Chapter 35 Chewing Lice and Sucking Lice

General Information Lice fall into one of two orders: Mallophaga - chewing lice, with chewing mouthparts; Anoplura - sucking lice, with sucking mouthparts Members of both orders are wingless and dorsoventrally flattened Eyes are reduced or absent Tarsal claws are often enlarged, an adaptation to allow them to cling to hair and feathers of their hosts

Life Cycle Eggs are cemented to the feathers or hairs of their hosts Hemimetabolous development: the young are similar to the adults except for size and development of the genitalia; there are 3 nymphal instars Members of these orders are highly adapted to a parasitic lifestyle: they have no free living stages and die very quickly in the absence of the host

Order Mallophaga: Biting Lice or Chewing Lice Head is slightly broader than the prothorax; mouthparts are primitive, resembling those of the primitive free-living forms Three suborders are recognized: Amblycera, Ischnocera, and Rhynchopthirina Trichodectes canis

Gliricola porcelli from Guinea pigs Order Mallophaga cont. The Amblycera are the most generalized and least host specific; their antennae are composed of 4 joints and lie in a ventrolateral groove on each side of the head and may not project beyond the sides of the head; amblyceran parasites of mammals include Gyropus ovalis and Gliricola porcelli of guinea pigs and Heterodoxus spiniger on dogs Gliricola porcelli from Guinea pigs

Order Mallophaga cont. The Ischnocera are the most specialized; their antennae are filiform in nature and composed of 3-5 joints; well known pests of cats, dogs and domestic cattle, horses, mules, etc. e.g., Bovicola bovis on cattle; Trichodectes canis is a common parasite of dogs and serves as the intermediate host of Diplydium caninum Trichodectes canis

O. Anoplura – Sucking Lice All are parasitic of mammals; possess piercing mouthparts; small fused thorax; antennae are visible and composed of 5 joints; second and third pair of legs are often the largest and are broad and flattened Head narrower than the remainder of the body The family Pediculidae includes the human head louse and the body louse, both in the genus Pediculus The family Pthiridae includes the human pubic or crab louse in the genus Pthirus

Pediculus humanus Occurs in 2 forms: the body louse, P. humanus humanus (=P. h. corporis) and the head louse P. h. capitis Head lice are smaller than body lice; body lice are seldom if ever found in the head, but head lice may be found on the body; head lice are adapted to clinging to hairs, but body lice find refuge in clothing Head lice and body lice can interbreed and produce fertile offspring Females can lay from 150-300 eggs (nits) during their lives; eggs are either cemented to clothing (body lice) or to hair (head lice)

Pediculus humanus cont. Body lice can be transmitted from one person to another through contact, clothing or bedding; head lice usually transmitted through physical contact Infestations with lice usually are not life threatening, unless the lice carry some sort of disease organisms (e.g., it is a major vector for relapsing fever, epidemic typhus and trench fever) The lice normally cause red papules and cause severe itching which can lead to dermatitis and secondary infection; years of infection can lead to darkened, thickened skin a condition known as vagabond’s disease

Phthirus pubis Possesses a wide thorax that constitutes most of the body, and the coxae are far apart at the margins of the thorax It frequents the pubic hairs and perianal regions of man, but may wonder to other parts of the body, including the head

Transmission is often from person to person by close personal contact Phthirus pubis cont. It is smaller and much broader than the other human lice, and its legs have the appearance of being attached to the edge of the flattened body The forelegs are slender with long, fine claws; the middle and hindlegs are thick, with thick claws Transmission is often from person to person by close personal contact