Epidemiological Surveillance of the Zoonotic Rat Lungworm (Angiostrongylus cantonensis) in Rats in Mainland Spain.

Norway rats (Rattus norvegicus) and black rats (Rattus rattus) are the definitive hosts and primary reservoirs of Angiostrongylus cantonensis, an emerging zoonotic parasite globally considered the leading cause of human eosinophilic meningoencephalitis. A. cantonensis surveillance in rodent populations in Europe has been conducted in restricted geographic areas, but large-scale epidemiological studies remain lacking. We aimed to determine the prevalence of A. cantonensis in rat populations across mainland Spain and assess the spatial distribution of the parasite. A prospective cross-sectional study was conducted between 2022 and 2025, comprising a total of 407 individuals (244 Norway rats and 163 black rats). During necropsy, cardiopulmonary tissues were systematically collected and examined under a stereomicroscope for the presence of adult A. cantonensis. In addition, a nested molecular technique was performed to confirm the taxonomic identity of adult nematodes visualized during stereomicroscopic examination. Cardiopulmonary dissection revealed that only two individuals out of 407 (0.5%; 95% CI: 0.1-1.8), both black rats (Rattus rattus) from Valencia (eastern mainland Spain), harboured adult nematodes morphologically compatible with A. cantonensis in the heart. These parasites were successfully sequenced and molecularly confirmed as A. cantonensis, exhibiting 100% nucleotide identity with A. cantonensis sequences previously reported from gastropods in Spain and the USA. These findings evidence a localized distribution of A. cantonensis in rats across mainland Spain. Nevertheless, conducting continuous One Health surveillance of A. cantonensis in Europe is essential to fully understand the epidemiology of this parasite and to assess the associated potential public health risks across the continent.