Introduction
Avian influenza ‘A’ or ‘bird flu’ is a highly contagious viral disease or infection of birds that primarily affects domestic birds or poultry such as pheasants, Guinea fowl, ducks, chickens, quail, ostriches, geese, and turkeys. According to Figueroa et al. (15), other wild species of birds, such as seabirds and waterfowl, can also act as carriers for the disease, though they hardly show signs. However, there are isolated instances when influenza ‘A’ can spread to humans and lead to severe outbreaks, for example, when people expose themselves or come in direct contact with excrement or blood from influenza A-infected birds or poultry. In addition, influenza types A viruses cause avian influenza ‘A,’ and the signs and symptoms may range from mild to severe, resulting in a devastating illness and ultimate loss of flocks. Notably, influenza ‘A’ viruses are more harmful than ‘B’ and ‘C’ and can cause a great deal of damage to a flock of both domestic and wild birds; wild aquatic birds are often the hosts of large doses of influenza ‘A’ viruses (Figueroa et al., 50). Therefore, the paper discusses the history, variants, signs, and symptoms of and effects of avian influenza ‘A’ on domestic birds or poultry.
History of Avian Influenza ‘A’
The history of avian influenza ‘A’ dates back to the 1990s when the first subtype or variant of influenza virus, A(H5N1), emerged in Hong Kong and Southern parts of China. The virus was highly pathogenic and killed considerably large flocks of domestic birds such as chickens, ducks, ostriches, and turkeys. However, the authorities did not report cases of birds-to-human transmissions in that period. In 2013, China reported a subtype A(H7N9), which affected poultry and devastated humans. Moreover, in 2021, several European countries, such as Spain and the United Kingdom, reported the A(H5N2) viruses, which affected nearly 60 million domestic and wild birds (Germeraad et al., 10). Generally, humans are not at high risk of contracting avian influenza ‘A’ viruses.
Transmission
Wild birds such as seabirds and waterfowl are the primary natural reservoir and distributors of avian influenza ‘A’ viruses. According to Kongsomros et al. (483), wild birds such as waterfowl may transmit avian influenza ‘A’ viruses to domestic birds or poultry farms through direct contact or mechanically by producing infective excrements into an area accessible by poultry. Contacts between the infected birds and healthy birds are a primary cause, and spread of avian influenza ‘A .’Notably, surface watering or feeding points are critical areas where poultry can pick the viruses, leading to immediate infections.
Consequently, farm staff and contaminated surfaces are also major spreaders of the viruses and can lead to severe infections across the farm. Also, the spread of viruses from one poultry farm to another is possible mechanically when feces containing high contents stay in the farms long enough to facilitate the survival of avian influenza viruses (Kongsomros et al., 483). Man is a critical transfer agent of avian influenza ‘A’ viruses in and out of poultry farms and can lead to widespread transmissions and, ultimately, the death of many birds in an area.
Effects on Poultry
Avian influenza A is associated with high morbidity and mortality rates in poultry. According to Liu et al. (65), highly pathogenic avian influenza (HPAI) has a high potential to cause sudden and rapid deaths in chickens, quail, pheasants, and turkeys. However, poultry species like geese and ducks are less likely to succumb to HPAI. Particularly, chickens and turkeys may exhibit signs and symptoms such as respiratory gasping and extreme diarrhea, followed by sudden deaths. Also, chickens infected with HPAI are susceptible to retractions or severe swellings around the eyes, necks, and even heads. The heads of influenza ‘A’ virus-infected birds or poultry may also turn purple (discoloration). Mentally and emotionally, HPAI-infected poultry such as quail, chickens, and turkeys experience severe symptoms such as laying down or sometimes pedaling, twisted necks, paralyzed wings, and constant tremors. Such signs are severe and often lead to low productivity and sudden deaths in poultry.
Remarkably, long exposures to low pathogenic avian influenza (LPAI) viruses severely impact the health and productivity of chickens, ducks, geese, and turkeys. According to Liu et al. (66), LPAI is a primary cause of lesions in the respiratory and digestive tracts of chickens, ducks, and geese, bringing about constant inflammations and congestions of such vital pathways in the body. In breeders or egg-laying poultry, LPAI causes decreased egg production and infertility issues, which may spell many losses to the farmers. For example, ova rapture and mucosal edema commonly impact LPAI on breeder and layer chickens. In addition, avian influenza ‘A’ viruses expose poultry to unprecedented infections such as sneezing and nasal discharges that typically lead to low production in the markets (Liu et al., 70)). Such phenomena are common in the Middle East and Africa. Avian influenza ‘A’ viruses are the primary cause of peracute infections in poultry. Yang et al. (50) note that peracute infections severely impair the development of the central nervous system in poultry and can lead to drooping wings, incoordination, torticollis, and, even more important, paralysis. Avian influenza ‘A’ viruses are also recipes for necrosis, edema, and hemorrhage in birds, especially chickens, and ducks. In most cases, birds or poultry do not survive avian influenza ‘A’ except for a few cases with immediate interventions such as vaccinations.
Intervention Measures
Timely diagnosis and detection of avian influenza ‘A’ viruses in poultry are crucial for prevention and treatment. According to Yang et al. (54), vaccination and immunization are some of the primary and immediate interventions or strategies for controlling the spread of both LPAI and HPAI. Biosecurity is also a practical intervention measure for protecting a poultry farm or premise against the effects of avian influenza ‘A’ viruses, covering outdoor feeding areas and regular clean-up exercises.
Conclusion
Avian influenza A has a worldwide distribution, and its outbreak is common in commercial poultry production. Influenza ‘A’ viruses are contagious and can affect all species of birds, from wild birds to domestic birds. Common subtypes or variants for avian influenza A include H7N9, H5N1, and H5N2. In poultry farming, such birds as turkeys, geese, chickens, ostriches, and ducks are prone to avian influenza ‘A’ or bird flu attacks. Wild bird species such as shorebirds, waterfowl, gulls, and seabirds are some of the natural carriers or reservoirs of influenza ‘A’ viruses. Signs and symptoms of avian influenza A in poultry include; sudden deaths, head, neck, and eye swelling, coughing, sneezing, respiratory gasping, decreased egg production, ruffled feathers, and diarrhea. LPAI and HPAI also cause a breakdown in the central nervous systems of poultry birds, leading to paralysis, necrosis, and in a worst-case scenario, sudden deaths. Practical intervention measures for avian influenza ‘A’ include biosecurity and routine vaccination of poultry.
Works Cited
Figueroa, A., et al. “Persistence of low and highly pathogenic avian influenza virus in reused poultry litter, effects of litter amendment use, and composting temperatures.” Journal of Applied Poultry Research 30.1 (2021): 10–96.
Germeraad, Evelien A., et al. “Virus shedding of avian influenza in poultry: a systematic review and meta-analysis.” Viruses 11.9 (2019): 8–12.
Kongsomros, Supasek, et al. “Rapid and efficient cell-to-cell transmission of avian influenza H5N1 virus in MDCK cells is achieved by trogocytosis.” Pathogens 10.4 (2021): 483.
Liu, Shuo, et al. “Control of avian influenza in China: Strategies and lessons.” Transboundary and Emerging Diseases 67.4 (2020): 63–71.
Yang, Qiqi, et al. “Assessing the role of live poultry trade in the community-structured transmission of avian influenza in China.” Proceedings of the National Academy of Sciences 117.11 (2020): 49–54.
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