Extended tissue tropism and vertical transmission in a murine model of Mayaro virus infection

Mayaro virus (MAYV) is an emerging mosquito-borne alphavirus associated with acute febrile illness and persistent arthralgia, with increasing reports in Latin America and potential for geographic expansion. However, its dissemination dynamics, tissue tropism and transmission routes remain incompletely defined. Here, we developed a murine model to characterize systemic viral dissemination, tissue tropism and the impact of gestational stage on maternal-fetal outcomes. A nanoluciferase-expressing MAYV reporter enabled non-invasive in vivo imaging, revealing rapid and widespread systemic dissemination under controlled conditions. Complementary infection with wild-type (WT) virus confirmed broad tropism across lymphoid, musculoskeletal and reproductive tissues. At 24 hours post-infection (hpi), viral distribution was relatively homogeneous across tissues, whereas at 48 hpi, tissue-specific differences emerged, with increased viral loads in selected organs, including the spleen and male reproductive tissues. Transient sex-dependent differences were observed at 24 hpi but were not sustained at later time points. Hematological and biochemical analyses revealed early systemic alterations consistent with changes in leukocyte distribution during acute infection. Infectious viral particles were detected in reproductive tissues of both sexes, including in sperm, supporting the biological plausibility of non-vector transmission, although detection in exposed animals was limited. Gestational stage influenced infection outcomes: early gestation (infected at 7.5-8.5 dpc; analyzed at 9.5-10.5 dpc) was associated with detection of infectious virus in fetal tissues, whereas mid-gestation (infected at 13.5-14.5 dpc; analyzed at 15.5-16.5 dpc) showed no detectable infectious virus in fetuses despite evidence of viral antigen persistence and sustained infectious viral presence in maternal and placental compartments. Together, these findings provide a preclinical framework for investigating MAYV pathogenesis and underscore the role of tissue tropism and gestational context in shaping infection dynamics and maternal-fetal involvement. Author summaryMayaro virus (MAYV) is an emerging mosquito-borne virus that causes fever and long-lasting joint pain, with increasing reports in Latin America and potential for wider geographic spread. Despite its growing relevance, key aspects of MAYV pathogenesis remain to be fully defined, including the mechanisms underlying systemic dissemination and tissue tropism, as well as its potential to affect pregnancy or be transmitted through non-vector routes. Here, we used a mouse model with a luminescent reporter virus to track MAYV dissemination in vivo, revealing rapid and widespread distribution across multiple tissues. In studies using wild-type virus, infectious virus was detected not only in muscle and immune-related organs but also in reproductive tissues of both females and males. Importantly, gestational stage influenced viral distribution. When infection occurred early in gestation, infectious viral particles were detected in fetal tissues. In contrast, at later stages of pregnancy, infectious virus was no longer detectable in fetuses, despite evidence of viral antigen persistence and sustained infectious viral presence in maternal and placental tissues. Together, these findings advance our understanding of MAYV infection, highlight gestational timing as a factor associated with fetal exposure and suggest the possibility of transmission through routes other than mosquitoes, providing a framework for future studies on this emerging virus.