Dennis J. O'Callaghan

Dennis John O'Callaghan (July 26, 1940 – March 30, 2026) was an American virologist, immunologist and biochemist. He was an internationally recognized expert on the molecular biology of the equine herpesviruses.

Life and career O'Callaghan was born in New Orleans, Louisiana, on July 26, 1940. He graduated in 1962 with a B.S. in biology from Loyola University New Orleans and in 1968 with a Ph.D. in microbiology from the University of Mississippi Medical Center. His Ph.D. thesis is entitled Biochemical studies of equine abortion virus replication in L-M cells. He trained under the direction of Charles Chandler Randall (1913–2007). At the University of Alberta Medical Center in Edmonton, Canada, O'Callaghan was from 1968 to 1970 a postdoctoral research fellow and from 1970 to 1971 an assistant professor of biochemistry. In the department of microbiology of the University of Mississippi Medical Center, he was an assistant professor from 1971 to 1974, an associate professor from 1974 to 1977, and a full professor from 1977 to 1984. From 1984 until his retirement as professor emeritus in 2018, he was a professor and chair of the department of microbiology and immunology at LSU Health Sciences Center Shreveport. There he established the Center for Molecular and Tumor Virology.

He served on the editorial boards of Virus Research, Virology, Recent Research Developments in Virology, and the Journal of Virology. He and Nikolaus Osterrieder contributed the chapter Equine herpesviruses (Herpesviridae) to the 1999 edition of the Encyclopedia of Virology.

O'Callaghan was the president of the American Society for Virology (ASV) for the academic year 2000–2001.

His research on the biochemistry of herpesviruses reveals how viral regulator proteins govern the viral genome's expression. He and his colleagues have elucidated "the functional domains of viral regulatory proteins, the interactions of viral and cellular proteins, and how these interactions either up-regulate or retard viral gene expression."

O'Callaghan died from cancer on March 30, 2026, at the age of 85.

Selected publications