Shedding of Ovine Herpesvirus 2 in Sheep Nasal Secretions: the Predominant Mode for Transmission

Abstract

Ovine herpesvirus 2 (OvHV-2), the major causative agent of malignant catarrhal fever in ruminant species worldwide, has never been propagated in vitro. Using real-time PCR, a striking, short-lived, peak of viral DNA, ranging from 10 5 to over 10 8 copies/2 g of DNA, was detected in nasal secretions from over 60.7% of adolescent sheep (n ‫؍‬ 56) at some point during the period from 6 to 9 months of age. In contrast, only about 18% of adult sheep (n ‫؍‬ 33) experienced a shedding episode during the study period. The general pattern of the appearance of viral DNA in nasal secretions was a dramatic rise and subsequent fall within 24 to 36 h, implying a single cycle of viral replication. These episodes occurred sporadically and infrequently, but over the 3-month period most of the 56 lambs (33, or 60.7%) experienced at least one episode. No corresponding fluctuations in DNA levels were found in either peripheral blood leukocytes or plasma. In a DNase protection assay, complete, enveloped OvHV-2 virions were demonstrated in the nasal secretions of all sheep examined during the time when they were experiencing an intense shedding episode. OvHV-2 infectivity in nasal secretions was also demonstrated by aerosolization of the secretions into OvHV-2-negative sheep. The data herein show that nasal shedding is the major mode of OvHV-2 transmission among domestic sheep and that adolescents represent the highest risk group for transmission.

Ovine herpesvirus 2 replicates initially in the lung of experimentally infected sheep

“…Recognition of the short window of time when lambs are free of infection during early life under natural flock conditions (Li et al, 1998) resolved the problem and provided an opportunity to develop a programme for production of OvHV-2-free sheep . A study of OvHV-2 shedding kinetics in sheep using quantitative real-time PCR revealed that adolescent lambs between 6 and 9 months of age shed virus more frequently and intensively than adults (Li et al, 2004). These studies have made it possible to establish a source of infectious virus by collection of nasal secretions from sheep during shedding episodes.…”

“…Earlier studies showed that viral transmission and shedding patterns are different between OvHV-2 and AlHV-1 in their natural hosts: sheep shed the virus sporadically with a short-lived episode and new born lambs are not the source of infection (Li et al, 2004), while most newborn wildebeest calves are infected and shed virus continuously until 3-4 months of age and are the primary source of transmission (Mushi & Wafula, 1983). Recent studies revealed that the transcripts of the open reading frame (ORF) 25, a gene encoding a capsid protein, were present in virtually all tissues of cattle, bison (Cunha et al, 2007) and rabbits (Gailbreath et al, 2008) with OvHV-2-induced MCF, but not present in the tissues (spleen and lymph nodes) of rabbits with AlHV-1-induced MCF (Dewals et al, 2008), suggesting that virus lytic replication and latency are different in clinically susceptible hosts.…”

Gammaherpesvirus Infection in Semidomesticated Reindeer (Rangifer Tarandus Tarandus): A Cross-Sectional, Serologic Study in Northern Norway

“…Typical clinical signs include fever, inappetence, ocular and nasal discharge, diarrhea, and depression. The mode of transmission of these viruses between carriers and susceptible ruminants is uncertain, but transmission via nasal secretions from sheep to other ruminants may be the most likely route for OvHV2 (Li et al, 2004).…”

A Geographic Cluster of Malignant Catarrhal Fever in Moose (Alces alces) in Norway

“…Lambing peaks on 1 May in Lesja; thus many lambs reach an age of 6 mo during October. OvHV-2 is shed particularly by 6-9-mo-old lambs (Li et al 2004). Stress related to gathering and fencing might increase shedding.…”