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Results from Post Mortem of garden birds

  • Gordon
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16 Apr 2013 19:27 #576 by Gordon
Salmonellosis in garden birds

Outbreaks of mortality in wild birds in gardens in the UK were first reported in the mid-1960s, when members of the general public began to put out bags of peanuts to feed the wild birds. In these first outbreaks most deaths were due to infection with the bacterium Salmonella Typhimurium (abbreviated to S. Typhimurium) and occurred in greenfinches (Carduelis chloris) and house sparrows (Passer domesticus). Mortality incidents have continued and since 1995 SAC Consulting Veterinary Services at Ayr Disease Surveillance Centre has carried out over 900 postmortem examinations on garden birds. The results from these investigations have shown that in Scotland two strains of S. Typhimurium, type 40 and type 56 variant, cause most of the deaths from salmonellosis in garden birds. In the north of Scotland type 40 predominates but in the south of Scotland type 56 variant is the commonest type. Most outbreaks of salmonellosis in garden birds occur between October and March, with losses peaking in January and February.

Deaths are most often seen in greenfinches, chaffinches (Fringilla coelebs), dunnocks (Prunella modularis), house sparrows and siskins (Carduelis spinus), but other birds such as goldfinches (Carduelis carduelis), redpolls (Carduelis flammea), tree sparrows (Passer montanus) and great tits (Parus major) have also been affected in smaller numbers. During outbreaks of disease, dead birds or sick birds are usually found in the vicinity of the bird feeders. If seen alive the birds are fluffed up, reluctant to fly, and may look as if they are breathing heavily or have difficulty in swallowing.

The postmortem examination of birds dying from salmonellosis often reveals substantial areas of damage to internal organs such as the oesophagus, crop, liver, spleen and sometimes the lungs and lower part of the digestive tract. The damage to the oesophagus can be so severe that it causes a partial blockage, preventing food getting to the bird’s stomach even if it continues to eat. Confirmation of the cause of death requires specialist laboratory facilities for the culture and identification of the bacteria.

Why are the deaths occurring?
Although the mortality incidents in the UK usually occur at sites providing supplementary feeding for wild birds, the food is not believed to be the initial source of the bacteria but rather the cause of the congregation of large flocks of birds in a small area. Some birds probably carry small numbers of Salmonella in their intestines, and when the birds congregate at bird tables and feeding stations a build up of these bacteria may occur, contaminating the feeders and drinkers and the surrounding environment. Under these conditions, the bacteria may then have the chance to overwhelm the birds and cause their deaths.

What has happened to the greenfinches?
Long term monitoring has identified a fall in the number of garden birds dying from salmonellosis. In addition, the proportion of birds with salmonellosis that were greenfinches has dramatically fallen. In the first few years almost every bird found dead from salmonellosis was a greenfinch, but in recent years most of the deaths are occurring in other species. For example, from September 1996 to August 1999, 34 out of 36 garden birds with salmonellosis were greenfinches, but from September 2008 to August 2012 only 1 bird out of 36 birds with salmonellosis was a greenfinch. Why? The most likely explanation is that another disease, trichomonosis, has reduced overall greenfinch numbers, leaving fewer birds to be affected by the salmonellosis.

General control measures
• Use several feeding sites, to reduce bird numbers at any one site
• Move the feeding sites regularly, to reduce any build-up of debris and infectious agents around the feeders
• Don’t use all the feeding sites all of the time – rest periods will help to reduce levels of contamination
• Clean and disinfect feeders and feeding stations regularly. Rinse the feeders and allow them to dry before using them again.
• Consider leaving birdbaths or drinkers empty for a short period. Otherwise be particularly vigilant to provide clean drinking water on a daily basis
• Consider significantly reducing or stopping feeding for two weeks. This will encourage the birds to disperse and reduce the chance of new birds becoming infected at the feeding station. Feeding can then be gradually re-introduced, monitoring for further signs of ill health
• Always wash and dry your hands thoroughly after cleaning bird feeders or handling sick or dead birds.

Illness in humans and cats
Human illness from wild bird strains of Salmonella is currently uncommon in the UK, but there is the potential for spread to humans. Disposable gloves should therefore be worn when cleaning bird tables or if the carcases of dead birds have to be handled, and hands must be thoroughly washed and dried, especially before preparing food. Wild birds should also be excluded from food preparation areas. Disease may also occasionally spread to pet cats that come in contact with sick or dead infected garden birds.

Tom Pennycott, VS Ayr
(November 2012)

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  • Barry C
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03 May 2013 16:48 #585 by Barry C
Replied by Barry C on topic Results from Post Mortem of garden birds
Trichomonosis of garden birds
Birds pass the infection to each other when feeding their young and during courtship feeding, and birds of prey may acquire the infection if they eat infected birds. Food and water may also become contaminated by discharges from infected birds, potentially spreading disease to other birds, but the organisms don’t survive for long periods outside the birds and are very susceptible to the effects of drying.

Affected birds look lethargic, are fluffed up and are reluctant or unable to fly. They may show laboured breathing, or have difficulty in swallowing. Food debris may be seen sticking to the beak, and the feathers of the head and neck may be wet. Affected birds may appear to be very hungry and reluctant to leave the bird feeding areas, but are unable to swallow much of the food they pick up.

General control measures
• Use several feeding sites, to reduce bird numbers at any one site. Move the feeding sites regularly, to reduce any build-up of debris and infectious agents around the feeders. Don’t use all the feeding sites all of the time – rest periods will help to reduce levels of contamination.
• Clean and disinfect feeders and feeding stations regularly. Rinse the feeders and allow them to dry before using them again.
• Consider leaving birdbaths or drinkers empty for a short period. Otherwise be particularly vigilant to provide clean drinking water on a daily basis.
• Consider significantly reducing or stopping feeding for two weeks. This will encourage the birds to disperse and reduce the chance of new birds becoming infected at the feeding station. Feeding can then be gradually re-introduced, monitoring for further signs of ill health.
• Always wash and dry your hands thoroughly after cleaning bird feeders or handling sick or dead birds.

Part of an original document by Tom Pennycott SAC Auchincruive

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  • Barry C
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06 May 2013 00:07 #586 by Barry C
Replied by Barry C on topic Results from Post Mortem of garden birds
When I have found a dead bird in the village or been handed casualties that have been found locally by other people, I have sent suitable ones on to the Scottish Veterinary Disease Surveillance Centre in Ayr to find out the cause of death. The results obtained are below and display a range of causes of death:-

E. coli; two Greenfinches
Predation / Pasteurella multocida; one Bullfinch
Salmonella typhimurium type 40; one Goldfinch and one Siskin
Trichomonosis; one Greenfinch, and four Chaffinches

E.coli is a bacterial disease that is often associated with Greenfinches.

Salmonella typhimurium is another bacterial infection, this time of the smaller finches. Different strains of the bacterium are known, and the different strains are found in different geographical areas.

The Pasteurella in the Bullfinch is interesting. The results of the postmortem, were consistent with predation, but by what? Pasteurella is commonly found in the mouth of some mammals, particularly cats. In this case the predator is likely to have been a cat. Human cases of the same infection are frequently caused by a cat bite.

Trichomonosis is caused by a single celled protozoan parasite that that has long been known to infect Pigeons and birds of prey, but has only as recently as 2005 been identified as a cause of disease in finches.

Birds with either of the two bacterial infections show general symptoms of ill health, such as fluffed-up plumage and lethargy.
Birds with trichomonosis have signs of general illness (again, lethargy and fluffed-up plumage) and may show difficulty in swallowing or laboured breathing. Some individuals may have wet plumage around the bill and drool saliva or regurgitate food that they cannot swallow. In some cases, swelling of the neck may be evident. The disease may progress over several days or even weeks. As the symptoms are so similar laboratory examination is needed to establish the cause of the infection, and in wild birds treatment is not possible.

What can I do to reduce the chance of birds in my garden becoming infected? Some notes from SAC Auchincruive can be found in the forum entry below – these can help you in reduce the chance of birds becoming infected.

Barry

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