**5. Conclusions**

Thanks to the deep knowledge of *Chlamydia* biology of and the use of more advanced techniques than those traditionally used, the presence of *C. pneumoniae* genomic material has been demonstrated in a large number of people suffering from different acute and chronic diseases. Over the past 10 years, an increasing number of reports have indicated a possible link between *C. pneumoniae* and atherosclerosis and CNS diseases including various neurobehavioral disorders, MS, and AD. The main obstacle to determining the exact role of *C. pneumoniae* in chronic diseases is the lack of any method to safely and reliably diagnose chronic infection. The causal role of *C. pneumoniae* infection in cardiovascular disease has not been definitively established. Despite molecular and genetic studies of the role of *C. pneumoniae* in the progression of atherosclerosis, some important questions urgently need answers, such as whether *C. pneumoniae* is an innocent passenger or whether it is actively involved in the onset or progression of atherosclerotic disease. In particular, *C. pneumoniae* Hsp60 should be further investigated as a potential culprit and therapeutic target [86]. Efforts should be made to find a truly effective treatment targeting chronic *C. pneumoniae*. At the same time, the development of an effective vaccine should continue [133].

Although astrocytes, microglia, and neurons have been shown to be host cells for *C. pneumoniae* in the brain of patients with AD, and infected cells can be found near both NSPs and NFTs, most studies have been conducted with different diagnostic methods, none of which have yet been standardized. This has led to wide variation in interlaboratory test performance even when using the same test and the same criteria. Therefore, the actual involvement of *C. pneumoniae* in AD remains a subject of debate and requires further understanding through standardized cultural and molecular protocols.

Recent molecular, ultrastructural, and cultural developments have provided evidence that *C. pneumoniae* is viable and metabolically active in different biological compartments such as CSF and PBMCs in MS patients compared to controls, suggesting a relationship between this pathogen and the disease. The role of *Chlamydia* has been demonstrated in a subgroup of relapsing-remitting MS patients with clinical and MRI disease activity who experience the early inflammatory phase representing the development of the disease [81, 82, 92, 96]. However, growing evidence suggests that *C. pneumoniae* is not just an innocent bystander epiphenomenon due to ongoing MS inflammation, but is a cofactor in the development and progression of the disease by strengthening a preexisting autoimmune response in a subset of MS patients [81, 92, 134].

*Chlamydia Infection's Role in Neurological Diseases DOI: http://dx.doi.org/10.5772/intechopen.110842*

*For both AD and MS, there is an urgent need for further well-designed studies to determine the importance of C. pneumoniae involvement in the disease and the usefulness of antibiotic treatment.*
