Correlates of resistance to gastrointestinal nematode infection in Nigerian West African dwarf sheep.

OBJECTIVE: To investigate correlates of resistance to GI nematode infection in Nigerian West African dwarf (WAD) sheep. METHODS: Thirty three sheep were randomly assigned to two groups, A (n=27) which were used for experimental infections, and B (n=6) which served as uninfected control. Each infected animal received weekly escalating infections with infective larvae (60%Haemonchus contortus (H. contortus) and 40%Trichostrongylus colubriformis (T. colubriformis) for 4 weeks. The responses of all the infected and control sheep were assessed by faecal egg count (FEC), worm burden (Wb), packed cell volume (PCV), body weight (Bwt), and body condition score (BCS). On the basis of their individual faecal egg output, Lambs in group A with epg ≤1,000 on any sampling day were classified as low faecal egg count (LFEC) phenotype (n=16), those with epg between 1,000 and 10,000 as intermediate (n=5) and lambs with epg > 10,000 as high feacal egg count (HFEC) phenotype (n=6). RESULTS: The difference between the FEC classes was highly significant (P=0.001). The BCS and weight gained at the end of the experiment by the control and LFEC sheep was significantly higher (P≤0.05) than those of the intermediate and HFEC phenotypes. There was a significant and negative correlation between the parasitological measures and the trio of BCS, PCV and Bwt of sheep. CONCLUSION: The result of the study indicated that the FEC, weight gain, PCV, and BCS are correlates and potential selection criteria of GI nematode resistant WAD sheep.

Changes in the body condition scores of Nigerian West African Dwarf sheep experimentally infected with mixed infections of Haemonchus contortus and Trichostrongylus colubriformis.

Weekly changes in body condition scores and body weights were determined in West African Dwarf sheep following trickle exposure to weekly escalating mixed infections with Haemonchus contortus and Trichostrongylus colubriformis starting with single doses of 500 infective larvae (L(3)) at wk1, 1000 L(3) at wk2, 2000 L(3) at wk3 and 4000 L(3) at wk4. Thirty-three animals were randomly assigned to two groups namely, Group 1 (n=27) and Group 2 (n=6). Group 1 animals were used for experimental infections and Group 2 animals served as uninfected controls. Body condition scores (BCS), body weights (BW), faecal egg counts (FEC) per gram of faeces and worm burden (Wb) were determined using standard procedures. Lambs in group 1 with epg ≤ 1000 were classified as strong responders (n=16), those with epg between 1000 and 10,000 as intermediate (n=5) and lambs with epg>10,000 on any sampling day were classified as weak responders (n=6). Based on this classification, the mean epg of lambs classified as strong responders was significantly lower (P<0.001) than the epg of lambs classified as weak responders. The body condition scores and body weights of the strong responder lambs were comparable with those of the uninfected control and they were significantly higher than those of the weak and intermediate responders from wk5 till the end of the experiment. There was an inverse and significant relationship between the average BCS of days 56 and 59 and the average FEC of days 56 and 59 (r(s)=-572; P=0.017; n=27) as well as with Wb (r(s)=-531; P=0.028; n=27). We concluded that changes in the body scores are good indicators of the intensity of gastrointestinal nematode infection in the Nigerian WAD sheep.

Responses of the humid zone ecotype of the Nigerian West African Dwarf sheep to mixed infections with Haemonchus contortus and Trichostrongylus colubriformis.

The responses of the Nigerian West African Dwarf sheep to experimental infections with two of its most important gastrointestinal (GI) nematodes, namely, Haemonchus contortus and Trichostrongylus colubriformis were studied by means of two measures of parasitological response, namely, faecal egg count (FEC) and worm burden (Wb), and three measures of host pathology, namely, packed cell volume (PCV), body weight (Bwt) and body condition score (BCS). Following exposure to weekly escalating infections (60% H. contortus and 40% T. colubriformis) starting with single doses of 500 infective larvae (L(3)) at week 1, 1,000 L(3) at week 2, 2,000 L(3) at week 3 and 4,000 L(3) at week 4, two distinctive worm burden response phenotypes were readily recognisable, namely, low Wb (LWb) and high Wb (HWb) phenotypes. The percentage of inoculums (adults and immature stages) recovered at necropsy were 3.75% and 33.08% respectively for H. contortus and T. colubriformis. The results showed that the FECs of the lambs belonging to the LWb phenotype were significantly lower than the FECs of their HWb counterpart. Among the measures of host pathology tested, the LWb phenotype sheep had similar Bwt, PCV and BCS to the uninfected control sheep, whereas the HWb phenotype sheep had significantly lower values than their LWb counterparts and the control sheep towards the end of the experiment. There was a highly significant positive correlation between worm burden transformed as log(10) (Wb + 10) and the average of D56 and D59 FECs. A highly significant negative correlation also was obtained between log(10) (Wb + 10) and the PCV, Bwt and BCS. The low percentage of H. contortus inoculums recovered at necropsy suggested that the sheep may be resistant to their most important GI nematode, H. contortus but less so to T. colubriformis.

The effects of combination of methanolic leaf extract of Azadirachta indica and diminazene diaceturate in the treatment of experimental Trypanosoma brucei brucei infection in rats.

OBJECTIVE: To investigate the effects of combination therapy of methanolic leaf extract of Azadirachta indica (A. indica) and diminazene diaceturate (DDA) in the treatment of experimental Trypanosoma brucei brucei (T. brucei brucei) infection in rats. METHODS: Acute toxicity study of the drug and extract combinations were done. Selection of the best drug and extract combinations was carried out using fifty four rats of both sexes separated into 9 groups. Three dose combinations were derived from selection of the best drug and extract combinations used for the final study viz: 7 mg/kg bw DDA plus 125 mg/kg bw extract (group B), 3.5 mg/kg bw DDA plus 250 mg/kg bw extract (group C), and 1.8 mg/kg bw DDA plus 500 mg/kg bw extract (group D). The final study had in addition to the three groups derived from the dose response study, four other groups viz: uninfected untreated negative control (group F), infected and treated with 3 000 mg/kg bw extract alone (group E), infected and treated with 7 mg/kg bw DDA alone (group A), and infected untreated positive control (group G). The parameters assessed were onset of parasitaemia (OP), level of parasitaemia (LOP), clearance of parasites post treatment (COPPT), relapse infection period (RIP), post infection survival period (PIST). RESULTS: There was no significant difference in OP between the groups (P < 0.05). One day post treatment, the mean LOP of groups A, B, and C were found to be significantly lower than that of group D which in turn was lower than that of group E and G respectively. The mean LOP of group E was significantly lower than group G two days post treatment and this trend continued throughout the experimental period. Mean COPPT of group D was significantly longer than that of groups A, C and B. There was no significant difference in the mean COPPT among groups B, C and A. The mean RIP of group D was significantly shorter than group C, and that of group C was significantly shorter than that of group A. There was no relapse of infection in group B. The PIST of group E did not differ significantly from group G. CONCLUSIONS: This experiment stands to conclude that combination of 125 mg/kg bw extract and 7 mg/kg bw DDA is very effective in the treatment of trypanosomosis, caused by T. brucei. This combination therapy proved to be better than single therapy of DDA.