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 Hawaiʻi since the 1950's. An increase in cases is being reported primarily from East Hawaiʻi 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 slugs and snails can contaminate water and 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 72–96 hours post drowning. 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 μm, 10 μm, 5 μm, and 1 μm filtration ratings, but not a 5 μm carbon block filter. These results demonstrate that live, infective-stage A . cantonensis larvae emerge from drowned snails and slugs, survive for extended periods of time in water, and may be able to enter a catchment user's 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.

Rainwater catchment on Hawai‘i Island

“…The semi-slugs often line the sides of the tank then drown as water levels rise with the rain, as they fall or get washed in. The microscopic parasitic worm escapes the drowned semi-slug and has survived 21 days in fresh water at the University of Hawai'i at Hilo School of Pharmacy's research lab (Howe et al, 2019). Infections of the A. cantonensis can cause moderate to severe brain damage to those who ingest the parasites, the damage relative to the quantity of parasitic worms entering the body (Jarvi et al, 2018).…”

“…Infections of the A. cantonensis can cause moderate to severe brain damage to those who ingest the parasites, the damage relative to the quantity of parasitic worms entering the body (Jarvi et al, 2018). Since the infectious worms have been observed migrating to the bottom of the water column (Howe et al, 2019) where the water intake valves are normally located, it is assumed that the chance of getting a high dose of parasites from an infested tank is possible. New studies from the University of Hawai'i Hilo School of Pharmacy show that treatment systems previously thought sufficient may not be adequate for blocking this new waterborne threat (Howe et al, 2019).…”

Validation of a death assay for Angiostrongylus cantonensis larvae (L3) using propidium iodide in a rat model (Rattus norvegicus)

“…Parmarion martensi are semi-slugs known to have high infection levels of A. cantonensis in Hawaii (Hollingsworth et al, 2007). Semi-slugs were collected from the University of Hawaii at Hilo campus and immersed in 50 mL dH 2 O in 50 mL Falcon tubes for 72 h. The bottom 15 mL from each tube was transferred to a culture plate (100 mm × 15 mm) (Howe et al, 2019) and observations were made under a dissection microscope (Wild Heerbrugg M4A APO) at 10-40× to detect the presence of larvae. Live larvae with S and Q swimming movements attributed to A. cantonensis L3 larvae (Lv et al, 2009) were collected using a 20 µL micropipette and transferred into 0.5% pepsin-0.5% HCl (pH 1.41) solution for 30 min at room temperature (Ash, 1970;Wang et al, 1991).…”

“…Tissue samples were stored frozen until DNA was extracted for PCR. DNA extractions and real-time PCR were carried out as described (Jarvi et al, 2012;Howe et al, 2019).…”

“…The L3 stage is the only stage known to infect vertebrate hosts, including the definitive (rat) host and accidental hosts such as humans (Mackerras and Sandars, 1955). Transmission to humans is thought to be due to ingestion of L3 larvae in infected gastropods, on improperly washed produce (Heyneman and Lim, 1967;Wang et al, 2008) or in contaminated water (Cheng and Alicata, 1964;Richards and Merritt, 1967;Crook et al, 1971;Howe et al, 2019). The invasive semi-slug, Parmarion martensi, is an extremely efficient host and is thought to be the primary cause of the increase in severe neuroangiostrongyliasis in Hawaii since its introduction in 2004(Hollingsworth et al, 2007Jarvi et al, 2018).…”