Biological parameters of Trichostrongylus colubriformis in Meriones unguiculatus

Meriones unguiculatus infected by Haemonchus contortus: evaluation of different experimental protocols

Many important studies on resistance reversion, anthelmintic efficacy and, especially, new molecules with antiparasitic effects are performed in laboratories using gerbils (Meriones unguiculatus) as the experimental model. This study aimed to evaluate the use of corticosteroids (dexamethasone and methylprednisolone acetate) in gerbils experimentally infected with different doses of infective larvae (sheathed or exsheathed) of Haemonchus contortus. In the first experiment, 28 gerbils were divided into seven groups infected by 2-6 × 103 larvae, with or without immunosuppression using corticosteroids. In the second experiment, eight gerbils were divided into two groups infected by 2 × 103 sheathed or exsheathed larvae. For the third assay, seven immunosuppressed gerbils were infected with 2 × 103 sheathed larvae and were killed 15 days post infection (PI). The highest number of parasites was recovered from methylprednisolone-immunosuppressed animals. We observed red and white blood cell alterations and biochemical parameters in infected animals that had undergone immunosuppression with methylprednisolone. We highlight that in the first and second experiments a satisfactory number of worms was recovered using sheathed larvae and immunocompetent animals. When exsheathed larvae were used, the number of worms recovered was unsatisfactory. A considerable larval burden was recovered from immunosuppressed gerbils 15 days PI, and body weight did not influence establishment of larvae.

Inflammatory responses in the intestinal mucosa of gerbils and hamsters experimentally infected with the adult stage of Taenia solium

The inflammatory response in gerbils and hamsters harbouring experimental infections with Taenia solium adult parasites as well as worm burden and duration of infections were examined. For this purpose, non-suppressed or immunosuppressed rodents were infected with eight cysticerci and necropsied at different times up to 35 days post-infection. Cells in the mucosa surrounding the implantation site of T. solium scolices (duodenum-jejunum) and in ileum were counted in stained sections. A competitive enzyme linked immunosorbent assay was used to determine histamine concentration in intestinal fluid. In non-suppressed hosts, an inflammatory reaction developed with scarce macrophages, a slight increase of plasma cells, lymphocytes and fibroblasts, a moderate increase of eosinophils and neutrophils, and high numbers of goblet and mast cells. Goblet cells began to increase at 6 days post-infection and peaked at 13 days post-infection with a four-fold increase with respect to the control group. Mast cells only increased in gerbils starting at 9 days post-infection with an eight-fold increase when cells peaked between 11 and 19 days post-infection. Histamine concentration in intestinal fluid of gerbils had a similar behaviour to mast cells. Minimal increase of mast cells was seen in hamsters. The recovery of tapeworms was inversely related to the number of both cell types, which decreased when tapeworms were eliminated. Infections lasted up to 25 days in gerbils and up to 46 days in hamsters. Worms measured only 1-2 cm in gerbils and up to 40 cm in hamsters. When gerbils were suppressed with the steroid methyl predinisolone, tapeworms could be recovered up to 35 days post-infection and tapeworms measured up to 22 cm, a minor increase of goblet and mast cells was observed and histamine concentration was similar to that in non-infected animals. Our results suggest that expulsion of T. solium in gerbils and hamsters may be related to the increase of goblet cells and mast cells, but these cells may have different roles in each rodent model of taeniosis.

Duration of infection of jirds (Meriones unguiculatus) with Trichostrongylus colubriformis

Jirds (Meriones unguiculatus) were infected with 700 infective larvae (L3) of Trichostrongylus colubriformis. The fecal egg counts (epg) were followed regularly until 340 days postinoculation, and worm numbers were determined on necropsy at 315 and 350 days postinoculation. The epg increased to a peak of 2,600 on day 24 postinoculation. Thereafter, the epg showed continuous decrease from day 31 until day 318 postinoculation. The rates of inoculum recovery were 0.29-1.43% on day 315 and 0.142-0.428% on day 350 postinoculation. On day 315 postinoculation, 12 male worms were recovered from 2 of 3 animals necropsied. On day 350 postinoculation, all 6 animals were infected, and 6 female and 4 male worms were recovered. The systemic IgM, IgG, and intestinal mucous IgA responses were significantly higher in infected groups compared with negative control groups necropsied on 315 and 350 days postinoculation (P < 0.001). These results confirm that the T. colubriformis-jird system is a useful model for studies on the various host-parasite relationships of chronic trichostrongylosis.