61.Pediculus humans, Phthirus pubis · Biology · MU Pleven

61.Pediculus humans, Phthirus pubis.

Covers lice of the order Anoplura, namely the head, body and crab lice, with their roles in causing pediculosis and crab infestation and in transmitting typhus, trench fever and relapsing fever. It sets out the morphology of the body, head, legs and female genital features, compares the sizes of the three species, and describes the egg, nymph and adult stages with cycle durations. It closes with transmission routes, species-specific behaviour, and the brief symptoms and diagnosis.

Inside: 7 sections · 4 labelled pictures · 10 flashcards · 2 min

Topic 61 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 7 sections, about 288 words (2 min of reading), with 10 flashcards.

Lice (Order: Anoplura)

Disease caused:

Pediculosis
Crabs (pubic lice infestation)

Vector role:

Epidemic typhus
Trench fever
Relapsing fever

Important Species (Morphologically Relevant)

Pediculus humanus capitis – head louse
Pediculus humanus humanus – body louse
Phthirus pubis – crab louse

Morphology

Small, wingless insects
Dorsoventrally flattened
Undergo incomplete metamorphosis
Body:
Flattened, elongated, greyish-white
Angular, ovoid head
Fused chitinous thorax
Segmented abdomen
Head structures:
Pair of simple lateral eyes
Pair of short antennae
Extensible piercing stylets
Legs:
Three pairs of segmented legs
Each leg ends in:
A single hook-like claw
Opposing tibial process
Adapted for gripping hairs or fibres
Female genital features:
Last abdominal segment bears:
Genital opening
Two blunt lateral gonopods
Gonopods clasp hair during oviposition

Comparative size:

Body louse is more robust than head louse
Crab louse is the smallest of the three

Hosts and Vector Importance

Humans are the definitive host
Head louse and crab louse:
Not implicated in disease transmission
Body louse:
Transmits:
Rickettsia prowazekii
Gram-negative, aerobic, parasitic bacteria
Borrelia recurrentis