Influenza, also known as the flu, is a contagious respiratory (nose, throat, and lungs) disease caused by the influenza virus. People with flu may have high fever, headache, dry cough, sore throat, runny or stuffy nose, and muscle aches. Nausea, vomiting, and diarrhea can occur but are not as common. Most people who get influenza will recover in one to two weeks, but some will develop serious complications, such as pneumonia.
The flu can spread when droplets from a cough or sneeze of an infected person are propelled through the air onto the mouth or nose of people nearby. Flu viruses can also spread when a person touches an object contaminated by respiratory droplets and then touches his/her own mouth or nose.
There are three types of flu viruses: influenza A, B, and C. The influenza A virus is divided into subtypes and named according to certain proteins, called HA and NA, found on the surface of the virus. For example, a type A virus designated as a “H7N2 virus” is a subtype with the HA 7 protein and the NA 2 protein.
Flu viruses change from year to year. For that reason, immunity (natural protection created against a disease after a person has had that disease) that is built up from having the flu caused by one virus does not provide protection when a different virus circulates. This also means that a vaccine made against flu viruses circulating before may not protect against the newer viruses. Thus, the flu vaccine is updated each year to include current viruses.
Influenza viruses that infect birds are also called avian influenza viruses. While influenza viruses A and B cause disease in humans, avian flu is caused by type A viruses. Influenza C is rarely identified as a cause of human illness.
There are 15 known avian influenza virus subtypes circulating in bird populations. The severity of the disease depends on the subtype that infects the birds. The illness can sometimes be mild, resulting only in ruffled feathers or reduced egg production. Illness can also become what is known as “highly pathogenic avian influenza.” This latter form is extremely contagious in birds and quickly fatal. Millions of domestic birds have been destroyed in the last few years in an attempt to control the spread of the viruses to animals and humans.
Migratory water birds, such as wild ducks, are the natural carriers of avian influenza viruses and are naturally resistant to infection. Domestic birds, on the other hand, are particularly vulnerable and can be infected by being in contact with wild birds, other infected domestic birds, or contaminated cages, water, or feed.
Avian influenza viruses do not normally infect species other than birds and pigs. The first recorded infection of humans with an avian flu virus occurred in Hong Kong in 1997, affecting 18 humans, of whom 6 died.
It is believed that most cases of avian flu infection in humans have resulted from contact with infected poultry or contaminated surfaces. Infected birds shed virus in saliva, nasal discharges, and feces. A person can catch the avian flu virus when an infected chicken coughs or sneezes onto his/her face, or by breathing in bird dropping particles. Other means of transmission of avian flu viruses are possible, such as through an intermediate host (including pigs).
There are no known cases of person-to-person transmission of the avian flu. Since influenza type A is a constantly changing virus, health entities worldwide are aware of the possibility of human-to-human transmission.
Reported symptoms of avian influenza in humans have ranged from typical influenza-like symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), pneumonia, and other severe and life-threatening complications.
Avian influenza viruses circulate among birds worldwide. In addition to the large outbreaks in birds that have occurred in several countries in Asia, smaller outbreaks have been reported in British Columbia, Texas, New Jersey, Maryland, and other locations in North America.
It is rare in humans. To date, a number of subtypes (including H5N1, H7N7, H9N2) of the avian influenza virus have been known to cause illness in people, with H5N1 associated with the most serious illness in humans. Since 1997, there have been several outbreaks of avian flu affecting dozens of people; over 30 people have died. The largest outbreak so far occurred in the Netherlands, where 89 people were confirmed to have H7N7 influenza virus infection associated with a poultry outbreak. One person died.
Most cases of avian flu in humans are linked to persons living close to and/or working with infected birds. People raising chickens are most commonly infected. Persons involved in outbreak control activities (e.g., killing, carcass disposal, and cleaning and disinfection of locations affected by avian influenza) on poultry farms or live bird markets are at increased risk for exposure to avian influenza.
There is no evidence that any human cases of avian influenza have been acquired by eating poultry products. Influenza viruses are destroyed by adequate heat. Following proper food preparation and handling practices (cooking the meat to at least 180 ° F and washing hands after handling raw poultry) will decrease the chances of acquiring foodborne infections.
Poultry producers should strengthen biosecurity practices to prevent the introduction of avian flu into their flocks, be aware of the clinical signs of the avian flu in birds, and report suspicious signs to animal health authorities. Poultry producers and dealers must also use biosecurity precautions at live bird markets. The government list biosecurity measures for poultry producers and dealers can be found at USDA APHIS | Defend the Flock - Biosecurity 101.
You should be evaluated by a healthcare provider in the first few days after the onset of illness to confirm avian influenza. Inform your healthcare provider if you develop any fever or worsening respiratory symptoms. Mention any recent exposures to infected poultry or to someone suspected of having avian influenza.
Healthcare professionals can collect respiratory (nose and throat) or blood samples for testing.
There are no vaccines against avian flu. There are four different influenza antiviral drugs for the treatment and/or prevention of influenza. However, some of the H5N1 viruses isolated from poultry and humans in 2004 in Asia have shown that the viruses are resistant to two of the medications.
Be aware of health travel advisories issued for other countries. Travelers to areas with outbreaks of avian infection should avoid live animal markets and poultry farms. Avoid touching any surfaces that appear to be contaminated with feces from poultry or other animals.
Scientists know that avian and human influenza viruses can exchange genes when a person is infected with viruses from both species at the same time. This process of gene swapping inside the human body can give rise to a completely new subtype of the influenza virus. This new virus might then be able to infect humans and spread from person to person. Few, if any, humans would have natural immunity to this new virus. In addition, the existing vaccines would not be effective against a completely new influenza virus. Scientists are concerned that the lack of natural immunity and the lack of effective vaccines against a new virus could lead to a pandemic (worldwide epidemic). National and international agencies are taking steps for dealing with this possibility.