Seroprevalence of Nipah virus and related paramyxoviruses in native frugivorous bats, Luzon, Philippines

Abstract

Nipah virus (NiV) is a highly virulent zoonotic virus classified as a priority pathogen and biohazard. In 2014, an outbreak of NiV-like disease in the Province of Sultan Kudarat, Mindanao, Philippines resulted in a 53% case fatality rate. Here, we identified wildlife bat hosts of NiV by conducting monthly serological surveillance of flying foxes and other native frugivorous bat species across Luzon. We estimated 13.92% NiV seroprevalence in native flying foxes. We also detected NiV neutralizing activity in some flying fox sera and identified factors such as age and seasonality as drivers of high anti-NiV antibody levels. In contrast, less than 10% NiV seroprevalence was detected in R. amplexicaudatus, C. luzoniensis, and P. jagori bats, and these bats have no detectable neutralizing antibodies. This is the first serological description of NiV in native flying foxes in the Philippines, highlighting a major wildlife host in an understudied region.

Keywords: Nipah virus; Philippines; bats; biosurveillance; spill over risk.

Figure 1.

Sampling sites and bat collection breakdown. Location of sampling sites within Luzon island, Philippines and the proportion of each sampled bat species at each location. Sites include Infanta, Agno, Doña Remedios Trinidad (DRT), Burdeos, and Tayabas. Species collected include flying foxes*, Rousettus amplexicaudatus, Eonycteris species (E. spp.**), Cynopterus luzoniensis, and Ptenochirus jagori. Red diamond indicates the location of the 2014 NiV-like outbreak in Sultan Kudarat province. *Flying foxes include Pteropus vampyrus, Pteropus hypomelanus, Acerodon jubatus bat species; **E. Spp. include Eonycteris spelaea and robusta bat species

Figure 2.

Sero-reactivity profiles of multiple bat species groups for paramyxoviruses. Radarcharts demonstrating sero-reactivity profiles to eight paramyxovirus G and HN antigens and a mock control protein for Philippine frugivorous bats, including (A) flying foxes (P. vampyrus, P. hypomelanus, A. jubatus; N = 654), (B) R. amplexicaudatus; N = 3147, (C) E.species (E. spelaea & E. robusta; N = 287), (D) C. luzoniensis (N = 872), and (E) P. jagori (N = 214) during monthly collections on Luzon island from July 2023 – August 2024, excluding August 2023. Radial axes represent each of the eight antigens used as the serological target for detection of antibodies. Scales are a continuous linear measurement of median fluorescence intensity (MFI) from 0 – 6000 that represent antibody levels. Connecting lines represent the individual mean values for each clusters based on k – medoids clustering after PCA to six components where cumulative explained variance is >70%.

Figure 3.

Comparison of anti-NiV-G antibody response among all bat species groups. Comparisons of anti-NiV-G antibody levels among flying foxes (green circle), R. amplexicaudatus bats (orange square), Eonycteris species bats (purple up triangle), C. luzoniensis bats (blue down triangle), and P. jagori bats (pink diamond) using a Kruskal – Wallis test (p<0.001). Multiple comparisons by Dunn’s test indicated that any comparisons among E. spp, C. luzoniensis, and P. jagori bats were non – significant. Comparison of flying foxes and R. amplexicaudatus was significant (p<0.01) and multiple comparisons of flying foxes and R. amplexicaudatus to any other species was significant (p<0.0001).

Figure 4.

Seasonal differences in NiV seroprevalence and occurrence of neutralizing activity in flying foxes. Monthly changes in NiV seroprevalence in flying foxes during the period of sampling from July 2023 to August 2024, excluding August 2023. Observed seroprevalence (blue circle, dotted line) was calculated using cutoff = 904 MFI for NiV seropositivity with lower and upper 95% CI indicated, estimated seroprevalence is based on Bayesian smoothing function, and 95% CI (grey shaded) were calculated for each month. Red stars mark the flying fox samples that had NiV neutralizing activity at their respective anti-NiV-G antibody levels (MFI).