RESPIRATORY DISEASES IN RABBITS

Transcription

1 Vet Times The website for the veterinary profession RESPIRATORY DISEASES IN RABBITS Author : BRIGITTE REUSCH Categories : Vets Date : April 7, 2008 BRIGITTE REUSCH discusses the aetiology, features, treatment options and prevention of upper and lower respiratory tract disease in domestic rabbits Upper respiratory tract disease Aetiology Pasteurella multocida should always be considered in upper respiratory tract (URT) disease, where it causes rhinitis, including turbinate atrophy, snuffles and sinusitis. This is a commensal organism of the mucous membranes that exhibits pathogenicity when the host s immune defences are compromised. Virulence factors of P multocida include adhesions, resistance to phagocytes, endo and exotoxins, iron regulation and production of filamanents (pili) to assist binding to membranes. Other bacteria associated with URT disease include Bordetella bronchiseptica, Staphylococcus aureus, Moraxella catarrhalis and Mycoplasma pulmonis. B bronchiseptica and S aureus are thought to act as co-pathogens, although pure cultures have also been isolated from affected rabbits. Co-infection with infectious agents that damage the mucociliary escalator (B bronchiseptica and cilia-associated respiratory [CAR] bacillus) will contribute to the severity of the respiratory disease. The most common contributing factor to bacterial upper respiratory disease is a compromised immune system. Factors that can reduce the immune system include: malnutrition; 1 / 11

2 chronic disease; husbandry problems (for example, high ammonia levels due to poor ventilation and high concentrations of urine); social changes (for example, addition or loss of a companion rabbit or member of the family, moving home etc); environmental problems for example, overheating (rabbits become heat stressed above 22 C) or poor ventilation; and immune suppression due to corticosteroid therapy or immune disease, which will also predispose the rabbit to bacterial infection. Viral disease is also seen as a cause of snuffles. Myxomatosis can cause snuffles. Herpesvirus has also been isolated in rabbits with upper respiratory disease. Allergies including hayfever are also seen occasionally in rabbits. Rarely, neoplasia of the nose causing disruption of the normal architecture may initially present as snuffles. Carcinoma of the nasal turbinates causes disruption of the normal architecture. However, other signs are seen with nasal tumours, including facial deformity. Trauma can be a cause of nasal disease and snuffles, as was seen in a five-yearold Netherland dwarf ( and ). Unfortunately, the hutch door had dropped on to its nose, damaging the sensitive nostrils. Secondary bacterial infection disrupted the normal healing and the scar tissue that formed left it with very small nostrils. Surgery was carried out to widen the nostrils; it is continuing to heal well. Foreign bodies (for instance, grass seeds or shafts and hair) getting stuck in the nose are not uncommon. Clinical features and diagnosis The clinical signs of URT disease include sneezing, snoring, dyspnoea, ocular discharge, conjunctivitis, dacryocystitis, nasal mucosa erosion and nasal discharge, which may be seen as discharge matted on the medio-distal aspect of the forelimbs. Auscultation of the trachea, sinuses and nares reveals rattles and rales. Inspiratory dyspnoea may be seen. Non-respiratory pasteurellosis may present with otitis, bacteraemia, generalised abscesses and reproductive infections. Direct bacterial culture (for example, deep, 1cm to 4cm, bilateral nasal swabs, or abscess capsule) and antibiotic sensitivity should be carried out wherever possible. Haematology may reveal heterophilia in acute bacterial infections, but more generally chronic disease is associated with a leucopaenia. Serology is available for P multocida, although rarely used in diagnosis of individual cases. False negatives due to immunosuppression and false positives due to cross-reaction with other related bacteria are possible. Radiography of the skull may reveal decreased density in 2 / 11

3 advanced disease, due to sinusitis and turbinate atrophy, or bone lysis as a result of nasal carcinoma. Increased density in the tympanic bullae, nares or sinuses indicates infectious disease. Treatment and prognosis In all cases, the primary factors causing a compromised immune system must be recognised and addressed. In bacterial URT disease, resistance has been seen in bacteria other than Pasteurella species. Several antibiotics that have been shown to be sensitive to P multocida, and that currently have the least resistance, include penicillin G, chloramphenicol, erythromycin, tetracyclines, fluoroquinolones, novobiocin and nitrofurans. The author uses enrofloxacin (Baytril, Bayer) at 20mg/kg q24h PO for seven to 14 days, depending on response to treatment as a first line. Antibiotics that P multocida is known to have resistance to include lincomycin, clindamycin and, to some degree, streptomycin and sulphonamides. In severe infections, the use of parenteral, nebulised and topical antibiotics may be indicated. Nasolachrymal duct flushing with sterile water or antibiotics is indicated in dacryocystitis. Non-steroidal, anti-inflammatory drugs are essential to reduce inflammation in the narrow URT and analgesia is essential, as this condition is painful. Mucolytics (bromhexine, N-acetyl-cysteine) and nebulisation are useful in the management of rhinitis. Assisted feeding is indicated if anorexia occurs. Prognosis is dependent on the severity of disease and response to treatment. Treatment of viral disease is supportive, but euthanasia may be indicated in severe cases. Avoidance of allergens and irritants is important in all cases of respiratory disease, as these predispose the respiratory tract to infection. Nasal carcinomas carry a grave prognosis. Foreign body removal by forceps or endoscopically and subsequent antibiosis is indicated. Prevention As most respiratory disease is secondary, preventive medicine has a large role to play in the improvement of rabbit welfare. A good diet, and investigation and treatment of all chronic disease, is important. A clean, low-dust and lowammonia environment are very important factors in prevention and management of this condition. Most rabbit hutches have inadequate ventilation, as there is often only the wire cage front as an air inlet, and no air outlet to encourage air to ventilate through the cage, rather than just past the hutch. By drilling holes or replacing the top 5cm of the back wall with wire mesh under the eve of the hutch roof, ventilation will be dramatically improved. This will also help keep the hutch cooler, as the warmer air will not be trapped in the hutch. The same approach should also be applied to the rabbit shed (see for modifications of the author s shed). Myxomatosis can be prevented by good insect control and regular vaccination (Nobivac Myxo, Intervet), but care must be taken to ensure a minimum of 0.1ml is administered 3 / 11

4 intradermally. Disorders of the lower respiratory tract Aetiology Bacterial. Pasteurella multocida should always be considered in lower respiratory tract (LRT) disease, where it causes bronchopneumonia. Other bacteria that are often diagnosed in pet rabbits with bronchopneumonia include: Pseudomonas aeruginosa, Staphylococcus aureus, Bordetella bronchiseptica, Mycobacterium bovis, M tuberculosis, Moraxella bovis, Francisella tularensis, Yersinia pestis, Chlamydophila species and CAR bacillus. Viral. Some viruses have also been found associated with bronchopneumonia; severe myxomatosis infection can result in haemorrhagic pneumonia and herpesvirus can also be involved. Neoplasia. Thymomas are seen in both young and adult rabbits. These tumours can be either lymphoid or epithelial in origin. Dutch, French silver, Havana and tan breeds older than four years of age have a 50 to 80 per cent incidence of uterine adenocarcinoma. Metastasis to local tissues and lungs, liver, brain and bones may occur within one to two years. Allergic. Allergens can stimulate bronchitis in rabbits. Cardiovascular. Pleural effusion has been seen with cardiovascular disease (cardiomyopathy, valvular disease, pericarditis and atherosclerosis) and corona virus infection, but this has not been reported as a spontaneous natural infection in pet rabbits. Traumatic. Irritants (for example, dust, ammonia, cigarette smoke or wood shaving vapours) will predispose the respiratory tract to infection. Aspiration pneumonia has been infrequently reported in rabbits, but foreign bodies of the LRT are rare. Rabbits cannot tolerate heat stress, and heat stroke can present as LRT disease, with pulmonary oedema, cyanosis and death. Clinical features and diagnosis Dyspnoea, cyanosis, anorexia, depression, pyrexia or hypothermia and lethargy are seen with LRT disease. Pulmonary rales, or increased respiratory effort particularly intercostal effort indicates LRT disease. Absence of lung sounds or very loud heart sounds may indicate replacement of normal lung tissue with consolidated lung tissue, abscesses or neoplasia. Friction sounds may be heard with pleuritis, and fluid sounds are heard with pulmonary oedema. Bilateral exophthalmos is occasionally observed in rabbits with thymomas; this may be related to interference of vascular 4 / 11

5 return to the heart by the mass. Presumptive diagnosis of bronchopneumonia can be made on historical and clinical findings. However, as with URT disease, direct bacterial culture on a deep nasal swab and antibacterial sensitivity is recommended. Haematology will be similar to that of URT disease. Radiography may reveal a bronchial pattern of doughnuts in bronchitis and an interstitial or alveolar pattern is seen with pneumonia. Cardiomegaly, evidence of pulmonary oedema and pleural effusion is seen with cardiovascular disease. A mediastinal mass or multiple pulmonary nodules are indicative of neoplasia or abscesses. Ultrasonography allows guided needle biopsy or aspiration of these lesions. Thoracocentesis and cytology are indicated if pleural fluids are present and are both diagnostic and therapeutic. Treatment Antibacterial treatment of bronchopneumonia should ideally be based on culture and sensitivity. In chronic cases, antibiotic therapy may be required for months. Treatment of bacterial pneumonia is similar to rhinitis. Humidification, or nebulisation, will reduce dyspnoea and aid absorption of antibiotics. Critical patients often require intensive nursing and oxygen therapy. Prognosis will depend on the severity of the disease and response to treatment. Viral pneumonia is generally unresponsive to treatment, and euthanasia on humane grounds should be considered. Removal of a thymoma via median stereotomy has been accomplished. Radiation chemotherapy has also been used in a rabbit with thymoma. Thoracic metastasis has a poor prognosis, but supportive therapy with antibiotics and bronchodilators may give temporary relief. Allergic respiratory disease should be managed by elimination of the allergen, where possible. Antihistamines can also be used to reduce inflammation. Prevention Prevention of P multocida infection can be carried out by serological screening and barrier housing, to establish Pasteurella free colonies in laboratory rabbits. Pet rabbits, however, are unlikely to originate from Pasteurella-free sources. Carrying out serological screening for P multocida, quarantining positive animals and treating infected rabbits may, however, reduce outbreaks and control disease in a multi-rabbit household. Several vaccinations have been developed against P multocida, although none are currently available for prevention of pasteurellosis. Careful attention to any contributing factors will decrease the individual s susceptibility to infection. Vaccination against myxomatosis is available in the UK (Nobivac Myxo, Intervet). It is a live 5 / 11

6 attenuated vaccine containing Shope fibroma virus that provides cross-immunity against the myxoma virus. Vaccination should commence from six weeks of age. Boosters are required every six to 12 months, depending on risk. Effective insect control is essential to reduce the risk of infection. Ovariohysterectomy before the rabbit is two years old is a preventive health measure for metastatic spread of uterine adenocarcinoma. 6 / 11

7 Figure 1. Trauma can be a cause of nasal disease and snuffles, as seen here in this fiveyearold Netherland dwarf rabbit. Secondary bacterial infection disrupted the normal healing, and the scar tissue that formed left it with smaller nostrils. Surgery was performed to widen them. 7 / 11

8 8 / 11

9 Figure 2. Trauma can be a cause of nasal disease and snuffles, as seen here in this fiveyearold Netherland dwarf rabbit. Secondary bacterial infection disrupted the normal healing, and the scar tissue that formed left it with smaller nostrils. Surgery was performed to widen them. 9 / 11

10 10 / 11

11 Powered by TCPDF ( Figure 3. Well-ventilated hutches and rabbit sheds can aid in the prevention of respiratory disorders. 11 / 11