F. W. Knapp

Amblyomma americanum: Sequential histological analysis of larval and nymphal feeding sites on guinea pigs

The sequential histopathological changes at the tick-host interface resulting from the feeding of immature Amblyomma americanum ticks on guinea pigs were examined. The following parameters were measured: depth of mouthpart penetration, extension of the lesion (dermal cellular infiltrate) from the cavity, size of the cavity beneath the mouthparts and the extension of epidermal and perirostral cement layers from the hypostome. A general description of the type of cells, as well as their abundance, within the cavities and lesions were recorded. Tick length and cuticular thickness were also measured. Larval and nymphal cavities increased substantially from 12 to 72 hr postattachment measuring 46 × 50 μm (width × depth) to 308 × 275 μm for the larva and 133 × 125 to 467 × 567 μm for the nymphs. The lesions also increased during the feeding period, measuring 67 to 275 μm for the larva and 183 to 700 μm for the nymphs. The epidermal and perirostral cement layers at the larval feeding site extended 41 and 6 μm, respectively, from the ticks after 12 hr attachment but at 72 hr were 93 and 9 μm, respectively. At the nymphal feeding sites these parameters were 163 and 41 μm, respectively, after 12 hr attachment. However, at 72 hr the epidermal cement was 242 μm with the perirostral cement measuring 67 μm. The predominant cell types in both larval and nymphal cavities were polymorphonuclear leukocytes (neutrophils), constituting the primary infiltrate, with erythrocytes appearing in large numbers toward the end of the feeding period. Eosinophils were the third most abundant cell type appearing as the secondary infiltrate with some macrophages, lymphocytes, mast cells, fibrocytes, and monocytes. The significance of these cell types in conjunction with the observed histopathological changes are discussed. During the feeding period, larval length increased from 0.46 to 1.27 mm with cuticular thickness increasing from 7 to 17 μm. The cuticles of replete larvae were found to be only 10 μm thick. This decrease (7 μm) was due to body expansion accompanying the final feeding phase. Nymphal length increased from 1.2 to 2.7 mm with cuticular thickness also increasing from 29 to 68 μm. Replete nymphs had a cuticular thickness of 50 μm, a decrease of 18 μm from the measurement after 72 hr attachment.

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.

A temperature study of the overwintering site of the sheep bot fly Oestrus ovis L.

Investigations of the overwintering habits of the sheep bot fly, Oestrus ovis L., necessitated obtaining data on temperatures of the nasal passages and sinuses. Sheep were confined at low atmo- spheric temperatures, and the temperature of their nasal passages, frontal and maxillary sinuses, and body was measured. Throughout the study, the body temperatures were normal, and the sinus tempera- tures remained relatively constant. Temperatures of the nasal passage varied directly with the depth at which the readings were taken and with the atmospheric temperatures. Atmospheric temperatures as low as 10 F probably do not affect the nasal temperature sufficiently to produce quiescence in 0. ovis larvae.