Pathogenesis of susceptible and resistant strains of Haemonchus contortus in sheep
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Date
2007-01
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
Haemonchus contortus is the most pathogenic gastrointestinal nematode of sheep and goats. The anthelmintics are the only practical method to reduce the menace of haemonchosis. The indiscriminate use of anthelmintics has led to emergence of resistant strain/subspecies of H. contortus throughout the world. There are numerous reports of benzimidazole resistance in H. contortus from the world as well as India.
The present study was planned to investigate differences in biological behaviour and pathogenecity of susceptible and FBZ resistant strain of H. contortus. The prepatent period of 17-18 days was recorded for both the strains. The mean total worm recovery of susceptible (1777.5), resistant (2680) and naturally infected sheep (1565) were recorded. The sex ratio, body weight loss and establishment rates were also measured for the both strains. The faecal egg count for susceptible strain 1683±33.0, for resistant strain 3775±118.3 and 1850±99.9 for naturally infected sheep were observed. Significant difference were observed between susceptible and resistant strain for worm count, sex ratio and establishment rates.
The degree of reduction in PCV and Hb% indicated pathogenecity of worms but no significant differences were observed between susceptible and resistant strains. Peripheral eosinophil count and total erythrocytic count indicated significant difference between the two strains. The erythrocytic indices indicated normocytic, normochromic anaemia. The total iron levels of resistant strain infected group decreased significantly as compared to susceptible strain infected group.
The total serum protein reduced from 6.95 ± 0.37 to 582 g/dl, 6.79 ± 0.20 to 3.53 ±0.28 and 6.88 ± 0.19 to 4.92 ± 0.47 from the day of infection to 49 DPI in susceptible, resistant strain infected sheep and sheep infected by grazing, respectively. The serum albumin levels also mirrored similar trends to total serum protein. Thus, hypoproteinaemia and hypoalbuminaemia was significantly more in resistant infected sheep. The serum pepsinogen level increased from 1.10 ± 0.23 to 2.67 ± 0.12 IU tyrosine in susceptible strain, 1.19 ± 0.27 to 3.23 ± 0.31 in resistant strain infected sheep and 1.37 ± 0.25 to 3.22 ± 0.03 IU tyrosine in sheep infected by grazing. Significant differences were recorded with regards to serum pepsinogen level between the two strains indicating higher abomasal damage in resistant strain infected sheep. Thus, it can be inferred that both the strains are different in their biological behaviour and the pathogenecity, with resistant strain being more pathogenic than susceptible strain.
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