Cutaneous and Systemic Pathologic Responses of the West African Dwarf Goat to Sarcoptes Scabiei Infestation

ABSTRACT The pathophysiology of Sarcoptes scabiei infestation in the West African Dwarf goat was evaluated in a natural transmission study. Twenty- five adult male West African Dwarf (WAD) goats consisting of 15 naturally infested goats assigned into three equal groups based on severity of clinical disease as: A (mild infestation), B (moderate infestation), C (severe infestation), and10 healthy WAD goats with no previous history of mange infestation assigned into two equal groups as D (for contact transmission experiment) and uninfested control (E) were used for this study. Parameters assessed at the beginning of the study (week 0) and every two weeks thereafter included packed cell volume (PCV), haemoglobin concentration (Hb), erythrocyte count (EC), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), total leucocyte count (TLC), differential leucocyte count (DLC), total protein, serum albumin, creatinine, adrenal and gonadal steroid hormones concentration (cortisol and testosterone), serum copper, zinc and vitamin A concentrations. At week 6 of the study, goats in the five groups were sacrificed and the testicular and epididymal sperm reserves were determined. Tissue sections of the infested skin of goats from groups A, B, C, D, and the normal control E were processed for histopathological studies. Data generated were analyzed using one-way analysis of variance (ANOVA), and variant means were separated using the Duncan’s multiple range test. Significance was accepted at p < 0.05. There was wide variation in the susceptibility and severity of infestation in the group D goats (in-contact) as only three out of the five goats showed clinical signs of disease by the 6th week while mite was only demonstrated in two out of five by the 6th week. Lesions were anterio-posterior in distribution. There were significant (p < 0.05) reductions in PCV, Hb and EC mean values of the goats naturally infested with Sarcoptes scabiei in groups A, B and C relative to uninfested control group E at weeks 0, 2 and 4, but at week 6 all the infested groups including in-contact group D had a significantly (p < 0.05) lower PCV, Hb and EC compared to the control group E. There were no significant (p > 0.05) differences in some erythrocytic indices (MCV, MCH, MCHC) among the five groups of WAD goats. However, there was a significant (p < 0.05) increase in mean TLC in groups B and C compared to groups A, D and the control, E. The increase in TLC was accompanied by a significant (p < 0.05) increase in both the absolute neutrophil and lymphocyte counts in groups B and C compared to groups A and E. Significant (p < 0.05) difference in the mean monocyte count was only observed among the groups at week 6 in the group C compared to A, B, D and E. There was a significant (p < 0.05) increase in mean eosinophil count in groups A and B compared to groups C, D and E throughout the period of study. Serum biochemical assay showed significant (p < 0.05) reduction in mean total protein in severely infested group C compared to groups A, B, D and E. There was no significant (p > 0.05) variation in mean serum albumin, globulin and creatinine levels among the groups throughout the period of study. The serum copper concentration was significantly (p < 0.05) lower in the naturally infested groups A, B and C when compared to in-contact group D and control group E. There were no significant (p > 0.05) differences in the serum vitamin A and zinc levels between the groups although their levels were lower in naturally infested groups A, B, and C when compared to groups D and E. Although serum cortisol and testosterone concentrations were lower in the naturally infested groups A, B and C when compared to the in-contact group D and control group E, the differences were not statistically significant (p > 0.05). The mean testicular and epididymal sperm reserves decreased significantly (p < 0.05) in all the Sarcoptes scabiei-infested groups A, B, C and D when compared to the control group E. Skin section of infested goats showed variable degrees of acanthosis, hyperkeratosis, parakeratosis 8 and intracorneal pustules while the dermis had variable degrees of cellular infiltrate (neutrophils, eosinophils, lymphocytes) and fibroblast proliferation. This study has established that sarcoptic mange in WAD goat led to decreased red blood cell counts, haemoglobin, packed cell volume (anaemia) but increased total white blood cell counts, neutrophils and lymphocytes. Serum biochemistry also indicated decreased total serum protein, albumin, copper, zinc, and vitamin A levels but increased creatinine. The most striking feature of the disease in WAD goats was the decreased testosterone levels and spermatogenesis. Histopathologic investigations showed that sarcoptic mange was associated with non-specific skin reactions such as parakeratosis, hyperkeratosis, acanthosis but most importantly epidermal pustules with varying degrees of dermal/epidermal cellular infiltration (neutrophils, eosinophils, lymphocytes) and dermal fibrosis.