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From: Food Quality & Safety magazine, December/January 2008

Ground Avian Flu Fears

Many fear contracting the H5N1 virus from eating tainted poultry, but a few simple steps offer protection

by Belinda Mak

The year 2007 marks 10 years since the H5N1 avian influenza virus (often called bird flu) was first reported, and it is getting more difficult to contain with every passing year. The virus has killed 202 people, and more than 50 million chickens infected with the virus or suspected of being infected have been killed or culled in more than 50 countries.

The infection is caused by influenza virus type A, which normally infects birds and is highly contagious. The first case of human infection with highly pathogenic H5N1 avian influenza was reported in Hong Kong in 1997. In 2003, the most devastating and widespread outbreak of H5N1 to date emerged in Asia before spreading to Europe, Africa, and North America. The most obvious victim of bird flu is the multibillion-dollar poultry industry. Estimates of global losses due to outbreaks amount to hundreds of billions of dollars.

The biggest threat to the poultry industry is the backlash due to customer fears. Several polls conducted in 2006 in the United States found that more than 40% of people thought they could get bird flu by eating poultry. Poultry sales in France fell by 30% following an outbreak last year. Consumer reaction was even more severe in Romania, which witnessed an 80% drop in poultry sales in May 2006; in Italy, sales fell by 70% after wild swans were infected. Early in 2007, the price of chicken in Indonesia dropped by 50%. Early victims of bird flu scares have also included global fast food chains. In 2005, a Japanese fast food chain slashed its profit forecast by 60% and spent £2 million on safety campaigns after bird flu was reported in Japan. When a bird flu outbreak in a region is contained, however, sales of poultry do bounce back, albeit slowly.

A Food Safety Risk?

But does H5N1 really pose a food safety risk? It is clear that globalization of food production and trade has made food safety an issue of international importance. Food safety must be tackled not only at the national level; it now requires international collaboration between food safety authorities.

Continuing outbreaks of bird flu in poultry in Asia, Europe, and Africa have raised concern about the various sources of infection and risks to humans. Based on current evidence, direct contact with infected live or dead poultry is responsible for a majority of infections in humans. There is also concern that the virus could spread to humans through contact with contaminated poultry products.

In developed countries, meat is bought, either refrigerated or frozen, from a butcher or supermarket. In Asia, however, it is common practice to buy chickens and other live animals at the market and slaughter them in kitchens. As a result of this practice, Asians have a high level of exposure to potentially disease-carrying animals, both in their homes and as they pass through the markets that line the streets of densely packed urban centers. Wet markets have been identified as one of the sources of H5N1 infection in humans.

Most recently, a nine-month-old in Hong Kong who was frequently taken to a wet market selling live poultry was infected with a mild form of bird flu. It is this kind of event that raises a number of questions about food safety during an influenza outbreak.

Proper Cooking Key to Safety

H5N1 is sensitive to heat; thus, it is safe to consume poultry as long as it has been cooked properly (70°C in all parts of the food). Consumers should also be aware of the risk of cross-contamination. Raw poultry juices and poultry products should never touch items that are eaten raw. People involved in the preparation of raw/frozen poultry products should thoroughly wash their hands and disinfect all utensils that contact the poultry. Hot water and soap are sufficient for this purpose.

But proper cooking and handling may not offer sufficient protection when it comes to delicacies like foie gras, raw duck blood pudding, raw duck blood, or bird’s nest soup. In Vietnam, three brothers contracted bird flu after drinking raw duck blood, a delicacy in some Asian cultures. The foie gras industry of France was threatened by a bird flu outbreak last year; while uncooked foie gras should be avoided, cooked foie gras is safe. The clear message is that consumption of raw poultry ingredients poses a high risk and should be discouraged.

The virus can also be present in the tissue of frozen chicken, because low temperatures maintain the viability of the virus. In 2004, Japan and Korea banned imports of both live and frozen poultry meat from China and Thailand following identification of the virus in frozen poultry samples. Once again, whether it is purchased fresh or frozen, the meat should be properly and thoroughly cooked.

The Incredible Inedible Egg?

The virus can also be found inside egg whites, egg yolks, and on the surfaces of eggs laid by infected birds, but proper cooking inactivates the virus inside the eggs. Uncooked eggs that have not been treated should not be used in food that will not be cooked, baked, or treated in any other way. Some examples include cake batter, cookie dough, fruit drinks made with raw eggs, dressings made with raw eggs—Caesar salad dressing, for example—homemade ice cream, or tiramisu. For such foods, eggs that have been pasteurized to inactivate the virus can be used. There have been no reported cases or epidemiological evidence to suggest that people have been infected by consuming eggs or egg products. To eliminate shell contamination, commercial egg suppliers in North America wash and disinfect the outsides of eggs with chlorine prior to breaking or packaging.

Another issue is that while consumers are mainly concerned about eating poultry and eggs during bird flu outbreaks, some food products are grown in agriculture and aquaculture using chicken litter as a fertilizer.

According to recent research conducted by Penn State University’s Animal Diagnostics Laboratory (University Park, Pa.), virus particles in chicken manure are inactivated after six days at 15-20°C, after 36 hours at 28-30°C, and after only 20 minutes at 56°C. Therefore, virus is inactivated during phase I and phase II composting. Patricia Dunn, DVM, MAM, ACPV, co-author of the Penn State study, says it is not likely that litter from an infected poultry farm would be released several weeks after the birds have been killed or removed from the premises and subsequently test positive for the presence of virus. Suppliers of poultry manure should assure their customers of biosecurity measures on their farms and should ensure that poultry litter is composted, properly ensiled, and dried with heat treatment.

Barriers in Food Manufacturing

Efforts to contain the virus need to include all three stages of the food chain: the first step, the poultry farms; the intermediate step, the marketplaces; and the tertiary end of the food chain, the food processing industry and consumers. Other than people who breed and rear birds, there are many workers (e.g., cleaners, packers, cooks, chefs, food handlers, and other kitchen workers) who come into contact with birds. People responsible for slaughtering birds must wear protective clothing. Workers cleaning and decontaminating poultry houses must also take special precautions; they are likely to have contact with contaminated feces.

Poultry growers and processors can ensure that no dead birds are delivered to slaughterhouses. They must also adopt zero tolerance of fecal contamination of carcasses and must dispose of tissues where the virus is most likely to reside such as the lungs, trachea, head, and intestines.

And although migratory birds are often the focus when it comes to the spread of H5N1, they are not solely responsible for spreading the virus, given the fact that infectious diseases travel from host to host in a chain. All too often, the infection occurs locally when H5N1 transmission is promoted among densely packed flocks of poultry. Sometimes there are 50,000 birds in two-story sheds; the consequent close contact offers opportunity for the virus to spread by way of secretions. Improved farming practices are needed to contain the spread of bird flu. These include improved biosecurity measures, quarantine for sick birds, disinfection of transport vehicles and cages, and protective clothing for farm workers.

Technology and Food Safety Testing

Outbreaks of bird flu have been occurring sporadically for the last 10 years, with no end in sight, imposing grave losses on the poultry industry. Vaccination, drug treatment, and other containment efforts cannot be maximized unless the infection is detected quickly enough. Diagnosing primary bird flu infection should be of the utmost concern; early diagnosis can allow swift implementation of biosecurity, quarantine, and culling, as well as other control measures to safeguard the poultry industry.

During the 2006 outbreak, the chicken industry in the United States sought to reassure the public by testing every flock for bird flu before the birds were slaughtered. Developed countries can afford to bear the financial costs of rapid and expensive tests for poultry diagnosis. But countries with limited resources need new, rapid, accurate, and cost-effective tests to diagnose bird flu, monitor contaminated food, and swiftly implement preventive measures. Current methods for diagnosing bird flu fall into three categories: virus culture, laboratory antigen detection tests, and tests using nucleic acid amplification techniques (NATs).

Virus culture is considered the gold standard for identifying viral infections. Virus isolation in embryonated eggs, along with subsequent H and N subtyping, can take up to 14 days. In an outbreak, time is the limiting factor; the sooner bird flu is diagnosed, the sooner control measures can be put into place.

The second type of test is the antigen detection test, which must be carried out in a laboratory. Antigen detection tests include the immunofluorescence assay and enzyme-linked immunosorbent assay (ELISA). Although these tests are inexpensive, easy to use, and fast, they are prone to coreactivity between proteins, which affects results. They are also less sensitive than virus isolation and other techniques such as NATs.

NATs provide results in a few hours. This type of testing also offers convenient and quick automated result analysis, achieves higher sensitivity compared with virus isolation, and is more specific than traditional immunological testing. NAT tests include polymerase chain reaction (PCR) and nucleic acid sequence-based amplification (NASBA). PCR amplifies millions of copies of DNA using a single polymerase in step-wise reactions and requires an expensive thermocycler and/or real-time PCR machine. NASBA amplifies RNA in a single reaction utilizing three enzymes. It is particularly good for RNA viruses such as bird flu. It also offers an exceptional advantage over other testing methods in that it requires no expensive machines.

NASBA-EOC assays utilize an ELISA plate reader, making them extremely cost-effective. Moreover, standardization among different laboratories is possible, because NASBA-EOC is an isothermal process. NASBA-EOC assay is in use in China and Japan to assist in the monitoring programs for H5N1 avian influenza diagnosis in poultry.

Early Diagnosis the Best Defense

In a crisis of global importance, standardized testing will play a key role in deterring a catastrophic outbreak of avian influenza. Early diagnosis is the best defense against avian influenza. Therefore, there is an obvious need for rapid testing to enhance food safety and to minimize economic losses to the poultry sector.

It is important for scientists, the food industry, and government agencies not to let their guard down against a virus that is becoming harder to control. When H5N1 is present in poultry, the virus can be present in meat and eggs from affected birds. It is safe, however, to consume poultry products that have been cooked thoroughly. Further, bird flu outbreaks must be controlled in poultry to maintain the profitability of the poultry industry and to guarantee food security. Rapid, accurate, and easy-to-use methods that give both state-of-the-art laboratories and those with limited resources a rapid testing system are needed to prevent the spread of the disease.

Dr. Lau is the general manager at Hai Kang Life Corporation Limited. Reach him at or (852) 2111-2123.


  1. Lau LT, Fung YW, Yu AC. Detection of animal viruses using nucleic acid sequence-based amplification (NASBA). Dev Biol (Basel). 2006;126:7-15.; discussion 323. Review.
  2. Lau LT, Banks J, Aherne R, et al. Nucleic acid sequence-based amplification methods to detect avian influenza virus. Biochem Biophys Res Commun. 2004;313(2):336-342.
  3. The World Health Organization. Avian influenza: food safety issues. Available at: Last accessed November 21, 2007.
  4. Meijer A. Importance of rapid testing to combat the global threat of bird flu. Expert Rev Mol Diagn. 2006:6(1):1-4.



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