Cutaneous changes and cellular infiltration in response to tick attachment in Namaqua Afrikaner, Dorper and South African Mutton Merino sheep

Host immune reaction to tick infestation is crucial for minimizing parasite burdens and reducing the transmission of pathogens, ultimately improving livestock health, welfare and productivity. It is unclear how divergent sheep breeds respond to tick infestation in South Africa. This study explored local cutaneous cellular immune responses in to tick infestation, a critical factor in reducing parasite burdens, limiting disease transmission, and improving livestock health, welfare and productivity. Breed-specific differences in cellular infiltration and skin responses at tick attachment and adjacent non-attachment sites were studied in 89 mature ewes maintained in the same flock. In total, 21 Namaqua Afrikaner (NA), 29 South African Mutton Merino (SAMM) and 39 Dorper ewes were used. Skin biopsies per ewe from both tick attachment and non-attachment control sites were analyzed histologically. The results showed marked variation in immune responses within and between breeds. Although skin changes were generally more pronounced at tick attachment sites across all breeds, four skin defects (spongiosis, apopthosis, necrosis and collagen degeneration) in the NA breed showed no difference between sites. All breeds exhibited similar frequencies of skin defects at tick attachment sites. Cellular infiltration was more common at tick attachment sites, with the NA and SAMM breeds showing more pronounced leukocyte infiltration than the Dorper breed. Notably, basophils, mast cells, and eosinophils were more frequently observed at tick attachment sites in NA sheep compared to the Dorper, followed by occasional increases in the SAMM breed. These findings highlight divergent breed-related immune responses to tick infestation and underscore the role of specific immune cells in mediating resistance, with the NA showing an enhanced response to tick attachment.