Managing and preventing feline respiratory diseases (Proceedings)
Herpesvirus 1 (rhinotracheitis; FHV-1) and calicivirus (FCV) 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. FHV-1 has now also been associated with chronic stomatitis, facial dermatitis, and endogenous uveitis. Viral rhinitis with or without secondary bacterial infection can be recurrent. FHV-1 can be documented by direct fluorescent staining of conjunctival scrapings, virus isolation, or polymerase chain reaction. Since FHV-1 DNA can be detected in conjunctival cells of approximately 25% of healthy cats, the positive predictive value of these tests in diseased cats is low. Quantitative PCR may ultimately prove to correlate to the presence or absence of disease. Currently used PCR assays also detect vaccine strains of FHV-1. RT-PCR assays can be used to amplify the RNA of FCV. However, these assays have the same problems with predictive value as those to detect DNA of FHV-1.
Feline viral rhinitis with or without secondary bacterial infection can be recurrent. There are no consistently effective primary therapies. I generally only use the following therapies if chronic disease is present. Lysine at 250-500 mg, PO, BID may be helpful in some cats and has been shown to be safe but should be given as a dose, not fed with food. Administration of alpha interferon at 30 U, PO, daily may help some cats with suspected chronic calicivirus or FHV-1 infection. Topical administration of alpha interferon in saline to the eyes of cats with conjunctivitis or the nose may aid in the management of some cats. 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 FHV-1 and FCV vaccines may lessen disease in some chronically infected cats. If there is a positive response to intranasal vaccination in a cat with chronic disease, I will use this form of immunotherapy up to 3 times per year. The intranasal vaccine has been shown to potentiate cell-mediated immunity to FHV-1 better than parenteral vaccination. In kittens with acute life-threatening infection, use of alpha interferon at 10,000 U/kg, SQ, daily for up to 2 weeks can be beneficial. Acyclovir is an anti-herpesvirus drug for use in people but can be toxic to cats. Famcyclovir seems to be safer and more effective than acyclovir and is now being used for long-term therapy. One dose that has been used is ½ tablet (62.5 mg) q12 hr for 14 days. The drug is safe at up to 90 mg/kg, PO, q8hrs and so the dose should be increased if the initial response is suboptimal and FHV-1 is still suspected. Topical cidofovir (product for humans) can be used for the treatment of FHV-1 conjunctivitis twice daily and was effective in a controlled research project. The drug was easier to administer (twice daily) than idoxuridine or other anti-FHV-1 ocular therapies and does not cause as much irritation. Gary Newton is a custom pharmacist that will formulate the drug for veterinary ophthalmic use (1 800 682 4664).Feline leukemia virus and feline immunodeficiency virus can induce immunosuppression predisposing to bacterial rhinitis. However, there is no universally effective treatment.
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 Chlamydophila felis. In one recent Morris Animal Foundation sponsored study, we showed Mycoplasmas to be more common that FHV-1 and were associated with illness. Recently it was shown that Bartonella spp. are not causes of rhinitis in cats. Both B. bronchiseptica and Mycoplasma spp. can be associated with bronchitis in cats. Chlamydiosis in general, is a mild infection resulting only in conjunctivitis. If primary infections are suspected, doxycycline 10 mg/kg, PO, once daily or topical administration of tetracyclines (conjunctivitis) are usually effective. Cats with acute disease only need to be treated for 7 to 10 days. Most cases of bacterial rhinitis are secondary to other diseases including trauma, neoplasia, inflammation induced by viral infection, foreign bodies, inflammatory polyps, and tooth root abscessation. Thus, if routine antibiotic therapy fails, a diagnostic workup should be performed.
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. Clindamycin, amoxicillin, amoxicillin-clavulanate, or metronidazole. Amoxicillin-clavulanate 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 routine 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 (10 mg/kg, PO, q 24-72 hr) or fluoroquinolones can be used for cats with chronic disease. For cats that are difficult to treat, cephalosporin injections can be considered. However, this drug class is ineffective for Mycoplasma spp..