# Age- and sex-associated differences in Lujo hemorrhagic fever pathogenesis in strain 13/N guinea pigs

## TL;DR

Young female guinea pigs survive Lujo virus infection better than others due to less severe immune responses, despite similar virus levels.

## Contribution

Identifies age- and sex-dependent immune responses as key determinants of Lujo virus disease severity in guinea pigs.

## Key findings

- Young female guinea pigs show improved survival with lower inflammatory cytokine profiles.
- Males and older animals exhibit severe disease linked to heightened cytokine storms.
- Viral burden alone does not determine disease outcome; immune response is critical.

## Abstract

Lujo virus (LUJV) is a highly pathogenic zoonotic arenavirus first identified during a 2008 viral hemorrhagic fever (VHF) outbreak in Southern Africa, exhibiting an 80% case fatality rate. Despite its public health significance, LUJV remains poorly understood, with no approved treatments, vaccines, or known reservoir. Existing small animal models have shown limited disease recapitulation, with strain 13/N guinea pigs emerging as a promising model for LUJV pathogenesis. In this study, we evaluate the influence of age and sex on LUJV disease progression in strain 13/N guinea pigs. We show that young females exhibit markedly improved survival, while all young males, as well as juvenile and adult animals of both sexes, succumbed to infection. Despite similar high titers of LUJV detected in the lungs, liver, spleen, kidneys, and serum of infected animals, survival outcomes strongly correlated with immune responses rather than viral burden. Adult animals and young males developed more severe clinical signs, heightened hematological and biochemical abnormalities, and pronounced cytokine storms, particularly elevated IL-1β, IL-2, IL-6, and CXCL10 levels. In contrast, young females displayed lower inflammatory cytokine profiles, and attenuated clinical disease. These findings underscore that LUJV pathogenesis in guinea pigs is influenced by host immune responses rather than viral replication alone. Our results provide critical insight into age- and sex-dependent mechanisms of LUJV disease and support the utility of the strain 13/N guinea pig model for future medical countermeasures development.

Lujo virus (LUJV) is a rare but highly lethal Mammarenavirus first recognized in 2008 during a small outbreak of viral hemorrhagic fever in Southern Africa, where four out of five infected people died. LUJV disease is not well understood, and there are currently no vaccines or treatments. Previously, inbred strain 13/N guinea pigs have been described as model for LUJV disease, but until now only older animals had been studied. In this study, we examined how age and sex affect the course of LUJV infection in guinea pigs. We found that male animals of all ages, as well as juvenile and older females, developed severe disease and succumb to infection, while young females often survived despite having similar viral burdens as older animals. The key difference between lethal and non-lethal infection was in the immune response, where young females showed a cytokine response similar to uninfected control animals while animals that developed lethal disease showed stronger and uncontrolled inflammatory responses. These findings suggest that the severity of LUJV disease is linked to the degree of immune activation than to viral levels, and they strengthen the guinea pig as a model for developing vaccines and treatments.