Neuropathogenesis of Old World Alphaviruses: Considerations for the Development of Medical Countermeasures.

Chikungunya virus (CHIKV) and other alphaviruses that primarily induce arthritogenic disease in humans, known as "Old World" alphaviruses, present an emerging public health concern as geographic ranges of mosquito vectors expand due to climate change. While a vaccine against CHIKV has recently been approved by several countries in North America and Europe, access to effective preventative countermeasures against disease induced by Old World alphaviruses remains elusive for the most vulnerable populations. Furthermore, treatment options continue to be limited to supportive care. Atypical neurological disease manifestations caused by Old World alphaviruses, which make up as many as 25% of the cases in some CHIKV outbreaks, present special challenges when considering strategies for developing effective countermeasures. This review focuses on Old World alphaviruses, specifically CHIKV, Ross River virus, O'nyoug-nyoug virus, and Mayaro virus, concentrating on the atypical neurological disease manifestations they may cause. Our current understanding of Old World alphavirus neuropathogenesis, gained from human cases and preclinical animal models, is discussed, including viral and host factors' roles in disease development. The current state of alphavirus preventatives and treatments, both virus-targeting and host-directed therapies, is then summarized and discussed in the context of addressing neurological disease induced by Old World alphaviruses.