Bat‐Borne RNA Viruses: Addressing the Rising Health Risks in Bangladesh

In January 2025, Bangladesh reported the first cases of bat reovirus infections, marking the emergence of a previously undetected bat-borne RNA virus [1]. Bat reovirus, like Nipah virus (NiV), is transmitted by fruit bats or flying foxes of the Pteropus genus. Although bat reovirus belongs to the Orthoreovirus genus, NiV is classified under the Henipavirus genus. The bat reovirus, identified through collaborative research by the Institute of Epidemiology, Disease Control, and Research (IEDCR) and Columbia University, was detected in five individuals with Nipah-like symptoms who fully recovered after treatment and returned home [2]. Since 2001, Bangladesh has faced seasonal outbreaks of NiV, a lethal bat-borne RNA virus, occurring between December and May, with a case fatality rate exceeding 70%. NiV has infected around 330 individuals and caused 237 deaths [3, 4]. Fruit bats are the primary carriers, whereas cows, goats, and pigs are secondary carriers. The World Health Organization (WHO) has classified NiV as a priority disease due to its high fatality rate, potential for human-to-human transmission, and lack of effective treatments or vaccines [4]. By May 2024, 5 countries reported 754 human NiV cases with 435 deaths (CFR: 58%). Bangladesh had the highest incidence, followed by Malaysia, India, the Philippines, and Singapore [5]. Raw date palm sap contaminated with bat saliva, urine, and excreta is believed to be the primary carrier of reovirus and NiV that infect humans in Bangladesh. NiV infection leads to acute respiratory illness, nausea, fever, headache, sore throat, cough, myalgia, fainting, and fatal encephalitis, a lethal inflammation of the brain. Depending on the strain and local capabilities for early detection and clinical management, the virus has a death rate of 40%–100% [6-8]. On the other hand, reoviruses have been associated with uncommon human cases of meningitis, encephalitis, pneumonia, and myocarditis and may also be linked to biliary atresia and choledochal cysts [9]. Scientists are expressing concerns about Pteropine orthoreoviruses (specifically the Nelson Bay orthoreovirus species) due to the recurring outbreaks of bat-related viruses in humans. Although inter-species transmission has not been confirmed, as no virus has been isolated from both bats and humans, phylogenetic studies suggest the possibility of bat-to-human transmission. These viruses are associated with pteropid bats, which are also known to carry deadly zoonotic viruses like Hendra and Nipah. Shared ecological factors may be contributing to the emergence of these bat-related RNA viruses [10]. Table 1 provides a summary of key cases and findings on bat-associated orthoreoviruses isolated from humans (2006–2013), highlighting transmission dynamics, critical insights, and implications for human health. NiV is a deadly pathogen that affects various cells and organs, leading to respiratory complications, systemic vasculitis, and damage to the central nervous system (CNS). The virus spreads through the bloodstream, using ephrin B-2 and B-3 receptors in arterial endothelium to invade multiple organs, resulting in thrombosis, encephalitis, and severe vascular damage. NiV reaches the CNS via both hematogenous and olfactory routes, or through immune cells. This invasion disrupts the blood–brain barrier and triggers inflammation driven by cytokines such as IL-1β and TNF-α. Both gray and white matter in the brain show significant vascular involvement. The virus infects various mammals by binding to ephrin B-2 and B-3 receptors on epithelial cells. This binding facilitates membrane fusion through its G and F glycoproteins and releases its genome for replication. Structural proteins, including N for transcription and replication and M for assembling new virions, are synthesized, enabling efficient transmission and a wide host range (Figure 1). Recent studies have highlighted the olfactory epithelium as a potential key entry point for CNS invasion, emphasizing the complex and aggressive nature of the virus [11, 12]. However, therapeutic development for bat-borne RNA viruses, including NiV, faces significant challenges in low-income countries like Bangladesh, often lacking business interest and encountering obstacles in clinical trial design [13, 14]. Currently, no established treatments or preventive measures exist for bat reovirus. Bats, being natural reservoirs for numerous emerging viruses that can cause severe diseases in humans, have fascinated researchers. Their unique immune systems enable them to host viruses, including those with pandemic potential, without disrupting their physiological stability. Bats harbor both RNA and DNA viruses, with Type 1 interferon inducing low-level viral expression and reducing immune stimulation. Their control of inflammation and a dampened STING response aids prolonged viral survival. This symbiotic relationship benefits viruses with habitat and dispersal while enhancing bats’ immune systems for cross-protection, predator defense, and maintaining robust defense mechanisms as “biological weapons.” Insights from this relationship could be vital in understanding viral persistence and combating future pandemics [15]. Bat-borne RNA viruses include Marburg, Hendra, Sosuga, and Nipah. Bats are also associated with other RNA viruses such as Ebola, SARS-CoV, SARS-CoV-2, and MERS-CoV [16]. Among these, SARS-CoV-2 is highly prone to rapid mutation, a characteristic that has already resulted in nearly 5 million deaths worldwide [14]. In conclusion, preventing outbreaks of RNA viruses transmitted by bats requires urgent actions. These include halting deforestation, promoting reforestation, controlling human population growth, and banning bat hunting and wildlife trade to reduce human exposure to virus reservoirs. Proactive measures such as wildlife surveillance, ecological research, and advancements in diagnostics and vaccine technologies, including mRNA and VSV (vesicular stomatitis virus), provide critical tools for predicting and mitigating virus spillovers. Additionally, strategies like covering containers of date palm sap can help curb the transmission of the bat-borne viruses. However, challenges such as vaccine hesitancy, geopolitical conflicts, and difficulties with wildlife vaccination pose significant obstacles. Coordinated global efforts are essential to minimize the risk of epidemics and pandemics caused by these emerging threats, bat-borne RNA viruses [16, 17]. Md Nasir Ahmed: conceptualization, visualization, resources, investigation, writing – original draft, review and editing. The author extends heartfelt thanks to the reviewers for their invaluable feedback. He also expresses profound gratitude to his lifelong soulmate, Chowdhury Alfi Afroze, for her unwavering support and pivotal role in conceptualizing this article. The authors declare no conflicts of interest. All relevant data are within the manuscript, and no new data have been generated.