Chapter 35 Chewing Lice and Sucking Lice

1. Chapter 35 Chewing Lice and Sucking Lice

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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)

9. 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

10. 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

11. 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