Genomic analysis for virulence determinants in feline herpesvirus type-1 isolates.

Feline herpesvirus type 1 (FHV-1) is a widespread cause of respiratory and ocular disease in domestic cats. A spectrum of disease severity is observed in host animals, but there has been limited prior investigation into viral genome factors which could be responsible. Stocks of FHV-1 were established from oropharyngeal swabs obtained from twenty-five cats with signs of infection housed in eight animal shelters around the USA. A standardized numerical host clinical disease severity scoring scheme was used for each cat from which an isolate was obtained. Illumina MiSeq was used to sequence the genome of each isolate. Genomic homogeneity among isolates was relatively high. A general linear model for fixed effects determined that only two synonymous single nucleotide polymorphisms across two genes (UL37/39) in the same isolate (from one host animal with a low disease severity score) were significantly associated (p ≤ 0.05) with assigned host respiratory and total disease severity score. No variants in any isolate were found to be significantly associated with assigned host ocular disease severity score. A concurrent analysis of missense mutations among the viral isolates identified three genes as being primarily involved in the observed genomic variation, but none were significantly associated with host disease severity scores. An ancestral state likelihood reconstruction was performed and determined that there was no evidence of a connection between host disease severity score and viral evolutionary state. We conclude from our results that the spectrum of host disease severity observed with FHV-1 is unlikely to be primarily related to viral genomic variations, and is instead due to host response and/or other factors.