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

•An FHV-1 ELISA was developed with the potential to recognize cat serum antibodies to almost any FHV-1 protein.•Antibodies to FHV-1 primarily recognized Late (L) proteins and were of the IgG isotype.•Antibodies were quantitated in serum from 100 client-owned cats.•FHV-1 antibody levels were higher in older cats than younger cats.•No drop in FHV-1 antibody levels was observed as the length of time since vaccination increased. 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.