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The complete virus is a recombination of three viruses found in Asia, H7 of the virus has been found to be closest to that found in domestic ducks in Zhejiang and the N9 closest to the wild bird strain in South Korea. Genetic changes have also been found that lead to increased virus binding and replication in mammalian respiratory cells and thus increased severity of infection. The virus has been shown to be weakly pathogenic in poultry and testing of different populations for H7N9 specific antibodies may be helpful in finding the source, though viruses with H7 HA may not trigger a strong antibody response. No cases have been reported outside of China.
The complete virus is a recombination of three viruses found in Asia, H7 of the virus has been found to be closest to that found in domestic ducks in Zhejiang and the N9 closest to the wild bird strain in South Korea. Genetic changes have also been found that lead to increased virus binding and replication in mammalian respiratory cells and thus increased severity of infection. The virus has been shown to be weakly pathogenic in poultry and testing of different populations for H7N9 specific antibodies may be helpful in finding the source, though viruses with H7 HA may not trigger a strong antibody response. No cases have been reported outside of China.
==Signalment==
There is a higher risk of LPAI on farms housing ducks, geese and game birds as compared to chickens, turkeys and indoor layer farms. This may be due to the rearing methods, as birds reared outside have a higher risk of coming into contact with wildfowl and thus becoming infected with LPAI. Contaminated drinking water, including water that wild birds have access to, increases the risk of infection, as does feeding uncooked meat and offal. Turkeys and ducks appear more susceptible to AI, as are many gallinaceous species. LPAI has been shown to be present in low levels in turkeys but HPAI rarely found, only five cases of HPAI since 1959 have been found to result primarily from turkeys. HPAI viruses are well adapted to poultry. Wild pigeons may not be as susceptible to AI as other wild birds. Psittacine birds are rarely affected and viruses found in ratites show a low level of virulence to chickens. The density of lamellae and feeding style within ducks has been shown to be associated with AI infection, suggesting feeding methods may have an effect on exposure to AI virus. AI has also been detected in asymptomatic swine and donkeys.
== Clinical Signs ==
== Clinical Signs ==
LPAI viruses cause milder disease, most commonly respiratory symptoms (e.g. rales, coughing) combined with reduced egg production and depression, though clinical signs can range from none to death. Other signs can include swelling of the infraorbital sinuses, pyrexia and loss of appetite. If other bacteria or viruses (e.g. ''[[Pasteurella species|Pasteurella spp]], [[Newcastle Disease Virus|Newcastle disease]], [[Mycoplasma gallisepticum|Mycoplasma spp]], [[Escherichia coli]]'') are present along with LPAI the consequences of infection can be more serious, often causing high mortality. The age, immune status and species of the infected bird can also have an impact on the severity of disease, as can the environment the bird is housed in. Many flocks are infected with LPAI every year and are only recognised due to seroconversion as the disease is asymptomatic. Most infections are transient due to lack of host adaptation, though some establish due to virus variation.
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By contrast, HPAI infection may only be recognised by sudden onset mortality within the flock, which can reach 100% within a couple of days. If the birds are still alive symptoms can include those of LPAI (though egg laying has often stopped) and excessive lacrimation, sinusitis, oedema of the head, subcutaneous haemorrhage, cyanosis of the skin (including comb and wattles), diarrhoea and occasional neurological signs. Severity of signs depends on the species and strain of the virus, for example some ducks infected with HPAI rarely showed clinical signs.
== Diagnosis ==
== Diagnosis ==