Summary: mapping the spread of a dangerous parasite
Angiostrongylus cantonensis, the rat lungworm, is an emerging zoonotic threat linked to eosinophilic meningitis in humans. A comprehensive field study conducted in four Philippine provinces (Agusan del Sur, Davao del Sur, Laguna, and Surigao del Norte) reveals substantial prevalence of Angiostrongylus spp. in wild rats, including evidence of two distinct species: A. cantonensis and A. malaysiensis. The work underscores new endemic foci on Mindanao, expands knowledge beyond Luzon, and highlights the need for integrated surveillance of rats, snails, and other intermediate hosts to prevent human infections.
Where the study was done and why it matters
The cross-sectional study targeted communities with close human-rodent interaction and traditional practices such as consuming raw snails. Rat trapping occurred from 2019 to 2023, with sampling limited by environmental permits to 240 rats across four provinces. The choice of Mindanao sites, alongside Luzon data, addresses a critical knowledge gap about Angiostrongylus distribution in the Philippines and informs risk assessments for foodborne transmission pathways.
Methods at a glance: how researchers detected Angiostrongylus
Researchers collected lungs and hearts from adult Rattus spp., screened for adult worms, and used artificial gastric digestion to recover larvae. Molecular identification relied on SSU-rRNA and COI gene sequences to distinguish A. cantonensis from A. malaysiensis. In total, 126 rats across four species were analyzed, with 37.3% testing positive for Angiostrongylus spp. The team also performed robust statistical analyses to explore potential risk factors and employed multiple phylogenetic approaches to interpret sequence data.
Key findings: prevalence, hosts, and species mix
- Overall prevalence: 37.3% of tested rats carried Angiostrongylus spp.
- Geo-variation: Agusan del Sur showed the highest prevalence (79.17%), Laguna 23.53%, Surigao del Norte 19.23%, while Davao del Sur had no detections.
- Rat hosts: R. exulans and R. tanezumi showed higher infection rates than R. norvegicus, suggesting species-specific dynamics but with no single host clearly driving risk across all sites.
- Species detected: Both A. cantonensis and A. malaysiensis were found. In Laguna, worms were 100% A. cantonensis; in Agusan del Sur, a mix of A. cantonensis and A. malaysiensis was observed, indicating overlapping endemicity.
Molecular insights: what the DNA tells us
SSU-rRNA results placed Philippine A. cantonensis within a global genotype cluster, while COI analysis revealed higher intraspecific diversity and clear geographic structuring. Notably, Philippine A. cantonensis COI haplotype Ac5 clustered with strains from Japan, Brazil, the USA, and French Polynesia, reflecting a complex, transborder parasite history. Philippine A. malaysiensis COI sequences aligned with Malaysian and Thai isolates, highlighting regional connections and ongoing introductions.
Implications for public health and future research
The discovery of new endemic foci on Mindanao confirms that the Philippines is not yet free of Angiostrongylus threats in wildlife. The focal distribution aligns with snail intermediate host ecology, suggesting that disease risk is not uniform across landscapes. The coexistence of A. cantonensis and A. malaysiensis in at least one area raises questions about pathogenic potential and interactions between species, including the possibility of hybrids. These findings support expanding surveillance to include intermediate hosts and human exposure pathways, particularly in rural, rice-field environments where contact between humans, rats, and snails is common.
Limitations and next steps
Limitations include incomplete sampling in some regions and the absence of sequences from Surigao del Norte larvae due to technical issues. Future work should increase sample sizes, incorporate snail and other intermediate hosts, and pursue full-genome sequencing to deepen phylogeographic understanding and monitor potential shifts in endemicity due to climate change or human movement.
Conclusion
The Philippine study offers the first molecular confirmation of Angiostrongylus spp. in Mindanao rats and documents both A. cantonensis and A. malaysiensis in selected communities. The results call for heightened, region-wide surveillance and targeted public health messaging about food safety and snail consumption practices to mitigate the risk of neuroangiostrongyliasis.
