New data on the life cycle of Nippostrongylus brasiliensis (Travassos, 1914) (Nematoda: Heligmosomidae): development of eggs and larval stages in the intestine of naturally infected Rattus norvegicus (Berkenhout, 1769).

Nippostrongylus brasiliensis is an intestinal parasite of rodents with a worldwide distribution. Due to the similarities between its life cycle and that of the human hookworms Ancylostoma duodenale and Necator americanus, N. brasiliensis has been widely used as a model in experimental research. We provide new data on the embryonation and hatching processes of N. brasiliensis eggs, not in the soil, but in the large intestine of naturally infected Rattus norvegicus. The parasite was investigated in 109 rats trapped in urban and periurban areas of Valencia, Spain. Rats were preserved at - 20 °C. After thawing, all the rat organs were examined. The contents of the large intestine were analysed by the Midi-Parasep® technique. N. brasiliensis (adult prevalence 69.72%) was identified by morphological and molecular techniques. Parasite eggs were found in 88.16% of the sediments. In addition to unembryonated eggs, eggs in different stages of embryonation were encountered in 67 of the 76 contents (88.16%). Free larval stages (L1 and more developed larvae) were also found in 47 of the 76 (61.84%) sediments studied. Filariform larval stages of N. brasiliensis were also sporadically detected in the lungs of the infected rats. According to our results, the development of eggs and larvae in the intestine of naturally infected rats opens up the possibility of autoinfection in the natural life cycle of N. brasiliensis, which could explain the high burdens of adult stages frequently found in the small intestine of infected rats.