What diseases do lice transmit? - briefly
Head lice rarely transmit systemic illnesses, though scratching can lead to secondary bacterial infections such as impetigo or cellulitis. Body lice are confirmed vectors of epidemic typhus, trench fever, and relapsing fever.
What diseases do lice transmit? - in detail
Lice are obligate ectoparasites that occasionally serve as vectors for pathogenic microorganisms. The three species that affect humans—head louse (Pediculus humanus capitis), body louse (Pediculus humanus corporis), and pubic louse (Pthirus pubis)—differ markedly in their capacity to transmit disease.
The body louse is the only species with a proven record of vector competence. It acquires pathogens while feeding on infected blood and releases them in its feces, which then enter the host through skin abrasions or mucous membranes. The principal louse‑borne infections are:
- Epidemic typhus – caused by Rickettsia prowazekii; characterized by high fever, rash, and severe complications if untreated. Transmission occurs when contaminated louse feces are scratched into the skin.
- Trench fever – caused by Bartonella quintana; presents with recurrent fever, headache, and bone pain. The organism is deposited in the skin via louse feces and enters the bloodstream.
- Relapsing fever – caused by Borrelia recurrentis; marked by alternating febrile and afebrile periods, headache, and myalgia. Infection follows the same fecal‑to‑skin route as the other two diseases.
In addition to these well‑documented illnesses, body lice have been implicated in occasional outbreaks of louse‑borne plague (Yersinia pestis) and murine typhus (Rickettsia typhi), though such events are rare and generally confined to conditions of extreme crowding and poor hygiene.
Head lice, while ubiquitous, are not recognized as vectors of systemic infections. Their feeding behavior and limited mobility reduce the likelihood of pathogen acquisition and transmission. Rare case reports describe secondary bacterial skin infections (e.g., impetigo) resulting from scratching, but no definitive link to specific pathogens has been established.
Pubic lice transmit no known infectious agents. Their clinical significance lies in causing pruritus, inflammation, and secondary bacterial infection of the genital skin. The primary health concern is the potential for co‑infection with sexually transmitted diseases, which may coexist due to shared risk factors rather than direct transmission by the louse.
Overall, the only lice species with a confirmed role in disease propagation is the body louse, responsible for epidemic typhus, trench fever, and relapsing fever. Head and pubic lice remain primarily a source of irritation and secondary bacterial skin complications.