Neurodegenerative diseases are often sometimes to a virus, in particular HERV-K, but this has never been demonstrated convincingly.
Hepatitis E virus (HEV) infections are not limited to the liver but can also affect other organs. Several neurodegenerative diseases including Guillain-Barré syndrome, neuralgic amyotrophy, meningitis, have been observed in the context of hepatitis E. Additionally, HEV infection has been observed with other neurological diseases, such as encephalitis, myelitis, and Bell's palsy. Patients may have normal liver function tests, which can often mislead doctors into inferring that there is no HEV infection.
Case-control studies are a type of epidemiological study. They have often been used in the study of rare diseases where little is known about the association between the risk factor and the disease of interest.
Case-control studies are used to identify factors that may contribute to a disease by comparing subjects who have that disease (the “cases”) with patients who do not have the disease but are otherwise similar (the “controls”).
In this case-control study, scientists from Spain assessed the association between serum antibodies against the hepatitis E virus and neurodegenerative disorders of the central nervous system in older people with dementia.
The presence of anti-HEV antibodies was related to a higher adjusted odds ratio of having neurodegenerative disorders by neuropathological diagnosis and clinical/neuropathological diagnosis.
Furthermore, serum anti-HEV antibodies were directly linked to neuropathological injury and a higher likelihood of having Alzheimer-like pathology.
The scientists conclude their article by assuming that the presence of anti-HEV antibodies was indeed linked to a higher risk of neurodegenerative disorders and neuropathological lesions in the elderly.
However, the reader should exercise caution. Case-control studies are observational in nature and do not provide the same level of information as randomized controlled trials. The results can be distorted by other factors, sometimes significantly.