PCOM Study Links COVID-19 and Bacterial Infection to Alzheimer’s Disease
July 1, 2025
A recent review by researchers at Philadelphia College of Osteopathic Medicine (PCOM) shows Chlamydia pneumoniae (Cpn) and SARS-CoV-2 infections may play a role in the
pathogenesis of Alzheimer's disease.
Published in Frontiers in Aging Neuroscience, the review highlights that both infections increase levels
of substances in the brain called cytokines, especially IL-6 and CCL2, which cause
inflammation. This ongoing inflammation can harm brain cells and may help speed up
the buildup of harmful proteins linked to Alzheimer's.
The review shows that Cpn and SARS-CoV-2 can invade the central nervous system through
both the blood brain barrier and potentially more importantly the olfactory route,
which is responsible for our sense of smell. The olfactory system is lined with a
specialized neuroepithelium that can serve as an entry point for pathogens to the
brain. After initial infection, these microbes can travel along the olfactory nerves,
ultimately reaching the brain's olfactory bulbs, which are linked to areas of the
brain for memory and cognition. This pathway is particularly relevant given that loss
of smell is an early symptom in both COVID-19 and Alzheimer's disease.
The research examined peer-reviewed studies on the associations of Cpn and SARS-CoV-2
with Alzheimer's, coupled with a special consideration for genetic risk factors such
as APOEε4, biomarkers (IL-6, CCL2, NRP1), and the structural and functional aspects
of infection and neuroinflammation. PCOM researchers documented that individuals carrying
this gene variant appear to be more susceptible to both Cpn and SARS-CoV-2 infections,
potentially amplifying their risk for developing the disease.
“These findings bring us one step closer to understanding the complex interactions
between infections and Alzheimer's disease,” said PCOM's Brian J. Balin, PhD, a professor of Neuroscience and Neuropathology and director of the Center for Chronic Disorders of Aging (CCDA), who co-authored the report. “As we continue to learn more about the role infectious
agents play in the development of this disease, we hope to create new avenues for
prevention and treatment.”
Balin and his team have dedicated over two decades working under the hypothesis that infectious agents could be a trigger for the process that causes the accumulation of amyloid and tau build-up, which are
key indicators of Alzheimer's disease. Most recently, he helped establish PCOM's Pathobiome Research Center to further examine the connections between infectious processes and other chronic
disorders in addition to Alzheimer's disease.
About Philadelphia College of Osteopathic Medicine
Established in 1899, Philadelphia College of Osteopathic Medicine (PCOM) has trained
thousands of highly competent, caring physicians, health practitioners and behavioral
scientists who practice a “whole person” approach to care—treating people, not just
symptoms. PCOM, a private, not-for-profit accredited institution of higher education,
operates three campuses (PCOM, PCOM Georgia and PCOM South Georgia) and offers doctoral degrees in clinical psychology, educational psychology, osteopathic
medicine, pharmacy, physical therapy, and school psychology. The college also offers
graduate degrees in applied behavior analysis, applied positive psychology, biomedical
sciences, forensic medicine, medical laboratory science, mental health counseling,
physician assistant studies, and school psychology. PCOM students learn the importance
of health promotion, research, education and service to the community. Through its
community-based Healthcare Centers, PCOM provides care to medically underserved populations.
For more information, visit pcom.edu or call 215-871-6100.
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