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Abstract

OBJECTIVE To determine whether prophylactic administration of valacyclovir hydrochloride versus initiation of treatment at the onset of fever would differentially protect horses from viral replication and clinical disease attributable to equine herpesvirus type-1 (EHV-1) infection.

ANIMALS 18 aged mares.

PROCEDURES Horses were randomly assigned to receive an oral placebo (control), treatment at detection of fever, or prophylactic treatment (initiated 1 day prior to viral challenge) and then inoculated intranasally with a neuropathogenic strain of EHV-1. Placebo or valacyclovir was administered orally for 7 or 14 days after EHV-1 inoculation or detection of fever (3 horses/group). Effects of treatment on viral replication and clinical disease were evaluated. Plasma acyclovir concentrations and viremia were assessed to determine inhibitory concentrations of valacyclovir.

RESULTS Valacyclovir administration decreased shedding of virus and viremia, compared with findings for control horses. Rectal temperatures and clinical disease scores in horses that received valacyclovir prophylactically for 2 weeks were lower than those in control horses. The severity of but not the risk for ataxia was decreased by valacyclovir administration. Viremia was decreased when steady-state trough plasma acyclovir concentrations were > 0.8 μg/mL, supporting the time-dependent activity of acyclovir.

CONCLUSIONS AND CLINICAL RELEVANCE Valacyclovir treatment significantly decreased viral replication and signs of disease in EHV-1–infected horses; effects were greatest when treatment was initiated before viral inoculation, but treatment was also effective when initiated as late as 2 days after inoculation. During an outbreak of equine herpesvirus myeloencephalopathy, antiviral treatment may be initiated in horses at various stages of infection, including horses that have not yet developed signs of viral disease.

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in American Journal of Veterinary Research

ewes from the contaminated environment, and the implementation of appropriate hygienic protocols to prevent spread of the organism via contaminated clothing, boots, and equipment. 16 Antimicrobial administration may also be considered to help minimize

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in American Journal of Veterinary Research

stimuli and cellular organelles are disassembled and degraded within apoptotic bodies while cellular membranes remain intact; this prevents release of injurious cellular contents into the extracellular environment. 7,8 Apoptotic bodies then signal for

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in American Journal of Veterinary Research

stressful events, such as recent capture, changing environments, or breeding. 2,3 Aspergillosis is the most common cause of death in recently captured or captive birds of prey. 4,5 Some of the more susceptible species include goshawks, gyrfalcons, and

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in American Journal of Veterinary Research

chloramphenicol, lipophilic β-lactams, fluoroquinolones, tetracycline, rifampin, novobiocin, fusidic acid, and nalidixic acid. 18,19 It is assumed that the evolutionary role of the MDR efflux pump is to protect bacteria against hostile environments (ie, through

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in American Journal of Veterinary Research

. Coates ME Fuller R Harrison GF , et al. A comparison of the growth of chicks in the Gustafsson germ-free apparatus and in a conventional environment, with and without dietary supplements of penicillin . Br J Nutr 1963 ; 17 : 141 – 150 . 10

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growth than are planktonic (free-living or nonbiofilm-associated) bacteria. Biofilms also provide a unique environment that facilitates the efficient exchange of resistance genes among bacteria. 9,10 Finally, the extracellular polymeric matrix acts as a

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in American Journal of Veterinary Research

enclosure. Fish were allowed to acclimate to the holding tank environment for 48 hours, which was a period intentionally kept to a minimum to reduce the time they were unavailable for exhibit. To allow identification of individuals, fish were sedated by

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in American Journal of Veterinary Research

disease have been investigated in earlier studies. 1–5 Transportation-associated fever is influenced by transportation stress and deterioration of the environment inside the vehicle, and it typically develops ≥ 20 hours after the start of transportation

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in American Journal of Veterinary Research

environment, there is minimal risk for exposure of enteric bacteria. Even though ceftiofur is metabolized rapidly within the gastrointestinal tract, data reported in another study 15 appear to indicate that there may in fact be a detectable effect of

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in American Journal of Veterinary Research