Migration of Strongyloides venezuelensis in Rats after Oral Inoculation of Free-Living Infective Larvae

Abstract

ABSTRACT. Strongyloides venezuelensis (SVZ) infection was chronologically monitored in 85 Sprague-Dawley rats (SDR), which were orally inoculated with approximately 1,000 infective larvae. In order to describe the characteristics of migrating larvae (MLS) in various visceral organs (the liver, lung, cardiac blood, and small intestine), 5 SDR were sacrified at 20 min, 45 min, 1 hr, 2 hr, 3 hr, 4 hr, 8 hr, 12 hr, 16 hr, 48 hr, 72 hr, 96 hr, 120 hr, 144 hr, 168 hr and 192 hr post inoculation (PI). MLS were recovered from the liver a nd blood 20 and 45 min PI and measured 788 ± 26 µm and 846 ± 40 µm in length, respectively. MLS were first observed in the lung tissue 45 min PI and measured 925 ± 38 µm on the average. In the trachea, MLS measuring 849 ± 75 µm appeared 3 to 96 hrs PI. Adult worms (AWS) measuring 1,926 ± 521 µm to 2,956 ± 159 µm in length were observed in the small intestine from 120 hr PI. The worms appeared to mature more than 168 hr PI and attained the average maximum length of 2,420 ± 532 µm. At 3 hr PI focal hyperemic and necrotic lesions were evidently observed in the liver and lung, together with eosinophilic infiltration in the stomach, liver, and lung. The parasites were histologically detectable in the lung tissues but were very difficult to find in the liver and the epithelial layer of small intestine. These data demonstrate that SVZ parasites take 20 min to reach the liver via the stomach and only three hours to reach the trachea through the same route. The development from eggs to adults takes 168 hr in the SDR model. This strongylid invades the host by skin penetration, migrates to the lungs where it molts to the 4th stage larvae, and then travels to the small intestine where it finally molts to mature adults [5,29,35]. The morphologic and kinetic time-lines, however, have not been fully elucidated. Takamure [27] observed intracorporal distribution of migrating filarial parasites (MFP) in Wistar rats and ddy mice from 24 to 96 hr after subcutaneous inoculation, and reported that the MFP were found in the subcutaneous tissue and muscles of rats for 42 hr after exposure. He also described the phenomenon of "concentration" of MFP in the lungs from 45 hr PI adult worms (AWS) appeared in the small intestine just 60 hr PI. On the contrary, the intracorporal migrating course of MLS has not been fully described in orally inoculated animals except the observation that the recovery rate of AWS was lower in the case of oral than in subcutaneous or percutaneous inoculation [26].Strongyloidiasis is a scarcely studied parasite that infects no fewer than 100 million people worldwide, generally in the regions between latitudes 35°N and 30°N. The disease is predominantly distributed in warm moist areas because such climates are suitable for the survival of the larval stage [14,18]. The soil-transmitted nematode, SVZ, occurs in two developmental stages: the free living and parasitic stages. When SVZ infects various species of animals (Mesocricetus auratus, Phodopus campbelli, Cricetulus griseus, Tscherskia ...

Interference of Dexamethasone in the Pulmonary Cycle of Strongyloides venezuelensis in Rats

“…are nematode parasites, generally distributed in warm, moist areas because such climates are suitable for the survival of the larval stage. 1,2 This worm has a complex life cycle (in humans or animals), where the larvae penetrate the skin and travel through the bloodstream to the lungs, where they break into the alveolar spaces, ascend the respiratory tree, are swallowed, and continue their development in the small bowel. 3 The obligate pulmonary phase of the life cycle typically occurs within hours after infection and lasts only a few days before the worms migrate to the intestine, where they develop into adults.…”