Morphology of the second‐ and third‐instar larvae of Dermatobia hominis by scanning electron microscopy

Abstract

Larvae of Dermatobia hominis 10-27 days old were collected from experimentally infected rats and their morphology was studied by scanning electron microscopy. The moult from the second to third instar occurs at 18 days, with emergence from the host at 30 days post-infection. The second-instar larvae bear on the pseudocephalon, antennae (coeloconic sensilla), and coeloconic and basicoconic sensilla on the maxillary sensory complex. The thoracic segments bear small backwardly-directed spines anteriorly and ventral trichoid and campaniform sensilla. The first four abdominal segments have small and large backwardly-directed spines that are absent on segments five and six. The seventh and eighth abdominal segments have medium-sized forwardly-directed spines. Abdominal segments are encircled by campaniform sensilla. The terminal end of the eighth abdominal segment bears the anus, prominent anal lobes and two spiracular openings on each spiracular plate. Spiracular plates show a radial sun ray pattern. The rear abdomen also bears an ecdysal aperture, several pores and eight coeloconic sensilla. Although there are slight morphological differences, the spines (predominantly flat and thorn-like) and sensilla (campaniform and coeloconic) of the third-instar larvae show a similar arrangement to that of second-instar larvae. Thoracic trichoid sensilla are not seen in third-instar larvae. A perispiracular gland aperture is situated above each posterior spiracular opening. These morphological features are compared with those of other cuterebrid larvae.

Cutaneous myiasis

“…6 Scanning electron microscopy of the first-and second-instar larvae of D hominis revealed small backwardly-directed spines on the thoracic segments, small and large backwardly-directed spines on the first four abdominal segments, and forwardly-directed spines on the seventh and eight abdominal segments. 128,129 de Filippis and Leite 128 reported small preoral spines on the first thoracic segment and flat, thorn-like spines on the second and third thoracic segments and the first four abdominal segments of the third instar larvae of D hominis. The spines of the third instar larvae were noted to have a similar arrangement to those of the second instar larvae except for a small number of forwardly-directed spines on the first to fourth abdominal segments.…”

“…Spines with double and triple points were also observed in the third instar larva. 129 Recently, Möhrenschlager et al 130 performed scanning electron microscopy on a third instar D hominis larva and noted small, forwardly-directed spines in several circular rows at the caudad end. Like de Filippis and Leite, 128 Möhrenschlager et al 130 also reported flat, thorn-like spines on the second and third thoracic segments and on the first four abdominal segments of the third instar larvae.…”

“…90 In all types of furuncular After occlusion has induced the D hominis larva to migrate towards the skin surface, removal in toto with toothed forceps remains a challenge. Two morphologic characteristics allow the D hominis larva to anchor itself in the subcutaneous tissue of the host and resist extraction: (1) the presence of backwardly-directed (toward the superficial caudad end of the larva) 19,128,129 and forwardly-directed (toward the deep cephalad end of the larva) spines, [128][129][130] allowing for numerous tissue fixation points, and (2) the cephalad end of the larva is wider than its caudad end. 6 Scanning electron microscopy of the first-and second-instar larvae of D hominis revealed small backwardly-directed spines on the thoracic segments, small and large backwardly-directed spines on the first four abdominal segments, and forwardly-directed spines on the seventh and eight abdominal segments.…”

Spleen cell proliferation during and after skin myiasis by human bot fly Dermatobia hominis

“…Animal infection: Each animal from 10 groups of six male Swiss mice (20-25g) was submitted to skin infection with one newly hatched larva of D. hominis reared in our laboratory 9 . The mice were sacrificed and spleens obtained from groups 1-5 at 5, 10, 15, 20 and 25 days-postinfection (dpi), respectively.…”

“…Five groups with five male adult Wistar rats (190-220g) were infested with four newly hatched larvae of D. hominis and sacrificed at 5, 10, 15, 20 and 25 dpi to collect the larvae from the skin tissues 9 . Larvae at each infested date were washed three times with RPMI-1640 medium (Sigma) and conditioned in Falcon tubes with 2 mL of RPMI for incubation at 37 ºC in a 5% CO 2 …”