Avian Influenza in Wild Birds in Public Parks and Aquatic Amenity Areas in Ireland

AVIAN INFLUENZA IN WILD BIRDS IN PUBLIC PARKS AND AQUATIC AMENITY AREAS IN IRELAND:

A RISK ASSESSMENT.

October 2006

1. Background:

Avian influenza is a disease of birds caused by an avian influenza A virus of which about 16 different types have been identified based on the structure of their surface attachment protein. Most of these viruses cause either no clinical disease, or only mild symptoms in the infected birds and are called Low Pathogenic Avian Influenza (LPAI). These LPAI strains are not unusual in waterfowl (ducks, swans and geese) around the world. However, a characteristic of the influenza virus family is their ability to mutate rapidly and for new strains to appear. Some of the mutants have the ability to cause more severe disease and they are then called Highly Pathogenic Avian Influenza (HPAI). In this manner the highly pathogenic H5N1 strain arose in Southeast Asia and has resulted in the current (2003-2006) epidemic affecting poultry, wild birds and rarely people or other mammals such as cats, dogs, and various wild carnivores.

The role of wild birds, and particularly waterfowl, in maintaining LPAI is well documented and once introduced into domestic poultry the LPAI strains can also mutate into HPAI. The question now is what role migratory waterfowl play in the spread of HPAI H5N1 in the current epidemic? The recent emergence of the Asian lineage of H5N1 in western Europe shows that long distance spread has occurred but further research is needed to determine how this has occurred. Migration of waterfowl from Asia and eastern Europe during a period of unusually cold winter weather in early 2006 was undoubtedly a significant risk factor. HPAI H5N1 first appeared in the EU in February 2006 when the virus was found in over-wintering waterfowl including ducks and mute swans (Cygnus olor). The closest known occurrence of HPAI H5N1 to Ireland was the discovery of a dead whooper swan (Cygnus cygnus) found on the Fifeshire coast in Scotland in March.

A previous risk assessment exercise conducted by DAF in collaboration with NPWS and BirdWatch Ireland has identified 24 species of water birds that pose the greatest risk of introducing avian influenza into Ireland, or spreading it once it has arrived. These include two species of swan, two species of geese, 10 species of ducks, two of rails, three of waders, and five of gulls (Table 1 & Fig. 1). A further four species of water birds (two grebes, brent geese, and the cormorant) pose a lesser risk. The risk assessment was based on the following criteria:

Ø  Migration from areas known to have HPAI H5N1.

Ø  Previously known to have been infected by H5N1 in other countries.

Ø  Known use of farmland as well as wetland habitats.

Ø  Species that are gregarious and have the potential to spread viruses.

Ø  Proximity of their natural habitat to areas of poultry farming.

Should HPAI H5N1 arrive in Ireland with migratory waterfowl during the coming winter season (2006/07) it could appear at any wintering site used by these birds. The distribution of wetland habitat in Ireland encompasses the coastal estuaries and bays and also inland lakes, callows, rivers, and bogs (Fig. 2). Because of the pattern of demographic settlement and land use in Ireland, none of these areas are remote from human settlement, farming, or amenity areas used for boating, fishing, hunting, swimming, or other pursuits that could bring people or domestic animals into contact with birds, bird droppings, carcases or other potential sources of influenza virus.

2. Issues

The purpose of this risk assessment is to describe the qualitative risk from avian influenza from water birds posed to members of the public using aquatic/wetland amenity areas or parkland also used by water birds. It also describes the risk to park workers, to staff of the NPWS, DAF, Local Authorities, Civil Defence, and to members of volunteer organizations such as BirdWatch Ireland who may be exposed to wild waterfowl, given:

Ø  The current distribution of avian influenza in Europe.

Ø  The epidemiology of virus spread and potential pathways that may present a risk to humans.

Ø  Our understanding of the environmental survival of the virus once excreted from an infected host.

Ø  The zoonotic potential and virulence of the virus.

3. Risk Assessment

In the six month period from May to October 2006 there have been 20 occurrences of HPAI H5N1 in wild birds in EU member states and 18 of those were in May at the tail end of the Winter / Spring incursion of the virus from the east. Since then there was one case of infection in a free-living great crested grebe in northern Spain in June and a single case in a captive swan in Dresden Zoo in August. Further afield the incidence of infection in wild birds has been equally unremarkable with a limited number of outbreaks in waterfowl in Siberia between June and September. The most recent outbreak occurred in the Omsk region of Russia in early September. At the present time in mid-October the autumn migration is well underway and peak numbers of wintering water birds should arrive in Ireland in the coming weeks. The current risk of HPAI H5N1 incursion is minimal but this situation could change with the arrival of birds from the east. It would be unlikely that avian influenza would appear in Ireland without first being detected in another EU member state.

Should HPAI H5N1 arrive in Ireland with returning migratory water birds, the main mechanism by which it could spread to other birds would be by faecal or respiratory excretion. For transmission to other animals and humans, ingestion of faeces or food contaminated by infected bird faeces is a more likely route. Thus, for a person to be infected, they must ingest food or water contaminated by the faeces of an infected bird, or have such material come in close contact with sensitive areas such as the conjunctivae of the eye in sufficient quantity. When water birds defecate, the faeces are semi-liquid and any viral particles are bound to the organic matter in the faeces. This is not particularly hazardous unless foodstuff is contaminated. The infective dose of virus will also decrease rapidly as the faeces dries out and is exposed to UV rays in sunlight, rain, wind and other environmental elements. In addition, viruses cannot multiply outside a host animal - further reducing the quantity that could infect a new host. Therefore in a situation where water birds are living in natural habitat, it is highly unlikely that humans would be exposed to an infective dose by ingestion or by dried viral particles blowing into eyes, mouth or airways. Such mechanisms of transmission are only likely under circumstances of intensive poultry production where large numbers of infected birds are housed indoors generating large quantities of infected aerosol.

Infected waterfowl excreting large quantities of virus into water bodies such as ponds, lakes, canals, reservoirs, or outdoor swimming pools could pose a theoretical risk to humans using these amenities. The risk is less where dilution results from greater water volumes or higher flow rates. The avian influenza virus is also sensitive to the elements and its survival is dependant on water temperature, water chemistry (pH, salinity), and exposure to the sterilizing effects of UV light all of which will deactivate the virus. Increasing temperature increases the rate of deactivation, with the virus being most stable between 4oC and 10oC. It can remain infectious for at least a month at 0oC but only six days at 37oC. So under Irish winter conditions it could survive in the environment for periods of hours to several weeks. It can also remain infectious for longer in fresh water habitats than in brackish estuarine or marine habitats.

The H5N1 strain of avian influenza is transmissible to people but it is poorly adapted to human hosts with only 256 people confirmed with infection worldwide since 2003. Approximately half of these have died as a result. Most of those who were infected had very close contact with infected poultry and were involved in slaughtering infected birds, plucking or dressing carcasses, had infected birds in their dwelling or allowed children to play with sick or dead birds. There is only one example of human infection from wild birds and that occurred in Azerbaijan when people plucked swans that had died from H5N1 infection.

No cases have been found in people involved in any of the following activities:

Ø  Culling infected poultry in commercial units throughout SE Asia.

Ø  Conducting survey work on poultry or wild birds.

Ø  Ornithological research such as bird banding or ringing.

Ø  Husbandry of birds in zoos or parks.

Ø  Refuse collectors including those involved in clean up after culling of flocks.

Ø  Veterinary work and poultry farm workers.

Ø  Wildlife rehabilitation.

4. Conclusions

Based on current scientific research and thinking with regard to avian influenza it may be concluded that:

Ø  The risk of infection in people, and particularly from wild birds, is very low for the circulating H5N1 strain of HPAI.

Ø  The most likely means of introduction of this virus to areas of public use such as parks and recreational waterways (rivers, lakes and beaches) is through faeces of infected waterfowl.

Ø  In respect to public use of parks and parklands, direct contact with fresh bird faeces should be avoided. Contamination of skin or clothing should be washed off with soap and water. Disinfectants are not required as the influenza virus is sensitive to detergents alone. Likewise, the virus is sensitive to UV light, and degradation will occur with exposure to the elements such as wind, rain, and sunlight.

Ø  Dogs and cats are also unlikely to be infected in parks or parklands barring scavenging of dead birds or consumption of large quantities of recently-excreted infected faeces.

Ø  Recreational activities such as boating, fishing, canoeing, water skiing or swimming would entail minimal risk of people contracting avian influenza. Wild waterfowl are unlikely to be present in significant numbers where many of these activities occur, and persons involved are not likely to ingest any or sufficient quantities of infected material.

Ø  The dilution capacity of the water body is also likely to dilute any infected material rapidly to a level where it is no longer infectious. As mentioned above, exposure to sunlight and other adverse environmental conditions will also inactivate the virus.

Ø  Small water bodies such as ponds or small shallow lakes with a high density of water birds and heavy faecal contamination of the water should be avoided for the recreational activities mentioned if that use entails a risk of ingesting contaminated water.

5. Recommendations

With the current distribution of HPAI H5N1 globally and current understanding of the epidemiology of infection it is recommended there is minimal risk to the public or their pets in normal use of parks, parklands for recreational purposes. Therefore:

1)  There should be no restrictions on use of these areas.

2)  Aquatic activities such as swimming, canoeing, boating, skiing etc in water bodies where there is ample dilution of faeces from birds entails minimal or no risk to the public. Such activities are only a risk in small water bodies heavily contaminated by faecal matter from infected birds. Such areas should not be used for these activities regardless of whether avian influenza is present or not.

3)  The advice on the Department of Agriculture and Food website: http://www.agriculture.gov.ie on the handling of dead birds and their safe disposal is appropriate and current.

4)  The advice to staff who may be exposed to wild birds through their occupation in regards to personal hygiene, proper use of personal protective equipment (PPE), and categorization of risk is also in concurrence with scientific thinking: http://www.agriculture.gov.ie.

5.1. These conclusions may be validated by assessment of risk in the following scenarios:

Ø  Scenario 1: There is no evidence of HPAI H5H1 in Ireland.

Ø  Scenario 2: HPAI H5N1 infection confirmed in a single migratory water bird in a park used for recreational purposes in Ireland.

Ø  Scenario 3: HPAI H5N1 detected in an endemic wild bird in a park in Ireland.

Ø  Scenario 4: A local die-off of endemic wild birds has occurred in a park and HPAI H5N1 is suspected.

Ø  Scenario 5: A local die-off of endemic wild birds has occurred in a park and HPAI H5N1 is confirmed.

5.1a. Scenario 1, HPAI H5N1 is not in Ireland:

·  There is no risk to the public using parks or waterways for recreational purposes.

·  Likewise, there is no risk to employees of the parks and wildlife service or local authorities who may come in contact with wild birds inhabiting these areas.

·  General hygiene standards should still be maintained to protect against any zoonoses that could be contracted from contact with wild bird faeces.

·  Dead birds should be handled as per the DAF guidelines.

·  Areas with hard surfaces where waterfowl may aggregate and be fed by the public should be kept as clean as possible by regular washing down to decrease the faecal load. Detergents or viricides are not necessary.

·  Normal public use of aquatic recreational areas should not be restricted.

5.1b. Scenario 2, HPAI H5N1 found in a single migratory bird in Ireland: