Rational and appropriate antibiotic use has increasingly become a major concern in veterinary (and human) medicine. Infections of the respiratory tract are a common concern in all species, and cats are no exception. The use of antimicrobials in the treatment of upper and lower respiratory infections has become increasingly controversial, as more conditions are found to be viral or self-limiting. This manuscript summarizes guidelines established by a panel of experts outlining diagnostic, therapeutic, and monitoring options for upper and lower respiratory tract infections in cats (URTI and LRTI). While guidelines such as these do not provide new information to the veterinary community, they attempt to collect, quantify and qualify the evidence available to allow veterinarians to make rational treatment decisions.
Upper Respiratory Tract Infections:
The authors first define acute upper respiratory infections as lasting less than 10 days, and chronic greater than 10 days. Most cats with upper respiratory signs are infected with feline herpesvirus 1 (FHV-1) or calicivirus, with secondary bacterial infections, though some bacteria may cause primary disease. Bacteria of concern include Staphylococcus spp., Streptococcus spp., Pasteurella multocida, Escherichia coli, Chlamydia felis, Bordetella bronchiseptica, Streptococcus equi subspp. zooepidemicus, and Mycoplasma spp, as well as assorted anaerobes.
For cats with acute upper respiratory disease the authors recommend a full physical exam with detailed history and retrovirus testing. Culture and cytology were not recommended for acute disease. If manifestation of disease is serous in nature, the infection is likely viral and therapy is not recommended. It should also be noted that mucopurulent discharge does not necessarily ensure or signal a bacterial infection.
Treatment of acute bacterial URTI is only recommended if there is a combination of mucopurulent discharge with fever, lethargy, or anorexia. Without these signs, a 10 day observation period is recommended. If treatment is initiated, the recommended therapy is a 7 to 10 day course of doxycycline. Doxyxcyline is generally well tolerated with minimal resistance and is effective against Bordetella, Chlamydia, and Mycoplasma spp., as well as many commensals. The authors also provide a detailed list of antimicrobial options including their general spectra of activity and pros and cons of their use. If doxycycline is not tolerated or not available, amoxicillin is a reasonable first choice if Mycoplasma and Chlamydia are not suspected.
The use of cefovecin was not recommended by the working group due to insufficient data. Fluoroquinolones and third generation cephalosporins should only be used based on culture results. Data has not suggested that azithromycin is more effective than amoxicillin for most infections, and is less effective against Chlamydia; as such it is not recommended as a first line option.
If clinical signs of infection persist for >10 days (especially if empirical therapy is not successful), further workup is warranted. Workup should include ruling out atypical infections (fungal, cuterebra, etc) and non-infectious causes (neoplasia, allergy, foreign body, polyps, trauma, etc). Workup may include imaging (including advanced imaging such as CT), rhinoscopy, exploration for polyps or stenosis, and nasal lavage or brushings with cytology, PCR, and culture.
For chronic URTI without any underlying cause, antibiotics should be chosen on the basis of culture and sensitivity results. Therapy should be continued for at least 7 days, and if well tolerated, for 1 week past resolution or plateau of clinical signs. If signs recur, an additional 7-10 days of therapy is warranted. The authors recommend restarting therapy with the previously effective drug, with change to a new class or more active drug if no improvement is seen in 48 hours.
Intranasal drops were not recommended, with the exception of 0.9% saline as a mucolytic.
Lower Respiratory Tract Infections:
Bacterial bronchitis refers to inflammation of the lower airways due to bacterial infection. This excludes causes of bronchitis such as heartworm and lungworm, allergies, irritants, and viruses. Bacterial bronchitis may occur due to primary respiratory pathogens such as Bordetella and Mycoplasma, or secondary to diseases such as laryngeal dysfunction, anatomical defects, or other conditions. Most animals with bronchitis present with a cough. Workup for bacterial bronchitis should include a full physical exam and thoracic radiographs. Advanced imaging and airway washes may be indicated. Based on history, heartworm testing, Baermann or standard fecal analysis, and other tests may be needed.
If bronchial diseases is suspected based on these diagnostics, airway washing should be performed with submission for culture and sensitivity, including Mycoplasma culture (preferred over Mycoplasma PCR). Bronchoscopy is ideal, however tracheal wash is acceptable.
Pending culture results, therapy should be initiated with doxycycline, or in mild cases, no therapy started. If therapy improves clinical signs, it should be continued for 1 week after the resolution of signs. Recurrent therapy may be required, especially in animals with underlying issues.
Pneumonia, or inflammation of the lungs, may occur due to bacterial or viral infection, or due to non-infectious causes. Common bacteria isolated include: Pasteurella spp., Streptococcus spp., B. bronchiseptica, E. coli, Enterococcus spp., Mycoplasma spp., S. pseudintermedius and other coagulase-positive Staphylococcus spp., and Pseudomonas spp. Most bacterial infections are secondary to viral infections, aspiration, or immunodeficiency syndromes.
Cats with pneumonia often present with a cough combined with fever, lethargy, anorexia, and tachypnea. Workup should include retroviral testing, full physical exam, thoracic radiographs, and a full CBC. Following confirmation of pneumonia, collection of samples for cytology and culture are recommended.
Initiation of antibiotic therapy should be performed after culture and sensitivity; however it should not be unduly delayed if clinical signs require it. If sepsis is present, antimicrobials should be started within 1 to hours. If animals are oxygen-dependent or have life-threatening pneumonia, blood cultures may be used to guide antimicrobial choices. In some cases, such as aspiration, chemical pneumonitis may play more of a role than bacterial infection, and antimicrobials may not be needed. Multiple bacteria are often cultured, which may necessitate consultation with an infectious disease specialist to determine ideal treatment plans.
Therapy for pneumonia should begin with parenteral antibiotics. Doxycycline may be reasonable for mild causes of pneumonia. For animals with aspiration pneumonia or suspected Streptococcus equi subsp zooepidemicus infection, penicillins are a reasonable choice. If sepsis is present, enrofloxacin or marbofloxacin are recommended, in combination with clindamycin, ampicillin, or potentially metronidazole. Animals should be re-evaluated 10-14 days after initiation of treatment, and decision to continue therapy based on response to therapy. Courses of 4-6 weeks are currently recommended, but may be excessively long.
The group did not have sufficient data to give an opinion regarding the use of systemic or inhaled glucocorticoids.
Pyothorax is the accumulation of pus between the lungs and the chest wall. In dogs this is often associated with migrating foreign bodies. While this also occurs in cats, it is more commonly associated with bite wounds. Diagnosis is based on radiographs and thoracocentesis. Thoracocentesis samples should be submitted for aerobic and anaerobic culture, Mycoplasma culture, cytology, and potentially gram and acid fast stains.
Therapy should include IV fluids and the placement of chest tubes with drainage of pus and intermittent or continuous suction. Lavage may or may not be necessary, however antimicrobials should not be administered into the pleural space. In some cases, surgical debridement may be needed. Pending culture and sensitivity results, therapy should be initiated with an injectable fluoroquinolone and either a penicillin or clindamycin. Regardless of culture results, therapy with anaerobic efficacy should be continued due to the possibility of fastidious anaerobes.
Therapy should be continued for 4-6 weeks, with recheck radiographs at 10-15 days an at the end of therapy.
While there are always grey areas and special cases that will not be covered by a set of guidelines, this consensus statement provides an excellent starting point and series of evidence based recommendations to manage lower respiratory tract infections in cats. Following these guidelines will help veterinarians to provide consistent care backed by evidence, allowing better quality management of sick cats while minimizing risks of antimicrobial resistance.
Reference: Lappin MR, Blondeau J, Boothe D, Breitschwerdt EB, Guardabassi L, et al. Antimicrobial use Guidelines for Treatment of Respiratory Tract Disease in Dogs and Cats: Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases. J Vet Intern Med. 2017 Mar;31(2):279-294. DOI: 10.1111/jvim.14627
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