Journal of Helminthology (1992) 66, 227-230
Experimental infections with Nematodirus spathiger in rabbits H. HOSTE ;ind G. FORT C.R. INRA Tours-Nouzilly, Station de Pathologie Aviaire et de Parasitologie, F-37380 Nouzilly, France
ABSTRACT The feasibility of infecting laboratory rabbits experimentally with the ovine nematode Nematodirus spathiger was examined. Eight-week-old rabbits were dosed either with 5000 or with 17 000 third-stage larvae and killed on days 10, 21 or 42 post-infection. With the lower dose, 20 to 40% of the inoculum were recovered at necropsy. Similar values were observed with the 17 000 dose on days 10 and 21 postinfection, but on day 42 the worm population was residual (0-6%). With both dose levels, during the course of infection, the worm populations were mainly composed of fourth-stage larvae and worm egg excretion was low. N. spathiger mainly inhabited the proximal jejunum. The results were compared with N. spathiger infection in sheep to assess the usefulness of the rabbit as an experimental model for Nematodirus infection. KEY WORDS: Nematodirus spathiger, rabbit, experimental model, Nematoda
INTRODUCTION
The need for adaptation of parasite nematodes of domestic ruminants to laboratory animals has often been stressed to facilitate studies on worm biology, pathology of infection, anthelminthic efficacy and/or immunological response of the host. However, because of the specificity of the nematodes, only a few models are currently available. Concerning the species inhabiting the small intestine, patent infections with Trichostrongylus colubriformis have been obtained in several laboratory rodents, i.e. mongolian gerbils, guinea-pigs and rabbits and the models have been used in various studies (ROTH WELL & DIN BEN, 1972; HERLICH, 1976; MCLEAN et al., 1987; HOSTE et al., 1988; BEZUBIK et al., 1988). On the other hand, attempts at experimental infections with species of the genus Nematodirus have been less frequent. Although the occurrence of N. filicollis or N. battus has sometimes been recorded in wild rabbits (BOAG, 1972), results on the success of experimental N. battus infections in rabbits are conflicting (GALLIE, 1972; HOPKINS, 1975). Attempts have also been made with N. spathiger but the information on the worm populations was variable (SOMMERVILLE, 1963; KNIGHT, 1977). We have thus conducted more extensive studies on N. spathiger infection in rabbits and the main characteristics of the parasite populations during the course of infection are described in this paper.
MATERIALS AND METHODS
Thirty-two 8-week-old, New Zealand male rabbits were reared under parasite-free conditions. They were allotted to two groups. Group 1 received 50(K) third-stage larvae (L3) of N. spathiger by means of a stomach tube. Group 2 was similarly infected with 17 000 L3. The larvae were cultured from eggs collected from an experimentally infected sheep. Worm egg counts in faeces were determined twice a week from day 14 post infection (PI) until the end of the experiment (RAYNAUD, 1970). Rabbits were killed on day 10 (6 animals per group); on day 21 (5 animals
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per group) and on day 42 (5 animals per group). At necropsy, the small intestines were isolated, divided into segments 50 cm long and frozen. After thawing, the segments were opened longitudinally and washed to collect the lumenal contents. A 0-8% pepsin digestion was performed on the mucosa for 3 h at 37°C. The worm populations were estimated from 10% aliquots of both lumenal contents and mucosal digesta. Sex and stages of N. spathiger were identified (MAPES & COOP, 1972). Analysis of variance and comparison of means (Newman Keuls' test) were used to compare the data between both groups and between the times of necropsy.
RESULTS The main characteristics of the N. spathiger populations are shown in Table I. Worm numbers in Group 2 showed a significant reduction by day 42 post-infection. This reduction was not observed in Group 1 which was given the smaller inoculum of L3. In both groups, worms recovered on days 21 and 42 PI were mostly fourthstage larvae. On day 10 PI, more than 99% of the worm populations were fourthstage larvae. On day 21 PI, the proportion of fifth stage and adult worms was respectively 6 0 and 6-3% in Group 1 and 2. On day 42 PI, 10% of the worm population in Group 1 were adult but the residual population in Group 2 was only composed of fourth-stage larvae. As a consequence of the small number of adult worms, egg counts remained quite low throughout the course of infection. In both groups, the egg excretion in faeces was first detected on day 19 PI. Positive egg counts were observed only in 6/10 animals in group 1 and in 5/9 rabbits in group 2. The maximal mean egg count was 30 eggs per gram faeces. The N. spathiger populations were mainly found in the first half of the small intestine (Fig. 1). In fact, the worms were mainly concentrated in the second 50 cm intestinal segment where at least 45% of the total worm populations were generally recovered irrespective of the date of necropsy and the dose of infection. Only a few worms occupied the distal ileum.
TABLE I.
Characteristics of Nematodirus spathiger populations in the small intestine of rabbits.
Day 10
Duration of infection Day 21
Day 42
Group I: 5(XM) third-stage larvae. Mean total worms Range Percent of initial dose Sex-ratio (a) Number of rabbits
975 (44
Experimental infections with Nematodirus spathiger in rabbits H. HOSTE ;ind G. FORT C.R. INRA Tours-Nouzilly, Station de Pathologie Aviaire et de Parasitologie, F-37380 Nouzilly, France
ABSTRACT The feasibility of infecting laboratory rabbits experimentally with the ovine nematode Nematodirus spathiger was examined. Eight-week-old rabbits were dosed either with 5000 or with 17 000 third-stage larvae and killed on days 10, 21 or 42 post-infection. With the lower dose, 20 to 40% of the inoculum were recovered at necropsy. Similar values were observed with the 17 000 dose on days 10 and 21 postinfection, but on day 42 the worm population was residual (0-6%). With both dose levels, during the course of infection, the worm populations were mainly composed of fourth-stage larvae and worm egg excretion was low. N. spathiger mainly inhabited the proximal jejunum. The results were compared with N. spathiger infection in sheep to assess the usefulness of the rabbit as an experimental model for Nematodirus infection. KEY WORDS: Nematodirus spathiger, rabbit, experimental model, Nematoda
INTRODUCTION
The need for adaptation of parasite nematodes of domestic ruminants to laboratory animals has often been stressed to facilitate studies on worm biology, pathology of infection, anthelminthic efficacy and/or immunological response of the host. However, because of the specificity of the nematodes, only a few models are currently available. Concerning the species inhabiting the small intestine, patent infections with Trichostrongylus colubriformis have been obtained in several laboratory rodents, i.e. mongolian gerbils, guinea-pigs and rabbits and the models have been used in various studies (ROTH WELL & DIN BEN, 1972; HERLICH, 1976; MCLEAN et al., 1987; HOSTE et al., 1988; BEZUBIK et al., 1988). On the other hand, attempts at experimental infections with species of the genus Nematodirus have been less frequent. Although the occurrence of N. filicollis or N. battus has sometimes been recorded in wild rabbits (BOAG, 1972), results on the success of experimental N. battus infections in rabbits are conflicting (GALLIE, 1972; HOPKINS, 1975). Attempts have also been made with N. spathiger but the information on the worm populations was variable (SOMMERVILLE, 1963; KNIGHT, 1977). We have thus conducted more extensive studies on N. spathiger infection in rabbits and the main characteristics of the parasite populations during the course of infection are described in this paper.
MATERIALS AND METHODS
Thirty-two 8-week-old, New Zealand male rabbits were reared under parasite-free conditions. They were allotted to two groups. Group 1 received 50(K) third-stage larvae (L3) of N. spathiger by means of a stomach tube. Group 2 was similarly infected with 17 000 L3. The larvae were cultured from eggs collected from an experimentally infected sheep. Worm egg counts in faeces were determined twice a week from day 14 post infection (PI) until the end of the experiment (RAYNAUD, 1970). Rabbits were killed on day 10 (6 animals per group); on day 21 (5 animals
228
H. HOSTE and G. FORT
per group) and on day 42 (5 animals per group). At necropsy, the small intestines were isolated, divided into segments 50 cm long and frozen. After thawing, the segments were opened longitudinally and washed to collect the lumenal contents. A 0-8% pepsin digestion was performed on the mucosa for 3 h at 37°C. The worm populations were estimated from 10% aliquots of both lumenal contents and mucosal digesta. Sex and stages of N. spathiger were identified (MAPES & COOP, 1972). Analysis of variance and comparison of means (Newman Keuls' test) were used to compare the data between both groups and between the times of necropsy.
RESULTS The main characteristics of the N. spathiger populations are shown in Table I. Worm numbers in Group 2 showed a significant reduction by day 42 post-infection. This reduction was not observed in Group 1 which was given the smaller inoculum of L3. In both groups, worms recovered on days 21 and 42 PI were mostly fourthstage larvae. On day 10 PI, more than 99% of the worm populations were fourthstage larvae. On day 21 PI, the proportion of fifth stage and adult worms was respectively 6 0 and 6-3% in Group 1 and 2. On day 42 PI, 10% of the worm population in Group 1 were adult but the residual population in Group 2 was only composed of fourth-stage larvae. As a consequence of the small number of adult worms, egg counts remained quite low throughout the course of infection. In both groups, the egg excretion in faeces was first detected on day 19 PI. Positive egg counts were observed only in 6/10 animals in group 1 and in 5/9 rabbits in group 2. The maximal mean egg count was 30 eggs per gram faeces. The N. spathiger populations were mainly found in the first half of the small intestine (Fig. 1). In fact, the worms were mainly concentrated in the second 50 cm intestinal segment where at least 45% of the total worm populations were generally recovered irrespective of the date of necropsy and the dose of infection. Only a few worms occupied the distal ileum.
TABLE I.
Characteristics of Nematodirus spathiger populations in the small intestine of rabbits.
Day 10
Duration of infection Day 21
Day 42
Group I: 5(XM) third-stage larvae. Mean total worms Range Percent of initial dose Sex-ratio (a) Number of rabbits
975 (44
