 The human body louse Pediculus humanus humanus had its genome sequenced in 2010 , and at that time it had the smallest insect genome known . This louse can transmit certain diseases while the human head louse ( P. h. capitis ) , to which it is closely related , cannot . With their simple life history and small genomes , the pair make ideal model organisms to study the molecular mechanisms behind the transmission of pathogens and vector competence . In 2015 there were 5 cases of louse @-@ borne relapsing fever being transmitted to locals reported in Italy . 
