Agricultural Technology
Research Program


Volume 17 | Number 3 | Fall 2005 | Safety Issue

In this special focus issue, PoultryTech, through a series of articles, takes a closer look at avian influenza, its threat to the U.S. poultry industry and humans, and innovations that are underway to help contain it.

page 1
Avian Influenza and Food Safety: An Overview

page 2
GTRI Receives USDA Grant to Develop Interferometric Biosensor as a Tool for the Detection of Avian Influenza

page 3
Veteran Flu Fighter Offers Advice

page 4
Poultry Industry Tells Senate Safeguards Are in Place to Keep “Asian Flu” Out of the United States

page 5
Study: Bird Flu Vaccine Can Stop Spread


<< ATRP Publications Page

Avian Influenza and Food Safety: An Overview

By David Gottfried

Migratory birds and avian influenza

Avian influenza, more commonly referred to as bird flu, is a contagious disease normally confined to wild and domestic birds. Inset photo shows the H5N1 strain of the virus, a highly pathogenic strain, which is the focus of the current Asian outbreak.

Photo by Gordon Smith. Inset photo courtesy of CDC/G.Goldsmith

What is Avian Influenza (AI)?

Pick up practically any newspaper or magazine in the world these days and you will likely find an article about avian influenza (AI), more commonly referred to as bird flu, and the impending human flu pandemic. This contagious disease, normally confined to wild and domestic birds, is caused by the same virus in the family Orthomyxoviridae, which produces significant numbers of infections, usually of the upper respiratory tract, in humans, horses, dogs, domestic pigs, and other species.

Migratory waterfowl and shorebirds are the natural genetic reservoir of all subtypes of influenza virus, while chickens, turkeys, and other gallinaceous birds are not natural reservoirs of AI viruses. However, AI viruses have been isolated sporadically as the cause of infection in domestic poultry.

AI Classification

Worldwide there are many strains of avian influenza virus, causing varying degrees of illness in poultry, which are characterized by two different proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). The 16 different H proteins and 9 different N proteins can combine to give different viral subtypes. The seasonal flu, which afflicts the human population on a yearly basis, has typically been caused by H1, H2, and H3 influenza subtypes. In birds, influenza viruses are further divided into two groups: low pathogenicity avian influenza (LPAI) and high pathogenicity avian influenza (HPAI) viruses.

Pathogenicity refers to the ability of the virus to produce disease, with the high path viruses producing far more severe clinical signs and higher mortality in birds. Low path AI has been identified in the United States and around the world for more than 100 years, and is a relatively common finding just as flu viruses are a common and seasonal occurrence in humans. These virus strains cause some infected birds to become ill and can be fatal to some, similar to its pathology in humans.

Highly Pathogenic AI

Highly pathogenic avian influenza is much rarer and has only been detected in the United States during three previous outbreaks (1924, 1983, and 2004). The most recent outbreak in 2004 was quickly detected and eradicated, being confined to one flock of 6,600 birds. There were no significant human health implications or reports of human health problems in connection with any of those outbreaks. For poultry, only H5 and H7 subtypes of the AI virus have developed into highly pathogenic strains. Recent research has shown that the H5 and H7 subtypes can, after circulation for sometimes short periods in a poultry population, mutate to highly pathogenic even if they start out in a low pathogenic form. The particular virus strain which has made the news and which is currently circulating in Asia (and moving through Europe) is an H5N1 virus, and it is highly pathogenic. At present, the United States does not have HPAI H5N1 and does not import poultry from countries currently experiencing H5N1 outbreaks. The unique aspect of this particular virus is that it has been transmitted from birds to humans, most of whom had reported extensive direct contact with infected birds. The infection of humans with this avian influenza virus, which began in Hong Kong in 1997, has resulted in necessary concern and caution regarding the role of avian species in the epidemiology of human influenza.

Sources of AI Infection

Since the reservoir of influenza viruses in wild birds should be considered a major source of infection for domestic birds, particularly free and open range poultry, it is important to reduce the contact between these two groups. Live bird markets are the second most important reservoir of influenza virus for commercial poultry.

When AI outbreaks occur in poultry, quarantine and depopulation (culling) of all infected, exposed, or potentially infected birds, followed by proper disposal of carcasses, and the quarantining and rigorous disinfection of farms and surveillance around affected flocks are the preferred eradication and control options. Avian influenza viruses are susceptible to control using chemical and physical measures such as heat, extremes of pH, nonisotonic conditions, and dryness, which can inactivate AI viruses. In addition, AI viruses are inactivated by organic solvents and detergents.

As mentioned above, only sporadic bird-to-human and suspected environment-to-human transmission has been observed by epidemiological findings. Two possible cases of human-to-human transmissions in 2004-2005 involved extremely close contact during the critical phase of illness. Studies from the 1997 H5N1 outbreak indicate that human-to-human transmission might have occurred through close physical contact but not through social contact, and no evidence to date indicates that there has been human-to-human transmission of H5N1 avian virus by small-particle aerosol exposure.

AI and Food Safety Issues

The primary route of infection by the influenza virus is via the respiratory tract (in birds and humans). However, because of the severity of the recent outbreaks of HPAI H5N1 in poultry in Asia (and Europe), which are compounded by the associated human illnesses and deaths, concerns about the risk of human transmission through food preparation and consumption have been raised. Although research is ongoing, the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and the United States Department of Agriculture (USDA) reports and websites indicate that there is little evidence to suggest that AI can be spread through contaminated foods, and there is no evidence that any human cases of AI have been acquired by eating properly prepared and cooked poultry products.

For poultry growers and processors, there are several barriers already in place that make delivery of contaminated product unlikely. These barriers to AI contamination in food manufacturing include: 1) delivery of birds with active AI virus infection to slaughter is rare; 2) antemortem and postmortem inspection by USDA Food Safety and Inspection Service personnel leads to the identification of sick birds and diseased carcasses at poultry processing plants; 3) zero tolerance for fecal contamination of carcasses; 4) discarding of the head, trachea, lungs, and intestines, which removes tissues more commonly found with AI virus; 5) antimicrobial carcass washes; and 6) processing by cooking of poultry products.

Available data tend to indicate that human infection may be associated with handling and preparing diseased birds prior to cooking. So far, there are no detailed descriptions of the route of infection for human cases of AI nor specific indications of the nature of poultry-human contacts that have produced or are required for virus transmission. From the information available, it is clear that the large majority of human cases have occurred in rural settings, linked to handling diseased poultry, which probably covers a series of high risk activities such as slaughtering, defeathering, eviscerating, and preparing raw poultry for cooking.

In general, good hygiene practices during handling of raw poultry meat and usual recommended cooking practices for poultry products would lower any potential risk to insignificant levels. Because eggs from infected poultry could also be contaminated with the virus, the same care should be taken in handling shell eggs or raw egg products. To date, according to the WHO, there is no epidemiological information to suggest that the disease can be transmitted through contaminated food or that products shipped from affected areas have been the source of infection in humans.

Fortunately, the virus is inactivated at temperatures achieved in usual cooking to at least 70 oC (158 oF) at the center of the product, so consumption of properly cooked poultry is not a high risk activity. While freezing and refrigeration would not substantially reduce the concentration or virulence of viruses on contaminated meat, proper cooking kills such viruses.

The USDA summarizes its basic food safety advice (which applies to all food pathogens) to consumers with the following procedures:

Clean: Always wash hands and surfaces that have come in contact with meat and poultry products before and after handling food.

Separate: Do not cross-contaminate. Keep raw meat, poultry, fish, and their juices away from other foods.

Cook: Using a food thermometer is the only sure way to know that meat and poultry have reached the proper temperature to inactivate bacteria and viruses. Appearance will not answer that question for you.

Chill: Refrigerate (<40 oF) or freeze (<0 oF) all perishable food promptly.

David Gottfried is a senior research scientist with the Georgia Tech Research Institute.

Related Links

For more information on avian influenza, visit the following websites:

United States Department of Agriculture

Centers for Disease Control and Prevention

American Veterinary Medical Association

Animal and Plant Health Inspection Service

International Association for Food Protection

World Health Organization

World Organization for Animal Health

The poultry industry has launched this new website to respond to any public concern that may occur over avian influenza, highlighting the fact that it is not a food issue and that H5N1 highly pathogenic avian influenza does not exist in the United States. Information is given in brief articles, a question-and-answer format, and in news releases. Some information is also given in Spanish. Links are also provided to sources of official information, such as the U.S. Department of Agriculture and the Centers for Disease Control and Prevention.

Taylor vortex-based ultraviolet disinfection system

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Photo by Gordon Smith. Inset photo courtesy of CDC/G.Goldsmith


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PoultryTech is published by the Agricultural Technology Resarch Program (ATRP), Food Processing Technology Division (FPTD) of the Georgia Tech Research Institute. ATRP is conducted in cooperation with the Georgia Poutry Federation with funding from the Georgia Legislature.