February 26, 2024
Infectious Diseases

What is Avian influenza?

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Last Update on September 30, 2022

| Overview | History | Transmission | Influenza Type A Viruses | Highly and Low Pathogenic Avian Influenza A Virus | Prevention |

1. Overview:

The virus known as avian influenza affects both domestic and wild birds, including ducks, gulls, and shorebirds (such as chickens, turkeys, ducks, and geese). Similar to humans, birds too have different flu virus strains, and much like humans, some bird flu strains are more severe than others. Based on the virus’s capacity to cause sickness in chickens, all strains are further categorized into two categories: low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI).

Because these viruses do not currently infect humans easily and do not readily spread among sick individuals, the US Centers for Disease Control and Prevention (CDC) considers the risk to people from HPAI infections in wild birds to be minimal. Standard antiviral medications work against avian influenza viruses.

The mortality rate of chicken and turkeys from HPAI, a deadly poultry illness, is significant (about 90%). Since Jan. 13, 2022, when a wild bird in South Carolina was verified to have the HPAI virus, wild birds and domestic poultry have been found in more than 20 states, most of which are along the Atlantic Coast and several others in the Midwest. All four of the country’s migratory bird flyways are being monitored by the United States Department of Agriculture’s (USDA) Avian and Plant Health Inspection Service (APHIS) to see if HPAI is still spreading.

Because HPAI has been discovered in wild ducks harvested by hunters and recorded along the Atlantic Flyway, which is a migratory bird pathway that includes Rhode Island, Rhode Island is in danger. Wild birds may continue to spread HPAI across the flyways as they migrate north this spring from their wintering grounds. This is one way the virus might get into Rhode Island. Domestic poultry in Rhode Island must be screened for the disease and infected flocks must be depopulated in order to stop it from spreading to other flocks. Neighboring flocks will also be tested to make sure that no spread has taken place.

2. History of Avian influenza:

The year 1878 is the most widely mentioned as the year when avian influenza (formerly known as fowl plague) became recognized as a distinct disease from others that had significant fatality rates in birds. However, before the 1950s, Newcastle disease was sometimes referred to as the fowl plague. There were 15 instances of HPAI virus emergence in poultry between 1959 and 1995, but losses were relatively small. However, there have been at least 11 HPAI outbreaks in poultry between 1996 and 2008, with 4 of these outbreaks involving millions of birds.

The world’s chicken population increased by 23% in affluent nations and by 76% in developing countries in the 1990s, which helped to boost the frequency of avian influenza. Previous to the 1990s, HPAI was intermittent and had a limited impact on poultry mortality. The high density and frequent movement of flocks from intensive chicken agriculture have led to an increase in outbreaks.

In 1996, influenza A/H5N1 was initially isolated from a goose in China. Hong Kong was the first place where human infections were noted in 1997.[9] Since 2003, approximately 700 human cases of Asian HPAI H5N1 have been reported to the WHO, mostly from 15 nations in Asia, Africa, the Pacific, Europe, and the Middle East, though more than 60 nations have been affected.

The World Health Organization (WHO) received 916 lab-confirmed cases of H7N9 in humans between early 2013 and early 2017[13]. On 9 January 2017, the National Health and Family Planning Commission of China notified the WHO of 106 cases of H7N9 that occurred from late November to late December, including 35 fatalities, 2 possible cases of transmission from person to person, and 80 of these 106 people reporting having visited live poultry markets. Jiangsu (52 instances), Zhejiang (21) Anhui (14) Guangdong (14) Shanghai (2), Fujian (2), and Hunan are the other listed states with cases (1). Similar abrupt rises in the number of H7N9 cases in humans have happened in December and January in past years.

3. Transmission of Avian influenza:

Although it can also spread inadvertently through contaminated equipment, the most common way that avian influenza is disseminated is through contact between sick and healthy birds. Infected birds’ nasal, oral, and eye secretions as well as their droppings contain the virus. People can contract the HPAI illness by coming into contact with contaminated birds directly, such as during slaughter or plucking.

The disease itself is not an airborne disease, even though the virus can spread through airborne secretions. Less pathogenic strains may impact egg production but are significantly less dangerous. Highly pathogenic strains travel swiftly throughout flocks and can wipe out a flock in less than 28 hours.

Despite the possibility of acquiring the avian influenza virus from birds, prolonged human-to-human interaction is significantly more difficult to avoid. Public health authorities are worried that bird flu strains could evolve and become easily spread between people. Numerous shorebirds and water-birds have some avian influenza strains in their digestive tracts; however, humans are rarely infected by these types.

Modern avian influenza virus ecology has been influenced by five man-made ecosystems: integrative indoor industrial poultry, commercial poultry raised on a range, live poultry markets, backyard and hobby flocks, and bird collection and trading networks, including cockfighting. The spread of HPAI has been primarily impacted by indoor commercial poultry, with increased commercial production throughout the 1990s being a major contributing factor to the rise in HPAI outbreaks.

Village poultry and their owners were commonly blamed for spreading the HPAI H5N1 epidemic in its early stages. Village poultry often referred to as backyard and hobby flocks are tiny flocks that are raised under strict guidelines and frequently given free rein in several homes. However, studies have shown that these flocks are less dangerous than commercial chickens produced intensively with homogenous genetic stock and inadequate bio-security. When compared to the transportation of poultry bred intensively, backyard and village fowl also do not travel as far and are less responsible for the development of HPAI.

4. Influenza Type A Viruses:

Influenza (flu) viruses come in four different subtypes: A, B, C, and D. Wild waterfowl like ducks, geese, and swans as well as wild aquatic birds like gulls, terns, and shorebirds are regarded as storage (hosts) for avian influenza A viruses.

4.1. Subtypes of Influenza Viruses:

Hemagglutinin (HA) and neuraminidase, two proteins on the surface of the influenza A viruses, are used to categorize them into different subtypes (NA). There are 11 NA subtypes and 18 HA subtypes, respectively. 16 HA and 9 NA subtypes have been discovered in birds. There are numerous potential combinations of HA and NA proteins (two new subtypes, H17N10 and H18N11, have been discovered in bats). An (H7N2) viruses, for instance, are subtypes of influenza A viruses that include the HA 7 and NA 2 proteins. The HA 5 and NA 1 proteins are both presents in an “A (H5N1)” virus.

All known influenza A virus subtypes, with the exception of subtypes A(H17N10) and A(H18N11), which have only been identified in bats, can infect birds. There are currently just two influenzas A virus subtypes that are circulating in people: A(H1N1)pdm09 and A(H3N2).

Humans, wild water birds, domestic poultry, swine, horses, dogs, and bats are among the seven animal species or groups where influenza A viruses have been found and are known to circulate. Avian influenza A viruses have been observed to occasionally infect many other animal species, although they do not frequently spread among them (e.g., cats and seals). Both the canine (dog) influenza A(H3N2) virus and the equine (horse) influenza A(H3N8) virus frequently circulate and have the potential to infect both animals.

4.2. Lineages of Influenza A Virus:

Depending on where they were first discovered, different genetic lineages of avian influenza A viruses that infect birds have developed. By examining the genetic makeup of these viruses, it is possible to discriminate between these several lineages.

For instance, avian influenza A viruses that were first found in birds in Asia can be distinguished from those that were found in birds in North America by their genetic differences. Genetic comparisons enable researchers to group the viruses with the closest genetic relationships together, thereby narrowing these wide lineage groupings. To further distinguish one lineage from another, the host, historical period, and region are frequently incorporated in the lineage name.

5. Highly and Low Pathogenic Avian Influenza A Virus:

High pathogenicity of avian influenza (HPAI) and low pathogenicity of avian influenza (LPAI) are the two subcategories of avian influenza A viruses, respectively.

Low Pathogenic Avian Influenza (LPAI): Low pathogenic avian influenza viruses either have no symptoms or very moderate symptoms in chickens and other fowl (such as ruffled feathers and a drop in egg production). Since most avian influenza A viruses are low harmful, sick wild birds rarely exhibit any symptoms. Several low-pathogenic viruses can evolve into avian influenza which is highly pathogenic in poultry.

Highly Pathogenic Avian Influenza (HPAI): High death rates and severe illness are brought on by highly pathogenic avian influenza viruses in infected chickens. The majority of A(H5) and A(H7) viruses circulating among birds are LPAI A viruses, while a small number of avian influenza A(H5) and A(H7) viruses are categorized as HPAI A viruses. Infections with the HPAI A(H5) or A(H7) virus can lead to an illness that affects several internal organs and can result in mortality rates of up to 90% to 100% in hens, frequently within 48 hours.

However, ducks can get the disease even in the absence of signs and symptoms. The HPAI A(H5) and A(H7) virus can potentially spread from infected poultry to wild birds, where it would then propagate further over the world when those birds travel. Other HPAI A(H5) and A(H7) virus subtypes can cause serious infection and ultimately death in both infected wild birds and poultry. While some HPAI A(H5) and A(H7) virus subtypes may cause mild illness in select wild bird species.

6. Prevention of Avian influenza:

High danger of catching avian influenza does not exist in people who do not frequently come into touch with birds. Workers in poultry farms, those in animal control, wildlife biologists, and ornithologists who work with live birds are among those at high risk. Prior to the detection of any cases, organizations with high-risk personnel should have an avian influenza response strategy in place. For prevention, the bio-security of chicken flocks is crucial. Birds from slaughter channels should not be brought back to the farm, and flocks should be kept separate from outside birds, especially wild birds, and their waste. Additionally, vehicles used near the flock should be frequently sanitized and should not be shared across farms.

The likelihood of infection is low with adequate infection management and the use of personal protective equipment (PPE). Because these are the most typical entry points for the virus into the body, protecting the eyes, nose, mouth, and hands is crucial for protection. A head cover or hair cover, gloves, boots or boot covers, and aprons or coveralls are examples of appropriate personal protective equipment. PPE that can be discarded is advised. The right PPE should also include an N-95 respirator and unvented or indirectly vented safety goggles. Another choice is a powered air purifying respirator (PAPR) with a hood, helmet, and face shield.


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