Overview: Emerging threat of Angiostrongylus in the Philippines
Neuroangiostrongyliasis, caused by the zoonotic nematode Angiostrongylus cantonensis, is an increasingly recognized threat to human and animal health. The parasite’s life cycle involves rats as the definitive hosts and snails or other intermediate hosts, with humans incidentally infected through consumption of raw or improperly prepared food, contaminated water, or produce harboring third-stage larvae. While globally widespread, data gaps persist for the Philippines, particularly outside Luzon Island. A recent cross-sectional study expanded surveillance to Mindanao and Luzon, revealing new endemic foci and confirming the presence of two Angiostrongylus species in Philippine rats.
Study scope and locations
The study surveyed 126 rats across four provinces: Agusan del Sur and Surigao del Norte on Mindanao, plus Laguna and Davao del Sur as comparisons on Luzon. The selection targeted areas with observable rodent activity, frequent human-rodent interaction, and cultural practices involving raw mollusks. Trapping occurred over nearly four years (2019–2023), with a total of 240 rats collected from 8 communities. Findings show a striking focal distribution, with Mindanao sites reporting the highest infection rates and Luzon sites showing variable, lower prevalence.
Key findings: Prevalence and host-species patterns
The study found an overall Angiostrongylus spp. prevalence of 37.3% in rats, but highly variable by site: Agusan del Sur 79.2%, Laguna 23.5%, Surigao del Norte 19.2%, and Davao del Sur 0%. Among rat species, infection rates ranged from 11.9% in Rattus norvegicus to 75% in R. exulans, underscoring how host ecology shapes transmission risk. No significant difference emerged between male and female rats, and the broader model suggested that sex and species were not strong predictors of infection, highlighting environmental drivers and local snail populations as pivotal factors.
Molecular insights: Two Angiostrongylus species identified
Using SSU-rRNA and COI gene markers, researchers detected two Angiostrongylus species in Laguna and Agusan del Sur: A. cantonensis and A. malaysiensis. Laguna samples aligned 100% with A. cantonensis, while Agusan del Sur yielded a mix: most worms resembled A. malaysiensis, with one worm matching A. cantonensis. This co-endemicity mirrors patterns seen elsewhere in Asia and indicates diverse Angiostrongylus spp. circulating within the Philippines.
The COI gene demonstrated greater intraspecific variation than SSU-rRNA, enabling a more nuanced view of haplotypes. In the Philippines, A. cantonensis haplotypes clustered with international sequences (Japan, Brazil, USA, French Polynesia), while A. malaysiensis aligned with Malaysia and Thailand isolates. The findings emphasize a complex, interconnected global phylogeography for Angiostrongylus, even as local transmission remains focal.
Public health and veterinary implications
The discovery of concurrent A. cantonensis and A. malaysiensis foci raises concerns about the potential severity of zoonotic infections in humans and animals. A. cantonensis is well-established as a cause of eosinophilic meningitis, but the pathogenicity of A. malaysiensis in humans remains less clear. The dual presence in Mindanao suggests that local public health strategies must address broader environmental risk factors, including snail intermediate hosts in agricultural and rural settings. Enhanced surveillance, including intermediate host sampling, and community education about safe food handling are urgently warranted.
Ecology and drivers of focal distribution
Focal prevalence likely reflects the overlap between rat and snail habitats, particularly in rice-field and irrigation zones. Previous Philippine studies highlighted higher infection in rural versus urban settings, consistent with this study’s Mindanao results. Environmental changes, such as climate-driven shifts in snail populations and flood events, could facilitate the parasite’s spread to new areas, underscoring the need for climate-informed risk mapping and proactive containment efforts.
Conclusions and recommended actions
This work represents the first documented evidence of Angiostrongylus spp. in Philippine rats on Mindanao and confirms simultaneous circulation of A. cantonensis and A. malaysiensis in at least one locality. The data advocate for: (1) expanded, nationwide surveillance integrating rodent and snail hosts; (2) molecular characterization to monitor haplotype diversity and potential hybrids; (3) public health campaigns highlighting safe food practices and intermediate-host risks; and (4) climate-aware models to predict and mitigate future spread. Continued investment in local capacity and cross-border collaborations will be crucial to understanding and curbing this neglected zoonosis.
Acknowledgments and limitations
The authors note sampling limitations in certain provinces and call for broader geographic coverage and deeper molecular analyses, including sequences from additional regions and life stages, to refine the epidemiology of Angiostrongylus spp. in the Philippines.
