In cattle, infestation with Psoroptes ovis mites may cause severe
dermatitis (psoroptic
mange) which compromises the health and welfare of the animals and may lead to significant economic losses. To investigate yet undocumented effects of psoroptic
mange mite infestations and how successful therapy promotes animal health, the present study examined alterations of the skin, lymph nodes and adrenal glands of P. ovis infested Fleckvieh (Simmental) bulls treated with either
ivermectin long-acting injection (IVM LAI;
IVOMEC(®)
GOLD, Merial; 3.15%
ivermectin w/v) or saline (n=16 each). Approximately 8 weeks subsequent to experimental infestation with P. ovis, the bulls had developed
mange and were administered either IVM LAI or saline once at 1 mL/50 kg
body weight by
subcutaneous injection. Mite counts were conducted in weekly intervals for determination of efficacy of treatment, and following humane
euthanasia of the animals 8 weeks
after treatment, skin samples from affected (mangy or previously mangy) and unaffected areas, prescapular lymph nodes and adrenal glands were collected for gross and pathohistological examination. In addition, four age-matching, uninfested Simmental bulls were sampled as controls for comparison. No P. ovis mites were detected on any IVM LAI-treated bull after 28 days following treatment whereas saline-treated bulls maintained infestation throughout the study. At sampling (approximately 16 weeks after experimental infestation and 8 weeks following saline or IVM LAI treatment), saline-treated bulls displayed a severe, exsudative
dermatitis with significantly increased skin thickness and inflammatory cell infiltration, significantly enlarged, hyperplastic prescapular lymph nodes, as well as significantly increased adrenal gland weights and volumes as compared to P. ovis-infested, IVM LAI-treated bulls and uninfested controls. Quantitative stereological analysis revealed that the adrenal gland enlargement in P. ovis-infested, saline-treated bulls was due to a selective increase of the volume of the zona fasciculata in the adrenal cortex. Compared to uninfested controls and P. ovis-infested, IVM LAI-treated bulls, the number of epithelial cells in the zona fasciculata was significantly increased in P. ovis-infested, saline-treated bulls, while the zona fasciculata cell volumes did not differ between the three groups of cattle. While the single point determination of serum
cortisol concentrations did not reveal significant differences between the three groups of cattle at tissue sampling, the hyperplastic growth of the adrenal cortex in the P. ovis-infested, saline-treated bulls provides morphologic evidence that a chronic stress reaction is one consequence of
mange mite infestations that can be prevented by efficacious acaricidal treatment.