Pathogenicity of equine herpesvirus: in vivo persistence in equine tissue macrophages of herpesviuus type 2 detected in monolayer macrophage cell culture.

This research investigated the potential of equine macrophages (immune cells) to host persistent and latent infections of equine herpesvirus type 2 (EHV 2), a common horse virus.

Experimental Setup

• Researchers obtained macrophages, immune cells responsible for detecting and destroying harmful bacteria and viruses, from two sources: a yearling filly and an 18-year-old mare. Both horses were non-lactating.
• These macrophages were cultured (i.e., grown in a laboratory setting) to form continuous monolayers, or single-cell-thick layers, which researchers can use to study the effects of various conditions or substances on the cells.

Initial Observations

• In the early iterations of these cell cultures, no cytopathic effect (CPE) was observed, meaning there was no visible sign of cell damage caused by a virus.
• Further investigations using electron microscopy (which provides highly magnified images of specimens) and immunofluorescence studies (which use antibodies to detect specific proteins in cells) found no evidence of the virus or any viral antigens, which are substances that trigger an immune response.

Virus Emergence

• Signs of the virus began to appear in the 3rd and 4th cell culture passages (or successive generations) from the filly and the mare, respectively. These signs were in the form of CPE clusters in the cell monolayers.
• As more passages took place, the severity and consistency of the CPE increased. The researchers identified the virus causing the effect as equine herpesvirus type 2 (EHV 2).
• The macrophages culture from the mare showed CPE more consistently compared to the filly’s culture. However, when the filly’s cells were co-cultured with equine embryo kidney cells, a higher presence of the virus’ CPE was noted compared to the mare’s.

Conclusions and Implications

• Based on these findings, the researchers concluded that tissue macrophages could be sites for herpesvirus infections to lie dormant in horses, only to re-emerge later and possibly cause disease.
• This insight could help in developing new treatments or preventive measures against equine herpesvirus and similar infectious diseases in other species.