Water transmission potential of Angiostrongylus cantonensis: larval viability, and effectiveness of rainwater catchment sediment filters

Abstract

Neuroangiostrongyliasis, caused by Angiostrongylus cantonensis, has been reported in Hawai i since the 1950s. An increase in cases is being reported primarily from East Hawai i Island, correlated with the introduction of the semi-slug Parmarion martensi. Households in areas lacking infrastructure for water must use rainwater catchment as their primary domestic water supply, for which there is no federal, state, or county regulation. Despite evidence that contaminated water can cause infection, regulatory bodies have not addressed this potential transmission route. This study evaluates: 1) the emergence of live, infective-stage A. cantonensis larvae from drowned, non-native, pestiforous gastropods; 2) larvae location in an undisturbed water column; 3) longevity of free-living larvae in water; and 4) effectiveness of rainwater catchment filters in blocking infective-stage larvae. Larvae were shed from minced and whole gastropods drowned in either municipal water or rainwater with >94% of larvae recovered from the bottom of the water column. Infective-stage larvae were active for 21 days in municipal water. Histological sectioning of P. martensi showed proximity of nematode larvae to the body wall of the gastropod, consistent with the potential for shedding of larvae in slime. Gastropod tissue squashes showed effectivity as a quick screening method. Live, infective-stage larvae were able to traverse rainwater catchment polypropylene sediment filters of 20 m, 10 m, 5 m, and 1 m filtration ratings, but not a 5 m carbon block filter. These results demonstrate that live, infective-stage A. cantonensis larvae can and do emerge from drowned snails and slugs, survive for extended periods of time in water, and that the potential exists that they enter the household water supply. This study illustrates the need to better investigate and understand the potential role of contaminated water as a transmission route for neuroangiostrongyliasis.