Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2004
Publication Date: 12/1/2004
Citation: Li, H., Taus, N.S., Lewis, G.S., Kim, O., Traul, D.L., Crawford, T.B. Shedding of Ovine Herpesvirus 2 in Sheep Nasal Secretions: the Predominant Mode for Transmission. Journal of Clinical Microbiology. 2004. 42(12):5558-5564. Interpretive Summary: Sheep-associated malignant catarrhal fever virus, also called ovine herpesvirus 2 (OvHV-2) is the major causative agent of malignant catarrhal fever in ruminant species worldwide. Domestic sheep are the natural carriers for the virus , but this virus has never been cultured in the laboratory. Little information is yet known about the nature of the virus-carrier host relationship, such as the sites of viral replication in sheep. A source of infectious virus is badly needed for studies of pathogenesis and immunological control for this disease. This study was designed to define the virus shedding patterns in sheep nasal secretions, as an early step toward the goal of identifying the sites of viral replication in sheep. Using real-time PCR, we found a striking, short-lived peak of viral genetic material (DNA) in nasal secretions from over 60.7% of young sheep at some point during the period from 6 to 9 months of age. In contrast, only about 18% of adult sheep experienced a shedding peak during the study period. We also demonstrated the presence of the virus in the nasal secretions from those high shedder sheep using a DNase protection assay. The viral infectivity in nasal secretions was also demonstrated by aerosolization of the secretions into uninfected sheep. The data herein show that nasal shedding is the major mode of sheep-associated MCF virus transmission among domestic sheep, and that young sheep between 6 to 9 months of age represent the highest risk group for transmission.
Technical 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 10,000 to over 100,000,000 copies/2 ug 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 hrs, 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. Using 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.