- Researchers have investigated the relationship between hospital-treated infections and neurodegenerative diseases.
- They found that hospital-treated infections, particularly during early and middle life, increased the risk of Alzheimer’s disease and Parkinson’s disease later in life.
- They noted that their study did not examine causation and that more research is needed.
Neurodegenerative conditions such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS) are progressive.
Some studies suggest that bacterial and viral infections as well a plus Neurodegeneration risks. However, this research has resulted in largely inconclusive results due to study design limitations.
A better understanding of the relationship between infectious diseases and neurodegeneration could help researchers develop treatment strategies for neurodegenerative conditions.
Recently, researchers analyzed Swedish health records to examine the link between infections treated in hospital and the risk of Alzheimer’s disease, pulmonary personality disorder, and amyotrophic lateral sclerosis.
They found that hospital-treated infections, particularly in early and middle life, were associated with an increased risk of Alzheimer’s disease and prominent, but not amyotrophic lateral sclerosis.
The study was recently published in MEDICINE PLOS.
For the studies, researchers examined the health care records of 12,275,551 individuals from several national registries in Sweden. They followed them between 1970 and 2016 and recorded diagnoses of neurodegenerative diseases, migration and death.
Infections were scored according to type—bacterial, viral, or other, and location—including central nervous system (CNS), gastrointestinal, respiratory, or skin infection. The data also included the age and frequency of injury.
The researchers excluded patients who developed an infection within 5 years of a neurodegenerative diagnosis to avoid observational bias and reverse causation.
In all, 291,941 people in the analysis had Alzheimer’s disease, 103,919 had Parkinson’s disease, and 10,161 had amyotrophic lateral sclerosis.
After analyzing the data, the researchers found that infections treated in hospital 5 or more years before diagnosis were associated with a 16% increased risk of Alzheimer’s disease and a 4% increased risk of Parkinson’s disease.
Similar risks were seen for bacterial, viral and other infections and for different sites of infection.
The association was primarily observed in those diagnosed with Alzheimer’s disease and PD before age 60, as opposed to those diagnosed later.
The greatest risk is observed among those with infections treated in hospital early in life; Multiple infections before age 40 have been linked to a nearly double risk of developing Alzheimer’s disease and a 40% higher risk of developing Parkinson’s disease.
However, the researchers noted that there was no link between infections treated in hospital and amyotrophic lateral sclerosis, and that their findings remained after controlling for factors including gender, family history of neurodegenerative disease, and educational level.
Although the study did not examine victims, the researchers wrote that similar findings for different types and sites of infection may indicate that the underlying mechanisms are related to systemic inflammation rather than the response to specific pathogens.
“Infectious events may [also] being a trigger or amplifier of a pre-existing disease process, leading to the clinical manifestation of neurodegenerative disease at a relatively young age among predisposed individuals,” Jianghui SunPh.D., a postdoctoral researcher in the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet in Sweden, said one of the study authors, MNT.
Professor Andrew DoigSaid, Ph.D., from the Department of Neuroscience and Experimental Psychology at the University of Manchester, who was not involved in the study, MNT: “[Furthermore]pathogens may produce compounds that promote the accumulation of beta-amyloid or alpha-synuclein, which may lead to Alzheimer’s disease or Parkinson’s disease, respectively.”
When asked why there was a link between hospital-treated infections and neurodegenerative conditions in those aged 60 and under, but not older, Dr. Timo E. Strandberg،, MD, an internist and professor of geriatrics at University Hospital Helsinki, Finland, was not involved in the study MNT:
“[In a study my team and I conducted in 2003, looking at our geriatric cohort]Indeed, there was a significant relationship between viral burden and cognitive decline in more than 75 subjects. However, in this age group, cognitive decline and dementia are typically multifactorial—hereditary, neurodegenerative, and vascular—which may be why the association was not observed in the elderly in this study.”
– Dr. Timo E. Strandberg, Ph.D.
The researchers concluded that hospital-treated infections are associated with an increased risk of Alzheimer’s disease and Parkinson’s diagnosis before age 60, although the underlying mechanisms remain unknown.
When asked about the study’s limitations, Dr. Sun noted that they did not have complete information on all risk or protective factors for neurodegenerative conditions, including lifestyle factors, medical factors such as trauma or blood vessel-related brain damage, and genetics.
Charlotte Warren GashPhD, associate professor in the School of Epidemiology and Population Health at the London School of Hygiene and Tropical Medicine, not involved in the study, also said MNT:
“The study covered a long period of time, from 1970 [to] In 2016, diagnostic criteria and clinical practice underwent significant changes. How the findings may be applied to today’s infected patients remains unclear.”
Doig added: “All of the people in the study were Swedes although both parents were also born in Sweden, so the results may not be generalizable outside this group.”
Dr. Strandberg noted that the key message should be that “infections should be treated carefully – as they should in any case – with a low threshold for cognitive testing as needed.”
He added that more studies could examine whether antimicrobial treatments for recurrent infections such as herpes could help treat well-established cognitive disorders.
Dr. Warren Gash agreed that more research is needed.
More studies using novel designs are needed to account for limitations such as confounders and inverse causation. While preventing and treating infections leads to overall health benefits, more research is needed on whether these interventions can specifically influence the risk of developing neurodegenerative diseases. “
Charlotte Warren Gash, PhD, associate professor at the London School of Hygiene and Tropical Medicine
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