Abstract
BackgroundMetastrongyloid parasites Angiostrongylus vasorum and Crenosoma vulpis infect wild and domestic canids and are important pathogens in dogs. Recent studies indicate that gastropod intermediate hosts infected with various metastrongyloids spontaneously shed infective third-stage larvae (L3) into the environment via feces and mucus under laboratory conditions. Shed L3 retain motility up to 120 days, but whether they retain infectivity was unknown.MethodsTo assess the infectivity of shed L3, the heart/lungs of six red foxes (Vulpes vulpes) were obtained from trappers in Newfoundland, Canada. Lungs were examined for first-stage larvae (L1) by the Baermann technique. A high number of viable A. vasorum L1 and a low number of C. vulpis L1 were recovered from one fox; these were used to infect naïve laboratory-raised Limax maximus. L3 recovered from slugs by artificial digestion were fed to two naïve purpose-bred research beagles (100 L3/dog). L1 shed by these two dogs was used to infect 546 L. maximus (2000–10,000 L1/slug). L3 shedding was induced by anesthetizing slugs in soda water and transferring them into warm (45 °C) tap water for at least 8 h. Shed L3 recovered from slugs were aliquoted on romaine lettuce in six-well tissue culture plates (80–500 L3/well) and stored at 16 °C/75% relative humidity. Four naïve research beagles were then exposed to 100 L3/dog from larvae stored for 0, 2, 4, or 8 weeks, respectively, after shedding.ResultsAll four dogs began shedding C. vulpis L1 by 26–36 days post-infection (PI). All four dogs began shedding A. vasorum L1 by 50 days PI.ConclusionsL3 infectivity for the definitive host was retained in both metastrongyloids, indicating the potential for natural infection in dogs through exposure from environmental contamination. As an additional exposure route, eating or licking plant or other material(s) contaminated with metastrongyloid L3 could dramatically increase the number of dogs at risk of infection from these parasites.Graphical
Highlights
Metastrongyloid parasites Angiostrongylus vasorum and Crenosoma vulpis infect wild and domestic canids and are important pathogens in dogs
Angiostrongylus vasorum First-stage larvae (L1) were recovered from the lung tissue of all six red foxes; high numbers of vigorously motile A. vasorum L1 were only recovered from one fox
The ability of Third-stage larvae (L3) to survive for that length of time outside of a host is inconsistent with the previous view of the transmission of these parasites; if an infection is only acquired by the ingestion of L3 contained in tissues, the larvae would be unlikely to have developed the ability to survive free in the environment
Summary
Metastrongyloid parasites Angiostrongylus vasorum and Crenosoma vulpis infect wild and domestic canids and are important pathogens in dogs. Recent studies indicate that gastropod intermediate hosts infected with various metastrongyloids spontaneously shed infective third-stage larvae (L3) into the environment via feces and mucus under laboratory conditions. Five of the seven Metastrongyloidea families have species requiring a gastropod intermediate host for larval development from the firststage (L1) to the infective third-stage (L3). Robbins et al Parasites Vectors (2021) 14:307 host infection with these metastrongyloids was previously thought to occur solely through the ingestion of L3 contained in the tissues of the gastropod intermediate host or, for some species, a paratenic host [1]. Recent laboratory studies have shown that gastropod shedding of L3 in feces and mucus into the environment is widespread throughout the metastrongyloids. Shedding has been reported in the Angiostrongylidae (Aelurostrongylus abstrusus, Angiostrongylus cantonensis, Angiostrongylus costaricensis, Angiostrongylus vasorum), Crenosomatidae (Crenosoma vulpis, Troglostrongylus brevior, Troglostrongylus wilsoni), and Filaroididae (Oslerus rostratus) [6,7,8,9,10,11,12,13]
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