Infectious Diseases of the Feline Upper Respiratory Tract
Michael Lappin United States
Herpesvirus 1 (rhinotracheitis) and calicivirus are the most common viral causes of sneezing and nasal discharge in the cat. If oral ulcers are present, calicivirus is most likely. If corneal ulcers are present, herpesvirus 1 is most likely. Viral rhinitis with or without secondary bacterial infection can be recurrent. Herpesvirus can be documented by direct fluorescent staining of conjunctival scrapings, virus isolation, or polymerase chain reaction. Since herpesvirus can be detected in conjunctival cells of approximately 25% of healthy cats, the positive predictive value of these tests in diseased cats is low.
There are no consistently effective primary therapies. I generally only use the following therapies if chronic disease is present. Lysine at 250 mg q12h may be helpful in some cats and has been shown to be safe. Administration of alpha interferon at 30 u q24h PO may help some cats with suspected herpesvirus 1 infection. Lysine and alpha interferon are unlikely to lead to a cure, but hopefully, will lessen clinical signs of disease. Intranasal administration of modified live, intranasal herpesvirus 1 and calicivirus vaccines may lessen disease in some chronically infected cats. In kittens with acute life-threatening infection, use of alpha interferon at 10,000 u/kg q24h SQ for up to three weeks can be beneficial. Acyclovir is an anti-herpesvirus drugs for use in people but can be toxic to cats. I would start with 10–25 mg/kg q12h PO and monitor the CBC every two to three weeks. I never prescribe acyclovir until the diagnostic evaluation has been completed.
Kittens presented at less that 12 weeks of age should receive a modified live or killed FVRCR with boosters given every three to four weeks until 12 weeks of age. Kittens presented at > 12 weeks of age should receive two killed or modified live FVRCP three to four weeks apart. One should not overvaccinate with modified live products in cats. At one year of age, booster FVRCP and rabies virus vaccines should be administered. After one year of age, risk of infection by herpesvirus 1, calicivirus, and panleukopenia should be assessed. In low risk cats, FVRCP vaccines can be administered every third year.
Almost all cats with mucopurulent or purulent nasal discharge have a bacterial component to their disease. Primary bacterial disease is rare but may be associated with Bordetella bronchiseptica, Mycoplasma spp. and Chlamydophyla. Chlamydiosis in general, is a mild infection resulting only in conjunctivitis. If primary infections are suspected, doxycycline at 5–10 mg/kg q24h PO or topical administration of tetracyclines is usually effective. L-form bacteria also occasionally infect the nasal cavity and usually respond to doxycycline or quinolones. Cats with acute disease only need to be treated for seven to 10 days. Most cases of bacterial rhinitis are secondary to other diseases including trauma, neoplasia, inflammation induced by viral infection, foreign bodies, inflammatory polps, and tooth root abscessation. Thus, if routine antibiotic therapy fails, a diagnostic workup should be performed.
Due to the large number of normal flora in the nasal cavity, culture and sensitivity results from nasal discharges are hard to interpret. Since bacterial rhinitis leads to chondritis and osteomyelitis, antibiotic therapy should be continued for weeks in cats with chronic disease. I generally use drugs with an anaerobic spectrum that also penetrate bone and cartilage. Amoxicillin, clavamox, metronidazole, and clindamycin are good first choices. Clavamox has the advantage of killing most Bordetella isoloates. Clindamycin has the advantage of effective against Mycoplasma spp. and the drug can be used once daily for bacterial infections in cats. Doxycycline and metronidazole may be superior to other drugs for the treatment of chronic infections since they may modulate the immune reaction, lessening inflammation. Azithromycin (5.0–15.0 mg/kg q12–72h PO) can be used for cats with chronic disease.
Feline leukemia virus and feline immunodeficiency virus can induce immunosuppression predisposing to bacterial rhinitis.
Chlamydophyla infection in cats generally only results in mild conjunctivitis, and so vaccination is controversial. The use of this vaccine should be reserved for cats with a high risk of exposure to other cats and in catteries with endemic disease. Duration of immunity for Chlamydophyla vaccines may be short-lived, so high-risk cats should be immunized prior to a potential exposure.
Many cats have antibodies against Bordetella bronchiseptica and there are sporadic reports of severe lower respiratory disease due to bordetellosis, primarily in young, stressed kittens. Most cases are from crowded environments like shelters and catteries. However, in pet cats, significance of the problem is undefined and for now, Bordetella vaccination should be considered primarily for use in cats at high risk for exposure. In a seven-year period at the Diagnostic Laboratory at Colorado State University, B. bronchiseptica was isolated from one of 109 (0.9%) lower airway cultures and four of 81 (4.9%) nasal cultures from clinically ill, client-owned cats. During this period, of the 15,000 cat admissions, approximately 1500 had respiratory disease. Since the disease is apparently not life threatening in adult cats, is uncommon, and responds to a variety of antibiotics, routine use of the vaccine in client-owned cats seemed unnecessary in this population.
Cryptococcus neoformans is the most common fungus causing upper respiratory disease in cats. Facial deformity and ulcerative lesions are common; neoplasia is a major differential diagnosis. Cytology, histopathology, culture, and serum antigen testing can confirm the diagnosis. Ketoconazole, itraconazole, and fluconazole are effective treatments. Of the published cases, fluconazole has the highest success rate. Due to increased toxicity, ketoconazole should not be used in cats. Current ocular disease, CNS disease, or coinfection with FeLV or FIV can worsen the prognosis. However, all FIV-infected cats in one study responded to fluconazole. Serum antigen tests often do not return to negative following treatment even though measurable disease has resolved. Itraconazole administered at 5.0 mg/kg q24h PO is recommended for uncomplicated nasal cryptococcosus. Fluconazole administered at 50 mg/cat q24h PO is recommended if ocular or CNS disease is occurring.
If life-threatening infection is occurring or the cat is failing to respond to the azole drugs, amphotericin B should be used. Liposomal or lipid encapsulated amphotericin B are safer than regular amphotericin B but are expensive. If the client cannot afford lipid or liposomal encapsulated products, regular amphotericin B can be given safely SQ to most cats. Dilute 0.5 to 0.8 mg/kg regular amphotericin B in 400 ml of 2.5% dextrose and 0.45 % NaCl and administer SQ in one site. This can be given twice weekly to most cats with approximately a 10% chance for sloughing/scarring. Give at least a 12 mg/kg cumulative dose. Continue azole therapy during the amphotericin B treatment. I generally treat cats for a minimum of eight weeks or for four weeks past resolution of measurable disease. Preferably, serum antigen titers should be measured. Optimally, the titer should become negative. However, some clinically normal cats maintain positive antigen titers. If the antigen titer drops 16–32 fold and the cat is clinically normal, recurrence is uncommon.
While nasal mites (Pneumonyssoides) and a nasal worm (Eucoleus) occur in dogs in the United States, there are no significant nasal parasites in cats of the United States.
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