Controlling Highly Pathogenic Avian Influenza

by 5m Editor
26 September 2005, at 12:00am

By Africa Fernández-Gutiérrez, Company Veterinarian, Aviagen, Scotland - In many outbreaks of highly pathogenic avian influenza (HPAI), special local situations have been found and exploited by the virus. These “Achilles heels” make giving general advice on bio-security for a region simple, but detailed advice more difficult as it requires local understanding and planning to be effective.

Although not all the following theories have been proven each area needs to be examined before it is exploited by HPAI.

In general the progenitors of these viruses are present in subsections of wild bird populations. Which birds and which virus varies from area to area but the separation of all wild birds from large populations of domestic poultry is essential for protection from AIV. The way viruses make the transition to domestic poultry is the Achilles heel of a bio-security programme.

In the Netherlands, free range layer populations, impossible to protect from contamination by migratory birds, were initially infected and these then became the source for housed poultry. Whether wild birds then played any further part in the outbreaks after the initial adaptation is not known but they may only have been a minor source of further outbreaks. Often viruses in wild birds may not be directly very infectious to chickens and are initially apathogenic, but passage though poultry may change both these characteristics. Domestic ducks seem to be a major factor in increasing the adaptation of these viruses from wild birds to chickens in outbreaks in Australia and Asia, with the viruses usually remaining apathogenic in ducks but becoming more infectious to domestic chickens. Australia has now separated domestic duck production from other sections of poultry production.

One outbreak in Australia was thought to be due to the use of water from a local river where ducks swam. The water was usually chlorinated before reaching the housed stock, but the chlorination unit had run out of chlorine. If wild birds could have had access to water available to chickens, it should be treated first by some effective method. Bore hole water should not be stored in tanks or dams where water fowl or other birds could have access to it unless it is treated after this storage. Such treatment not only provides protection from AI, but also from NDV and EDS-76.

Further local factors may play a major part in the spread of AI from flock to flock. Fighting cocks were responsible for the spread of Newcastle disease in USA but equally the virus could have been Avian Influenza. The sale of AI infected birds in local live markets in Asia, to try and salvage some of the value of the stock, played a big part in the dissemination of the virus. In addition, in Asia, small village flocks act as a reservoir of infection and the lack of separation of commercial poultry from contaminated environments considerably increases the chances of outbreaks.

A further contributor to the spread the disease is livestock transport and in Italy, vehicles were the main cause of the spread of AI in turkeys.

As highlighted, bio-security plays a major role in preventing the spreading of diseases and in the case of AI there are added complications because of its epidemiology.

There are several species that could be infected with the virus but poultry (chickens, turkeys, ducks, geese, pheasant), swine and humans are the focus in the case of AI. Species of waterfowls can be refractory and therefore carry the virus without showing clinical signs. In this situation they could be the source of infection to other animals that they come in contact with; for example when ducks use ponds near poultry houses, wild birds feed from free range equipment or when wild birds gain access to the inside of poultry houses to find feed, shelter, nesting material or even to breed.

Another important point to consider it is that when the different AI viruses infect domestic poultry and mammalian species at the same time, the passage of viruses from one species to another as well as the confluence in the same individuals of different IA viruses could make the viruses more virulent.

The wild bird population acts as a reservoir for AI viruses and as the contact of feral animals with domestic ones increases so it does the risk of outbreaks. The migratory route of wild birds posses a particularly high risk of new outbreaks in domestic poultry in previously unaffected areas. The density of domestic and wild populations in the same area and the mixing of different domestic species in the same production facilities are factors that can increase the likelihood of a LPAI virus mutating and causing an outbreak of HPAI. The close living proximity in high density conditions of several susceptible species (pigs, poultry and humans) will increase the chances of LPAI viruses becoming HPAI.

The AI virus although highly contagious can be deactivated by a wide range of chemicals from detergents to bleach. It is very important that the cleaning procedures in farms follow a strict pattern:

  • Cleaning using water and detergent
  • Disinfection
  • Fumigation (If possible with formalin)

Visual inspection is a very valuable and cheap way of assessing cleaning standards: “If it looks dirty it must be dirty.”

Another important biosecurity measure is to locate farms as far away as possible from wild birds’ migration routes and from reservoirs to avoid potential gatherings of waterfowl. Any areas of water in the proximity of farms should be covered and if the water supplied to the birds comes from an open reservoir and is therefore at the risk of contamination, it should be chlorinated before being given to the birds.

Raw feed materials can be a source of infection as they may have been contaminated at harvesting or during storage. Feed that is fed to poultry should not be stored in the open as it will attract wild birds and other vermin. Feed spillages should be cleaned up as soon as possible.

The poultry houses should be always be wild bird proof and in open sided housing it is advisable to use a small size wire mesh. Equipment should not be left outside for two reasons. Not only would it be exposed to wild birds, but it may encourage nesting by wild animals. Any equipment must be cleaned and disinfected before it is moved into the poultry house.

Critical aspects of biosecurity:

  • An all-in all-out policy is the best practice but if the introduction of new birds in a flock is unavoidable, information on their health status must be sought first.

  • Mortality should be monitored closely and if there is any suspicion of AI the authorities should be informed. The disposal of mortality must avoid spreading any potential contamination.

  • Vehicles (egg and feed lorries, farm staff transport) should be kept thoroughly clean and at the very least their wheels sprayed before entry to the farm.

  • Staff should not be shared between different species farms and preferably not even between poultry farms, especially in areas where the disease is endemic.

  • Clothing should be provided on each farm or at least new or freshly laundered clothes wore on each visit.

  • Foot wear should either be changed or footbaths always used at the entrance to all poultry accommodations or related buildings.. The virus can remain viable for long periods in organic material such as faeces and be walked into sheds.

  • Water and feed should be decontaminated by chlorination and heat treatment respectively and delivery systems should prevent recontamination.

  • All poultry houses should be wild bird proof.

Good cooperation between the industry, small scale farmers, and the government is essential in the control of the disease. To be effective, collaboration has to reach all levels (local, national and regional). It would be very difficult to control an outbreak in a region if the control procedures in place are not coordinated from local level to intra-country and inter-county level.

The bio-security measurements should be realistic and adapted to the local situation and conditions. Particular attention needs to be paid to local customs that pose a significant risk of dissemination of AI, for example free range populations, live markets, transport of fighting cocks etc. Live markets pose a very great risk since animals of different species and from different areas and sources are brought together in very close proximity, or even mixed.

A census of all poultry farms including all small flocks and free range birds is vital as well as an effective system (radio, TV, phone ,e mail, internet) of disseminating information to every concerned party; of a possible outbreak or the establishment of restriction measures until results are received.

International collaboration is vital during an outbreak to help provide the latest research and control information. Financial support, to encourage local farmers to ask for help if they think there is a problem and the reassurance of farmers that they will be compensated if HPAI is confirmed, is an important step in the control of the disease.

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Source: Aviagen - Taken From website September 2005