Avian Influenza

Also know as: Fowl Plague

Introduction

Highly Pathogenic Avian Influenza (HPAI) is caused by H5 and H7 isolates. The disease is notifiable in the UK and is found worldwide. H1-15 and N1-9 have all been isolated, but these are of varying pathogenicity.

The disease has caused so much concern over the last few years due to the fact it can mutate in the pig and gain attachment proteins for humans. This means that the deadly H5N1 strain of HPAI can be transmitted to humans, making it a feared zoonotic disease. A 2003 Dutch outbreak of a pathogenic H7 virus caused widespread conjunctivitis and flu-like symptoms with recovery among poultry workers and more recently, rural chinese children became infected with H5N1 via aerosol transmission, which was limited to upper respiratory symptoms and did not show horizontal spread.

In the USA, many farmed turkeys die each year from avian influenza and this is due to migrating birds contaminating their housing. With the current and severe H5N1 strain, Chinese poultry are the main reservoir, not wild birds. HPAI is spread by faeces and infected viscera (kidney/spleen are 100X more infectious than faeces). H7 and other viruses are carried by 6% of the wild bird population and outbreaks mirror migrating patterns, this poses significant risk to free-range flocks.

Clinical Signs

Clinical signs of HPAI include haemorrhages, diarrhoea and sometime nervous symptoms such as staggers and coma. This is followed in a few hours by sudden death. Mortality can reach 100% very quickly. Other signs include cessation of egg-laying, respiratory signs such as nasal discharge and increased respiratory rate, excessive lacrimation and oedema of the head.

Diagnosis

Clinical signs are indicative of the disease. The government should be notified immediately and all premises shut down if the disease is suspected.

Haemoagglutination inhibition (HI) should be performed on serological samples to detect a four fold increase in the viral antibodies. Samples should be taken at the acute phase, when the virus is first suspected and then a convalescent stage sample taken around two weeks later to detect the increase in antibodies.

Control

All birds must be slaughtered immediately and all birds on the premises must also be destroyed. The premises must be isolated and mass disinfection before new stock are brought in should occur. There must be a firebreak cull in local poultry farms or poultry keepers in a certain radius from the infected farm to control the spread.

Prevention is by proper hygiene and preventing contact with the wild bird population, such as ensuring housing is of excellent quality so as no wild birds can land in or on it and defaecate into it etc.

Vaccination is not currently practiced for the following reasons:

• Eradication policy prevents it from being allowed.
• Vaccination favors the evolution of the virus, which might increase its virulence and drift.

References

Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition) Elsevier Science

Bridger, J and Russell, P (2007) Virology Study Guide, Royal Veterinary College

Cowart, R.P. and Casteel, S.W. (2001) An Outline of Swine diseases: a handbook Wiley-Blackwell

Jordan, F, Pattison, M, Alexander, D, Faragher, T (1999) Poultry Diseases (Fifth edition) W.B. Saunders

Saif, Y.M, (2008) Diseases of Poultry (Twelfth edition) Blackwell Publishing

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