Sensory features of the human louse antenna: new contributions and comparisons between ecotypes

Detailed morphological structure and phylogenetic relationships of Degeeriella punctifer (Phthiraptera: Philopteridae), a parasite of the bearded vulture Gypaetus barbatus (Accipitriformes: Accipitridae)

Habitat loss is one of the main threats to species survival and, in the case of parasites, it is their hosts that provide their habitat. Therefore, extinction even at local scale of host taxa also implies the extinction of their parasites in a process known as co-extinction. This is the case of the bearded vulture (Gypaetus barbatus), which almost became extinct at the beginning of the twentieth century. After several attempts, this species was successfully reintroduced into the Alps at the end of the twentieth century. We collected 25 lice specimens from an electrocuted bearded vulture from Susa (Italian Alps) that were morphologically identified as Degeeriella punctifer. Six individuals were studied by scanning electron microscopy, with particular emphasis on their cephalic sensorial structures, while four further specimens were characterized at molecular level by amplifying partial regions of the 12SrRNA, COX1 and elongation factor 1 alpha (EF-1) genes. From a morphological perspective, the number, type and arrangement of the sensillae on the two distal antennal segments is quite similar to that of other species of the family Philopteridae (Phthiraptera: Ischnocera). The mandibles and tarsal claws allow lice to cling firmly to their host's feathers. Phylogenetic analyses help unravel the paraphyletic nature of the genus Degeeriella and demonstrate the clear differentiation between lice parasitizing Accipitriformes and Falconiformes, as well as the close relationship between D. punctifer, D. fulva, D. nisus and Capraiella sp. that, along with other genera, parasitize rollers (Aves: Coraciiformes).

Human pediculosis, a global public health problem

Background

Human pediculosis is caused by hematophagous lice, which are transmitted between individuals via direct and/or indirect contact. Despite the public health importance of louse infestation, information concerning the global burden of pediculosis and the epidemiological landscape of louse-borne diseases is limited. The aim of this review was to summarize the biology, epidemiology, diagnosis, and control of lice infestation in humans. We also discussed the latest advances in molecular taxonomy and molecular genetics of lice.

Methods

We searched five electronic bibliographic databases (PubMed, ScienceDirect, CNKI, VIP Chinese Journal Database, and Wanfang Data) and followed a standard approach for conducting scoping reviews to identify studies on various aspects of human lice. Relevant information reported in the identified studies were collated, categorized, and summarized.

Results

A total of 282 studies were eligible for the final review. Human pediculosis remains a public health issue affecting millions of people worldwide. Emerging evidence suggests that head lice and body lice should be considered conspecific, with different genotypes and ecotypes. Phylogenetic analysis based on mitochondrial (mt) cytb gene sequences identified six distinct clades of lice worldwide. In addition to the direct effect on human health, lice can serve as vectors of disease-causing pathogens. The use of insecticides plays a crucial role in the treatment and prevention of louse infestation. Genome sequencing has advanced our knowledge of the genetic structure and evolutionary biology of human lice.

Conclusions

Human pediculosis is a public health problem affecting millions of people worldwide, particularly in developing countries. More progress can be made if emphasis is placed on the use of emerging omics technologies to elucidate the mechanisms that underpin the physiological, ecological, and evolutionary aspects of lice.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-022-00986-w.

The closer the better: Sensory tools and host-association in blood-sucking insects

Many hematophagous insects acquire medical and veterinary relevance because they transmit disease causing pathogens to humans. Hematophagy is only fulfilled once a blood feeder successfully locates a vertebrate host by means of fine sensory systems. In nature, blood-sucking insects can exploit environments with differential association with their hosts. Given the relevance of the sensory systems during host searching, we review the current state of knowledge of the sensory machinery of four blood-sucking insects: human lice, bed bugs, kissing bugs and mosquitoes. Each one is representative of highly anthropophilic behaviours and a different degree of association with human hosts. We compare the number, arrangement and functional type of cuticular sensory structures dispersed on the main sensory organs. We also compare the genetic machinery potentially involved in the detection of host stimuli. Finally, we discuss the sensory diversity of the insects studied here.

The morphology of Colpocephalum pectinatum (Phthiraptera: Amblycera: Menoponidae) under scanning electron microscopy

Here, we describe under scanning electron microscopy (SEM) the morphology of Colpocephalum pectinatum (Phthiraptera, Menoponidae), an ectoparasite found in burrowing owls, Athene cunicularia. We devote particular attention to the morphology of the main structures of the head (antennae and mouth-parts) and legs (tarsi and femoral ctenidia). Moreover, we describe the main peripheral sensory organs, located in the labial palpi and the distal end of antennae. We also detected that the structure of antennae and antennal sensilla arrangement are very similar to that described for other Colpocephalum and Menoponid species, and we discuss the function of each type of sensilla. We suggest that SEM studies combined with other microscopy and physiological techniques could be useful for elucidate the function of each structure, lice behaviour, as well as their taxonomy.