APPLICATION OF BIOLOGICAL AND MOLECULAR TECHNIQUES TO THE DIAGNOSIS AND CONTROL OF AVIAN INFLUENZA AND OTHER EMERGING POULTRY PATHOGENS
Location: Exotic and Emerging Avian Viral Diseases Research Unit
Title: What are the possible transmission methods for H5N1 high pathogenicity avian influenza viruses to people
Submitted to: Meeting, Center for Food Safety, University of Georgia
Publication Type: Abstract Only
Publication Acceptance Date: January 30, 2009
Publication Date: March 3, 2009
Citation: Swayne, D.E. 2009. What are the possible transmission methods for H5N1 high pathogenicity avian influenza viruses to people [abstract]. In: Abstracts of the 16th Annual Meeting, Center for Food Safety, March 3-4, 2009, Atlanta, Georgia. p. 2-3.
The H5N1 high pathogenicity avian influenza (HPAI) virus has caused an unprecedented epizootic affecting poultry in Asia, Africa and parts of Europe, but has crossed multiple species barriers to infect captive and wild birds, carnivorous mammals and humans. Human infections (391 infections with 247 fatalities) have been associated with direct or indirect contact with live or dead poultry while in carnivores, consumption of infected birds or their products have been associated with infections. Theoretical modes of transmission of H5N1 HPAI virus from birds-to-humans would include: 1) inhalation of contaminated dust from rearing or slaughter, or fine water droplets generated during household or live poultry market slaughter process; 2) direct contact with oral, nasal or conjunctival mucus membranes such as from hand-transplantation of virus from contaminated surfaces, direct exposure to contaminated dust or feathers, or swimming or bathing in contaminated household water source; and 3) consumption of raw or undercooked infected poultry products.
Using the ferret model, H5N1 HPAI virus did not transmit efficiently by either respiratory droplets or direct contact between ferrets confirming the observation that human-to-human transmission has been inefficient and limited. However, an H5N1 HPAI virus was transmitted to ferrets by exposure to airborne virus generated during simulated home slaughter of asymptomatic infected chickens. The H5N1 HPAI virus was detected in slaughter room air samples.
Using both ferret and pig models, transmission of H5N1 HPAI virus was demonstrated by oral or direct digestive tract exposure and closely mimicked human infections and disease, but production of infection by such exposure required a much higher dose of virus than exposure via the upper respiratory tract. The predominate site of virus replication following oral consumption of H5N1 virus infected meat was the respiratory tract, initiated through infection of tonsil followed by nasal cavity infection, but with A/Vietnam/1203/04 (H5N1) strain (a virus isolated from a fatal human case), the ferrets were simultaneous infected via the upper digestive tract with spread to liver and pancreas. Five H5N1 and one H7N3 HPAI viruses consumed via chicken meat resulted in infection in ferrets, but production of such infections was dependent on virus strain and the amount of virus in the meat. Cooking or pasteurization was effective at killing the virus.
These results suggest consumption of infected raw poultry products could produce human infections based on the ferret model. However, the risk or probability of producing such infections would be greatly influenced by several factors. First, because most ethnic groups consume cooked poultry and general education programs have taught complete cooking of poultry, most humans are unlikely to consume uncooked or undercooked poultry. Second, if a person were to consume uncooked or undercooked poultry, a high dose would be needed to produce an infection. A greater potential for human infection would be through direct airborne exposure to infected birds or processing of infected birds. This emphasizes the need for early detection of HPAI infected poultry and their destruction before entry into slaughter process. Considering the rarity of human avian influenza (AI) cases associated with eating raw infected products and the ease with killing avian influenza virus (AIV) by cooking, AI has not become a food safety issue.