Effects of lambda-carrageenan on in vitro replication of feline herpesvirus and on experimentally induced herpetic conjunctivitis in cats.

PURPOSE: To evaluate the inhibitory effect of lambda-carrageenan type IV on feline herpesvirus (FHV)-1 in an in vitro model and in experimentally induced conjunctivitis in vaccinated cats. METHODS: Standard plaque reduction assay, virus titration, and quantitative polymerase chain reaction (qPCR) were used to assess the effect of carrageenan on FHV-1 in vitro. Eighteen adult specific pathogen-free cats, vaccinated against FHV-1 several months earlier, were used to determine the ocular irritative effects of carrageenan, followed by the effect on FHV-1-induced conjunctivitis. Ocular examinations, virus isolation, and partial thromboplastin time (PTT) were evaluated during the study period. RESULTS: When added before virus adsorption, the 50% inhibitory concentration (IC50) of carrageenan was 5 microg/mL, and the 90% inhibitory concentration (IC90) was 25 microg/mL. When added after virus adsorption, there was no inhibitory effect on plaque formation at any concentration. There was no effect of carrageenan on virus titer. Virus copy numbers assessed by quantitative PCR were significantly but marginally reduced when carrageenan was added before and after virus adsorption. Topical application of carrageenan at 250 microg/mL in cats with FHV-1-induced conjunctivitis resulted in a significant reduction in positive virus isolation samples on day 21 of the study but did not alter clinical signs of disease. There was no adverse effect on PTT values. CONCLUSIONS: lambda-Carrageenan type IV blocked FHV-1 adsorption in the plaque assay. Carrageenan shortened the time period in which infected cats had positive virus isolation from the conjunctiva but did not alter the clinical course of FHV-1 conjunctivitis in cats.

Development of a reverse transcriptase-polymerase chain reaction assay to detect feline herpesvirus-1 latency-associated transcripts in the trigeminal ganglia and corneas of cats that did not have clinical signs of ocular disease.

OBJECTIVE: To develop a reverse transcriptase-polymerase chain reaction (RT-PCR) assay to detect feline herpesvirus-1 (FHV-1) latency-associated transcripts (LATs) in the corneas and trigeminal ganglia of cats that did not have clinical signs of ocular disease. SAMPLE POPULATION: Corneas and trigeminal ganglia obtained from 21 cats necropsied at the Indiana Animal Disease Diagnostic Laboratory and 25 cats euthanatized at a humane shelter; none of the cats had a recent history of respiratory tract or ocular disease, and all had normal results for ophthalmic examinations. PROCEDURE: Both corneas and both trigeminal ganglia were harvested from each cat. An initial PCR assay detected FHV-1 DNA in the corneas and trigeminal ganglia. The RNA was then isolated from samples positive for FHV-1 DNA, and an RT-PCR assay was used to detect LATs. RESULTS: FHV-1 DNA was detected in 45 of 92 (48.9%) corneas and 38 of 92 (41.3%) trigeminal ganglia. In many samples, the RNA had degraded and RT-PCR assay was not possible. Of the samples subjected to RT-PCR assay, none of the 39 corneas but 4 of 16 trigeminal ganglia had positive results when tested for LATs. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of the results indicated that a high percentage of cats that did not have clinical signs of ocular disease had detectable FHV-1 DNA in their corneas and trigeminal ganglia. This study documents that the RT-PCR assay can successfully identify LATs and may serve as a tool to better understand the biologic characteristics of FHV-1 and its relationship to clinical disease.