Chapter 36 Parasitic Insects: Phthiraptera – Chewing and Sucking Lice

Chapter 36: Parasitic Insects: Phthiraptera – Chewing and Sucking Lice

Characteristics of Lice

  • Lice are wingless insects belonging to the order Phthiraptera.

  • Are all lice parasitic?

    • Yes, all lice are obligate ectoparasites that depend on their hosts for survival.

Chewing Lice

  • Approximately 4400 known species of chewing lice.

  • These parasites primarily target birds and mammals.

    • Some species are known to be pests on domestic animals.

  • Feeding Behavior:

    • Chewing lice feed on skin debris, blood, feathers, or hair from their host.

  • Effects of Bovicola bovis on Cattle:

    • Causes irritation, reduced weight gain, and can lead to decreased milk production due to stress on the cattle.

  • Effects of Bovicola ovis on Sheep:

    • Results in wool damage, decreased fleece quality, and potential wool marketability issues after shearing.

  • Preventive Measures:

    • Regular grooming, using anti-lice treatments, and maintaining good animal husbandry practices.

  • Marketability of Infested Wool:

    • Wool infested with chewing lice is often considered non-marketable or receives a lower price due to quality degradation.

  • Intermediate Hosts:

    • Chewing lice may serve as intermediate hosts for other parasites such as the nematode genus
      Dirofilaria, which can lead to other health issues in livestock.

Sucking Lice

  • Much smaller group with fewer than 500 species.

  • Primarily parasites of mammals, with significant medical and veterinary importance.

  • Feeding Methods: Intensity of Blood Feeding

    • 1. Direct feeding on host blood: Generally used by most bloodsucking arthropods.

    • 2. Salivary enzyme secretion: Causes blood to thin, allowing easier access to the blood vessels.

  • Pediculus humanus:

    • Known as human lice, exists in two distinct forms:

    1. Pediculus humanus capitis (Head lice)

    2. Pediculus humanus corporis (Body lice)

  • Reason for Separate Subspecies:

    • Likely due to different habitats and feeding patterns, reflecting adaptations to their respective locations on the host's body.

Body Lice

  • Life Cycle Description:

    • Body lice undergo a complete metamorphosis, including the egg (nit), nymph, and adult stages.

    • Nits attach to clothing, making transmission dependent on proximity to infested garments.

  • Influences on Life Cycle:

    • Clothing Impact: Provides a protective environment for nits and nymphs, facilitating survival.

    • Host Temperature: Warmer temperatures may accelerate development from egg to adult.

  • Transmission Potential:

    • Highest during close contact situations, particularly in crowded environments.

Head Lice

  • Clinical Signs:

    • Symptoms include itching, irritation, and visible lice or eggs on the scalp.

  • Vagabond’s Disease:

    • A severe form of infestation leading to secondary infection and significant skin damage due to scratching.

  • Plica Polonica:

    • Characterized by darkened, thickened skin due to chronic, heavy infestation leading to hair being in a matted condition associated with fungal diseases.

Phthirus pubis

  • Commonly known as the crab louse or “crabs.”

  • Morphological Characteristics:

    • Terminal claws resembling crab pincers.

  • Habitat:

    • Primarily found in the pubic area of hosts.

  • Transmission Mode:

    • The most common form of transmission is through sexual contact.

  • Association with Other Diseases:

    • Infestations of pubic lice may predict other sexually transmitted diseases such as gonorrhea.

Haematopinus suis

  • Impact on Pigs:

    • Acts as a vector for swine diseases such as swine cholera and swine pox, thereby limiting pork production.

Lice as Vectors of Human Disease

  • Three Diseases Transmitted by Pediculus humanus humanus:

    • Epidemic (Louse-Borne) Typhus:

    • Caused by the pathogen Rickettsia; has a high fatality rate; spread via louse feces.

    • Trench Fever:

    • Caused by Bartonella; not fatal but leads to debilitating symptoms.

    • Epidemic Relapsing Fever:

    • Caused by Borrelia; characterized by periodic episodes of fever; transmitted when scratching lice crush them, releasing spirochetes into the host.

Control of Lice

  • Control Measures in Humans:

    • Use of Permethrin solution and physical methods such as combing out lice manually.

  • Control Measures in Domestic Animals:

    • Application of insecticide sheets (ivermectin) and conducting mass treatment by running animals through an insecticide spray chute.

Wild Animals

  • Healthy mammals and birds often employ natural grooming and preening behaviors to maintain low louse populations.

  • Poorly nourished or ill animals often fail to groom effectively, leading to higher infestations.

  • Anting Behavior in Birds:

    • A behavior where birds use insects (such as lice) in their feathers to combat parasitic infestations, thus indirectly serving as a form of treatment against lice in effector species.