Amblyomma americanum: Sequential histological analysis of adult feeding sites on guinea pigs

Abstract

Sequential histological analysis of the lesions caused by the feeding of adult Amblyomma americanum ticks in guinea pigs were examined. Biopsies of female feeding sites were taken at 12, 48, 96, 240 hr (mated and unmated ticks at this time) postattachment and 96 hr postrepletion. Male feeding sites were biopsied at 12, 48, and 96 hr postattachment. The following parameters were measured: size of the cavity beneath the mouthparts, size of the lesion, degree of extension of the epidermal and perirostral cement layers from the tick, and thickness of the female cuticle. The numbers and types of cells within the definitive cavities were also recorded along with a general description of the major cell types in the lesion. At the female feeding sites, all parameters increased progressively from 12 to 96 hr postattachment. Mated female sites biopsied at 240 hr postattachment revealed an increase of all parameters from the 96-hr observation with the exception of perirostral cement which decreased. Unmated female sections also biopsied at 240 hr postattachment showed an increase in only cavity and epidermal cement size, with the other parameters showing a substantial decrease. Analysis of the 96-hr postrepletion biopsies revealed an obvious lesion in the dermis with a small layer of perirostral cement engulfed in a scab-like structure on the epidermal surface. In the cavities formed by feeding females, erythrocytes and neutrophils, and to a lesser extent eosinophils, were the dominant cell types. Within the lesions outside the cavities, neutrophils dominated with eosinophils predominating in the postrepletion biopsies. Analysis of male feeding sites showed no cavities or lesion formation at 12 hr postattachment, but by 48 hr a lesion was apparent. At 96 hr postattachment, the last day of feeding and attachment, a lesion and cavity was observed in each section. Neutrophils and eosinophils dominated the cavities and lesions with only a few erythrocytes apparent. The extent and sequence of tissue damage and cellular infiltration are described and the significance of these reactions is discussed.