What is the pathophysiology of pubic lice (Pthirus pubis) infestation?

From the Guidelines

Pubic lice (Pthirus pubis) infestation is primarily transmitted through sexual contact, leading to an infestation characterized by intense itching and parasitic attachment to pubic hair. The pathophysiology of pubic lice infestation involves the attachment of crab-shaped lice to pubic hair and occasionally other coarse body hair, where they feed on human blood multiple times daily by piercing the skin with their mouthparts 1. This process triggers an inflammatory response in the host, causing characteristic intense itching (pruritus) that typically begins 5 days after initial infestation.

Key Aspects of Pathophysiology

• Adult lice attach to hair shafts using specialized claws and feed on human blood
• Female lice lay eggs (nits) that firmly adhere to hair shafts near the skin surface, hatching within 7-10 days and developing through nymph stages before reaching adulthood in about 2-3 weeks
• The entire life cycle occurs on the human host, with transmission primarily through direct sexual contact, as noted in the 2015 guidelines for sexually transmitted diseases treatment 1
• Scratching due to pruritus often leads to secondary bacterial infections, and small bluish-gray macules (maculae ceruleae) may appear at feeding sites due to lice saliva interacting with blood breakdown products

Transmission and Survival

• Unlike head lice, pubic lice cannot survive long away from a human host, typically less than 24 hours
• The infestation remains localized to areas with coarse hair unless left untreated, when it may spread to other body regions including eyelashes, eyebrows, axillary hair, and rarely scalp hair in children The primary mode of transmission being sexual contact highlights the importance of considering pubic lice infestation in the context of sexually transmitted infections. Management and treatment should prioritize not only the elimination of the lice and their eggs but also the prevention of further transmission and the addressing of any secondary complications that may arise from the infestation.

From the Research

Pathophysiology of Pubic Lice Infestation

The pathophysiology of pubic lice (Pthirus pubis) infestation involves the feeding of lice on the blood of the host, leading to various clinical manifestations.

• The infestation is usually transmitted through sexual contact or through contaminated items such as toilet seats and bedding material 2.
• Pubic lice are ectoparasites that feed on the blood of infested hosts, and their morphotype dictates their clinical features 3.
• The main complaint of patients with pediculosis pubis is itch in the pubic area, and the parasite can be spotted with the naked eye 4.
• Blue macules can be observed in the pubic area due to the feeding activity of the lice 4.

Clinical Features and Diagnosis

• Pubic lice infestation is diagnosed by the visualization of insects or viable nits (eggs) 5.
• The disease can be sexually transmitted, and patients may present with itching in the pubic area 4.
• The incidence of pubic lice is increased in population groups living in crowded spaces with scarce sanitary conditions 4.

Treatment and Management

• First-line therapy for pediculosis pubis consists of permethrin or pyrethrins with piperonyl butoxide 4.
• Second-line therapy includes phenothrin, malathion, and oral ivermectin 4.
• Partner management is essential, and a look-back period of 3 months is recommended 4.
• Environmental measures, such as washing and changing clothing and bedding, are important to prevent recurrent infestation 5.