One Health Lessons from Pteropus medius: Nipah Spillover, Microbiota, and Antimicrobial Resistance

Nipah virus and antimicrobial resistance may be converging in the same human-altered landscapes, according to a review that places Bangladesh’s Indian flying fox, Pteropus medius, at the center of a complex One Health threat. The bat is a natural reservoir of Nipah virus (NiV), a zoonotic pathogen that can cause severe encephalitis, respiratory disease and death in people. At the same time, its gut microbiota and guano can carry bacteria and antimicrobial-resistance genes acquired from polluted environments. The review does not suggest that bats created the global resistance crisis or that Nipah virus directly causes antibiotic resistance. Instead, it identifies a shared ecological pattern: deforestation, urban expansion, intensive farming, wastewater pollution and closer contact between people, livestock and wildlife can simultaneously increase opportunities for viral spillover and the circulation of resistant bacteria. The findings highlight why emerging infections and antimicrobial resistance can no longer be treated as separate problems.

Pteropus medius, also known as the Indian flying fox and formerly classified as Pteropus giganteus, ranges across much of South Asia and Southeast Asia. In Bangladesh it has been recorded from cities, villages, botanical gardens, islands and forested regions, including areas where people live and farm. Its ability to travel long distances, forage widely and roost in large colonies makes it an important ecological connector between otherwise separated habitats. Unlike humans and domestic animals, the bats generally show no obvious illness from NiV, allowing the virus to circulate without causing the severe disease seen after human infection. NiV is a negative-sense, single-stranded RNA virus in the henipavirus genus of the Paramyxoviridae family. Human case-fatality rates vary between outbreaks but have reached approximately 40 to 70 percent in Bangladesh, India and other parts of Asia. In some outbreaks, person-to-person transmission has further amplified the initial spillover.

In Bangladesh, one of the best-established routes into the human population begins with raw date palm sap. During the winter harvesting season, fruit bats may lick the exposed surface of a date palm or urinate and defecate near collection containers. If the sap is consumed without boiling, infectious material can be ingested. The winter timing of outbreaks reflects several overlapping factors: raw sap consumption rises during the cooler months, bats may visit palms more frequently when alternative foods are scarce, and nutritional or physiological stress may influence viral shedding. NiV can remain infectious in bat urine under certain laboratory conditions, including at 22°C and neutral pH, for as long as four days. Other possible pathways include contact with contaminated fruit, bat excreta or intermediate animals. Serological evidence from Bangladesh has indicated exposure in peridomestic animals such as dogs and cats, which may encounter infected material beneath roosts.

The review’s central advance is to connect this viral spillover ecology with the less visible world of the bat microbiome. Guano is a practical, non-invasive material for studying wildlife health because it can be collected without capturing or injuring bats. It contains fragments of DNA, intestinal microbes, pathogens and antimicrobial-resistance genes, although samples can also contain degraded genetic material and substances that interfere with molecular tests. Culture-based investigations have recovered organisms including Escherichia coli, Salmonella, Enterococcus, Staphylococcus, Klebsiella, Pseudomonas and Enterobacter from bat-associated material. These bacteria may be harmless gut residents, environmental organisms or potential pathogens, and their significance depends on the strain and the setting. High-throughput sequencing reveals a much broader community than culture alone, detecting organisms that cannot easily be grown in the laboratory. But sequencing identifies genetic potential, not necessarily active or clinically meaningful resistance, so genomic surveys and antibiotic-susceptibility testing provide complementary evidence.

Particularly concerning are extended-spectrum beta-lactamase-producing E. coli and other bacteria carrying resistance to important antibiotics. Beta-lactamases are enzymes that break open the characteristic beta-lactam ring found in penicillins and cephalosporins, rendering these drugs ineffective. Genes such as blaCTX-M, blaTEM and blaSHV are frequently associated with hospitals, sewage, livestock operations and agricultural runoff, and their detection in wildlife is consistent with environmental acquisition. In P. medius, one cross-sectional investigation found that 37 percent of E. coli isolates displayed ampicillin resistance and 37 percent had ESBL-producing characteristics; 46 percent were multidrug resistant, although only one isolate was classified as extensively drug resistant and none were pandrug resistant. Another study examining 369 fecal samples reported antimicrobial-resistant Salmonella in 7.9 percent of bats. Among those isolates, resistance to tetracycline reached 93 percent, nalidixic acid 86 percent and sulfamethoxazole-trimethoprim 80 percent. These figures are notable, but they represent snapshots from particular populations rather than a definitive estimate for the species as a whole.

Resistance can move through bacterial communities by several molecular routes. Mutations may alter antibiotic targets, reduce membrane permeability or increase the activity of efflux pumps that eject drugs from bacterial cells. More significantly for environmental spread, mobile genetic elements can carry resistance genes between unrelated bacteria. Plasmids can transfer DNA through direct cell-to-cell contact, while transposons and integrons can capture, rearrange and mobilize groups of resistance determinants. Biofilms—structured communities encased in a protective matrix—can help bacteria survive chemical stress and create dense conditions for gene exchange. In a bat roost, resistant organisms shed in feces or saliva may enter soil, surface water, crops or livestock environments. The review emphasizes that bats are more plausibly environmental sinks and transporters than primary evolutionary sources of clinically important resistance. Their resistance profiles often resemble those of bacteria found in nearby people, domestic animals or polluted habitats, suggesting shared exposure rather than independent evolution inside bats.

That distinction matters because the presence of a resistance gene in a bat does not prove that the animal is transmitting it to humans. Much of the available evidence is observational, and studies differ widely in sampling locations, seasons, sample sizes, bacterial culture methods, sequencing platforms and antibiotic panels. Some reports are based on only a handful of isolates, while others include hundreds. Cross-sectional sampling cannot reveal whether bats acquired resistant bacteria recently from contaminated water or whether they maintain and repeatedly disseminate them over time. Nor can it show whether a resistance gene moved from a bat-associated bacterium into a human pathogen. Demonstrating that chain would require longitudinal sampling, bacterial whole-genome sequencing, analysis of plasmids and other mobile elements, and direct tests of horizontal gene transfer. The authors therefore caution against portraying bats as drivers of the global antimicrobial-resistance epidemic, while still arguing that they can serve as useful sentinels of environmental contamination and as local vehicles of microbial redistribution.

The most important risk areas are places where the three pressures identified by the review overlap: NiV spillover opportunities, environmental reservoirs of resistance and intense human disturbance. Date palm sap collection sites are one example, because they combine bat excreta, food handling and seasonal human consumption. Peri-urban orchards and backyard fruit trees can bring bats, people, livestock and food markets into close proximity. Floodplains create another potential mixing zone when untreated municipal or hospital wastewater, livestock waste and agricultural runoff enter fields and standing water. Flooding can move bacteria and resistance genes through large areas, while bats forage over the contaminated landscape and may transport microbes between roosts and feeding sites. Urban roosts near markets, healthcare facilities or wastewater channels may similarly connect wildlife microbes to dense human populations. These settings do not guarantee transmission, but they create repeated opportunities for contact among environmental bacteria, bat-associated communities and organisms carried by people or livestock.

A practical response would combine surveillance for NiV with monitoring of bacterial resistance and the environmental conditions that shape both. Teams could sample bat urine and guano, date palm sap, roost substrates, nearby water, soil, livestock and wastewater at sentinel sites, using polymerase chain reaction or serology for viral detection, bacterial culture and susceptibility testing for phenotypes, and shotgun metagenomic sequencing for the wider resistome. Mapping land use, sanitation, livestock locations, seasonal flooding, harvesting practices and bat movements could help identify locations where viral shedding and resistance exchange are most likely to coincide. Prevention need not depend on killing bats or destroying colonies. Physical covers on sap-collection containers can block bat access, while boiling sap, cleaning fruit and improving food hygiene can reduce exposure. Better wastewater treatment, safer hospital-effluent disposal, improved manure management and responsible antimicrobial use can reduce the environmental selection pressure that favors resistant organisms. Protecting roosts and restoring feeding habitat may also reduce the displacement that pushes bats into closer contact with people.

The review concludes that P. medius should be understood as part of a dynamic ecological system rather than as a villainous reservoir of disease. Its mobility and adaptability make it valuable for studying how pathogens and resistance move through altered environments, but the available science still cannot establish a direct mechanistic link between NiV shedding and the acquisition or spread of antimicrobial-resistance genes. Future studies will need to follow bat colonies across seasons, reproductive cycles, rainfall patterns and changes in food availability, while pairing microbiome data with viral detection and measurements of host immune status. Long-read sequencing could clarify which resistance genes are carried on transferable plasmids, and comparative genomics could trace whether the same bacterial lineages or genetic elements appear in bats, livestock, wastewater and people. Such work would turn a compelling ecological association into a testable transmission model. For Bangladesh and other regions where human livelihoods depend on shared landscapes, the most effective strategy may be to protect wildlife, improve environmental health and reduce risky contact at the same time.