Gnathostomiasis in Assam: I. On the prevalence of Gnathostoma spinigerum larvae in fishes, experimental infection in first and second intermediate host with a description of an advanced third stage larva recovered from Opiocephalus punctatus

A total of 4520 freshwater fishes (29 different species) were examined for the presence of larval helminths in Assam (India) over a period of one year. Overall larval helminth was found in 1369 (30.28%) fishes, of which, 21 (0.4%) and 1348 (29.82%) numbers had L₃G. spinigerum and other helminth larvae, respectively. Opiocephalus punctatus harboured L₃G. spinigerum larvae (3.09%), distributed in muscles only. Morphology of L₃G. spinigerum recovered from O. punctatus in experimental infection was also studied. The larva measured 2.1426 X 0.3007 mm, contained a distinct globular head bulb with 4 rows of uninterrupted hooklets, the approximate number being 40, 42, 48 and 52 from 1^st to 4^th row, respectively. Hooklets in the first three rows appeared rectangular and the last row triangular in shape. Length of 1^st row hooklet was smallest, 2^nd and 3^rd being the same and the 4^th row was largest. Both LM and SEM studies revealed two transverse pseudolabia surrounding the oral opening, containing two labial papillae in each with an amphid in between. The entire larval body was covered with numerous rows of single pointed spines up to the end of the body, the length and density of which varied from anterior to the posterior.