A comparative study on clinical pathology changes in experimentally infected sheep with active and arrested larvae of Haemonchus contortus

Hypobiosis is the larval arrest of parasites and is an adaptation to host and environmental conditions. This study was conducted to compare clinicopathological changes in sheep experimentally infected with fresh and arrested larvae of Haemonchus contortus. Twenty-eight apparently healthy 6-month-old Shal lambs, whose stool samples were eggs per gram (EPG) negative, were divided into four groups: A, B, C and D. Groups A and D received fresh larvae and placebo, respectively. Treatment groups (B and C) were infected by arrested larvae obtained under different conditions such as humidity (B, 70%; C, 40– 50%), temperature (B, 8–10°C; C, 35–37°C) and light intensity (B, low; C, high). Clinical signs were monitored until day 60, haematological examination [hematocrit (Hct), haemoglobin (Hb), red blood cells (RBC), mean corpuscular haemoglobin (MCH), mean corpuscular volume (MCV), mean corpuscular haemoglobin concentration (MCHC), white blood cells (WBC) and differential cell count] and biochemical examination (Ca, Mg, P, total Pro, Alb, Globulins and Alb/Glob ratio) were performed on the first day and 2 months after infection with the larvae. In addition to the faecal egg count, the number of larvae and adult worms were determined in abomasal contents. The mean number of adult worms and faecal egg count in group A were significantly higher than in other groups (p<0.01). The proportion of arrested larvae and percentage of hypobiosis in group B differed significantly from other groups (p<0.05). The body weights of group A, B and C were significantly different compared with group D (p< 0.01). No difference in weight gain was observed between the treatment groups B and C. Considerable reduction in RBC, Hb and PCV were observed in the different treatment groups, but these reductions were highly significant in group A (p<0.05) while MCV, MCH and MCHC did not show any change. The comparison of total WBC and differential cell count between groups indicated the presence of eosinophilia in group A (p<0.0005). Serum protein, albumin and calcium concentration decreased only in group A (p<0.01).