In late summer 1970, a skin disease characterized by small elevated nodules appeared in a Minnesota dairy cattle herd. Samples of affected tissue and blood were cultured and examined by electron microscopy, revealing a herpes virus. Researchers compared this Minnesota isolate with three known viruses: bovine herpes mammillitis (BHM), Allerton virus, and Neethling poxvirus. Using electron microscopy of thin sections and an indirect ferritin-tagging antibody method, the researchers identified viral particles in infected cells and performed cross-reaction studies with virus-specific antisera. The three bovine herpes viruses showed cross-reactivity with each other but not with the poxvirus. Differential staining confirmed the Minnesota isolate possessed a DNA nucleoid, characteristic of herpes viruses. Morphological examination revealed the virus particles were indistinguishable from BHM and Allerton viruses. The researchers concluded that the Minnesota outbreak was caused by a bovine herpes virus strain of the mammillitis group, likely an exotic disease previously uncommon in the United States.

Key findings

• A herpes virus was isolated from nodular skin lesions in Minnesota cattle in 1970, subsequently identified as bovine herpes virus of the mammillitis group
• The Minnesota isolate showed morphological similarity to previously known bovine herpes viruses (BHM and Allerton) but could be distinguished through serological cross-reactions
• Electron microscopy and differential staining confirmed the virus possessed a DNA core, confirming its classification as a herpes virus
• The three bovine herpes viruses tested displayed cross-reactivity with each other's antisera, while the poxvirus showed no reaction