Infectious diseases

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When considering disease control, veterinarians need to reflect on three fundamental aspects: individual patient care; disease control within the facility; and avoiding the spread of disease from the facility to the outside world. This chapter discusses specific considerations for biosecurity in the veterinary practice that deals with birds and offers a detailed guide to common pathogens in avian practice.

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19.1 Dirty cages contaminated with leftover food, faeces, damp bedding and even fungal growth provide a great environment for pathogens, resulting in a high risk of infection. Thorough cleaning and removal of all organic matter is vital before considering disinfection.
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19.4 Spreading disease by handling different patients is an obvious risk, particularly in a veterinary practice. This threat can be minimized by using a detergent soap as well as a hand disinfectant to wash hands between patients. Hands-free dispensers as well as disposable paper towels are recommended next to every sink, not only those in the operating theatre.
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19.5 Birds affected with circovirus present with feather dysplasia, haemorrhages in the feather, progressive feather loss and/or necrotic lesions to the beak. The clinical signs may progress with each moult, potentially resulting in completely featherless individuals. Other individuals, mainly those infected as adults, are able to eliminate the virus after a viraemic period. (b–c, © Deborah Monks)
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19.6 The clinical picture of polyomavirus differs depending on the species (Budgerigars non-Budgerigar psittacine birds) and the age (nestlings adult birds) of the birds affected. In nestlings, abdominal distension and scattered haemorrhages are the predominant clinical signs. Adult birds might be able to clear the virus without distinct clinical disease. (Courtesy of Robert J. Doneley)
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19.7 Internal papillomatosis is caused by psittacine herpesvirus and mainly presents as papillomatous lesions protruding from the cloaca. Oral papillomas may also occur. Approaches to permanently surgically remove these papillomas from the cloacal mucous membranes proved to be of no avail. (Courtesy of Robert J. Doneley)
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19.8 Proventricular dilatation disease (PDD) has been a concern for many years and is now thought to involve bornavirus as the aetiological agent. Clinical signs vary, including weight loss, regurgitation, polydipsia, polyuria and, in progressed cases, there is often an obviously dilated proventriculus on radiography or post-mortem examination. The histological proof for this disease is cytoplasmic infiltrations in the nerve plexi of the gastrointestinal tract.
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19.10 mites are not restricted to poultry and pigeons; they are also found in Passeriformes and parrots, particularly in Budgerigars. The birds develop typical lesions with bore holes over the cere, around the beak or on the feet. As only the larval state can be eliminated by treatment, it is crucial to repeat the applications weekly as long as lesions are visible.
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19.11 spp. are flagellated single-celled organisms that manifest themselves in the oropharynx and/or crop of birds. This sample is from a crop wash from a budgerigar. There is no species specificity. The organism is diagnosed via wet mount examination of crop smears by identification of their circulating movements. In order to maintain the live organism it is important to perform the examination straight after swabbing the crop and to provide a warm environment (using warm water and warmed slides). (© John Chitty)
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19.12 Ascarides are not species-specific and can cause serious disease, particularly in small birds such as passerines or Budgerigars. If during treatment too many worms die off at the same time, there is the risk of endotoxicosis or an intestinal ileus. Controlled and carefully dosed treatment allows the bird to excrete the dead worms. The need for regular microscopic faecal examinations should be self-evident in open-roofed aviaries.
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19.13 Conjunctivitis is only one clinical sign of psittacosis. Some affected birds show rhinitis, diarrhoea or are simply ‘off colour’. This airborne disease needs to be considered when birds from different backgrounds are kept in close proximity. Furthermore, the zoonotic potential of this disease needs to be taken into account. This is a mild conjunctivitis in a Cockatiel, with subtle swelling and erythema and is not pathognomonic of psittacosis.
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19.15 causes miliary necrotic lesions in the spleen. This bacterial infection is predominantly seen in Passeriformes and, as it often results in peracute death, diagnosis is mainly made by post-mortem examination. Rodent control is crucial when trying to control the spread of this pathogen. (© John Chitty)
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19.16 spp. are still causing disease among companion birds. The atypical form presents with diffuse enlargement of the liver and spleen. The lepromatous form shows nodular to diffuse subcutaneous lesions. In the tubercular form, discrete granulomas develop within and around the liver, spleen and intestines. Sometimes granulomas in the conjunctiva (pictured) might be the only clinical signs. It is crucial to identify such lesions via acid-fast staining methods.
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19.17 is a yeast that causes haemorrhagic lesions in the mucous membrane of the proventriculus. Multiple species are susceptible, including passeriformes and parrots; Budgerigars are particularly affected. As the disease progresses, the birds lose weight but with continuous appetite. The organism can be identified in the faeces via wet mount. (© Deborah Monks)
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