Abstract
Human gnathostomiasis is a food-borne zoonotic helminthic infection widely reported in Latin America, Asia and Southeast Asia, particularly in Thailand. There are increasing reports of the parasite in countries where it is not endemic. A study of the survival drug-treated immature stage (STIM) of Gnathostoma spinigerum recovered from infected patients focused on their integument surface using scanning electron microscopy (SEM). STIM displayed a specific, characteristic head bulb, with a pair of large thick equal-sized trilobulated lips in the centre. Cephalic spines had eight transverse rows on the head bulb with single-ended tips curved posteriorly. Body cuticular spines on the anterior half of the STIM were not sharp-pointed but distributed more densely, with multi-dentated-cuticular spines, irregularly arranged in a lining pattern of velvety cuticular folds. The length of cuticular spines increased caudally. The size of spines became gradually smaller, and numbers decreased towards the posterior end. Spines were still widely dispersed posteriorly as their density dropped. The morphology of STIM of G. spinigerum are described in detail for the first time. These specimens showed structural adaptation based on changes on integument surfaces, probably to protect against damage induced by the toxic effects of albendazole.
Highlights
Human gnathostomiasis is endemic in Thailand and is caused by the random migration of only G. spinigerum larvae
Viable STIM continually moved in saline for several hours after removal from patients
Numerous crooked and wicked cuticular spines, with velvety cuticular folds were distributed on the anterior one-third of the body and these structures were not found in L3, AL3 and fully-grown adult control specimens (Figs 1 and 2)
Summary
Human gnathostomiasis is endemic in Thailand and is caused by the random migration of only G. spinigerum larvae. According to the summary of the Immunodiagnostic unit under the Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, the infection rates of gnathostomiasis from positive results of western blot analysis were 44.5%, 35.0% and 33.4% evaluated during 1995–2005, 2006–2009, 2019–2021, respectively (Unpublished data). These immature helminths cannot develop into mature adult worms, and humans are accidental and dead-end hosts [1–5]. The most common clinical manifestation is associated with advanced third-stage larvae (AL3) Helminths in this stage are localised in intermittent cutaneous migratory swellings.
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