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Genetic Welfare Problems of Companion Animals
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Siamese
Chronic Bronchial Disease
Related terms: chronic bronchitis; feline asthma; feline bronchial asthma; allergic airway disease, allergic bronchitis; feline asthma syndrome; bronchial asthma; eosinophilic bronchitis.
Outline: The cause of chronic bronchial disease is unclear. It is common in cats and Siamese cats appear to be particularly predisposed. This suggests a genetic basis but this has not been investigated. The disease and its effects on welfare can range from mild to very severe and the signs can include difficulty in breathing, reduced exercise tolerance and frequent episodes of coughing. The time course of the disease can be many months or years.
Summary of Information
(for more information click on the links below)
1. Brief description
Chronic bronchial disease is the commonest lower respiratory disorder in cats and is particularly prevalent in the Siamese (Byers & Dhupa 2005, Venema & Patterson 2010).
The disease causes inflammation of the airways (Johnson 2006) with thickening (hypertrophy) and contraction (bronchoconstriction) of the smooth muscle in the walls of the bronchi and bronchioles. Excessive secretion of mucus also occurs and together these processes lead to narrowing and obstruction of the airways and difficulties with breathing and gas exchange (Rozanski et al no date).
Signs vary widely and may include one or all of the following: lethargy, exercise intolerance with reduced play, frequent episodes of coughing, wheezing, and dyspnoea (difficulty with breathing, which, if severe, may show as mouth breathing or panting [Johnson 2006, Mardell 2007]). These signs can be intermittent or persistent (Johnson 2006, Mardell 2007).
Occasionally, individuals present with rapid-onset, severe breathing difficulties such as seen in a typical human asthma attack (Johnson 2006, Mardell 2007). In these cases, there is mouth breathing and distress and emergency veterinary intervention is required immediately. Without treatment, there may be collapse and rapid death.
Treatment of the chronic disease traditionally involves administration of oral anti-inflammatory drugs, such as corticosteroids, and bronchodilators (Johnson 2006, Mardell 2007, Venema & Patterson 2010). More recently, treatments have involved the use of inhaled corticosteroids and bronchodilators (Venema & Patterson 2010). Whilst treatments help control signs in many cats, a significant proportion suffers relapses or persistence of the condition (Johnson 2006). Most affected cats require life-long medication (Johnson 2006).
2. Intensity of welfare impact
Cats affected with chronic bronchial disease may experience a reduced quality of life due to episodic bouts, or in some cases continuous periods, of lethargy, wheezing or coughing and an inability to exercise or play normally (Johnson 2006, Mardell 2007, Venema & Patterson 2010). For those with the severest disease, or which develop acute respiratory dyspnoea, the condition is life-threatening (Johnson 2006, Mardell 2007, Venema & Patterson 2010) and causes extreme distress and individuals to struggle for breath.
3. Duration of welfare impact
The condition is recurrent or life-long and may be progressive. It can occur at any age with the mean age of onset being four years old (Venema & Patterson 2010).
4. Number of animals affected
Chronic bronchial disease is perceived to be a common disease in the Siamese but we are unaware of data on the proportion of the breed affected (Byers & Dhupa 2005, Mardell 2007, Venema & Patterson 2010, Moise et al 1989, Dye et al 1996; http://www.fabcats.org/breeders/inherited_disorders/siamese.php; AHT no date).
5. Diagnosis
Diagnosis is not straightforward and is usually made by ruling out other possible causes the signs. Diagnostic tests performed to help confirmation might include a full examination, blood and urine tests, chest radiography, tracheal endoscopy and/or bronchoalveolar lavage (in which a bronchoscope is passed through the mouth or nose into the lungs and fluid is squirted into a small part of the lung and then recollected for examination).
6. Genetics
The observed predisposition of this breed to the condition suggests genetic influences but this has not been investigated.
7. How do you know if an animal is a carrier or likely to become affected?
It is currently not possible to predict which cats will develop chronic bronchial disease, or if carrier animals (that may be able to pass the condition on to their offspring but remain unaffected themselves) exist.
8. Methods and prospects for elimination of the problem
Until further progress is made in unravelling the underlying causes of chronic bronchial disease, including possible genes involved, progress on preventing and eliminating this condition from the Siamese might prove to be slow. In such situations, a good case can be made for avoiding breeding from affected animals, or from those with affected relatives, since such an approach is likely to lead to a reduction in the prevalence of the condition.
For further details about this condition, please click on the following:
(these link to items down this page)
- Clinical and pathological effects
- Intensity of welfare impact
- Duration of welfare impact
- Number of animals affected
- Diagnosis
- Genetics
- How do you know if an animal is a carrier or likely to become affected?
- Methods and prospects for elimination of the problem
- Acknowledgements
- References
1. Clinical and pathological effects
Chronic bronchial disease is the commonest lower respiratory disorder in cats and is seen particularly in Siamese (Byers & Dhupa 2005, Venema & Patterson 2010).
The underlying disease process is not fully understood and there is a wide range of clinical presentations. Some affected cats have characteristics which fit with the human conditions of “asthma”, “chronic bronchitis”, and/or “chronic obstructive pulmonary disease” (COPD) (Mardell 2007). The feline syndrome has had various names and some authors have classified cases as feline asthma or chronic bronchitis depending on the signs (Padrid 2000). However, there is currently no standard agreed position on terminology (Venema & Patterson 2010) and so here the term chronic bronchial disease is used to encompass all the various clinical presentations observed.
In humans, asthma is characterised by an acute (rapid onset), reversible constriction of airways (bronchi and bronchioles) that are hyper-reactive to stimuli (allergens and irritants), and, with time, by the development of chronic inflammation (characterised by eosinophil infiltration). Chronic bronchitis and COPD in humans tend to lead to permanent narrowing of the airways, due to chronic inflammation (characterised by neutrophil infiltration), excessive mucus production and irreversible changes in the airways (Mardell 2007). The underlying causes of asthma, chronic bronchitis and COPD are different in humans and a wide range of tests is available to help differentiate between these conditions. This is not the case for cats
To understand the disease in cats a basic understanding of respiratory anatomy and immunology in the cat is useful:
The lungs are the largest organs of the body and are divided into two – the left and right lung - which are made up of many repeatedly divided and branched airways, that allow air to flow deep into them. The trachea (windpipe) takes air from the back of the nose and mouth into the chest cavity. Here it divides into the primary bronchi (airways) – which supply air either to the left or right lung - and then further divides into lobar bronchi and then into smaller and smaller bronchi and then into bronchioles (smaller airways). The bronchioles finally branch into the alveolar ducts and the alveoli, which are sac-like, very thin-walled structures where the gas exchange between air and blood takes place. The trachea and the bronchi are supported by cartilage in their walls, which helps keep them open. The smaller bronchioles do not have cartilage but do have smooth muscle within their walls, which influence their diameter. The airways and the smooth muscle are controlled via nerve fibres from the autonomous part of the nervous system, which controls involuntary activities in the body. When this smooth muscle contracts the diameter of the tube is decreased (bronchoconstriction).
Several mechanisms act to protect the lungs from infection and damage. Except in the alveoli, the airways are lined with ciliated epithelial cells (cells with small finger-like projections on their surface), which are interspersed with mucus-producing cells. Mucus lines the airways and acts to catch any inhaled foreign particles and the cilia beat in a coordinated manner to help move the mucus and any trapped particles up out of the airways to then be coughed up.
The immune system, comprising tissues, cells and proteins, functions to protect the body against invaders including pathogens (disease causing organisms). Anything that stimulates an immune response is termed an antigen. Various immune cells and proteins are found within the respiratory system and those of particular relevance to chronic bronchial disease include mast cells and eosinophils. Both of these cells, when activated by suitable stimuli, can release chemical messengers which stimulate inflammatory processes in the local tissue.
Chronic bronchial disease in cats involves inflammation of the airways (Johnson 2006), bronchial smooth muscle hypertrophy (thickening) and bronchoconstriction, and excessive secretion of mucus. Such responses result in narrowing and obstruction of the airways and difficulties with breathing (Rozanski et al no date).
There are various theories about the causes of the chronic inflammation but this remains somewhat unclear at present (Rozanski et al no date).
- It may be caused by an allergic reaction. There are various ways the immune system can over-react to stimuli leading to an allergic reaction. It could be due to a type I hypersensitivity reaction. In this, mast and other immune cells become hypersensitized to a particular foreign antigen. Specific IgE antibodies are made against the antigen (also called an allergen in this case as it stimulates an allergic reaction). When the body is re-exposed to the allergen at a later date the allergen-specific IgE antibodies attach to mast cells and cause them to release chemical messengers which attract other immune cells and stimulate inflammation. T-lymphocytes and eosinophils (two other types of cells) are drawn to the area and they in turn release chemicals which cause bronchoconstriction and stop the cilia working so allowing mucus to accumulate and block small airways. The chemicals released also lead the cells which line the airways (pneumocytes) to slough off. This exposes sensory nerve endings to the allergens which causes them to become hypersensitive and to stimulate smooth muscle constriction and additional bronchoconstriction. Fluid and other cells are drawn to the area causing the tissue to be swollen and thickened resulting in further narrowing of airways.
- Another possibility is that the disease is due to stimulation of the nerves that control the smooth muscle of the bronchi, by irritants, allergens, viruses or chemicals produced by cells of the immune system. Aberrations in the nerve system controlling bronchi may lead to lack of normal maintenance of airway tone. Once airways have collapsed or fluid is present within them, nerve endings within the lung tissue may be stimulated and alter the breathing pattern.
Various trigger factors may be involved in inducing or exacerbating the problem, including:
- allergens, including inhaled allergens such as house dust mites, storage mites and pollens (Prost 2004);
- parasites or fungal infections;
- viral infections eg cat flu; and
- irritation by particulate matter in the air eg smoke, dust, dirt, pollution, perfumes, or flea powders .
Genetic influences have been found to be involved in human asthma, and may be also in cats as suggested by the predisposition of the Siamese.
Affected individuals may show one or all of the following: lethargy, exercise intolerance with reduced play, coughing, wheezing and dyspnoea (difficulty breathing) which, when severe, may show as mouth breathing or panting (Johnson 2006, Mardell 2007). Breathing may be loud, rapid (tachypnoea) or laboured, and there may be a harsh cough with abdominal effort which owners may interpret as trying to cough up a hairball, regurgitate or vomit (Johnson 2006). These signs can be intermittent, or chronic and persistent (Johnson 2006, Mardell 2007).
Occasionally, individuals present with rapid-onset, severe, breathing difficulties as seen in a human asthma attack (Johnson 2006, Mardell 2007). These cats may have cyanotic colouring within the mouth (ie tissues appear slightly blue in colour), mouth-breathe, and are distressed and very fragile. They need immediate but gentle veterinary intervention and may rapidly collapse and, unless successfully treated, die.
Treatment of acute-onset severe dyspnoea involves intensive care, oxygen and fast-acting bronchodilating drugs. Treatment for the underlying chronic disease traditionally involves oral anti-inflammatory drugs, such as corticosteroids, and bronchodilators (Johnson 2006, Mardell 2007, Venema & Patterson 2010). These can have significant side-effects, particularly when given systemically and over longer periods of time. For example, some bronchodilators can alter heart function and corticosteroids often cause altered appetite, drinking and diabetes - which may be permanent. More recently, treatments have involved delivering drugs via inhalers and there is interest in using specific immunotherapy against identified allergens (Venema & Patterson 2010). Antibiotics may be used if concurrent infection is suspected (Johnson 2006).
Treatments do help to control signs in many cats but a significant proportion of affected individuals suffer relapses or persistence of the condition (Johnson 2006). Most cats require life-long medication (Johnson 2006) and some need euthanasia due to deterioration or persistence of severe disease (Rozanski et al no date).
2. Intensity of welfare impact
The clinical effects, and thus the welfare impacts, of chronic bronchial disease vary between individual and range from mild to severe. Many cats have episodic bouts of lethargy, an inability to exercise or play normally, together with wheezing or coughing. In others, these problems, and their impacts on quality of life, are persistent and continuous (Johnson 2006, Mardell 2007, Venema & Patterson 2010). In those with the severest disease, or which develop acute respiratory dyspnoea (difficulty in breathing), the condition is life-threatening (Johnson 2006, Mardell 2007, Venema & Patterson 2010). These cats are likely to experience extreme distress as they struggle to breathe and achieve adequate oxygen intake. Some may collapse and die.
3. Duration of welfare impact
The condition usually develops in young to middle-aged cats with the mean age being four years, but it can occur at any age (Venema & Patterson 2010). It is usually a life-long condition but signs may be episodic with recurrent bouts or persist with cats having constant signs. The duration of the disease and its welfare effects therefore can be many months or years. Some cats have sudden unexpected bouts of severe signs after being apparently normal.
4. Number of animals affected
Chronic bronchial disease is a common disease in cats (Byers & Dhupa 2005, Mardell 2007, Venema & Patterson 2010). Although Siamese are perceived to be predisposed to the condition (Moise et al 1989, Dye et al 1996, Mardell 2007, Venema & Patterson 2010 http://www.fabcats.org/breeders/inherited_disorders/siamese.php; AHT no date), as far as we are aware there are no data on the proportion affected.
5. Diagnosis
Although veterinary surgeons would have a high suspicion of chronic bronchial disease in a young to middle-aged Siamese cat with suggestive signs, because of the prevalence of the disease in the breed, confirmation is not straightforward and generally depends on excluding other possible causes of the signs(Johnson 2006). There are many other conditions which can cause similar signs in cats such as pulmonary oedema (fluid build up in the lungs often due to heart failure), lung worm and heart worm infections, tumours, infections, pulmonary embolisms and idiopathic pulmonary fibrosis (Johnson 2006, Mardell 2007).
Investigations which may be used to help confirm a diagnosis include thorough examination, blood tests, x-rays of the chest; bronchial endoscopy (using a fine endoscope to look down into the airways) and bronchoalveolar lavage (in which small amounts of saline solution are put into the airways and then sucked out for microscopic examination to determine which cells are predominant in the airways and to culture for possible infections). More specialised tests may sometimes be performed including lung function tests, exhaled breath condensate analysis (to look for oxidative damage within the lungs) and allergen testing to try and identify particular allergens that may be involved (Johnson 2006, Venema & Patterson 2010).
6. Genetics
Several studies and practitioner experience, in the USA and UK, suggest that Siamese cats are predisposed to the condition (Moise et al 1989, Dye et al 1996, Mardell 2007, Venema & Patterson 2010, http://www.fabcats.org/breeders/inherited_disorders/siamese.php; AHT no date) and also that they are vulnerable to an increased severity of the disease and from a younger age (Moise et al 1989, Dye et al 1996, Mardell 2007). Other studies disagree; one study, in Australia, concluded that Siamese cats did not have a particular predisposition (Foster et al 2004). Generally, however, it is believed that there is a breed predisposition and that this may have a genetic basis, as in human asthma (Johnson 2006).
7. How do you know if an animal is a carrier or likely to become affected?
It is currently not possible to predict which cats will develop chronic bronchial disease or if carrier animals (those that may pass the disease on to their offspring without developing the disease themselves) exist.
It seems sensible when choosing a kitten to select one whose parents are healthy and free from chronic bronchial disease
8. Methods and prospects for elimination of the problem
Until further progress is made in unravelling the underlying causes of chronic bronchial disease, including possible genes involved, progress on preventing and eliminating this condition from the Siamese might prove to be slow. In such situations, a good case can be made for avoiding breeding from affected animals, or from those with affected relatives, since such an approach is likely to lead to a reduction in the prevalence of the condition.
9. Acknowledgements
UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section.
10. References
Animal Health Trust (AHT) no date Your cat & feline asthma and chronic bronchitis. Client Information leaflet. Animal Health Trust: Newmarket, UK
Byers CG and Dhupa N (2005) Feline Bronchial Asthma: Pathophysiology and Diagnosis. Compendium of Continuing Education for Practising Veterinarians 27(6): 418-425
Dye JA, McKiernan BC, Rozanski EA, Hoffmann WE, Losonsky JM, Homco LD, Wesiger RM and Kakoma I (1996) Bronchopulmonary disease in the cat: historical, physical, radiographic, clinicopathologic, and pulmonary functional evaluation of 24 affected and 15 healthy cats. Journal of Veterinary Internal Medicine 10: 385–400
Foster SF, Allan GS, Martin P, Robertson ID and Malik R (2004) Twenty-five cases of feline bronchial disease (1995–2000). Journal of Feline Medicine and Surgery 6: 181–188
Johnson L (2006) Bronchial Disease in August JR Ed. Consultations in Feline Internal Medicine Volume 5 pp361-367. St. Louis, USA: Elsevier Saunders
Mardell E (2007) Investigation and treatment of feline chronic bronchial disease. In Practice 29: 138-146
Moise NS, Wiedenkeller D, Yeager AE, Blue JT and Scarlett J (1989) Clinical, radiographic, and bronchial cytologic features of cats with bronchial disease: 65 cases (1980–1986). Journal of American Veterinary Medical Association 194: 1467–1473
Padrid P (2000) Feline asthma. Diagnosis and treatment. Veterinary Clinics of North America Small Animal Practice 30: 1279–1293
Prost C (2004) Treatment of allergic feline asthma with allergen avoidance and specific immunotherapy: 20 cats. Veterinary Dermatology 15: 45
Rozanski E, Nicholls PK and Watson P no date Allergic bronchitis (On-line) Available at
http://www.vetstreamfelis.com/ACI/May08/VMD2/ dis00952.asp. Accessed 10.5.11
Venema CM and Patterson CC (2010) Feline asthma: what's new and where might clinical practice be heading? Journal of Feline Medicine & Surgery 12: 681-92
http://www.fabcats.org/breeders/inherited_disorders/siamese.php
© UFAW 2011
Credit for main photo above:
By Karin Langner-Bahmann, upload von Martin Bahmann (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons