AVIAN INFLUENZA OR BIRD FLU IN INDIAN CONTEXT
| DR. SURINDER KHANA,POULTRY CONSULTANT Just three months after India declared itself to be free of the avian influenza outbreak, the highly pathogenic avian influenza subtypes, H5N1 and H5N8, have been reported from a dozen epicentres in four States — Rajasthan, Madhya Pradesh, Himachal Pradesh and Kerala. In addition, thousands of poultry birds have died in Haryana, while Jharkhand and Gujarat, too, have sounded an alarm; the cause in these three States is still unknown. The two subtypes have targeted different birds — crows in Rajasthan and Madhya Pradesh, migratory birds in Himachal Pradesh, and poultry in Kerala. While tests have confirmed H5N1 for causing the deaths of over 2,000 migratory birds in Himachal Pradesh, H5N8 has been identified for killing thousands of poultry in Kerala, and hundreds of crows in Rajasthan and Madhya Pradesh. In a bid to stop the spread, as on Wednesday over 69,000 birds, including ducks and chickens, were culled in Alappuzha and Kottayam as per India’s 2015 National Avian Influenza Plan. Other States have been asked to be vigilant of any unusual deaths or disease outbreak signs amongst birds, particularly migratory ones. Migratory birds have been largely responsible for long-distance transmission of the virus into India during winter. It then spreads through local movement of residential birds and poultry. Movement of men and material from poultry farms too has been a cause for further spread. This is why States have been asked to strengthen biosecurity of poultry farms, disinfection and proper disposal of dead birds. With backyard rearing of poultry birds common, the task of elimination will be particularly difficult. · A recent European Food Safety Authority report says 561 avian influenza detections were made between August-December in 15 European countries and the U.K. The virus was predominantly found in wild birds, and a few in poultry and captive birds. H5N1 and H5N8 were two of three subtypes found in Europe. Genetic analysis helped confirm the spread from Asia to west-central Europe, suggesting a “persistent circulation of this virus strain, likely in wild birds in Asia”. While avian influenza virus crossing the species barrier and directly infecting humans happens occasionally, human-to-human spread has been rare. But mutations or genetic reassortment of an avian influenza A virus and a human influenza A virus in a person can create a new influenza A virus that could likely result in sustained transmission between humans, thus increasing the risk of a pandemic influenza. Hence, all efforts should be directed at stamping out the outbreaks in the affected States. It is also important to undertake genome sequencing of virus samples to track the evolution of the virus. The H5N8 is a sub-type of the Influenza A virus that causes flu-like symptoms in birds and mammals. Before Russia reported its first case of human transmission H5N8 was largely believed to be restricted to birds and poultry.
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. The highly pathogenic avian influenza (HPAI) H5N1 virus, which is panzootic in poultry, continues to spread and pose a major challenge to animal and human health . Since pandemic influenza virus has its origins in avian influenza viruses , HPAI H5N1 virus has to be considered a potentially serious pandemic threat. New influenza virus pandemics in the 21st century are a certainty, but whether H5N1 will be the next pandemic virus is far from certain. What is already true, however, is that H5N1 viruses are taking a huge toll on the poultry industry in many developing countries, and this directly or indirectly impacts both economic and social well-being. The potential impact of HPAI H5N1 virus (and human reaction to its spread) on wildlife and ecology has received less attention but is also worthy of consideration . While the H5N1 virus transmits zoonotically from infected poultry to humans, often with fatal consequences, such transmission remains inefficient. Although the virus replicates efficiently in diseased humans, it has not yet adapted to efficient human-to-human transmission. H5N1 therefore continues to challenge our understanding of interspecies transmission of influenza viruses. Here, we review the biology and ecology of HPAI H5N1 viruses in the broader context of animal and human influenza viruses in general. We discuss options for the control of H5N1 transmission in animals and humans and assess its pandemic risk.
Nature of the disease |
| Virulent avian influenza (AI) – fowl plague – is a highly contagious fatal disease of poultry. Infection with the virus is accompanied by respiratory, gastro-intestinal and /or nervous signs. Wild water birds such as waterfowl and seabirds are recognised as important reservoir of infection. |
| Classification |
| OIE List A disease |
| Susceptible species |
AI infects almost all commercial, domestic and wild bird species.
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| Distribution |
| AI viruses have been found on all continents where research has been carried out. It appears to be endemic in water birds, though disease in these species is rare. Migrating waterfowl are one way that the disease can spread between continents.
Within the region, there have been several outbreaks of virulent AI in India, the most recent in 2021. |
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Clinical signs The incubation period is hours to days, depending on age, sex, species affected, concurrent infections and pathogenicity of virus. Respiratory distress, coughing, sneezing, rales, depression, sinusitis, emaciation, off feed, nervous disorder, and diarrhoea may be seen. Rapid mortality, up to 100%, occurs with virulent high pathogenic strains (fowl plague) (H5 and H7 subtypes). Multiple pathotypes can occur. Low pathogenic strains causing only a mild respiratory disease, but their presence in flocks can lead to trade restrictions among countries. A drop in egg production and shell quality, watery eyes, excessive lacrimation, oedema of head and face, and cyanosis may be observed. |
| Clinical signs are variable and influenced by the virulence of the virus strain, the species affected, age, environmental conditions and presence of pre-existing bacterial infections.
Low pathogenicity strains
High pathogenicity strains
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| Post-mortem findings |
| Haemorrhages in various parts of the body are common. The oviducts and intestines often have severe haemorrhages in them. As the disease progresses, pancreas, liver, spleen, kidney and lungs may display yellowish necrotic areas. Small haemorrhages cover the abdominal fat and lining of the body cavity.
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| Differential diagnosis |
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| Specimens required for diagnosis |
| Samples should be taken from live, clinically affected birds and recently dead birds. Samples should be collected from at least six birds.
Live birds Cloacal and tracheal swabs, fresh faeces and serum. Swabs should be mixed with transport media. Blood samples from several birds should be collected for serum. Dead birds Alimentary tissue samples (proventriculus, intestine, caecal tonsil) and respiratory tissues (lung, trachea) should be collected fresh (not preserved). Impression smears of internal organs can be made. If delays of more than 48 hours in transit are expected, samples should be frozen. |
| Transmission |
| Direct or indirect contact with migratory water birds is the likely source of infection for poultry. Virus in faeces and water can remain viable for up to 32 days. Transmission between poultry appears to depend on close contact.
AI can spread very rapidly and can be carried over long distances by contaminated materials such as birdcages, pallets, manure and feed. |
| Risk of introduction |
| Evidence suggests that waterfowl are the likely source of many AI outbreaks in domestic poultry. The virus can be introduced through close contact with wild birds, or indirectly through untreated water from ponds streams that has been contaminated with bird droppings.
Importation of material, manure and feed from an infected country should also be considered.
Prevention Treatment
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| Control / vaccines |
| Vaccines have been used in the past but have not proven very effective. Because of the risk of producing pathogenic strains, live virus vaccines are not appropriate. In the USA inactivated commercial vaccines have been developed. When vaccine is used in an outbreak, the risk that vaccination teams may spread the disease is a concern.
For eradicating the disease, a slaughter policy is preferable to a vaccination policy. Affected flocks should be slaughtered and the carcases buried or burned and the premises cleansed and disinfected. What is H5N8? The H5N8 is a sub-type of the Influenza A virus that causes flu-like symptoms in birds and mammals. Before Russia reported its first case of human transmission H5N8 was largely believed to be restricted to birds and poultry. The more widely known strain of avian influenza is the H1N1, which is responsible for all the major flu outbreaks, like 1918 Spanish flu, the 2009 Swine flu outbreak et al.
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| References |
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