Cutaneous Basophilia in the Resistance of Goats to Amblyomma cajennense Nymphs after Repeated Infestations

The acquisition of resistance in goats against Amblyomma cajennense after repeated infestations and the role of inflammatory cells in this mechanism were investigated. Ten naive goats aged 6 months were distributed into two groups: test (n = 5), infested thrice at 30-day intervals; and control (n = 5), infested once. Nymphs (n = 115 per animal per infestation) were released inside alimentary chambers glued to the animal's dorsum and the following biological parameters were evaluated: yielding rate, nymphal engorgement weight, engorgement period, ecdise rate, and ecdise period. Skin fragments of tick bite sites were collected at 24, 48, 72, and 120 h post attachment for histopathology and inflammatory cells counts. The engorgement weight decreased significantly (P < 0.05) from the first infestation onward; nymphs weighed 41.7% and 37.1% less after the second and third infestations, respectively, as compared to those collected after the first infestation (12.55 mg +/- 3.21). Furthermore, the ecdise period increased significantly (P < 0.05) in the third infestation (18 days +/- 2.83) in comparison with the first infestation (15 days +/- 0.82) and the ecdise rate was significantly lower after the second infestation (71.91% +/- 17.38) in comparison with the first infestation (96.89% +/- 3.38). There were no significant differences with regard to both the engorgement period and yielding rate. A cutaneous basophilia was evidenced between 48 and 72 h (P < 0.05) after both the second and third infestations. We conclude that goats develop resistance against nymphs of A. cajennense and that basophils may play an important role in such a mechanism.