Feline Upper Respiratory Tract Infections: a Review of Pathogens and Therapeutics

BACKGROUND AND ETIOLOGICAL AGENTS Upper respiratory tract disease (URTD) and it is the most common disease reported among the approximately 2 million to 6 million cats housed in US shelters annually and is often a cause of euthanasia because of the risks of transmission of infection throughout the shelter population and the negative effects on adoptability of infected cats. The combination of stress associated with relocation to a shelter, the presence of large numbers of cats in potentially crowded conditions, and variability in immune status increases morbidity and mortality rates attributed to URTD in shelter cats. Managing and treating feline URTD is challenging in a multi-cat environment because it is highly infectious and readily spread by direct cat-to-cat contact or indirectly by fomites. The most common pathogens are feline herpesvirus type 1 (FHV-1), feline calicivirus (FCV), Mycoplasma felis, Bordetella bronchiseptica, and Chlamydia felis. The isolation of FCV, Mycoplasma spp., and C. felis were significantly associated with clinical signs of URTD in that study, including conjunctivitis, ocular or nasal discharge, gingivitis, and oral vesicles. Four other studies have yielded statistical evidence of an association between clinical signs of URTD and the presence of FHV, FCV, Mycoplasma spp., C. felis, and B bronchiseptica, and investigators of 1 study reported more severe clinical signs in cats infected with multiple pathogens. Cats that appear to be clinically recovered from URTD may remain persistently infected and serve as sources of infectious agents in the shelter. Whereas primary viral infections with FHV and FCV are prevalent in cats with URTD, secondary bacterial invasion by Pasteurella spp., Escherichia coli, Staphylococcus spp., Streptococcus spp., or Micrococcus spp. regularly develops.