were told that it was chicken cholera. Soon other farms became infected, farmers were given medicines to treat the disease but the chickens continued to die.
In a vain attempt to control the outbreak, Thai agricultural officials instructed farmers to slaughter all chickens within a six-kilometre radius of the first infected farm. Veterinary scientists began to suspect something more serious as the chickens were already vaccinated against cholera.

Within days the virus moved to neighbouring Suphan Buri and Nakhon Pathon districts and by January 2004 over a million chickens had been slaughtered. Rumours began to spread that the “chicken-killer” virus was the same bird flu virus already reported in South Korea.


While the world’s attention focused elsewhere, avian influenza H5N1 was quietly brewing in south-east Asia.


The spread of the avian flu in South Korea, Japan, Vietnam, Thailand, Cambodia, Laos, Indonesia and China has once again put the world on alert; prompting the World Health Organisation (WHO), the UN Food and Agricultural Organisation (FAO) and the World Organisation for Animal Health (OIE) to launch an urgent appeal for international donor funds and technical assistance to combat the spread of a virus that could take months to bring under control.


UN: ‘brief window of opportunity’

A joint statement recently released by the three agencies described the serious pathogenic strain as “a threat to human health and a disaster for agricultural production.”

“We have a brief window of opportunity to eliminate that threat,” said Dr. Jacques Diouf, FAO Director-General.

“Farmers in affected areas urgently need to kill infected and exposed animals and require support to compensate for their losses. This will represent a huge cost, especially to struggling economies and small farmers. The international community has a stake in the success of these efforts and poorer nations will need help.”

Although it has not happened yet, the so-called “bird flu” presents a risk of evolving into an efficient and dangerous human pathogen, the three agencies warned.

“This is a serious global threat to human health,” said Dr Lee Jong-wook, WHO director-general.

“But we have faced several emerging infectious diseases in the past. This time, we face something we can possibly control before it reaches global proportions if we work cooperatively and share needed resources. We must begin this hard, costly work now.”

The epicentre

Over the past 12 months, southern China has been under the spotlight for its notorious live animal and bird markets. It is here you will see every conceivable wild and domestic animal being bargained for, sold and slaughtered for consumption. The conditions in which the animals and birds are kept are branded by animal rights advocates as "inhumane" and "unsanitary".

Hygiene guidelines for slaughtering animals are virtually non-existent. Those that are in place are not properly enforced by health officials.

The slaughter areas or "wet stalls" here are often described as a deplorable scene of blood, guts, faeces and urine left to stew in the marketplace and are only cleaned periodically by high-pressure hoses.

In farms, chickens, ducks, geese and pigs are bred together and fish ponds are sometimes used as dumping grounds for their manure, creating a breeding pool for viruses like influenza. Scientists have long-argued that such practices allow perfect conditions for cross infections between animals and humans to take place, as is thought to have happened in the recent outbreaks of Severe Acute Respiratory Syndrome (SARS).



Little wonder the region is regarded as the epicentre for new emerging viruses and diseases. Aquatic and domestic poultry may provide fresh meat - a culinary must for Cantonese cooking - but their gene pool provides an unlimited breeding ground for death and disease.


Since the 1990’s three avian influenza viruses have jumped the species barrier.

H5N1, H7N7 and H9N2 are made up of a conglomerate of subtype strains constantly interacting with other avian viruses creating new ones that will evidently cause new infections. Scientists call this an "antigenic shift". The flu’s fickleness makes it the perfect virus.


The first bird flu experience was in Hong Kong in 1997, which infected 18 people, killing six. It sent an early warning that an avian flu virus becoming a potential human flu threat was and is a very real one. Since then the virus has appeared twice again in Hong Kong - in 2001 and 2002 - each time baffling flu experts.

Part of the problem is a lack of co-operation on the part of those who have economic interests vested in the multi-million dollar poultry industry.

Watching the flu

After the 1997 outbreak, the Hong Kong Government launched an influenza research team, comprised of some the world’s leading microbiologists and virologists specialising in animal influenzas from Hong Kong University.

Headed by Dr Kevin Shortridge, along with Dr Malik Perris, Dr Guan Yi and Robert G Webster from St Jude Children’s Research Hospital, Memphis, Tennessee, the team’s primary role, with the backing of the WHO, the US National Institute of Health and other key international health organisations, is to watch and stop new potential avian flu viruses before they can infect people.


Segregation policies regarding the housing of live birds within the markets were also set up.

Poultry stocks arriving from the mainland are now health checked but this is not a foolproof system, health regulations governing record-keeping and surveillance remain lax on the mainland.


In any given week Hong Kong imports up to 500,000 birds from the mainland and only a batch of birds are tested for virus antibodies. Whether any reports of sick chickens are recorded in the place of origin is anyone’s guess.

Once in Hong Kong, chickens and other live poultry are kept apart from ducks and geese which are slaughtered at a central slaughtering facility and once a month health officials enforce a "rest day" so cages can be disinfected.


In April 1999, the researchers carried out a virological surveillance over live markets in Hong Kong, Kowloon and the New Territories Fecal and cloacal samples were collected from terrestrial poultry in nine live markets and from ducks and geese kept at a central slaughterhouse in the Western Wholesale Food Market in Hong Kong's Western district..


Unwelcome return

For a time no H5N1 virus showed up then in 2000, H5N1 viruses began re-appearing in aquatic poultry. After a series of more checks, 11 H5N1 viruses showed up in April 2001, in "healthy" poultry as well as a quail, pigeon, pheasant and silky chickens.

Health authorities widened the surveillance to 30 other poultry markets, isolating 52 additional H5N1 viruses found in dead chickens. By mid-May, three markets began reporting an increase in dead chickens.


For the first time since 1997, H5N1 was back. The surveillance findings were enough to raise concern that another bird flu outbreak might be imminent and the government’s Environment and Food Bureau took the decision to destroy 1.3 million chickens in markets and farms across Hong Kong.


The surveillance worked, it provided answers to questions but also created new ones like: How did the virus transmission from aquatic to terrestrial poultry take place when the birds were kept a part?

The question remains unanswered and no evidence of the virus re-emerging locally was found. This could only mean the culprit originated from "ground zero" – where the birds were kept before being shipped off to Hong Kong.


The researchers were able to investigate the internal workings of the viruses and noticed that rather than a one-way transmission taking place as previously thought, these viruses were exchanged between their aquatic and terrestrial hosts several times over.

Upon sequencing the viruses’ DNA, researchers found a mutation in the neuraminidase (NA) protein - the critical protein on the surface membrane; found only in influenza A and B strains.

The protein helps release newly-replicated virus cells from the host cell and aid the virus to bypass the immune system and start infecting the entire respiratory tract.


This same NA mutation occurred in H5N1/97, leading the researchers to believe this makes it possible for the virus to adapt to its new host.

What is even more interesting is - while studying one H5N1’s precursors, H9N2, in chickens - researchers also detected the same NA mutation in its protein make-up.

This discovery - along with the finding that one of the virus sub-types isolated from a quail in south-eastern China contained six internal genes related to the H5N1, thought to be involved in the creation of the 1997 virus - raises the disturbing possibility of H9N2 playing a role in the next influenza pandemic.


Evolution

In the last decade, H9N2 has become widespread among terrestrial poultry, especially in chickens and quails. Before the 1990’s the virus was only detected in North American avian species and in ducks in south-eastern China.

By 1997, the virus was identified in China, Korea, Pakistan, India, Saudi Arabia, Germany, Italy, Ireland and South Africa.


In another study carried out in the live markets of Shantou, south-eastern China, 498 viral swabs were taken, mainly from domestic ducks, isolating subtypes ranging from H1 to H12 and N1 to N9. Fifty-three swabs were of H9, a number four times higher than that found in the 1970’s.

Genetic analysis revealed H9 isolated from ducks and chickens were closely related to the genes of H5N1/97, Qa/HK/G1/97 and H5N1 reassortant viruses found in Hong Kong 2001; further providing proof that domestic ducks are the original reservoir for generating H5N1-like viruses.



H9N2 - human-like viruses found in two Hong Kong children in 1999 - revealed an even more troubling aspect, namely that the strain acquired a receptor-binding-like ability to latch onto human cells.

The fact that H9N2 is not pathogenic in chickens gives the virus a silent, cunning persona as there is no hint of infection in the host thus giving the virus greater opportunity to spread undetected and further reassort into a virus that would eventually lead to human-to-human transmission.


Disaster

In this current outbreak, an estimated 60 million chickens have been destroyed, the economic fallout is expected to be in the millions if not billions of dollars.

Vietnam and Thailand have also been hit hard by the crisis; every week new human cases are reported with at least 20 deaths reported to date. The virus has a 78 per cent mortality rate.


Little is known about it because the only previous clinical experience is limited to studies from the 1997 outbreak.

In both episodes the viruses are genetically distinguishable from each other. The 2004 H5N1 virus appears to be "associated with fatal infections among poultry and also a variety of wild bird species, which is unusual" according to the WHO.


Now that China has confirmed it has bird flu, with new reported cases of infected chickens, the world waits with bated breath to see if there are any human cases.

Given the unprecedented time and rate of infection across eight countries so far, this virus obviously didn’t just become virulent overnight. It would have had time to settle and incubate in its aquatic and poultry hosts "assorting" with other avian influenza viruses until it found the right gene constellation to infect on a mass scale.

Therefore the possibly of H5N1 coming into contact with human influenza viruses and re-assorting again into a more easily transmitted human-to human-influenza virus is not only massively frightening, but perhaps inevitable.