AVIAN INFLUENZA IN POULTRY & OTHER DOMESTIC AVIAN SPECIES: CLINICAL SIGNS Avian influenza typically has an incubation period of hours to days in most birds, though it can take up to 2 weeks for signs to be noted within a flock 4 . Clinical signs of avian influenza will vary, depending on the overall health of the bird and the pathogenicity of the virus. LPAI produces subtle signs in affected poultry, including may be sudden death, with little to no clinical signs evident. Affected chickens and turkeys may present with nonspecific signs including lethargy, anorexia, edema and cyanosis of unfeathered skin, and echhymotic hemorrhage 6 . There are no pathognomonic signs of this virus, but infected poultry flocks will demonstrate high morbidity and high mortality and this virus should be suspected whenever a sudden die-off is noted 6 .
decreased egg production and quality, lethargy, and decreased thirst and appetite. Respiratory signs may include sneezing, coughing, ocular discharge, nasal discharge, and swollen infraorbital sinuses. Mild increases in flock mortality may be noted, though this change is typically subtle 4 . LPAI viruses can cause more severe clinical signs in populations that are stressed by environmental factors or other infections, as well as in naïve populations of young birds 4 . HPAI, however, produces dramatic clinical signs and high mortality rates. The first sign of disease in an affected flock Necropsy findings In patients affected with LPAI, necropsy typically reveals only upper respiratory disease. Affected poultry will demonstrate rhinitis, sinusitis, and tracheitis, but pulmonary lesions (such as pneumonia) are only seen when a secondary bacterial infection is present. Less common necropsy findings in LPAI can include lesions in the reproductive tract (ovarian abnormalities such as hemorrhage and involution), acute renal failure, and visceral urate deposition 4 . In turkeys and chickens affected with HPAI, necropsy findings vary but often indicate widespread systemic disease. Common findings include edema and cyanosis of nonfeathered skin, excess fluid (that may be hemorrhagic) in the nares and oral Diagnostic testing Avian influenza viruses are shed in respiratory secretions and the gastrointestinal tract. Therefore, influenza viruses can typically be detected in oropharyngeal, tracheal, or cloacal swabs from live birds. Recovery rates from each site may vary, depending on the species of bird, the virus strain, and environmental factors. In dead birds, internal organ samples can also be used for virus detection 4 . There are a variety of diagnostic tests available, though the sensitivity and specificity of the test may vary based on which bird species is being tested. Therefore, it is important to use a test that has been validated for the particular bird species being tested 4 . Rapid enzyme-linked immunosorbent assay (ELISA) tests Control The most important method of controlling the spread of avian influenza is biosecurity, utilizing structural and operational measures to prevent the introduction of pathogens to a facility. In HPAI, which is spread by wild birds, one of the most effective methods of biosecurity is to decrease the number of wild birds near poultry. There are three key considerations in doing this: 1. First, decrease features that may attract wildlife. For example, remove food sources and standing water, which may attract wild birds and also may become contaminated with fecal material. Poultry workers should also be educated to stay away from any standing water on the premises, to reduce the likelihood of fomite transmission. 2. Next, limit the ability of wild birds to access poultry houses; keep holes in barns and chicken houses covered with wire, remove old wild bird nests, and inspect enclosures regularly for signs of wildlife. 3. Finally, consider the use of wildlife deterrents and scare devices. All of these measures can be used to decrease contact between poultry and wild birds, thus decreasing the likelihood of introducing HPAI to the flock 8 .
In domestic birds of other species, the effects of HPAI can vary. Clinical disease in game birds may range from mild, subclinical infection to neurologic signs and sudden death. Domesticated waterfowl and pigeons appear to have a high resistance to clinical disease; however, there are reports of limited outbreaks even in these species. Young ostriches can be severely affected with both HPAI and LPAI, although adult ostriches are typically more resistant to infection 4 . cavity, edema and diffuse subcutaneous hemorrhages on the feet and shanks, and petechiae on the viscera and sometimes in the muscles. Other abnormalities may include internal hemorrhage, air sacculitis, and peritonitis (due to ovarian rupture and yolk-induced inflammation) 4 . HPAI may produce different internal lesions in other species of domestic game birds and these birds may lack the classic edema and cyanosis often noted in poultry. Findings may include lesions of the lungs, pancreas, spleen, liver, and kidneys. Additionally, hemorrhage may be noted in the internal organs and within skeletal muscle 4 . can be used to detect viral antigens, but this method is often used as a flock screening tool as it is less reliable for individual birds. Individual birds are typically tested using virus isolation in embryonated eggs, followed by subtyping with specific antisera in hemagglutination and neuraminidase inhibition tests, by reverse transcription polymerase chain reaction (RT- PCR), or by sequence analysis of the viral HA and NA genes. Many laboratories will also use real-time RT-PCR to detect avian influenza virus directly from clinical samples. Serology can be useful as a surveillance tool, but does not provide a means of diagnosing disease in individual birds; infected birds typically die before producing measurable antibody levels 4 . If biosecurity measures fail and a flock is found to be infected with HPAI, there are no effective options for treatment. The USDA must be notified and the facility will be placed under quarantine. During this quarantine, only authorized personnel will be allowed to enter and leave the farm. Nearby poultry owners will be informed of the presence of avian influenza and their birds will be tested to assess the extent of the outbreak. Next, the USDA will perform an appraisal to determine the fair market value of the birds so the owner may be appropriately compensated. As soon as possible (ideally within 24 hours of virus detection), the flock will be depopulated 9,10 . The American Veterinary Medical Association has approved the use of water-based foam as a method of depopulation in these circumstances; this foam is designed to rapidly occlude the airway of poultry while being rapidly cleared, biodegradable, and not posing a threat to human health 11 . Once euthanized, infected birds must be disposed of under USDA guidance via composting (under approved, carefully controlled conditions), landfill, incineration, or rendering, depending on the specifics of the case and facility 9,10 .
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