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Effect of valacyclovir on EHV‐5 viral kinetics in horses with equine multinodular pulmonary fibrosis

Easton‐Jones, Charlotte A., Madigan, John E., Barnum, Samantha, Maxwell, Lara K., Taylor, Sandra D., Arnesen, Terry, Pusterla, Nicola
Journal of veterinary internal medicine 2018 v.32 no.5 pp. 1763-1767
blood, etiology, fibrosis, genes, glycoproteins, horses, lungs, nose, oral administration, prospective studies, quantitative polymerase chain reaction, secretion, viral load
BACKGROUND: Equine herpesvirus‐5 is commonly isolated from the lungs of horses with EMPF, suggesting an etiological link. Valacyclovir is used empirically to treat EMPF; however, no data is available concerning its impact on EHV‐5 viral kinetics. OBJECTIVES: To determine the effect of oral administration of valacyclovir on EHV‐5 viral load measured by qPCR in blood, nasal secretions (NS) and BALF in horses with EMPF. ANIMALS: Six horses diagnosed with EMPF. METHODS: A prospective clinical trial was performed. Horses received 10 days of PO administered valacyclovir (loading dose 30 mg/kg, maintenance dose 20 mg/kg). Blood, NS, and BALF were collected for EHV‐5 viral kinetics analyses during treatment. Blood and NS were collected every other day. BALF was collected on day 0 and day 10. RESULTS: There was no statistical difference in median EHV‐5 viral load between day 0 and day 10 for all samples tested. In blood median EHV‐5 viral load was 7676 (range 575‐39 781) on day 0 and 6822 (range 1136‐18 635) glycoprotein B (gB) gene copies per million cells on day 10. For NS median EHV‐5 viral load was 2.944 × 10⁶ (range 184 691‐3.394 × 10⁹) on day 0 and 8.803 × 10⁶ (range 251 186‐9.868 × 10⁸) gB gene copies per million cells on day 10. For BALF median EHV‐5 viral load was 59,842 (range 61‐315 655) on day 0 and 185 083 (range 3562‐542 417) gB gene copies per million cells on day 10. CONCLUSIONS AND CLINICAL IMPORTANCE: Valacyclovir might not be an effective short‐term antiviral treatment but efficacy in treatment of EMPF is unknown.