The family of Dr. Dennis John O’Callaghan is sad to announce his passing on March 30, 2026, in Shreveport, Louisiana, after a nearly four-year fight with cancer. Dennis, or “Doc” as he was known to many for both his doctorate and his use of his preferred initials, DO’C, was a scientist, a teacher, and a beloved family man who served the LSU Health Science Center and its community for the last 42 years.
Dennis was born in New Orleans in 1940 to John Jeremiah O’Callaghan and Odeal Fitzpatrick O’Callaghan. He attended St. Rita School and Jesuit High School. Dennis developed his legendary work ethic young, throwing two paper routes during the school year and holding summer jobs unloading box cars and working in a sheet rock factory on the Industrial Canal. To earn money for college, Dennis served as an ordinary seaman on the S.S. Hastings on a European cargo run, setting a ship record for overtime earned in a single voyage.
Dennis attended Loyola University in New Orleans. Despite his heavy course load and continuing to work his paper routes, Dennis found time to join Sigma Alpha Kappa fraternity and enjoy the scene at the famous La Casa de Los Marinos in the French Quarter. Dennis graduated in 1962 with a B.S. in Biology with a minor in Chemistry. He then enrolled at the University of Mississippi Medical Center (never call it Ole Miss to him) in Jackson for graduate studies in microbiology. While there, Dennis met the love of his life, Helen Frances Briscoe (Frances), who was working as a genetics researcher after obtaining her masters in microbiology. They were married June 24, 1967, forming a union that would last 51 years until Frances’s death in 2018. After Dennis received his Ph.D. in 1967, the couple moved to Edmonton, Alberta, Canada, for Dennis to complete a postdoctoral fellowship at the University of Alberta Medical. In Edmonton, Frances continued to work as a research geneticist while Dennis completed his postdoctoral studies.
In 1971, Dennis returned to the University of Mississippi as an Assistant Professor and rose to full Professor in 1977. In 1972, Dennis and Frances welcomed their only child, son Brady Dennis O’Callaghan.
Dennis was recruited as Professor and Head of the Department of Microbiology and Immunology at LSUHSC in Shreveport in 1984. He was selected as the Willis-Knighton Chair of Molecular Biology in 1995, the first endowed Chair on the Shreveport campus. He was subsequently appointed as the 63rd Boyd Professor of the LSU System, the highest academic honor bestowed to faculty in the state-wide network of nine universities and research centers. Dennis retired as chairman in 2018 and served as Boyd Professor Emeritus in the department until his final retirement in December of 2025. In his research career, Dennis was personally awarded grants totaling nearly 40 million dollars.
Dennis’s greatest joy and purpose for his work was his family. His wife Frances was an accomplished scientist herself, having graduated from Millsaps College at 19. She turned from science to art and became a nationally published watercolorist. Frances was also a tireless volunteer at the Feist-Weiller Cancer Center and other local charities. Dennis was also proud of his only son, who attended Yale University and LSU Law School and served several years as a prosecutor before being elected a District court judge in Caddo Parish in 2013. He adored his daughter-in-law Amy Vogel O’Callaghan, and took great pride in her expertise managing numerous large community events for the Louisiana Prize Foundation in Shreveport and New Mexico. His greatest honor was receiving the title of “PopPop” when his twin grandsons Logan and Marshall were born in 2006. He and Frances, or “GiGi” would keep the boys at every opportunity. PopPop cheerfully pulled them up hills for sledding when it snowed and filled his home and theirs with toys and happiness. He was proud of their many accomplishments and was thrilled that they are presently attending Brown University together.
Dennis and Frances were also close to Dennis’s brother and sister-in-law, Dr. Richard O’Callaghan and Jackie Marziale O’Callaghan. Richard followed Dennis into Microbiology and served as a professor for many years at LSU’s medical school in New Orleans before becoming Chair of the Microbiology department back at the University of Mississippi. For many years, a student could not receive a medical degree from LSU without being taught by an O’Callaghan, a fact that gave Dennis great satisfaction and pride.
Dennis was preceded in death by his parents, John and Odeal, his wife Frances, and his sister-in-law, Jackie. He is survived by his son, Brady, his beloved daughter-in-law Amy, and his grandsons Logan Brady O’Callaghan and Marshall Dennis O’Callaghan. He is also survived by his brother Richard, his nephew Kevin O’Callaghan and wife Stephanie, his nephew Dr. Patrick O’Callaghan and wife Heather, his grandnieces Caitlin O’Callaghan and Lauren O’Callaghan, and grandnephew Christian O’Callaghan.
“Doc” had too many professional accomplishments to list, but even the highlights are voluminous. Dennis was a founding member of the American Society of Virology and was elected as its President in 2000. He was an elected Fellow of the American Association for the Advancement of Science. He was on the editorial board of numerous scientific journals and chaired or served on numerous scientific review panels for the National Institutes of Health, the United States Department of Agriculture, and others. He developed one of the largest groups of molecular and tumor virologists in the country, which is organized as the Center for Molecular and Tumor Virology. This Center is comprised of 27 faculty members working in all areas of virology and was funded by over 22 million dollars in NIH Center grants.
As a teacher in Mississippi, Dennis was selected as Professor of the Year six times by the medical students and Teacher of the Year once by the dental students. He was grateful for his own mentors, Dr. Joseph Cooney at Loyola, Dr. Charles Randall in Jackson, and Dr. John Colter in Edmonton. Dennis took great pride in building the Department of Microbiology and Immunology faculty at LSUHS Shreveport department to its current nationally recognized status for teaching and research under the continuing leadership of Dr. Matthew Woolard. Dennis taught over 10,000 medical students over his career and over 150 doctoral students. Many of Doc’s former students now serve on the faculties of medical centers and universities or hold leadership positions at biomedical research institutions, biotechnology companies, and national and global scientific agencies. Dennis will be remembered by many as the hardest working man they had the opportunity to know, and he never asked students or colleagues to put in more effort than he was willing to give.
Dennis was grateful to the numerous medical professionals who attended to him during his fight with cancer, with too many outstanding nurses, doctors, and medical support personnel to name. He was particularly appreciative of Dr. Terry Lairmore and Dr. Mindie Kavanaugh.
The family will hold a celebration of Dennis’s life later this summer, as he was adamant that his grandsons not miss class because of his passing. In lieu of flowers, the family notes that Dennis and Frances were long-time supporters of St. Jude Children’s Research Hospital (stjude.org), the Tunnels to Towers Foundation (T2T.org), and the LSU Health Sciences Foundation (lsuhsfoundation.org).