Wood pigeon

Disease: Trichomonosis (pigeon canker)

This page provides general information about this condition. Text can be revealed by clicking on the green headers. Links to press releases, results from DWHC investigations as well as other useful documents and relevant literature available on the DWHC website can be found at the bottom of the page.

Pathogen

Avian trichomonosis is caused by Trichomonas gallinae, a flagellated protozoan parasite that can cause disaese in the upper gastrointestinal tract of birds. There are several different strains of T. gallinae and these vary in terms of virulence (i.e. the degree to which they can cause disease). The parasite survives poorly in the environment and is particularly sensitive to dehydration.

 

Susceptible species

Trichomonas infection is perhaps best-known in pigeons, doves and birds of prey and it is though that the rock dove (Columba livia) is the main natural host.
In pigeons and doves the disease is also referred to as canker [2, 8]. A recent study comparing previously reported prevalences in the different bird orders showed large discrepancies with infection ranging from 1.1 to 99.4% in Columbiformes; and from 2.7 to 85% in birds of prey [9]. Until recently Trichomonas infection was rarely if ever seen in other orders of wild birds [9] and the occasional reports of cases in chickens, turkeys and some domestic birds [2,10] typically involved prior contact with doves or pigeons [9]. Recently a new pattern of infection has been observed with, in 2005, trichomonosis being reported In greenfinches (Carduelis chloris)in France and other finches (Fringilla coelebs) in the UK. By 2007 in these areas the corresponding populations had decreased in size by 35 and 21%, respectively [11]. There have subsequently been reports of infection in finch populations in Scandinavia [6] and Canada [5] as well as in other species of songbird and members of the crow family in California [11]. Trichomonas has also been detected in green finches in the Netherlands.
Possible sources of infection amongst these birds include food and water sources that have been contaminated with the saliva from infected birds. Indeed, there is indirect evidence to suggest that this is the predominant means of spread of infection amongst finches [5,9,11,13]. In birds of prey and possibly also in members of the crow family it Is the ingestion of infected pigeons and doves is likely to be the main source of infection [8,9]. It is typically young birds that develop disease whilst older birds that become infected tend not to develop or show signs. The young may be infected via crop-milk produced by parent birds [2, 12].
The reason for this recent appearance of Trichomonas gallinae in finches is unclear and is likely to be multifactorial. For example, changes in the environment, namely the increase in garden-feeders may increase the number of potentially infectious contacts between birds; furthermore, a change in the virulence of Trichinella strains may be behind the outbreak in the UK in which all cases appeared to be caused by the same strain [14].

Signs in animals

Trichomonosis causes birds to become weak, puff up their feathers and show reluctance to fly. In addition they may have difficulty eating and drinking which can present with regurgitation and typically leads to weight loss [6]. The disease can develop rapidly and in serious cases can lead to death within 1-2 weeks [15]. Infection can be recognised by the presence of a yellow-white, pasty substance in the mouth and throat that sometimes extends to the oesophagus and crop. In later stages, weeping eyes may obscure vision and there may be yellow, necrotic lesions in some internal organs such as the liver whose involvement ranges from minimal to severe. Liver involvement, sometimes in the absence of gastrointestinal lesions, is often seen in birds of prey [9]. Whilst the lesions are very suggestive of trichomonas infection a definitive diagnosis depends on further microscopic and molecular testing (PCR and sequencing of infectious material) [15].

 

Preventative measures

Daily cleaning of bird baths and feeders is recommended to minimise the risk of an infectious hub developing. During an outbreak feeding should be stopped.

Research results

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