The domestic cat antibody response to feline herpesvirus-1 increases with age

Herpesviruses establish lifelong infections, normally characterized by prolonged periods of latency with intermittent episodes of viral reactivation. Feline herpesvirus-1 (FHV-1) infects domestic cats, and epidemiological studies indicate that many or most domestic cats are exposed to FHV-1, but the strength and longevity of the antibody response to FHV-1 is not fully characterized. Here we describe development of an ELISA, using lysates of cat cells infected with FHV-1, that measure feline antibodies against FHV-1. The assay is sensitive, quantitative and has a large dynamic range. We found that serum anti-FHV-1 antibodies primarily recognize FHV-1 proteins of the Late (L) class and are primarily of the IgG isotype. We then analyzed serum from a cross-sectional cohort of 100 client-owned cats that differed in age, sex and vaccination history. While there was no difference in FHV-1 antibody responses between females and males, antibody levels were significantly increased in older cats in comparison with younger animals (p = 0.01). Surprisingly, as the length of time since the most recent vaccination increased, there was no corresponding drop in serum anti-FHV-1 antibody. These data suggest that FHV-1 immunity is very long-lived and support the current recommendation that many cats do not require revaccination against FHV-1 annually.