Respiratory symptoms are a common reason to present small mammal patients to veterinary practices. Respiratory issues can be caused by disease states such as bacterial or viral diseases or can be attributed to or exacerbated by poor husbandry.
It is important to gain a detailed husbandry while obtaining a clinical history, especially ventilation, new arrivals, the number of animals in the group or herd and any changes that have occurred in the environment.
Respiratory issues can be caused by disease states such as bacterial or viral diseases or can be attributed to or exacerbated by poor husbandry
Signs of respiratory disease should be treated as a priority, and any small exotic mammal presenting with respiratory disease should be seen within a maximum of 24 hours. Any small mammal with signs of nasal obstruction should be treated as an emergency, as rabbits, guinea pigs, chinchillas and degus are obligate nasal breathers (Ardiaca García et al., 2021).
If a patient presents with dyspnoea, increased respiratory effort (Video 1) or profuse nasal discharge, care must be taken with handling, as an invasive physical examination may exacerbate the clinical signs. In these cases, flow-by oxygen can be useful, or the patient can be placed in an oxygen tent/cage while you gain a history to allow for pre-oxygenation (Video 2).
Respiratory disease may also present as subtle clinical signs, such as general malaise, a poor-quality haircoat (Figure 1), weight loss and porphyrin staining (Figure 2) (Goodman, 2009).
Diagnostic work-up is important, as not all respiratory clinical signs are caused by bacterial disease, and clinicians are often tempted to treat symptomatically with enrofloxacin. Cardiac disease, thoracic masses, toxin exposure and/or conditions that cause abdominal distension (placing pressure on the diaphragm) can all present with respiratory signs.
In cases of rhinitis, deep nasal swabs should be taken while under sedation or general anaesthesia before commencing antibiotic therapy (Goodman, 2009).
Thoracic and skull radiographs are an excellent way to assess the upper and lower respiratory tract (Figure 3) (Capello and Lennox, 2011). Obtaining well-positioned high-quality radiographs should be a priority, as many of these patients have small thoracic cavities. In most cases, general anaesthesia is required to obtain correctly positioned radiographs (Capello and Lennox, 2011), as inadequately positioned radiographs can be non-diagnostic. Manual restraint should not be considered as an option for positioning for radiographs because it is likely to stress an already compromised patient (Zwingenburger and Silverman, 2009). Care should be taken to follow radiation safety protocols.
Thoracic ultrasound can be used to identify lung masses, abscesses, consolidation and thoracic effusion and can be used to help guide thoracocentesis for sampling and treatment (Ardiaca García et al., 2021).
Computed tomography (CT) can give a detailed view into the sinuses. This is particularly important when assessing cases of chronic rhinitis that may be associated with foreign bodies, otitis media or dental disease where tooth roots may be growing into nasal cavities, causing an obstruction (Jekl, 2021).
Nasal endoscopy can be used to directly visualise respiratory structures and take biopsies for culture and histopathology (Capello and Lennox, 2011).
Causes of respiratory diseases in small mammals
While there are many causes of respiratory disease in small mammals, both primary and secondary, several common causes are discussed below.
Infectious respiratory diseases in rats
Rat respiratory disease is a complex and multifactorial presentation, often caused by several infectious organisms and husbandry-related issues.
There are three main bacterial components of respiratory disease in rats: Mycoplasma pulmonis, Streptococcus pneumoniae and Corynebacterium kutscheri (Brown and Donnelly, 2012). Other pathogens may also be present and can cause clinical disease when the individual is co-infected with these main components. These include Sendai virus, pneumonia virus of mice, rat respiratory virus, cilia-associated respiratory bacillus and Haemophilius spp. (Brown and Donnelly, 2012). When several of these pathogens are causing disease simultaneously, they can result in chronic respiratory disease or acute bacterial pneumonia.
The most common inciting cause of respiratory disease in rats is Mycoplasma pulmonis (Goodman, 2009), which is spread via aerosol and considered ubiquitous in pet rats. Clinical signs are variable and often patient-specific, depending on age and environmental factors (Brown and Donnelly, 2012). Environmental factors play a significant role in infections, especially in enclosures with poor ventilation, where excessive ammonia levels (over 25ppm) can exacerbate the condition (Goodman, 2009).
Diagnosis is often based on increased respiratory effort and respiratory rattles; however, tracheal lavage can be useful to identify the organism and any concurrent co-infections (Goodman, 2009). Radiographs are often unremarkable, but pulmonary lesions can be identified on CT (Brown and Donnelly, 2012).
Nebulisation therapy can be used to deliver antibiotics and bronchodilators directly to the airways and is often well tolerated by rats
Treatment involves bronchodilators, non-steroidal anti-inflammatories, broad-spectrum antibiotics and supportive care. Nebulisation therapy can be used to deliver antibiotics and bronchodilators directly to the airways and is often well tolerated by rats. The author recommends a minimum treatment course of 21 days, with some cases requiring further therapy following this initial course.
Antibiotic therapy can improve clinical signs; however, the infection can never be fully eliminated. Patients often have recurring “flare-ups” of clinical signs, especially at times of physiological stress (Kling, 2011). It is important to communicate this fact to owners so they can prepare for further episodes and manage environmental triggers.
Bordetella bronchiseptica as a cause of respiratory disease in guinea pigs
Bordetella bronchiseptica is an important cause of respiratory disease in guinea pigs. It is spread by direct contact, aerosol and fomites and can be triggered by inappropriate husbandry conditions (Yarto-Jaramillo, 2011). The organism is a Gram-negative aerobic rod or coccobacillus that can be harboured by in-contact species, such as rabbits (Goodman, 2009).
Infection with B. bronchiseptica can result in pleuropneumonia, with clinical signs including ocular and nasal discharge, anorexia, lethargy, sneezing, wheezing and a progression to dyspnoea as the infection continues (Yarto-Jaramillo, 2011). Suspected cases should have samples taken via deep nasal swabs or tracheal lavage for culture and sensitivity testing.
Treatment includes antibiotics based on sensitivity profiles and supportive care. Any guinea pig that recovers from the disease has the potential to carry the bacteria (Goodman, 2009), so consideration should be given before introducing new cage mates not exposed to the bacteria.
Pasteurella multocida as a cause of rhinitis in rabbits
Pasteurella multocida is an important respiratory pathogen in rabbits. This bacterium has multiple serotypes and strains, though respiratory disease in rabbits is often caused by serotype A (Jekl, 2021). Transmission occurs via aerosol, direct contact or fomites, usually through the nasal passages or wounds (Meredith, 2006).
While P. multocida is commonly cultured from the rabbit upper respiratory tract, as with rat respiratory disease, several pathogens are often involved in the same infection. Common co-infections in rabbit rhinitis include Staphylococcus aureus, Moraxella catarrhalis, Bordetella bronchiseptica, Klebsiella pneumoniae and Mycoplasma spp. (Jekl, 2021). In addition, rabbits frequently act as carriers of P. multocida, and clinical disease can be triggered by stressors, such as elevated ammonia levels, overcrowding, poor ventilation, malnutrition, conspecific bullying or corticosteroid treatment (Meredith, 2006).
Clinical signs of a P. multocida infection include mucopurulent nasal discharge, sneezing, dyspnoea, conjunctivitis and dyspnoea (Figure 4) (Jekl, 2021). Infection can occur in the nasal passages, resulting in significant dyspnoea as rabbits are obligate nasal breathers; in the middle ear, causing otitis media and vestibulitis; or in the lung, as is often the case with chronic infections.
Diagnosis should be based on bacterial culture and head and thoracic diagnostic imaging. However, a lack of the organism from deep nasal swabs or tracheal lavage does not necessarily rule out the presence of disease as the bacterium is difficult to isolate (Meredith, 2006).
Treatment involves antibiotics based on sensitivity profiles; however, P. multocida is often sensitive to several broad-spectrum antibiotics. Antibiotic therapy should be used for at least 7 to 14 days but can be required for up to three months (Meredith, 2006). In rabbits with chronic disease, treatment can alleviate clinical signs but cannot necessarily eliminate the bacteria completely, resulting in a carrier state (Meredith, 2006).
Respiratory disease in small mammals is often multifactorial, involving several concurrent pathogens on top of poor husbandry and environmental stressors. Causative agents should be determined based on diagnostic testing rather than pattern recognition of clinical signs.
It is important to understand and to communicate to owners that treatment does not always cure disease and that small mammal patients that do recover from respiratory disease can be lifelong carriers
It is important to understand and to communicate to owners that treatment does not always cure disease and that small mammal patients that do recover from respiratory disease can be lifelong carriers. This is particularly important when owners are considering introducing new animals into a group of previously affected animals.