Tissue distribution and transmission of Rift Valley fever phlebovirus in European and mosquitoes following intrathoracic inoculation.

Rift Valley fever virus (, RVFV) poses significant economic challenges, particularly in African nations, causing substantial livestock losses and severe haemorrhagic disease in humans. In Europe, the risk of RVFV transmission is deemed moderate due to the presence of competent vectors like and , along with susceptible animal vertebrate hosts across member states. This study investigates RVFV infection dynamics in European mosquito populations, aiming to enhance our understanding of their vectorial capacity and virus transmission, which can be useful for future investigations to improve RVFV surveillance, control programmes, and preventive treatments. Intrathoracic inoculation of European and with an RVFV virulent strain (RVF 56/74) enabled the assessment of virus tissue distribution and transmission. Immunohistochemistry analyses revealed widespread RVFV infection in all analysable anatomical structures at 5 and 14 days post-inoculation. Notably, the ganglionic nervous system exhibited the highest detection of RVFV in both species. showed more frequently infected structures than , particularly in reproductive structures. The identification of an RVFV-positive egg follicle in hints at potential vertical transmission. Saliva analysis indicated a higher transmission potential in (71.4%) compared to (4.3%) at the early time point. This study offers the first description and comparison of RVFV tissue distribution in and , shedding light on the susceptibility of their nervous systems, which may alter mosquito behaviour, which is critical for virus transmission. Overall, enhancing our knowledge of viral infection within mosquitoes holds promise for future vector biology research and innovative approaches to mitigate RVFV transmission.