Surveillance of land molluscs infected by Angiostrongylus cantonensis (Nematoda) reveals risk areas for zoonotic eosinophilic meningitis in the State of Rio de Janeiro, Brazil.

Background: The nematode Angiostrongylus cantonensis, which is endemic to Southeast Asia and adjacent Pacific Islands, has already been recorded in more than 30 countries, including Brazil and other South American nations. It is one of the principal etiological agents of the zoonosis Eosinophilic Meningitis (EoM), which has a number of different species of terrestrial gastropods that act as its intermediate hosts.

Objective: The present study investigated the occurrence of the larvae of this nematode in specimens of terrestrial molluscs collected in half of the municipalities of the Brazilian State of Rio de Janeiro.

Methods: The study is based on the surveillance of this nematode in the Brazilian State of Rio de Janeiro, where terrestrial snails and slugs were collected in more than half of the state's municipalities (46 in all), and examined for parasitological infections. The nematode larvae retrieved from these specimens were identified based on their morphology and cytochrome oxidase I (COI) mitochondrial DNA sequences.

Findings: Angiostrongylid larvae were found in 230 (8.8%) of the 2,600 terrestrial molluscs examined, collected from 26 municipalities. Overall, 14 terrestrial gastropod species were identified, including both native and exotic taxa, and six were found to be infected naturally by A. cantonensis. The natural infection rates by Angiostrongylus in the different terrestrial molluscs species were 12.5% in Angustipes erinaceus, 9.7% in Achatina fulica, 6.8% in Bradybaena similaris, 6.3% in Sarasinula linguaeformis, 3.9% in Leptinaria unilamellata, and 4.6% in Subulina octona. A. fulica was the most frequent and extensively distributed species, with infected snails being found in 22 municipalities.

Main Conclusions: The data from this first comprehensive survey of A. cantonensis in Rio de Janeiro highlights the potential epidemiological risk of human infection in this state. Mapping the spread of infected molluscs will also provide essential information for the evaluation of the risk of human infection, and should help local health authorities to provide a faster and more accurate diagnosis whenever neuroangiostrongyliasis is suspected.