Mechanisms of Flavivirus Cross-Protection against Yellow Fever in a Mouse Model

Area of Science:

• Virology
• Immunology
• Epidemiology

Background:

• Yellow fever virus (YFV) is notably absent in Asia, and urban transmission is lacking in South America, despite the presence of the primary vector, *Aedes aegypti*.
• A large, immunologically naive population in Asia resides in areas with the urban YFV vector, posing a potential risk.
• A leading hypothesis suggests prior immunity to related flaviviruses, such as dengue (DENV) and Zika virus (ZIKV), modulates YFV infection and transmission.

Purpose of the Study:

• To investigate the role of pre-existing immunity to DENV and ZIKV in YFV infection using a mouse model.
• To elucidate the mechanisms of cross-protection against YFV conferred by prior flavivirus exposure.

Main Methods:

• Utilized an interferon-alpha/beta receptor knock-out mouse model.
• Administered DENV-2 and ZIKV to induce prior immunity before challenging with African and Brazilian YFV strains.
• Assessed YFV viremia and disease outcomes.
• Investigated the role of humoral immune responses in cross-protection.

Main Results:

• Pre-existing immunity to DENV-2 and ZIKV significantly suppressed YFV viremia in the mouse model.
• The protective effect on disease outcomes varied, suggesting complex interactions.
• Humoral immune responses were identified as the primary mediators of this cross-protection.

Conclusions:

• Prior flavivirus immunity, particularly from DENV and ZIKV, can suppress YFV infection.
• Cross-protection is mainly mediated by antibodies, influencing YFV transmission dynamics.
• Re-evaluation of YFV outbreak risks is crucial, considering endemic flavivirus immunity in populations.