Equine Transport and Changes in Equid Herpesvirus' Status

Abstract

The risk of respiratory disease in the transported horse can increase as a consequence of immunosuppression and stress associated primarily with opportunistic bacterial proliferation and viral reactivation. This study examines the ecology of equid herpesviruses (EHV) in these horses, exploring reactivation and changes in infection and shedding associated with transport, and any potential contributions to transport-related respiratory disease. Twelve horses were subjected to an 8-h road-transport event. Antibodies to EHV-1 and EHV-4 were detected by ELISA in serum collected prior to, immediately after and 2 weeks post transport. Respiratory tract endoscopy and tracheal washes were collected prior to and 5 days after transportation. Nasal swabs collected prior to, immediately after, 1 and 5 days following transport were screened for EHV-1,-2,-4,-5 using qPCR. Six horses had persistent neutrophilic airway infiltrates post transportation, indicative of subclinical respiratory disease. No horses were qPCR positive for either of the alphaherpesviruses (i.e., EHV-1/-4) nor did any seroconvert to either virus. Four out of nine horses positive for either EHV-2 or EHV-5 on qPCR prior to transport developed neutrophilic airway inflammation. Five horses showed increasingly positive readings on qPCR (i.e., reduced Cq) for EHV-2 after transportation and seven out of eleven horses positive for EHV-2 after transport shared strains of high sequence similarity with other horses in the study. One EHV-2 virus detected in one horse after transport was genetically different which may be due to reactivation. The clinical significance of EHV-2 and EHV-5 remains in question. However these results indicate that transportation may lead to increased shedding, transmission and reactivation of EHV-2 and EHV-5 but not EHV-1/-4. Unlike previous work focusing on the role of alphaherpesviruses, this research suggests that investigation of the gammaherpesviruses (i.e., EHV-2/-5) in transport-related disease should not be dismissed, particularly given that these viruses can encode suppressive immunomodulators that may affect host health.

Keywords: equine herpesvirus; reactivation; shedding; stress; transport.

Figure 1

Scatter plots showing Cq values from EHV-2 (A) and EHV-5 (B) qPCR of nasal samples collected from each horse prior to transport (+), at unloading (X), 1 day post transport (○), and 5 days post transport (□).

Figure 2

Unrooted phylogenetic trees comparing EHV-2 reference strain 86/87 and multiple strain types within individual horses 2 (A), 5 (B), 6 (C), 7 (D). Sequences are labeled according to Horse (H-), time point of sample taken (Pre Transport [-P], Unloading [-U], 1 day post transport [-1D], 5 days post transport [-5D]) and clone (c-) number if more than one sequence was isolated from each sample. Scale bars represent substitutions per site.

Figure 3

Neighbor joining phylogenetic tree illustrating relationships amongst sequences obtained from study, reference EHV-2 87/67 strain (GenBank accession number U20824.2) and outgroup EHV-5 Strain 2-141/67 (GenBank accession number KM924295). Sequences are labeled according to Horse (H-), time point of sample taken [Pre Transport [-P], Unloading [-U], 1 day post transport [-1D], 5 days post transport [-5D]] and clone (c-) number if more than one isolate was sequenced from each sample. Tip labels highlighted in red denote sequences obtained from horses positive for EHV-2 only after transport, tip labels in blue denote sequences that may have originated from reactivated virus. Scale bar represents substitutions per site.