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BROCHURE RACK

Great tits worst affected by new bird virus

21/11/2012 22:20:44
birds/birds_2011_june/great_tit_avian_pox_wx

Avian pox seems particularly prevalent in Great tits. Photo credit Wildlife Extra

New strain of bird virus sweeps across Britain

November 2012. A new strain of avian pox is taking its toll on garden birds in Britain, according to new research. Scientists from the Zoological Society of London (ZSL), University of Oxford, the British Trust for Ornithology (BTO) and RSPB report on the impact avian pox is having on great tit populations.

New strain of virus in Great tits
Avian pox has been recorded in British bird species such as house sparrows and wood pigeons for a number of years. However, the emergence of a new strain of this viral disease in great tits is causing concern amongst vets and ornithologists.

Wildlife vet Dr Becki Lawson from ZSL says: "Infection leads to warty, tumour-like growths on different parts of a bird's body, particularly on the head around the eyes and beak. Although the disease can be relatively mild in some species, great tits suffer severe growths that can prevent them from feeding and increase their susceptibility to predation," Dr Lawson added.

"Wildlife vet Dr Becki Lawson from ZSL says: 'Infection leads to warty, tumour-like growths on different parts of a bird’s body, particularly on the head around the eyes and beak. Although the disease can be relatively mild in some species, great tits suffer severe growths that can prevent them from feeding and increase their susceptibility to predation.'”

Wildlife vet Dr Becki Lawson from ZSL says:
"Infection leads to warty, tumour-like growths on
different parts of a bird's body, particularly on the
head around the eyes and beak. Although the
disease can be relatively mild in some species,
great tits suffer severe growths that can prevent
them from feeding and increase their
susceptibility to predation."

Avian pox is caused by avian pox virus.
Affected birds develop warty or tumour-like
growths, on the head (particularly next to the
eye or beak), legs, wings, or other body parts.
The growths are usually grey, pinkish, red or
yellow in colour.

Whilst a range of species are known to be
susceptible to avian pox infection (e.g. house
sparrow, wood pigeon, dunnock, starling), the
recent cases of infection in tits are not typical
of the type of avian pox we are used to seeing
because the lesions are particularly large. In
most cases lesions are distributed on the head
around the eyes and beak. The extent to
which different bird species are susceptible to
different avian pox virus strains is unknown.

The virus is spread between birds by biting
insects that carry the virus, direct contact with
other birds and indirect contact, possibly
through contaminated bird feeders. Avian
poxvirus is not known to be infectious to
humans or other mammals.

Although large pox growths can be very
characteristic, smaller or medium-sized growths
can easily be confused with a number of other
conditions, such as ticks. The disease can only
be confirmed by further investigation, such as
post mortem examination and subsequent
laboratory tests.

Whilst supportive treatment can be attempted
in captive birds, effective treatment of free-living
birds under field conditions is not possible.
Maintaining optimal hygiene at feeding stations
can help to prevent outbreaks of disease. Where
disease outbreaks occur, temporary removal of
supplementary food may be appropriate to
reduce close congregation of birds and
reduced the risk of further disease transmission.

 

Can affect a range of birds
Whilst a range of tit species are susceptible to this novel form of the disease, detailed monitoring of birds in Wytham Woods by scientists at the University of Oxford show that great tits are by far the most susceptible.

"Although recovery from infection can occur, our results show that this new strain of avian poxvirus significantly reduces the survival of wild great tits and has particularly large effects on the survival of juvenile birds," says Dr Shelly Lachish of the Edward Grey Institute at Oxford University

"Based on the numbers of affected great tits that we have observed at Wytham Woods, our models do not predict that this new disease will cause an overall population decline of the species. However, pox-affected populations have lower yearly growth rates. Hence, they are likely to have greater difficulty in recovering from other environmental factors that might reduce their numbers," Dr Lachish added.

Rapid spread
With help from the public, scientists at the RSPB and ZSL have tracked the disease, which has spread rapidly in five years from south-east England to central England and into Wales. The annual seasonal peak of observed cases occurs in the early autumn months and incidents continue to be reported at this time of year.

Spread from Scandinavia & Central Europe
Genetic studies on the virus show that it appears to be the same strain seen previously in Scandinavia and more recently in central Europe, and is unlikely to have originated within Great Britain. BTO data on bird movements confirms that great tits rarely migrate outside the country. The spread of the virus to Britain is, therefore, thought to have occurred through the arrival of an infected vector, such as a mosquito.

Funding from NERC (the Natural Environment Research Council) enabled the detailed research reported here, and scientists are continuing to work together to monitor impacts of this new avian poxvirus strain on the population of great tits in the UK. They are calling on the public to assist in these efforts by reporting any signs of disease in garden birds to the RSPB, and have also highlighted that avian pox is not known to be infectious to humans or other mammals.

The new research was published in PLOS ONE.

Report sightings

Sightings of birds displaying symptoms of avian pox should be reported to the RSPB Wildlife Enquiries Unit preferably online or by telephone on 01767 693690. 

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