Scanning electron microscopy of adult head lice (Pediculus humanus capitis) with focus on clinical implications

Morphological discrimination of human lice (Anoplura: Pediculidae) by eggs' cap-like operculum

Human lice have long been parasites of humans and are responsible for several epidemics in human medical history. However, their morphology, particularly head and body lice, remains very similar. In this study, we discriminate human louse species based on the number, shape and size of aeropyles (respiratory pores) of the egg operculum as well as the size of the respiratory orifice in the aeropyles. For this purpose, lice and eggs were collected from infested patients referring to Parasitology Department of Avicenne Hospital (Bobigny, France) and analyzed morphologically. The microscopic examination of the aeropyles revealed a large variation in the number ranging from 5 to 12 for head lice, 10 to 16 for body lice and 13 to 18 for pubic lice with a statistically distinct average of 8.3, 12.9 and 15.7, respectively. Although the length of the head and body louse eggs were almost similar, the width of body louse eggs were bigger than those of head louse (412.9 μm and 363.5 μm, respectively), while pubic louse eggs had the smallest length (692.9 μm) and width (286.1 μm). In addition, pubic louse eggs had a greater operculum length and width (253.7 μm length and 220.7 μm width) than head (230.6 μm length and 210.2 μm width) and body lice (227.9 μm length and 199.9 μm width). Moreover, pubic lice had the smallest average aeropyle size (41.2 μm) compared to head (51.1 μm) and body lice (49.1 μm). The respiratory orifice on the aeropyles of head and body lice (9.9 μm) were almost twice as big as those of pubic lice (4.9 μm). There was an inverse correlation between the number of aeropyles and their size in head, body and pubic lice. These findings are helpful in accurate identification of human louse species using their eggs, which could be useful for control management strategies against these ectoparasites.

Attachment performance of the ectoparasitic seal louse Echinophthirius horridus

Marine mammals host a great variety of parasites, which usually co-evolved in evolutionary arms races. However, little is known about the biology of marine mammal insect parasites, and even less about physical aspects of their life in such a challenging environment. One of 13 insect species that manage to endure long diving periods in the open sea is the seal louse, Echinophthirius horridus, parasitising true seals. Its survival depends on its specialised adaptations for enduring extreme conditions such as hypoxia, temperature changes, hydrostatic pressure, and strong drag forces during host dives. To maintain a grip on the seal fur, the louse's leg morphology is equipped with modified snap hook claws and soft pad-like structures that enhance friction. Through techniques including CLSM, SEM, and histological staining, we have examined the attachment system's detailed structure. Remarkably, the seal louse achieves exceptional attachment forces on seal fur, with safety factors (force per body weight) reaching 4500 in average measurements and up to 18000 in peak values, indicating superior attachment performance compared to other insect attachment systems. These findings underscore the louse's remarkable adaptations for life in a challenging marine environment, shedding light on the relationship between structure and function in extreme ecological niches.

D-limonene nanoemulsion: lousicidal activity, stability, and effect on the cuticle of Columbicola columbae

The current study was conducted to investigate the efficacy and stability of D-limonene (DL) and its nanoemulsion (DLN) against pigeon feather lice (Columbicola columbae) and their mode of action. DL pure form and DLN were prepared and characterized freshly and after storage for 50 days. In vitro bioassay on live lice was conducted with different concentrations of DL, DLN, and deltamethrin (DM). The results revealed significant mortality rates in the DL-, DLN-, DM-treated groups when compared with the control (p < 0.05). The scanning electron micrographs of lice treated with DL and DLN revealed collapsed bodies with destruction in the cuticle of the mouthparts and damaged antennae. The 50 days stored DLN showed stability in their effectiveness when compared with the freshly prepared formulation. DL and DLN caused significant inhibition (p ≤ 0.05) in acetylcholinesterase activity (AchE). Malondialdehyde level (MDA) was significantly increased while glutathione was significantly decreased in DL- and DLN-treated lice. In conclusion, DL and DLN have significant lousicidal activities. DLN showed better stability than DL after storage for 50 days. In addition, the mode of action of DL may associate with its effect on the cuticle of the lice body, inhibition of AchE, and increasing oxidative stress in the treated lice.

Do drowning and anoxia kill head lice?

Chemical, physical, and mechanical methods are used to control human lice. Attempts have been made to eradicate head lice Pediculus humanus capitis by hot air, soaking in various fluids or asphyxiation using occlusive treatments. In this study, we assessed the maximum time that head lice can survive anoxia (oxygen deprivation) and their ability to survive prolonged water immersion. We also observed the ingress of fluids across louse tracheae and spiracle characteristics contrasting with those described in the literature. We showed that 100% of lice can withstand 8 h of anoxia and 12.2% survived 14 h of anoxia; survival was 48.9% in the untreated control group at 14 h. However, all lice had died following 16 h of anoxia. In contrast, the survival rate of water-immersed lice was significantly higher when compared with non-immersed lice after 6 h (100% vs. 76.6%, p = 0.0037), and 24 h (50.9% vs. 15.9%, p = 0.0003). Although water-immersed lice did not close their spiracles, water did not penetrate into the respiratory system. In contrast, immersion in colored dimeticone/cyclomethicone or colored ethanol resulted in penetration through the spiracles and spreading to the entire respiratory system within 30 min, leading to death in 100% of the lice.

Safety, Efficacy, and Physicochemical Characterization of Tinospora crispa Ointment: A Community-Based Formulation against Pediculus humanus capitis

The high prevalence of pediculosis capitis, commonly known as head lice (Pediculus humanus capitis) infestation, has led to the preparation of a community-based pediculicidal ointment, which is made of common household items and the extract of Tinospora crispa stem. The present study aimed to evaluate the safety, efficacy, and physicochemical characteristics of the T. crispa pediculicidal ointment. The physicochemical properties of the ointment were characterized, and safety was determined using acute dermal irritation test (OECD 404), while the efficacy was assessed using an in vitro pediculicidal assay. Furthermore, the chemical compounds present in T. crispa were identified using liquid-liquid extraction followed by ultra-performance liquid chromatography quadruple time-of-flight mass spectrometric (UPLC-qTOF/MS) analysis. The community-based ointment formulation was light yellow in color, homogeneous, smooth, with distinct aromatic odor and pH of 6.92±0.09. It has spreadability value of 15.04±0.98 g·cm/sec and has thixotropic behavior. It was also found to be non-irritant, with a primary irritation index value of 0.15. Moreover, it was comparable to the pediculicidal activity of the positive control Kwell^®, a commercially available 1% permethrin shampoo (P>0.05), and was significantly different to the activity of the negative control ointment, a mixture of palm oil and candle wax (P<0.05). These findings suggested that the community-based T. crispa pediculicidal ointment is safe and effective, having acceptable physicochemical characteristics. Its activity can be attributed to the presence of compounds moupinamide and physalin I.

Electron Microscopic Alterations in Pediculus humanus capitis Exposed to Some Pediculicidal Plant Extracts

Head lice, Pediculus humanus capitis, infestation is an important public health problem in Egypt. Inadequate application of topical pediculicides and the increasing resistance to the commonly used pediculicides made the urgent need for the development of new agents able to induce irreversible changes in the exposed lice leading to their mortality. The aim of the present work is to evaluate pediculicidal efficacy of some natural products such as olive oil, tea tree oil, lemon juice, and ivermectin separately in comparison with tetramethrin-piperonyl butoxide (licid), as a standard pediculicide commonly used in Egypt. The effects of these products were evaluated by direct observation using dissecting and scanning electron microscopes (SEM). Results showed that after 1 hr exposure time in vitro, absolute (100%) mortalities were recorded after exposure to 1% ivermectin and fresh concentrate lemon juice. The mortalities were decreased to 96.7% after exposure to tea tree oil. Very low percentage of mortality (23.3%) was recorded after 1 hr of exposure to extra virgin olive oil. On the other hand, the reference pediculicide (licid) revealed only mortality rate of 93.3%. On the contrary, no mortalities were recorded in the control group exposed to distilled water. By SEM examination, control lice preserved outer smooth architecture, eyes, antenna, respiratory spiracles, sensory hairs, and legs with hook-like claws. In contrast, dead lice which had been exposed to pediculicidal products showed damage of outer smooth architecture, sensory hairs, respiratory spiracles and/or clinching claws according to pediculicidal products used.

Fomite transmission in head lice

Control of various infestations requires an accurate understanding of transmission. After thousands of years of lice infestation, scientific documentation of indirect contact transmission has been substantiated. Lice can be transferred in the egg, instar, and adult stages. Lice have now been shown in the laboratory to be readily dislodged by air movements such as blow-drying one's hair, combing, and toweling. Moreover, passive transfer to adjoining fabric is also frequently observed. Louse transmission by fomites occurs more frequently than has been commonly believed. Close proximity suffices to increase the likeliness of a new infestation. Thus louse control measures should take account of fomite transmission and include screening of all individuals within an infested person's immediate circle of contact, laundering of everything within the infested individuals' bed or quarantining of such material for 10 days, thorough vacuuming of floors, carpets, upholstery, with a standard vacuum cleaner.

Surrogate nits impregnated with white piedra - a case report

White piedral spores packed inside empty pedicular nits were accidentally found on microscopic examination in a 42-year-old Indian woman who presented with hair loss. The diagnosis of piedra was confirmed on culture. She responded to topical 2% miconazole nitrate solution and manual removal of the nits. This is the first case report of pedicular nits found to be impregnated with spores of white piedra.

Managing head lice in an era of increasing resistance to insecticides

Head lice are present in all age groups, however, the peak age for infestation is 7-8 years and the incidence varies throughout the year with higher incidence during the winter. Different insecticides have been used over the past 60 years to manage this condition. There is now strong evidence of insecticide resistance established in many countries to such an extent that some of these chemicals have become obsolete. Resistance to some pediculicides can vary from country to country and region to region within a country. The lack of a local monitoring system of resistance patterns means that parents and pupils are hampered in making an informed decision regarding how to treat head lice. One should no longer assume that treatment failure is due to poor treatment compliance or re-infestation. Clear treatment guidelines drawn up by healthcare professionals with an interest in head lice and taking into account regional/national resistance patterns should be implemented. These guidelines should combine chemical and non-chemical approaches to treatment and be coordinated and regularly reviewed by local public health departments. Drug companies should be made to provide up-to-date efficacy of their products.