How is Avian Influenza transmitted?

Discussion about an avian influenza pandemic and its potential costs to economies leads to the question, “What will spread this virus around the world?” and “How do we prevent it?” Migratory birds, the poultry trade, bird trafficking and human travel are among the possible mechanisms that experts believe to be globalizing the avian influenza A/H5N1 epidemic in poultry and could introduce pandemic flu into the United States (NIAID, 2006 and Wong et al., 2006).

Bird-to-bird

This virus is appropriately named avian (bird) flu. According to Sheff (2005), AI virus “is found in the nasal secretions and droppings of wild and domestic fowl.” The virus has the ability to spread through direct contact, from bird-to-bird. “The risk that infection will be transmitted from wild birds to domestic poultry is greatest where domestic birds roam freely, share a water supply with wild birds, or use a water supply that might be contaminated by droppings from infected wild-bird carriers.” (WHO, 2004). The USDA (2006) also warned that “AI viruses can also be spread by manure, equipment, vehicles, egg flats, crates, and people whose clothing or shoes have come in contact with the virus.” and “one gram of contaminated manure can contain enough virus to infect one million birds.”

The symptoms that birds display if they are infected are as minor as ruffled feathers, reduced egg production but can be as serious as respiratory distress or sudden death (Mayo Clinic, 2005, USDA, 2006). The World Health Organization (2004) stated “birds that survive infection excrete virus for at least 10 days” yet often “birds can die on the same day that symptoms first appear.”

Worldwide effort to prevent the spread of bird flu is multidimensional, focusing on the health of both birds and humans. Measures to help control the virus among domestic poultry included: “culling” (sick or exposed birds — primarily chickens — are destroyed), “quarantining” (affected farms were under forced isolation), “banning birds” (restricted the importation of birds and hatching eggs from regions with bird flu epidemics), and initiating surveillance programs (prevented bird smuggling) (Mayo Clinic, 2005). Procedures to control H5N1 are in place; the USDA (2006) stated that “imported birds (poultry, pet birds, birds exhibited at zoos, and ratites) [are required] to be quarantined and tested for the avian influenza virus before entering the country.” As well, considering that the birds from Laos, China, Cambodia, Indonesia, Japan, South Korea, Thailand and Vietnam potentially could affect humans with influenza A (H5N1), the CDC (2004) issued an order for an immediate ban on the import of all birds from affected countries. These steps to eradicate, isolate and control bird-to-bird transmission of avian influenza could prevent a human pandemic of H5N1.

Bird-to-human

It is possible that a virus called “bird flu” could cross the species barrier from birds to humans. The WHO (2004) stated, “There is mounting evidence that this strain [H5N1] has a unique capacity to jump the species barrier and cause severe disease, with high mortality, in humans.” Proof of this claim became apparent several years ago. Mid-2003, there was an avian flu outbreak in several eastern countries that did cross the species barrier. The first three human cases were confirmed in Viet Nam and resulted in death (World Health Organization, 2006).

Since the first human outbreak of avian influenza, many losses have occurred. More than 200 human cases of avian influenza virus infection due to A/H5, A/H7, and A/H9 subtypes mainly as a result of poultry-to-human transmission have been reported with a > 50% case fatality rate for A/H5N1 infections (Wong, &Yuen, 2006). As of March 24, 2006, 186 humans were infected with the bird flu in the following countries: Azerbaijan, Cambodia, Indonesia, Iraq, Thailand, Turkey, China, and Viet Nam (World Health Organization, 2006). Sadly, one hundred and five of theses laboratory-confirmed cases, between December 26, 2003 and March 24, 2006, have resulted in death (World Health Organization, 2006). This indicates a death rate of 56 percent due to H5N1 infection. Trampuz et al. (2004) reported human cases of avian influenza may even be underestimated in an attempt to minimize the seriousness of the epidemic and thus preventing economic despair for the countries affected.

Considering the prognosis for avian influenza is poor, information discussing methods of transmission have been identified. A quote from the website of the World Health Organization (2005) stated, “From the information currently available, a large number of confirmed human cases of avian influenza acquired their infection during the home slaughtering and subsequent handling of diseased or dead birds prior to cooking”. The CDC (2004) and Mayo Clinic (2005) reported that the majority of the human H5N1 cases are apparently associated with direct exposure to infected birds or to surfaces contaminated with excretions (saliva or droppings) or feathers from infected birds. The USDA (2006) had insight and stated that there have “been no documented cases of human highly pathogenic H5N1 disease resulting from contact with wild birds.”

In addition to those that come into contact with H5N1 infected poultry or contaminated surfaces children seem to be at greater risk. According to Sheff (2005), due to their immature immune systems, young children are especially susceptible to avian influenza. Similarly Trampuz et al. (2004, p. 523) pointed out “Deaths have occurred in otherwise healthy young individuals, which is reminiscent of the 1918 Spanish influenza pandemic.” The seriousness of avian influenza is evident in the deaths that have already occurred and the pattern of infection is mirroring a previous major pandemic.

Human-to-human

The transmission of H5N1 from birds to humans is of great alarm as it is causing illness and death. “The real concern evolves however, around the possibility of this flu mutating into the type that is easily transferable from human to human.” (Rodts, 2005). At this time, the Centers for Disease Control and Prevention (2004) declares, “No evidence of genetic reassortment between avian and human influenza viruses has been identified. If reassortment occurs, the likelihood that the H5N1 virus can be transmitted more readily from person to person will increase.” Mutation of the virus or incorporation of human genes into its viral blueprint will lead to superior transmission of H5N1 from human to human. This fact leads to concern for those people who are not poultry farmers, exposed to contaminated poultry products or traveling to affected countries. Transmission of the virus then becomes a threat to those in close contact with ill and infected persons.