Natural reservoir Rousettus aegyptiacus bat host model of orthonairovirus infection identifies potential zoonotic spillover mechanisms

Bat organoids reveal antiviral responses at epithelial surfaces

Bats can host viruses of pandemic concern without developing disease. The mechanisms underlying their exceptional resilience to viral infections are largely unresolved, necessitating the development of physiologically relevant and genetically tractable research models. Here, we developed respiratory and intestinal organoids that recapitulated the cellular diversity of the in vivo epithelium present in Rousettus aegyptiacus, the natural reservoir for the highly pathogenic Marburg virus (MARV). In contrast to human counterparts, bat organoids and mucosal tissue exhibited elevated constitutive expression of innate immune effectors, including type I interferon-ε (IFNε) and IFN-stimulated genes (ISGs). Upon infection with diverse zoonotic viruses, including MARV, bat organoids strongly induced type I and III IFN responses, which conferred robust antiviral protection. Type III IFNλ3 additionally displayed virus-independent self-amplification, acting as an ISG to enhance antiviral immunity. Our organoid platform reveals key features of bat epithelial antiviral immunity that may inform therapeutic strategies for viral disease resilience.

Modeling natural coinfection in a bat reservoir shows modulation of Marburg virus shedding and spillover potential

The Egyptian rousette bat (ERB) is a natural reservoir for Marburg virus (MARV; family Filoviridae), a putative reservoir for Sosuga virus (SOSV; family Paramyxoviridae), and a vertebrate reservoir for Kasokero virus (KASV; family Orthonairoviridae); however, the effect of naturally occurring coinfection by those viruses on MARV shedding and spillover potential is unknown. To answer this question, we experimentally infected one cohort of captive-bred ERBs with SOSV+MARV (n=12 bats) or MARV only (n=12 bats) and a second cohort with KASV+MARV (n=12 bats) or MARV only (n=12 bats), and then collected blood, oral swab, and rectal swab specimens throughout the course of infection to monitor viral shedding. Compared to the MARV-monoinfected bat group, the SOSV+MARV-coinfected bat group exhibited a significantly shortened duration of MARV oral shedding and a significantly decreased anti-MARV IgG response, which may increase the capacity for MARV reinfection. In contrast, relative to the MARV-monoinfected bat group, the KASV+MARV-coinfected bat group exhibited significantly increased peak magnitudes and durations of MARV viremia and oral shedding, as well as a significantly increased anti-MARV IgG response. Correspondingly, cumulative MARV shedding loads, a measure of infectiousness, were significantly higher in the KASV+MARV-coinfected bat group than the MARV-monoinfected bat group. Four of the KASV+MARV-coinfected bats were classified as MARV supershedders, together accounting for 72.5% of the KASV-MARV experimental cohort's total shedding. Our results demonstrate that SOSV+MARV and KASV+MARV coinfection of ERBs differentially modulates MARV shedding and anti-MARV IgG responses, thereby implicating MARV coinfection as playing a critical role in bat-to-bat MARV transmission dynamics and spillover potential.

Evidence-Based Guidance for One Health Preparedness, Prevention, and Response Strategies to Marburg Virus Disease Outbreaks

OBJECTIVES

Marburg virus disease (MVD) is on the WHO list for pandemic-prone pathogens. The current outbreak in Rwanda provides an opportunity to map outbreaks and generate information to inform policymaking, resource mobilization, and guide the implementation of cost-effective response strategies.

METHODS

We synthesized available information about MVD to build holistic, up-to-date evidence to inform policymakers, public health leaders, and healthcare and public health services providers in their development and implementation of cost-effective preparedness, prevention, and control measures.

RESULTS

We have identified 20 outbreaks of MVD that occurred in 14 countries between 1967 and 2024; these outbreaks led to 580 confirmed cases and 423 deaths in total. We summarize the available information about the main clinical signs, diagnostic tools, primary reservoir, transmission dynamics, and case management protocol. We also document the best practices in the prevention and control of MVD outbreaks, including the implementation of a multisectoral One Health strategy for preparedness, prevention, and response to MVD outbreaks that incorporates the strict implementation of WASH and infection prevention measures, contact tracing, and the isolation of infected and suspected humans and animals, and enhances the implementation of the International Health Regulations, particularly efficient cross-country coordination.

CONCLUSIONS

In the absence of a licensed treatment or vaccine for MVD, the response strategy to MVD should focus on preventive measures, including community engagement to promote the reduction in contact between humans and reservoirs, the supportive care and isolation of patients, and proper waste management. High risk populations such as frontline responders, including healthcare providers and community health workers, should be prioritized so that they can access all currently available protection measures.

Disease tolerance as immune defense strategy in bats: One size fits all?

Bats are natural reservoirs for zoonotic pathogens, yet the determinants of microbial persistence as well as the specific functionality of their immune system remain largely enigmatic. Their propensity to harbor viruses lethal to humans and/or livestock, mostly in absence of clinical disease, makes bats stand out among mammals. Defending against pathogens relies on avoidance, resistance, and/or tolerance strategies. In bats, disease tolerance has recently gained increasing attention as a prevailing host defense paradigm. We here summarize the current knowledge on immune responses in bats in the context of infection with zoonotic agents and discuss concepts related to disease tolerance. Acknowledging the wide diversity of bats, the broad spectrum of bat-associated microbial species, and immune-related knowledge gaps, we identify research priorities necessary to provide evidence-based proofs for disease tolerance in bats. Since disease tolerance relies on networks of biological processes, we emphasize that investigations beyond the immune system, using novel technologies and computational biology, could jointly advance our knowledge about mechanisms conferring bats reservoir abilities. Although disease tolerance may not be the "one fit all" defense strategy, deciphering disease tolerance in bats could translate into novel therapies and inform prevention of spillover infections to humans and livestock.

Rousettus aegyptiacus Fruit Bats Do Not Support Productive Replication of Cedar Virus upon Experimental Challenge

Cedar henipavirus (CedV), which was isolated from the urine of pteropodid bats in Australia, belongs to the genus Henipavirus in the family of Paramyxoviridae. It is closely related to the Hendra virus (HeV) and Nipah virus (NiV), which have been classified at the highest biosafety level (BSL4) due to their high pathogenicity for humans. Meanwhile, CedV is apathogenic for humans and animals. As such, it is often used as a model virus for the highly pathogenic henipaviruses HeV and NiV. In this study, we challenged eight Rousettus aegyptiacus fruit bats of different age groups with CedV in order to assess their age-dependent susceptibility to a CedV infection. Upon intranasal inoculation, none of the animals developed clinical signs, and only trace amounts of viral RNA were detectable at 2 days post-inoculation in the upper respiratory tract and the kidney as well as in oral and anal swab samples. Continuous monitoring of the body temperature and locomotion activity of four animals, however, indicated minor alterations in the challenged animals, which would have remained unnoticed otherwise.

Tick-borne viruses and their risk to public health in the Caribbean: Spotlight on bats as reservoirs in Cuba

In recent decades, tick-borne diseases (TBDs) have surged and expanded globally due to factors like changes in human activities, land use patterns, and climate change, and it have been associated with the emergence of zoonotic diseases. Cuba faces the impact of ticks on human health and the economy. Although Cuba has studied TBDs extensively for the past 50 years, focus on tick-borne viral pathogens affecting humans remains scant. Despite TBDs not currently being a major health concern in Cuba, factors like inadequate clinician awareness, climate conditions, global tick emergence, and evidence of zoonotic pathogens in ticks underscore the importance of enhanced TBD surveillance in the country. Here we revised the available information on ticks as vectors of pathogenic viruses to humans, spotlighting bats as potential reservoirs of tick-borne viruses (TBVs). Ticks on bats have gained interest as potential reservoirs of pathogenic viruses to humans in Cuba and worldwide. Understanding their role in maintaining viruses and their potential transmission to humans is crucial for the implementation of surveillance and control programs to reduce the risk of tick-borne viral diseases and public health management.

Tick salivary gland components dampen Kasokero virus infection and shedding in its vertebrate reservoir, the Egyptian rousette bat (Rousettus aegyptiacus)

BACKGROUND

The human-pathogenic Kasokero virus (KASV) circulates in an enzootic transmission cycle between Egyptian rousette bats (ERBs; Rousettus aegyptiacus) and their argasid tick ectoparasites, Ornithodoros (Reticulinasus) faini. Although tick salivary gland components have been shown to potentiate virus infection in vertebrate non-reservoirs (i.e. incidental hosts or small animal models of disease), there is a lack of information on the effect of tick salivary gland components on viral infection and shedding in vertebrate reservoirs.

METHODS

To determine the impact of tick salivary gland components on KASV infection and shedding in ERBs, KASV loads were quantified in blood, oral swab, rectal swab, and urine specimens collected daily through 18 days post inoculation from groups of ERBs intradermally inoculated with KASV or KASV + O. (R.) faini tick salivary gland extract (SGE).

RESULTS

Bats inoculated with KASV + tick SGE had significantly lower peak and cumulative KASV viremias and rectal shedding loads compared to bats inoculated with KASV only.

CONCLUSIONS

We report for the first time to our knowledge that tick salivary gland components dampen arbovirus infection and shedding in a vertebrate reservoir. This study advances our understanding of biological factors underlying arbovirus maintenance in nature.