Altered Corneal Innervation And Ocular Surface Homeostasis In Fhv-1-Exposed Cats: A Preliminary Study Suggesting Metaherpetic Disease

Metaherpetic disease is recognized in humans affected by herpes simplex virus-1 but is not reported in cats affected by feline herpesvirus-1 (FHV-1) despite the high prevalence of herpetic disease in this species and strong similarities in viral biology between alphaherpesviruses of humans and cats. This preliminary work evaluated cats naive to FHV-1 (n = 9 cats, 18 eyes; control population) and cats naturally exposed to FHV-1 (n = 4 cats, 7 eyes), as confirmed by serologic testing and review of medical records. Antemortem assessment included clinical scoring, blink rate, corneal aesthesiometry, tear film breakup time (TFBUT), and Schirmer tear test-1 (STT-1) with or without the nasolacrimal reflex. Post-mortem assessment involved confocal microscopy of the corneas and evaluation of corneal nerves with ImageJ. Groups were compared with Student's t-tests and results are presented as mean +/- standard deviation. Compared to control, herpetic cats had significantly higher (P <= 0.010) clinical scores (0.2 +/- 0.4 vs. 4.6 +/- 2.8) and response to nasolacrimal stimulation (7.8 +/- 10.8% vs. 104.8 +/- 151.1%), significantly lower (P < 0.001) corneal sensitivity (2.9 +/- 0.6 cm vs. 1.4 +/- 0.9 cm), STT-1 (20.8 +/- 2.6 mm/min vs. 10.6 +/- 6.0 mm/min), TFBUT (12.1 +/- 2.0 s vs. 7.1 +/- 2.9 s), and non-significantly lower blink rate (3.0 +/- 1.5 blinks/min vs. 2.7 +/- 0.5 blinks/min; P = 0.751). All parameters evaluated for corneal nerves (e.g., nerve fiber length, branching, occupancy) were notably but not significantly lower in herpetic vs. control cats (P >= 0.268). In sum, cats exposed to FHV-1 had signs suggestive of corneal hypoesthesia and quantitative/qualitative tear film deficiencies when compared to cats naive to the virus. It is possible these are signs of metaherpetic disease as reported in other species.