Contact Variables for Exposure to Avian Influenza H5N1 Virus at the Human-Animal Interface

Abstract

Although the highly pathogenic avian influenza H5N1 virus continues to cause infections in both avian and human populations, the specific zoonotic risk factors remain poorly understood. This review summarizes available evidence regarding types of contact associated with transmission of H5N1 virus at the human-animal interface. A systematic search of the published literature revealed five analytical studies and 15 case reports describing avian influenza transmission from animals to humans for further review. Risk factors identified in analytical studies were compared, and World Health Organization-confirmed cases, identified in case reports, were classified according to type of contact reported using a standardized algorithm. Although cases were primarily associated with direct contact with sick/unexpectedly dead birds, some cases reported only indirect contact with birds or contaminated environments or contact with apparently healthy birds. Specific types of contacts or activities leading to exposure could not be determined from data available in the publications reviewed. These results support previous reports that direct contact with sick birds is not the only means of human exposure to avian influenza H5N1 virus. To target public health measures and disease awareness messaging for reducing the risk of zoonotic infection with avian influenza H5N1 virus, the specific types of contacts and activities leading to transmission need to be further understood. The role of environmental virus persistence, shedding of virus by asymptomatic poultry and disease pathophysiology in different avian species relative to human zoonotic risk, as well as specific modes of zoonotic transmission, should be determined.

Seroprevalence of Antibodies against Highly Pathogenic Avian Influenza A (H5N1) Virus among Poultry Workers in Bangladesh, 2009

“…Other methods to assess the cellular immune response such as measuring H5N1-specific T-cell responses might help identify prior HPAI H5N1 virus infections that resulted in asymptomatic or mild illness [28]. Exposure to HPAI H5N1 virus in poultry workers can potentially include self-inoculation of mucous membranes (including conjunctivae) of the respiratory tract after direct contact with poultry or surfaces contaminated with feces, internal organ tissues, or poultry blood; or through inhalation of large or small droplets that are aerosolized such as those generated through slaughtering, defeathering, or evisceration [29]. …”

Comparative Analysis of Avian Influenza Virus Diversity in Poultry and Humans during a Highly Pathogenic Avian Influenza A (H7N7) Virus Outbreak

“…Nonetheless, this study suggests that the effective control of influenza virus in poultry can prevent avian influenza viruses from acquiring all their prerequisites to become human tropic, in addition to the reduction of human exposure (39). Increased awareness by veterinary and medical authorities is needed to design more efficient surveillance, diagnostic algorithms, and prepandemic planning strategies.…”

Predicting Disease Severity and Viral Spread of H5N1 Influenza Virus in Ferrets in the Context of Natural Exposure Routes

“…Currently, outbreaks occur in regions where H5N1 is endemic in migratory birds and where a large proportion of the population rear backyard poultry (5) or visit live-bird markets (4). Transmission to humans can occur through multiple exposure pathways (6), with the potential for infection to be established via aerosol, droplets, or ingestion (5,7). Currently, it is unclear whether and how exposure routes influence the disease severity of H5N1 infection for people.…”