Respiratory diseases in pet rodents

Transcription

1 Vet Times The website for the veterinary profession Respiratory diseases in pet rodents Author : Elisabetta Mancinelli Categories : Vets Date : September 26, 2011 Elisabetta Mancinelli examines the presenting signs of respiratory tract problems in these increasingly popular pets and advises on treatment RESPIRATORY tract disease is a common health problem in many pet rodent species. Rats, mice and guinea pigs are more frequently affected, while respiratory tract infections seem less commonly encountered in species such as chinchillas and hamsters. they are thought to be rare in gerbils and degus. Because rats and other small rodents are used in biomedical research, an extensive amount of the information on respiratory tract diseases is based on lab animals. However, these animals are becoming more popular as pets. Practitioners are, therefore, more frequently asked to deal with such species and their specific diseases. Clinical diagnosis, treatment and preventive measures in the pet field, rather than in the laboratory setting, are an emerging, but often confusing, challenge for many veterinarians. A variety of microbial agents have been recognised to affect the respiratory tract of pet rodents. Their pathogenicity is extremely variable as they can act as primary or opportunistic pathogens. Subclinical infections are very common, as well as synergistic interactions in which combined infections can have an additive effect in producing severe respiratory disease. Inadequate housing and the inappropriate environmental conditions in which these animals are often kept, such as overcrowding and poor ventilation, can all play an important role in predisposing to respiratory disease. Moreover, dietary deficiencies (such as vitamin C in guinea 1 / 7

2 pigs and vitamin A and E deficiencies), the strain of the affected animals and their immune status may also have an important part in the pathogenesis of these conditions. A few simple rules can simplify the clinician s job when he or she is presented with a concerned and often overprotective owner. Educating clients and receptionists can help make the trip to the vet a less stressful experience for the pet, with a more positive outcome for the owner. The waiting area, for example, should be set up to be a quiet and safe place. Bear in mind that the rodent s sense of smell is well developed, so try to avoid planning appointments for natural predators when a pet rodent is scheduled to arrive. Rodents are more sensitive to the effect of heat, so the waiting area should be a cool temperature (18 C to 26 C). Physical examination As many diseases are the result of poor husbandry and improper diet, a complete history, including the dietary habits and the environmental condition in which the animals are normally kept, needs to be taken as it can provide very useful information. Always record the patient s weight. This will give you the possibility to assess, during future visits, any weight loss. First, observe the rodent in its cage for activity, grooming and presence of head tilt or any discharge. Reduce handling to a minimum, especially if the animal is in respiratory distress. An appropriate handling technique and minimal restraint is always essential to reduce stress and avoid bites that might result in a reflex response from the handler and the unfortunate pet dropping on the floor. A full physical examination should always include evaluation of the head, starting with ears, eyes and nose, looking for any discharge. Then the oral cavity can be assessed for dentition if possible, in the conscious patient. Palpate the lymph nodes, the abdomen and examine the anogenital area. Observe the condition of the fur and assess the general body condition. Respiratory and heart rate can be difficult to measure in rodents because they are very rapid, but lung fields can be auscultated with a paediatric stethoscope, keeping the animal on the client s arm to reduce stress. Always look for signs of dyspnoea. Clinical signs Clinical signs of respiratory disease are often non-specific and can include weight loss, reduced appetite or anorexia, poor coat condition or red ocular or nasal staining (excessive porphyrin staining can be a general sign of stress or disease, or might be due to rhinitis causing secondary obstruction of the lacrimal ducts). 2 / 7

3 Sneezing, dyspnoea, laboured breathing or head tilt secondary to otitis (middle ear invasion via the eustachian tube) can also be present. A wheezing, clicking or rattling respiratory noise can be audible even without auscultation in some animals. If the animal is dyspnoeic, oxygen therapy should be started immediately and clinical examination delayed. Common infectious agents Mycoplasma pulmonis is ubiquitous in pet rodents and is considered to be the most important infectious agent responsible for chronic respiratory disease in rats, whereas Sendai virus usually results in acute disease. The two infectious agents can be present at the same time. Sendai virus can exacerbate clinical signs due to mycoplasmosis because of its marked tropism for the respiratory tract, including the nasal cavities. Gerbils can be carriers of Sendai virus. Mycoplasma can affect the respiratory tract, nasal cavities and middle ear. Progression to bronchopulmonary disease can occur and the infection is persistent for life. Many other pathogens may be involved, also causing concurrent infections. Therefore, Pasteurella pneumotropica, Bordetella bronchiseptica, Streptococcus pneumoniae, Corynebacterium kutscheri, ciliaassociated respiratory bacillus (CAR) and rat coronaviruses need to be considered in the differential diagnosis. CAR bacillus, in rats in particular, is a potentiator of M pulmonis-induced respiratory disease. Clinical signs are similar to those seen in rats with Mycoplasma infection. Rats, mice and hamsters are natural hosts for the gram-positive bacterium Corynebacterium kutscheri. The infection usually is associated with immune-suppression and poor husbandry. Anorexia, weight loss, hunched posture and dyspnoea usually are associated with severe pulmonary lesions. Pasteurella pneumotropica can complicate Mycoplasma and Sendai virus infections in rats, causing conjunctivitis, otitis, abscesses and reproductive tract infections, mainly in immunocompromised animals. Rats, mice, hamsters and guinea pigs can be natural hosts. Sialodacryoadenitis virus (SDAV) and Parker s rat coronavirus (RCV) are strains of rat coronavirus that can cause endemic infections and mild clinical signs in rat colonies. In case of an outbreak, more severe clinical signs are seen. Streptoccoccus pneumoniae can cause otitis media and interna, rhinitis, pneumonia and pleural effusion in many rodent species. Klebsiella pneumoniae has also been reported as a cause of bronchopneumonia in rodents, including degus. 3 / 7

4 Bordetella bronchiseptica is the most common cause of rhinitis, sinusitis ( snuffles ) and pneumonia with consolidation of lung lobes, especially in guinea pigs. It can also cause otitis media and interna, abscesses and metritis. This bacterium is often present in asymptomatic carriers with clinical signs being triggered by stress. Mixing rabbits and guinea pigs is not recommended because Bordetella can be carried by rabbits, a species in which it is not pathogenic. It is pathogenic instead in guinea pigs. Chlamydophila caviae is common in guinea pig colonies, where it can cause conjunctivitis, rhinitis and abortion. Asymptomatic carriers are also possible. Many rodents kept as pets have short lives, but their owners are often devoted and willing to treat these infections, thereby extending the quality time for their beloved pets. Diagnosis History and clinical signs are usually strongly suggestive of respiratory disease, but a definitive diagnosis should be based on a culture and sensitivity test where an infectious cause is suspected. Chest radiographs can be taken to confirm the suspicion of lung disease. Chest x-rays can be difficult to interpret in such small patients, but they can provide useful information in many cases. They can also be useful to assess the cardiac silhouette and the cardiac size, to identify any area of possible lung consolidation or suspected areas of lung abscesses or neoplasia. Other tests, very commonly used in dogs and cats, can also be performed in case of respiratory disease in rodents. They are summarised in table 1. Treatment Therapy can be unrewarding in eliminating the disease and, in many cases, only alleviates the clinical symptoms. It is very important that clients are made aware that infected animals may initially respond to the prescribed medical treatment, but relapses, with even more severe clinical signs, are possible and they can lead to a more guarded longterm prognosis. Management of respiratory diseases can include a combination of the following: humidified oxygen therapy for severe dyspnoeic animals; provision of additional heat (21 C to 24 C), taking care not to overheat the animal because rodents cannot pant or sweat; nebulisation therapy (antibiotics, mucolytics, bronchodilators or mucokinetics) for 30 to 45 minutes two to three times daily with 5ml of fluid at a time; 4 / 7

5 fluid therapy and nutritional support are essential to correct any underlying deficit; mucolytics (bromexine 0.3mg/animal on food) and bronchodilators (clenbuterol and terbutaline empirically used at dog and cat doses) can also be provided orally; systemic antimicrobial therapy, based on culture and sensitivity when possible, should be started if an infectious agent is suspected, although no antibiotic is approved for use in rodents and many can cause life-threatening enterotoxaemia and should be avoided. A list of antibiotics that can be used is reported in table 2 ; consider NSAIDS, such as meloxicam (dose depending on the species); bronchodilators (aminophylline or theophylline) can be used in severe cases; in cases of severe pneumonia and in terminal cases, corticosteroids may be used at antiinflammatory dosage (dexamethasone 0.2mg/kg to 0.5mg/kg SC) as rescue shots ; private eating time and soft moist food has to be considered with severe dyspnoea and if the animal appears to be in discomfort; and euthanasia may be indicated in severe non-responsive cases on welfare grounds. Consider that one day of quality rat life is worth one month of human life. Prophylaxis In small rodent medicine, husbandry and correct management play an essential role in preventing and managing respiratory diseases. Cleaning the cage regularly and providing appropriate ventilation are particularly important to avoid the build-up of ammonia (NH3), which is a potent respiratory irritant. According to a study, there is a positive correlation between rising NH3 levels and the prevalence of Mycoplasma pulmonis lung lesions. Therefore, animals should be housed in a large wire enclosure (glass vivaria are not recommended) with good ventilation and an absorbent, dust-free bedding. Avoid using cedar shavings because anecdotal reports show evidence of respiratory and skin effects in different pet rodent species. Liver enzymes can also be affected in rats and mice, but no clinical signs have been documented so far. The cage should be cleaned at least twice weekly to help prevent disease, but without causing stress. Rats are active and inquisitive animals so nest materials, toys and other accessories to play with should always be provided in the cage. They are also social animals that can be kept in a single sex group or as a breeding pair. Avoiding stress from overcrowding is essential. 5 / 7

6 Ensure the cage is out of direct sunlight, but keep the temperature within the recommended range (17 C to 24 C) with an environmental humidity of 45 to 55 per cent. Always provide adequate shelters. Provide clean, fresh water daily and balanced fresh food to prevent obesity. Do not house together different species to prevent interspecies transmission of diseases and isolate sick animals. Miscellaneous noninfectious conditions A variety of other lesions can occur in the respiratory tract of pet rodents. Pulmonary and alveolar histiocytosis has been occasionally reported in mice and rats respectively and is characterised by accumulation of irregular eosinophilic crystals in the terminal respiratory airways. Foreign body pneumonitis has been described and seems to occur as an incidental finding in rats, mice and guinea pigs following inhalation of, for example, bedding material with subsequent granulomatous inflammation. Primary pulmonary neoplasia is considered to be rare in pets, but common in laboratory rodents and usually related to species, age and strain. Benign papillary adenomas are reported in guinea pigs. Mammary carcinomas and hepatocellular carcinomas must be considered in the differential diagnosis, as these tumours commonly metastasise to the lungs. Clinical signs of respiratory distress can occur in cases of heart failure resulting from atrial thrombosis that can be encountered spontaneously in mice, rats and older hamsters. As with other species, diagnosis, treatment and prevention of respiratory disease in pet rodents follow the same principles, but application of more specific knowledge regarding diseases occurring in each species is also necessary. To download published articles visit References Donnelly T M (2004). Disease problems of small rodents. In E V Hillyer and K E Quesenberry (eds) Ferrets, Rabbits and Rodents Clinical Medicine and Surgery (2nd edn) W B Saunders, Philadelphia. Flecknell P (2002). Guinea pigs. In A Meredith and S Redrobe (eds) BSAVA Manual of Exotic Pets (4th edn). BSAVA, Gloucester. Goodman G (2004). Infectious respiratory disease in rodents, In Practice April Goodman G (2009). Rodents: respiratory and cardiovascular system disorders. In A Meredith and E Keeble (eds) BSAVA Manual of Rodents and Ferrets. BSAVA, Gloucester. Orr H E (2002). Rats and mice. In A Meredith and S Redrobe (eds) BSAVA Manual of Exotic Pets. BSAVA, Gloucester. Schoeb T R (2000). Respiratory diseases of rodents, Veterinary Clinics of North America 6 / 7

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