Some species including "Pediculus humanus" (lice) have multiple chromosomes in the mitochondrion. The causative organism is "Rickettsia prowazekii", transmitted by the human body louse ("Pediculus humanus corporis"). Pediculus humanus is a species of louse that infects humans. Parthenogenesis, the production of viable offspring by virgin females, does not occur in "Pediculus humanus". Curiously, this pattern is not found in the human body louse ("Pediculus humanus"). The human body louse "Pediculus humanus humanus" has (2010) the smallest insect genome known.