Discovery of new bat flu strain with potential to infect other species

By Dr. Sanchari Sinha Dutta, Ph.D.Reviewed by Benedette Cuffari, M.Sc.Feb 25 2025

A newly identified bat influenza virus, H18N12, carries mutations that may enhance its ability to jump between species, underscoring the need for vigilant surveillance to prevent future outbreaks.

Study: Genomics of novel influenza A virus (H18N12) in bats, Caribe Colombia. Image Credit: Shutterstock AI Generator / Shutterstock.com

In a recent study published in Scientific Reports, scientists determined the phylogenetic, evolutionary, and antigenic characteristics of a novel influenza A virus (IAV) identified in fishing bats in the Colombian Caribbean.

Bats: Natural reservoirs for emerging viruses

Bats serve as a key reservoir for a wide range of viruses, some of which include coronaviruses, paramyxoviruses, filoviruses, Venezuelan Equine encephalitis, and dengue virus.

Bats are not considered a reservoir for influenza viruses; however, several IAV subtypes have recently been detected in them. These include the H17N10 subtype identified in fruit bats in Guatemala and H18N11 isolated from bats in Peru, Bolivia, and Brazil. A virus similar to avian IAV strains has also been detected in Egyptian bats.

How do avian IAVs infect bats?

Bat IAVs likely originated from a common ancestor shared with avian IAV subtypes. Existing evidence suggests that either geographic separation and multiple early transmission events divided these viruses into two branches or significant mutations allowed them to adapt specifically to bats.

Hemagglutinin (H) and neuraminidase (NA) are glycoproteins present on the surface of IAVs. They are involved in viral attachment to host cell entry receptors, including major histocompatibility complex class II (MHC-II). X-ray crystallography of these proteins has confirmed structural similarities between bat and avian IAVs; however, bat IAVs exhibit specific molecular modifications that may be responsible for their adaptation to bats.

For example, the NA protein of bat IAVs does not exhibit any catalytic activity, leading researchers to hypothesize that this glycoprotein may induce low MHC-II molecules through a different mechanism. However, further research is needed to fully understand the mechanisms by which IAVs infect bats to ensure the effectiveness of influenza control strategies.

Study findings

A total of 159 rectal samples were randomly collected from bats in the Colombian Caribbean and analyzed using ribonucleic acid sequencing (RNA Seq). These bat species belonged to the Phylostomidae, Molossidae, Noctilionidae, and Emballonuridae families. Notably, only four Noctilio albiventris samples contained a viral genome associated with the Orthomyxoviridae family.

Three segments of this viral genome exhibited 90% similarity with H18N11. Comparatively, 93% of the A/bat/Colombia 23 viral genome sample was structurally similar to the H18N11 sequence isolated in Peru; however, the NA gene in this sample exhibited greater divergence from this reference genome.

The phylogenetic analysis indicated that the A/bat/Colombia 23 viral isolate is related to bat-specific IAVs and that it significantly differed from avian IAVs. For example, the H gene segment was structurally similar to the H18 segment isolated in Peru, Brazil, and Bolivia, whereas the PB2, PA, and M segments likely share a common ancestor with these reference gnomes. Comparatively, the A/bat/Colombia 23 NA gene segment was the most phylogenetically distant from that of recent IAV isolates and is phylogenetically related to a previous NA segment isolated over 50 years ago.

These findings suggest that genetic reassortment events with the HA and NA segments contribute to their genetic diversity and the adaptability of these mutated viruses to infect new hosts. An average of one reassortment event for every 31 years in the HA and NA segments was observed, which is considered a low reassortment rate that may be due to differences in genetic compatibility between the segments, ecological restrictions that prevent co-infections, or alterations from the bat’s immune system that led to viral evolution.

Based on this experimental data, the researchers utilized computational modeling to predict divergence and similarities between the isolated viral structure and H18N11 reference genomes. For example, the hypothetical active site pocket of the A/bat/Colombia/23 NA protein appears to be narrower than that of the Peru H18N11 protein, which is likely due to greater plasticity of loop 150 and the K363R mutation that altered the stability of this structure. Moreover, five mutations in Ser361, Ar363, and Lys242 appear to increase the strength and specificity of binding between bat and viral proteins.

These findings significantly impact our understanding of viral protein interactions and could potentially inform future research and drug development, particularly in the design of antiviral drugs targeting the NA protein.”

Study significance

The current study identified a novel IAV in fishing bats in the Colombian Caribbean. The H gene of this virus was the only segment related to all 16 known avian subtypes, whereas the PB1, PA, M, and NA segments likely originated from a rearrangement event between existing viral strains circulating in bats.  

The molecular divergence of the NA segment…suggests a new subtype called H18N12.”

Existing studies have reported that H18N11 cannot efficiently infect non-bat hosts. Although the H gene of A/bat/Colombia/23 is identical to that of the H18 subtype, the identified mutations in the NA gene can improve this virus's ability to infect and be transmitted between new species. Thus, it is imperative to monitor the emergence of new IAV strains and preemptively determine their potential to cause epidemiological outbreaks before they occur.