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.