Host transmission dynamics of first- and third-stage Angiostrongylus cantonensis larvae in Bullastra lessoni

Abstract

Given the importance of angiostrongyliasis as an emerging infectious disease of humans, companion animals, and wildlife, the current study focused on the transmission dynamics of first- and third-stage larvae of the parasitic nematode, Angiostrongylus cantonensis. The migration of infective larvae and their subsequent distribution within the Lymnaeidae snail, Bullastra lessoni, were investigated over time using microscopic examination of histological sections and fresh tissue. Snails were divided into four anatomical regions: (i) anterior and (ii) posterior cephalopedal masses, (iii) mantle skirt and (iv) visceral mass. The viability of free-swimming third-stage larvae, after their release from snail tissues, was evaluated in vitro by propidium iodide staining and infectivity by in vivo infection of Wistar rats. Snails were sequentially dissected over time to assess the number and anatomical distribution of larvae within each snail and hence infer their migration pathway. Herein, ongoing larval migratory activity was detected over 28 days post-infection. A comparison of infection rates and the larval distribution within the four designated snail regions demonstrated a significant relationship between anatomical region and density of infective larvae, with larvae mostly distributed in the anterior cephalopedal mass (43.6 ± 10.8%) and the mantle skirt (33.0 ± 8.8%). Propidium iodide staining showed that free-swimming third-stage larvae retained viability for between 4 and 8 weeks when stored under laboratory conditions. In contrast to viability, larval infectivity in rats remained for up to 2 weeks only. Knowledge gained from the current work could provide information on the development of new approaches to controlling the transmission of this parasite.

Stressed snails release Angiostrongylus cantonensis (rat lungworm) larvae in their slime

“…1 ). Prior studies have shown that A. cantonensis L3 shed from snails were infectious to rats [ 45 , 49 , 50 ]. Infectivity of shed larvae has also been confirmed in the congeneric A. vasorum [ 51 ].…”

Potential intermediate hosts of Angiostrongylus cantonensis in the European Mediterranean region (Mallorca, Spain)

“…We should take into consideration that the sensitivity of the sequence-based identification of A. cantonensis is limited when it comes to mild infections [ 33 ]. Furthermore, recent studies suggest that the parasite may be at higher densities in the anterior part of the gastropod [ 34 ]. However, these data should be taken cautiously as explained by Cowie et al [ 35 ].…”

Rat lungworm (Angiostrongylus cantonensis) active larval emergence from deceased bubble pond snails (Bullastra lessoni) into water

“…A population of Angiostrongylus-free snails, and a separate tank of long-term infected snails are currently maintained at Westmead Hospital. The infected snail population is regularly maintained by exposing groups of naïve snails (kept separately) to thousands of L1s in a large glass Petri dish, and adding them to the infected tankas described in Pai et al (2022). Throughout the duration of these experiments, all B. lessoni were held in 25°C and 80% humidity aquarium tanks fitted with an air pump, and crushed marble substrate.…”

“…Larvae manually liberated via digestion from gastropod tissue 3 weeks ( = 21 days) after infection with A. cantonensis were infective to rats (Wang et al ., 2012 ). Recent experiments investigating the active migration of A. cantonensis L3s out of dead/dying gastropods when drowned are scarce, and in both cases the snails and slugs were at least 37 days post-infection (DPI) before submersion experiments were undertaken (Modrý et al ., 2020 ; Pai et al ., 2022 ). Early studies on emerged larvae's infectivity to rats either used naturally infected gastropods or did not disclose how long the gastropod was infected prior to passage (Cheng and Alicata, 1964 ; Richards and Merritt, 1967 ; Crook et al ., 1971 ).…”