| Summary: | Nematodes life-cycle consists of four larval stages (L1, L2, L3, and L4) and a fifth, adult stage (L5). During this development four molt processes occur. Nevertheless, it seems that this feature is not shared by all nematodes. To date, three larval stages and the adult stage are known for the particular case of Gnathostoma binucleatum Almeyda-Artigas, 1991; thus, the existence of its fourth stage is uncertain. The aim of this investigation was to clarify for the first time the molt processes and the stages that take part in its life cycle, etiological agent of human gnathostomiasis in Mexico. For such purpose, its life cycle was experimentally recreated beginning with fertilized eggs laid by females isolated from gastric tumors of dogs Canis lupus familiaris trapped in Temascal, Oaxaca. The first molt was observed between the first-stage larva and the second-stage larva (L1-L2), inside the egg; the second molt occurred between the L2 and the early-third stage larva (EaL3) in the hemocoel of its first intermediate host (Copepoda: Cyclopoida). In turn, the third molt process was discarded between the EaL3 and the advanced third stage (AdvL3), in livers of second intermediate hosts (Mammalia: Rodentia). Therefore, the remaining molts (third and fourth) were investigated in definitive inadequate (immunosuppressed mice with the aid of a corticosteroid) and suitable (cats) hosts. A single molt was observed in the latter, due to the presence of three types of worms: premolt, molting, and postmolt (L5). Based on the morphological comparison of the above mentioned worms, it is concluded that these nematodes molt only once in its definitive host (AdvL3-L5); in other words, this Gnathostoma species lacks a fourth-stage larva. Thus, nowadays the life cycle of G. binucleatum comprises three larval stages (L1, L2, and L3) and adult forms (L5). El ciclo de vida de los nemátodos está conformado por cuatro estadios larvarios (L1, L2, L3 y L4) y un quinto estadio, el adulto (L5). Durante este desarrollo se llevan a cabo cuatro ...
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