Chapter 5: The olfactory system of human lice

The human louse is an obligate blood-feeding ectoparasite that lives permanently on its host, and an important disease vector  that mediates the transmission of pathogens to humans. The adaptation to this particular lifestyle is reflected in the morphology of  the peripheral olfactory system and in the diversity of the chemosensory gene repertoires. In comparison with other  haematophagous insect species, the number and diversity of chemosensory sensilla on the main olfactory organ, the antennae, are very low. Similarly, analysis of the genome sequence of this insect reveals a massive reduction in the repertoires of chemoreceptors and other olfactory gene families. Multiple studies have explored the contribution of the olfactory system in human lice chemical communication, mostly using bioassays designed to measure the insect behaviour towards synthetic and natural odours. Experimental evidence supports a critical role of the sense of smell in the detection of ecologically-relevant volatiles from the human host, conspecific faecal matter and repellent substances. However, the chemical ligands used by this insect for host colonisation and intraspecific communication are still unknown, mainly due to the lack of physiological characterisation of the peripheral olfactory system.