Avian influenza has become a hot topic, with a great deal of discussion about its possible impact. This includes speculation about the potential of an avian influenza pandemic.
To examine the issues more closely, we begin with an explanation of what avian influenza is.
Avian influenza refers to a group of viruses that most commonly infect only birds. These pathogens are usually quite species specific, but on rare occasion have crossed the species barrier to infect humans.
Wild birds worldwide carry these viruses in their intestines, but usually do not get sick from them. The viruses are very contagious among birds though, and can make domesticated birds such as turkeys, chickens and ducks very sick, often resulting in death. In fact, the most pathogenic forms may result in multiple organ dysfunction and consequent death in as early as 48 hours after infection.
Influenza A viruses are comprised of many subtypes with some particularly more devastating than others. The H5N1 avian influenza A virus is one of the more deadly of the subtypes. Since 2003, more than 150 million birds died either from the disease or were euthanized to prevent further spread. The H5N1 virus was determined to be the culprit.
Risk to humans
Of the few avian influenza viruses that have crossed the species barrier to humans, H5N1 has caused the largest number of cases of severe disease and death. Unlike normal seasonal influenza, avian influenza has proven to have an aggressive clinical course, with rapid deterioration and high mortality rates. As of January 2006, there were 139 laboratory confirmed cases of avian influenza in humans with a resulting 71 deaths, meaning greater than 50 percent of the cases resulted in death.
Infection in humans is most commonly the result of direct contact with infected poultry or surfaces or other objects contaminated with bird feces containing the virus. Instances of human-to-human transmission of H5N1 and other avian influenza viruses have occurred only rarely, and transmission beyond first generation contacts has not been documented.
So far, the risk of human infection is considered low, but scientists warn that subtle adaptive mutations in the virus may result in increased transmissibility. Because these viruses do not typically infect humans, there is little or no immune protection against them in the human population. If the H5N1 virus were able to infect people and spread easily from person to person, an influenza pandemic or worldwide outbreak would occur.
Signs and symptoms of avian influenza in humans are nonspecific, ranging from fever, cough, sore throat and muscle aches to conjunctivitis (inflammation and redness of the eyeball, often accompanied by discharge), pneumonia and acute respiratory distress.
Presently, four antiviral drugs are FDA approved for treatment of influenza, three of which are approved for prophylaxis. They all maintain activity against influenza A viruses, however, with mutations, resistant strains will invariably develop. In fact, analysis of some of the H5N1 viruses isolated from poultry and humans in Asia have shown the viruses to be resistant to two of the medications.
The World Health Organization is stockpiling antiviral drugs at this time. Their future efficacy remains uncertain at best.
Health care workers can protect their patients, themselves and their families by adhering strictly to some familiar precautionary measures. For any patient being seen with fever, respiratory symptoms and a history of intercontinental travel, it is imperative to employ standard contact and airborne precautions until another diagnosis is made and/or laboratory tests definitively rule out avian influenza.
Use of personal protective equipment such as gowns, goggles or face shields should be considered mandatory when treating these patients. Dedicated equipment should be utilized, such as disposable blood pressure cuffs, thermometers and stethoscopes.
Although pandemic risk does exist, unconditional adherence to established precautions essentially curbs that risk. It is imperative to remain vigilant and take the time to protect ourselves.
Brian Johnson is a registered nurse on the medical/surgical intensive care units at Mount Nittany Medical Center.