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Abstract:Background: Data on ovicidal activity of pediculicides are essential to determine the efficacy of commercial products, and to define application schemes. We present an adaptation of historical methods for rearing head lice, and describe their development ex vivo.Methods: Adult head lice were collected and fed on volunteers to obtain fertile eggs of known age. Two methods of feeding were applied: interval feeding (performed every 8-12 hours), and continuous feeding (placing lice in a round Plexiglas receptacle, closed with gauze attached to the skin). Eggs were incubated at 25-28,6°C and 51,8% -69,3% relative humidity. The following outcome measures were used: appearance of eye spot; presence of embryonic structures; presence of embryonic movements; and hatching. A total of 340 eggs were obtained by continuous feeding. Of these, 205 were examined daily. The remaining 135 eggs and those obtained by interval feeding (n=159) were observed once, to confirm hatching status.Results: Eye spots of the embryos started to appear 6 days after oviposition (median = 7 days), and embryonic movements were first seen 9 days after oviposition (median =11 days). Interval feeding of head lice revealed a hatch rate of 10,7% (17/159), as compared to a hatch rate of 80,9% (275/340) achieved with continuous feeding. Hatching started 9 days after oviposition (median = 12 days). Skin irritation (papular rash; moderate to severe itching) appeared after continuous feeding of adult lice on volunteers.Conclusions: Continuous feeding of head lice on a human host is a suitable approach to obtain head lice eggs for ovicidal testing. The method is simple and cheap, offers conditions similar to the natural habitat, and hatch rates are high. However, side effects on volunteers are considerable.

We performed head lice movement studies to elucidate factors influencing orientation and movement of head lice. Studies included observation of lice movements on hand and forearm at different positions of the upper limb; movements exposed to unshaved and shaved forearm; and movements with and without antennae. In 57 of 60 (95.0%) observations while holding the hand down, lice moved proximal, and 3 (5%) distal. While holding the hand up, 37/60 (61.7%) moved proximal, and 23 (38.3%) distal (p < 0.0001). On the unshaved limb, 29/30 (96.7%) moved proximal, with clockwise movements in 26/30 (86.7%). After shaving, 9/30 (30%) walked proximal and 18 (60%) distal, with 12/30 (40%) clockwise movements. After antennectomy, while holding the hand up, 16/25 (64%) lice did not move, 1 (4%) walked proximal, and 8 (32%) distal. While handing the hand down, 17/25 (68%) did not move, 5 (20%) walked proximal, and 3 (12%) distal. Transmission of head lice may not only occur by head-to-head contact, but also via head-to-body contact, with movement to the head against gravitational pull. Surface factors of hand and forearm may be important in orientation for lice, in addition to gravity. Movement of lice against gravity is not governed by organs in the antennae.

Background: Data on ovicidal activity of pediculicides are essential to determine the efficacy of commercial products, and to define application schemes. We present an adaptation of historical methods for rearing head lice, and describe their development ex vivo. Methods: Adult head lice were collected and fed on volunteers to obtain fertile eggs of known age. Two methods of feeding were applied: interval feeding (performed every 8-12 hours), and continuous feeding (placing lice in a round Plexiglas receptacle, closed with gauze attached to the skin). Eggs were incubated at 25-28,6°C and 51,8%-69,3% relative humidity. The following outcome measures were used: appearance of eye spot; presence of embryonic structures; presence of embryonic movements; and hatching. A total of 340 eggs were obtained by continuous feeding. Of these, 205 were examined daily. The remaining 135 eggs and those obtained by interval feeding (n=159) were observed once, to confirm hatching status. Results: Eye spots of the embryos started to appear 6 days after oviposition (median = 7 days), and embryonic movements were first seen 9 days after oviposition (median =11 days). Interval feeding of head lice revealed a hatch rate of 10,7% (17/159), as compared to a hatch rate of 80,9% (275/340) achieved with continuous feeding. Hatching started 9 days after oviposition (median = 12 days). Skin irritation (papular rash; moderate to severe itching) appeared after continuous feeding of adult lice on volunteers. Conclusions: Continuous feeding of head lice on a human host is a suitable approach to obtain head lice eggs for ovicidal testing. The method is simple and cheap, offers conditions similar to the natural habitat, and hatch rates are high. However, side effects on volunteers are considerable.