Background: Angiostrongylus as a Growing Public Health Concern
Angiostrongylus cantonensis, the rat lungworm, is a zoonotic nematode with a global footprint. It migrates through the host’s lungs when adult worms inhabit the rat’s pulmonary arteries, and humans can become infected by ingesting undercooked or raw snails, slugs, crustaceans, planarians, shrimps, or contaminated produce. In severe cases, larvae can reach the central nervous system, causing eosinophilic meningitis or meningoencephalitis. While patients in many regions contend with this disease, surveillance and diagnosis remain uneven, leaving knowledge gaps in several endemic countries, including the Philippines.
Study Aim and Setting
This cross-sectional study sought to determine the prevalence and molecular identity of Angiostrongylus spp. in rats from selected communities on Luzon and Mindanao. Researchers targeted sites with habitual rodent contact with humans and where raw snail consumption is reported, to assess local endemicity and potential risks to public health and veterinary health alike.
Methods: From Field to Gene
Fieldwork occurred from 2019 to 2023 across four Philippine provinces: Agusan del Sur and Surigao del Norte on Mindanao, plus Laguna on Luzon, with Davao del Sur as a non-endemic comparison site. Live-capture traps were placed near households, and only adult Rattus spp. were studied. Captured rats were humanely euthanized, and lungs and hearts were processed to recover adult worms and larvae. Morphological checks were followed by molecular characterization.
Adult worms were preserved for DNA analyses. Molecular work targeted two genes: a nuclear SSU-rRNA marker for species confirmation and a mitochondrial COI marker for intraspecific variation. PCR and Sanger sequencing allowed comparisons to global GenBank references, enabling robust species identification and phylogenetic placement.
Key Findings: Prevalence and Species Composition
The study collected 126 rats, representing four Rattus species. Overall Angiostrongylus prevalence among rats was 37.3%, with substantial geographic variation: Agusan del Sur showed the highest prevalence at 79.17%, Laguna 23.53%, Surigao del Norte 19.23%, and Davao del Sur reported no infections in sampled rats. Among rat species, R. exulans and R. tanezumi showed the highest infection rates, while R. norvegicus had the lowest.
On the molecular front, a striking finding emerged: two Angiostrongylus species were present in the Philippines. Laguna’s worms aligned with A. cantonensis, whereas Agusan del Sur harbored both A. cantonensis and A. malaysiensis, highlighting regional co-endemicity. In some Laguna samples, all sequences matched A. cantonensis, while Agusan del Sur revealed a mixed infection pattern, underscoring the parasite’s complex distribution in the archipelago.
Phylogenetics and Haplotypes: What the Genes Reveal
Phylogenetic analyses using SSU-rRNA and COI genes demonstrated clear species separation. A. cantonensis isolates from the Philippines clustered with global cohorts (including Japan, Brazil, and the USA) and fell into haplotypes consistent with Ac5 in the COI marker, while A. malaysiensis sequences aligned with Malaysian and Thai isolates. The COI data revealed greater intraspecific diversity than SSU-rRNA, making it especially useful for tracking haplotype distributions and potential introductions across regions.
The presence of both species in Mindanao’s Agusan del Sur indicates a broader, more intricate landscape of Angiostrongylus endemicity than previously recognized. The authors emphasize that environmental factors—such as snail intermediate host ecology and rice-field habitats—likely shape focal transmission patterns and should guide future surveillance and control strategies.
Public Health and Surveillance Implications
These findings underscore the need for expanded surveillance that includes both definitive hosts (rats) and intermediate snail hosts. The observed focal distribution suggests that risk mitigation must be locally tailored, addressing cultural practices such as raw snail consumption and improving food handling and water safety. Given climate change, human movement, and environmental shifts that alter snail distributions, ongoing monitoring is essential to map endemicity and forecast spread.
Limitations and Future Directions
While the study provides valuable insights, it did not obtain molecular data from all regions (Surigao del Norte samples produced some sequencing challenges), and environmental sampling of snail hosts remains limited. Future work should incorporate intermediate hosts and explore whole-genome analyses or additional markers to capture finer-scale diversity and potential hybrids. This will enhance risk assessment and inform targeted interventions for both human and animal health.
Conclusion: A Call for Proactive Action
The first molecular confirmation of Angiostrongylus spp. in Philippine rats outside Luzon, including the coexistence of A. cantonensis and A. malaysiensis, marks a pivotal step in understanding the country’s endemic landscape. Public health authorities should leverage these findings to expand surveillance, educate communities about bite- or ingestion-related risks, and adopt integrated One Health strategies to curb the spread and impact of angiostrongyliasis.
