To Örebro University

As disease risk for many conditions can start earlier in life, an essential aspect of these studies was to take a life-course approach using Swedish national register data to identify whether infectious or other inflammatory exposures are associated with a raised risk of subsequently diagnosed neurological diseases, and infectious mononucleosis whichis a risk factor for subsequent neurological sequelae.

Study I investigated the risk of dementia at older ages associated with an atopic dermatitis diagnosis at around 18 years of age or at any point in life, using data from national Swedish registers. No association was found between atopic dermatitis and the risk of dementia among men or women.

Study II examined a potentially causal association between hospital-treated infections and the subsequent risk of Parkinson’s disease (PD). Hospital-treated gastrointestinal and respiratory infections at ages 21-30, but not at ages 31-40 years, were associated withan elevated risk of PD.

Study III examined whether a positive SARS-CoV-2 test only (less severe exposure) or hospital admission with COVID-19 (more severe exposure) could be a risk factor for demyelinating diseases of the central nervous system. Only the more severe exposure was associated with a raised risk of both multiple sclerosis (MS) and non-MS demyelinating diseases.

Study IV explored whether SARS-CoV-2 infection is associated with a heightened risk of subsequent infectious mononucleosis due to Epstein-Barr virus (EBV-IM). National registers in Sweden were used for this research, covering the entire population betweenthe ages of 3 and 100. Both a positive SARS-CoV-2 test only and hospital admission with COVID-19 were associated with a raised risk of subsequent EBV-IM. This suggests that the immune perturbation caused by COVID-19 increases the risk of a more substantial immune response against EBV, resulting in IM.

These studies indicate that infections occurring many years earlier in life may be aetiologically important in Parkinson’s disease and that the SARS-CoV-2 pandemic may be associated with conditions such as demyelinating diseases of the central nervous system and an increased risk of EBV-IM. Atopic dermatitis does not appear to be a risk factor for dementia.