Therefore, we conducted a meta-analysis to quantitatively assess the association of several infectious diseases with the risk of PD.

Parkinson Disease (PD) is a progressive age-related neurodegenerative disorder that presents with tremors, cogwheel rigidity, bradykinesia, postural instability, and cognitive symptoms. Different etiologies leading to the neurodegenerative pathology of the substantia nigra compacta have been suggested. Different inflammatory and immunological factors were proposed as a potential cause of the neurodegenerative process in PD patients. This hypothesis is supported by the increased incidence of PD after different infections such as bacteria, parasites, and viruses. 

A systematic search of 13 databases was performed to ultimately include studies that address the association between infections and PD in humans. The databases included PubMed, Embase, Cochrane, Scopus, Google Scholar, Web of Science (ISI), Popline, New York Academy of Medicine (NYAM), System for Information on Grey Literature in Europe (SIGLE), Global Health Library (GHL), Virtual Health Library (VHL), Clinical Trials (mRCT) and WHO International Trials Registry Platform (ICTRP). Methodological quality was assessed via the National Institute of Health quality assessment tools. Our primary endpoint was assessing the statistical and clinical associations between PD and different infections. The study protocol has been registered in PROSPERO with registration number CRD42017079452.

60,493 records were identified in our literature search, and 20 articles were finally included in the meta-analysis. Bacterial infections showed an overall significant association with PD (OR= 2.45; 95% CI= 1.52-3.93). None of the parasitic infections nor the overall viral infections showed a significant result; however, individual viral infections including CMV, HBV, measles, rubella, and VZV showed statistical significance (OR= 4.56; 95% CI= 2.44-8.54, OR= .74; 95% CI= .56-.98, OR= .64; 95% CI= 1.37-5.09, OR= 2.69; 95% CI= 1.23-5.88, OR= 1.2; 95% CI= 1.04-1.39, respectively).

Certain bacterial and viral infections are associated with higher rates of PD.