To examine the fate of Strongyloides venezuelensis. Mongolian gerbils (Meriones unguicalatus) were orally infected with 1,000 L3 larvae per animal. Altogether, 50 gerbils divided into 5 groups of 10 each were monitored for a period of 570 days to document the kinetics of faecal egg output, adults worm population, morphological development, fecundity, and hematological changes including peripheral blood eosinophilia. This study chronicled a life long parasitism of S. venezuelensis in the gerbil host, and showed that S. venezuelensis infection was quite stable throughout the course of infection and the worms maintained their normal development as evidenced by their body dimension. A progressive loss of body condition of the infected gerbils was observed as the level of infection advanced. However, no detectable pathological changes were observed in the gastrointestinal tract. The present findings indicate that an immunocompetent host, such as the Mongolian gerbil, can serve as a life long carrier model of S. venezuelensis if the worms are not expelled within 570 days after infection.

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 ...