"Louse" - what is it, definition of the term
The term denotes a minute, wingless ectoparasite of the order Phthiraptera that inhabits the external surface of mammals, extracting blood or skin debris for nutrition, and is frequently found on rodents such as rats and mice.
Detailed information
The ectoparasitic insect that infests rodents belongs to the order Phthiraptera, family Pediculidae. Adult individuals are wingless, laterally compressed, measuring 1–3 mm in length. Their bodies consist of a hardened exoskeleton, six legs equipped with clawed tarsi for clinging to host fur, and compound eyes reduced to simple ocelli. Mouthparts are adapted for piercing skin and sucking blood.
Reproduction occurs entirely on the host. Females lay 2–5 eggs (nits) per day, attaching them to hair shafts with a cementing secretion. Eggs hatch in 5–7 days, releasing nymphs that undergo three molts before reaching maturity. The complete life cycle—from egg to adult—lasts 2–3 weeks under optimal temperature (25–30 °C) and humidity (70–80 %). Development slows markedly at lower temperatures, extending the cycle to over a month.
Feeding behavior involves intermittent blood meals lasting 10–15 minutes. Each meal provides sufficient protein for egg production. Blood loss per infestation rarely exceeds 5 % of the host’s total blood volume, but repeated feeding can cause anemia, skin irritation, and secondary bacterial infections.
Host specificity varies among species. Some taxa parasitize only rats (Rattus spp.), while others prefer mice (Mus spp.) or exhibit a broader rodent range. Transmission occurs primarily through direct contact between individuals, grooming, or shared nesting material. Infested nests retain viable eggs for up to two weeks after removal of the host, facilitating re‑infestation.
Control measures focus on environmental sanitation and chemical treatment. Effective steps include:
- Regular cleaning and replacement of bedding to eliminate deposited eggs.
- Application of topical insecticides containing pyrethroids or ivermectin, following label dosage.
- Monitoring host populations for signs of infestation, such as crusted skin or visible nits.
- Implementing quarantine protocols for newly introduced rodents to prevent introduction of external parasite strains.
Resistance to common insecticides has been documented in several populations, prompting rotation of active ingredients and integration of non‑chemical methods, such as heat treatment of nesting material (≥ 55 °C for 30 minutes), which destroys all life stages.
In research settings, the parasite serves as a model for studying host‑parasite interactions, vector‑borne pathogen transmission, and insecticide resistance mechanisms. Accurate identification relies on microscopic examination of morphological features, especially the shape of the head capsule and the arrangement of setae on the thorax. Molecular techniques, including PCR amplification of mitochondrial COI genes, provide species‑level resolution and aid in tracking geographic distribution.