Bird Flu (Avian Influenza)
Avian influenza-known informally as avian flu or bird flu is a variety of influenza caused by viruses adapted to birds. The type with the greatest risk is highly pathogenic avian influenza (HPAI). Bird flu is similar to swine flu, dog flu, horse flu and human flu as an illness caused by strains of influenza viruses that have adapted to a specific host. Out of the three types of influenza viruses (A, B, and C), influenza A virus is a zoonotic infection with a natural reservoir almost entirely in birds. Avian influenza, for most purposes, refers to the influenza A virus.
Though influenza A is adapted to birds, it can also stably adapt and sustain person-to person transmission. Recent influenza research into the genes of the Spanish flu virus shows it to have genes adapted from both human and avian strains.
Pigs can also be infected with human, avian, and swine influenza viruses, allow for mixtures of genes to create a new virus, which can cause an antigenic shift to a new influenza A virus subtype which most people have little to no immune protection.
Avian influenza strains are divided into two types based on their pathogenicity: high pathogenicity (HP) or low pathogenicity (LP). The most well-known HPAI strain, H5N1, appeared in China in 1996, and also has low pathogenic strains found in North America.
Companion birds in captivity are unlikely to contract the virus and there has been no report of a companion bird with avian influenza since 2003. Pigeons can contract avian strains, but rarely become ill and are incapable of transmitting the virus efficiently to humans or other animals.
Between early 2013 to early 2017, 916 lab-confirmed human cases of H7N9 were reported to the World Health Organization (WHO).On 9 January 2017, the National Health and Family Planning Commission of China reported to WHO 106 cases of H7N9 which occurred from late November through late December, including 35 deaths, 2 potential cases of human-to-human transmission, and 80 of these 106 persons stating that they have visited live poultry markets. The cases are reported from Jiangsu (52), Zhejiang (21), Anhui (14), Guangdong (14), Shanghai (2), Fujian (2) and Hunan (1).
Similar sudden increases in the number of human cases of H7N9 have occurred in previous years during December and January.Bird flu is caused by a type of influenza virus that rarely infects humans. More than a dozen types of bird flu have been identified, including the two strains that have most recently infected humans — H5N1 and H7N9. When bird flu does strike humans, it can be deadly.
Outbreaks of bird flu have occurred in Asia, Africa, North America and parts of Europe. Most people who have developed symptoms of bird flu have had close contact with sick birds. In a few cases, bird flu has passed from one person to another. Only sporadic human cases have been reported since 2015.
Health officials worry that a global outbreak could occur if a bird flu virus mutates into a form that transmits more easily from person to person. Researchers are working on vaccines to help protect people from bird flu.
What is Bird Flu (Avian Influenza)?
Bird flu or avian flu is an infectious disease of birds caused by type A strains of the influenza virus. Bird flu, which was first identified in Italy more than 100 years ago, occurs worldwide.
Fifteen subtypes of influenza virus are known to infect birds, thus providing an extensive reservoir of influenza viruses potentially circulating in bird populations. To date, all outbreaks of the highly pathogenic form have been caused by influenza A viruses of subtypes H5 and H7.
Within a country, bird flu can spread easily from farm to farm. Large amounts of avian flu is secreted in bird droppings, therefore contaminating dust and soil. An airborne virus can spread bird flu from bird to bird, causing infection when the avian flu is inhaled.
Contaminated equipment, vehicles, feed, cages or clothing – especially shoes – can also carry bird flu from farm to farm. Avian flu can be carried on the feet and bodies of animals, such as rodents, which act as “mechanical vectors” for spreading the bird flu. Limited evidence suggests that flies can also act as mechanical vectors.
Droppings from infected wild birds can introduce avian flu into both commercial and backyard poultry flocks. The risk that the bird flu nfection 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 become contaminated by droppings from infected wild-bird carriers. So-called “wet” markets, where live birds are sold under crowded and sometimes unsanitary conditions, can be another source where bird flu spreads.
Bird flu viruses do not usually infect humans, however, several cases of human infection with bird flu viruses have occurred since 1997.
Progression of Bird Flu (Avian Influenza)
Based on data from six of the cases of bird flu, the median time between exposure to avian flu and onset of illness is 3 days (range 2-4 days). In these ten patients, the mortality rate was high, with death occurring a mean of 10 days after onset of bird flu.
However, these cases were identified by alert clinicians in tertiary care hospitals and cannot be taken to be representative of the full range of illness that H5N1 may cause.
How avian influenza is spread
Human to human spread of bird flu occurs rarely. However, the bird flu virus can change (mutate) and may then be able to spread between humans. In the past there have been global pandemics (infections in people all around the world) of bird flu in humans caused by these changed viruses. The main risk for human infection is direct or indirect exposure to infected live or dead domestic birds (for example chickens and ducks), or to environments contaminated by infected birds.
Signs and symptoms of bird flu may begin within two to seven days of infection, depending on the type. In most cases, they resemble those of conventional influenza, including:
- Sore throat
- Muscle aches
- Shortness of breath
Some people also experience nausea, vomiting or diarrhea. And in a few cases, a mild eye infection (conjunctivitis) is the only indication of the disease.
Bird flu occurs naturally in wild waterfowl and can spread into domestic poultry, such as chickens, turkeys, ducks and geese. The disease is transmitted via contact with an infected bird’s feces, or secretions from its nose, mouth or eyes.
Open-air markets, where eggs and birds are sold in crowded and unsanitary conditions, are hotbeds of infection and can spread the disease into the wider community.
Undercooked poultry meat or eggs from infected birds can transmit bird flu. Poultry meat is safe to eat if it’s been cooked to an internal temperature of 165 F (74 C). Eggs should be cooked until the yolks and whites are firm.
Experts say bird flu is probably spread by migrating birds. The affected people are thought to have caught avian flu from direct contact with infected poultry.
Infected birds shed the bird flu virus via their saliva, faeces, or nasal secretions. Birds can become infected when they have contact with surfaces contaminated with excretions, or contaminated excretions themselves.
Apart from being highly contagious between birds, avian flu viruses are readily transmitted by mechanical means, such as by contaminated equipment, vehicles, feed, cages, or clothing. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low.
Fears persist that bird flu could combine with a human flu virus to become a deadly disease that could spread among people. There is also concern that avian flu may have crossed into other species after the deaths of a rare leopard and two domestic cats in Thailand.
The greatest risk factor for bird flu seems to be contact with sick birds or with surfaces contaminated by their feathers, saliva or droppings. The pattern of human transmission remains mysterious. In very few instances, bird flu has been transmitted from one human to another. But unless the virus begins to spread more easily among people, infected birds present the greatest hazard.
People with bird flu may develop life-threatening complications, including:
- Pink eye (conjunctivitis)
- Respiratory failure
- Kidney dysfunction
- Heart problems
Although bird flu may kill more than half the people it infects, the number of fatalities is still low because so few people have had bird flu. Fewer than 500 bird flu deaths have been reported to the World Health Organization since 1997.
In contrast, the Centers for Disease Control and Prevention estimates that seasonal influenza is responsible for thousands of deaths each year in the United States alone.
Two classes of bird flu drugs are available. These are the M2 inhibitors (amantadine and rimantadine) and the neuraminidase inhibitors (oseltamivir and zanimivir). These bird flu drugs have been licensed for the prevention and treatment of human influenza in some countries, and are thought to be effective regardless of the causative strain.
However, initial analysis of avian flu isolated from the recently fatal cases in Vietnam indicates that the viruses are invariably resistant to the M2 inhibitors. Further testing is under way to confirm the resistance of amantadine. Network laboratories are also conducting studies to confirm the effectiveness of neuraminidase inhibitors against the current H5N1 strains.
Current bird flu vaccines, when administered to high-risk groups such as poultry cullers, protect against circulating human strains. Avain flu vaccines reduce the threat of infection from human and avian viruses simultaneously for those who are at high risk of exposire. Dual infections give the avian and human viruses an opportunity to exchange genes, possibly resulting in a new influenza virus subtype with pandemic potential.
Annual bird flu vaccines are produced for routine use in protecting humans during seasonal epidemics of influenza. They offer no protection against infection by the H5N1 avian virus.
WHO has issued guidelines for the vaccination, using the current trivalent influenza vaccine, for groups considered at high risk of exposure in countries experiencing outbreaks of highly pathogenic H5N1 avian influenza in poultry.
Travellers to countries in Asia with documented H5N1 outbreaks should avoid poultry farms, contact with animals in live food markets, and any surfaces that appear to be contaminated with faeces from poultry or other animals.
Bird flu vaccine
The Food and Drug Administration has approved one vaccine to prevent infection with one strain of H5N1 bird flu virus. This vaccine isn’t available to the public, but the U.S. government is stockpiling it and will distribute it in the event of an outbreak.
This vaccine could be used early in such an outbreak to provide limited protection until another vaccine — designed to protect against the specific form of the virus causing the outbreak — is developed and produced. Researchers continue to work on other types of bird flu vaccines.
Recommendations for travelers
If you’re traveling to Southeast Asia or to any region with bird flu outbreaks, consider these public health recommendations:
- Avoid domesticated birds. If possible, avoid rural areas, small farms and open-air markets.
- Wash your hands. This is one of the simplest and best ways to prevent infections of all kinds. Use an alcohol-based hand sanitizer containing at least 60 percent alcohol when you travel.
- Ask about a flu shot. Before traveling, ask your doctor about a flu shot. It won’t protect you specifically from bird flu, but it may help reduce the risk of simultaneous infection with bird and human flu viruses.
Poultry and egg products
Because heat destroys avian viruses, cooked poultry isn’t a health threat. Even so, it’s best to take precautions when handling and preparing poultry, which may be contaminated with salmonella or other harmful bacteria.
- Avoid cross-contamination. Use hot, soapy water to wash cutting boards, utensils and all surfaces that have come into contact with raw poultry.
- Cook thoroughly. Cook chicken until the juices run clear, and it reaches a minimum internal temperature of 165 F (74 C).
- Steer clear of raw eggs. Because eggshells are often contaminated with bird droppings, avoid foods containing raw or undercooked eggs.
Birds, just like people, get the flu. Bird flu viruses infect birds, including chickens, other poultry, and wild birds such as ducks. Usually bird flu viruses only infect other birds. It is rare for people to get infected with bird flu viruses, but it can happen. Two types, H5N1 and H7N9, have infected some people during outbreaks in Asia, Africa, the Pacific, the Middle East, and parts of Europe. There have also been some rare cases of other types of bird flu affecting people in the United States.
Most of the people who get bird flu have had close contact with infected birds or with surfaces that have been contaminated by the birds’ saliva, mucous, or droppings. It is also possible to get it by breathing in droplets or dust that contain the virus. Rarely, the virus has spread from one person to another. It may also be possible to catch bird flu by eating poultry or eggs that are not well cooked.
Bird flu illness in people can range from mild to severe. Often, the symptoms are similar to the seasonal flu, such as
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Eye redness (or conjunctivitis)
- Difficulty breathing
In some cases, bird flu can cause serious complications and death. As with seasonal flu, some people are at higher risk for serious illness. They include pregnant women, people with weakened immune systems, and seniors aged 65 and older.
Treatment with antiviral medicines may make the illness less severe. They may also help prevent the flu in people who were exposed to it. There is currently no vaccine available to the public. The government does have a supply of a vaccine for one type of H5N1 bird flu virus and could distribute it if there was an outbreak that spread easily from person to person.0 200