Lice

INSECTA PARASITES

Phthiraptera introduction

Arthropod Classification - copyright nabrown RVC

Lice are obligate ectoparasites of every avian and most mammalian species. They are only a few millimeters long and like fleas, are wingless but unlike fleas are dorsoventrally flattened.

Lice are host specific, permanent parasites which cause pediculosis. The louse saliva and faeces contain allergenic substances which cause irritation, rubbing, licking and skin damage leading to decreased host productivity.

Mammalian lice species have a single pair of claws on the ends of stout legs, whereas avian lice species have a double claw on each leg.

There are two main groups of veterinary importance, the mallophaga (chewing lice) and anoplura (sucking lice).

Mallophaga

Also known as chewing lice or biting lice

• Broad head

• Thorax narrower than the head

• Rasping mouthparts

• Feeds on epithelial scales, scabs, feathers and other bodily debris

• Species occur on both mammals and birds

Anoplura

Sucking Louse Pediculosis humanus - From: Genetic Analysis of Lice Supports Direct Contact between Modern and Archaic Humans Reed DL, Smith VS, Hammond SL, Rogers AR, Clayton DH PLoS Biology Vol. 2, No. 11, e340 doi:10.1371/journal.pbio.0020340

Also known as sucking lice

• Narrow head

• Thorax wider than the head

• Powerful legs

• Piercing mouthparts

• Feed on blood and tissue fluids

• Heavy infestations can cause anaemia

• Species occur only on mammals

Life cycle

• The whole life cycle takes 2-3 weeks

• The louse spends its whole life on the animal
  • It can however survive for one week off the animal

• In some species parthenogenesis can occur

• Close contact transmission can occur

1. Eggs

• Known as nits

• Cemented to hairs

2. Nymphs

• Nymphs hatch from the egg (no larval stage)

• Undergoes several moults

3. Adults

• Females can lay up to 10 eggs per day

Pediculosis

• Pediculosis is an infestation of lice

• Pediculosis in farm animals is most often seen in winter when the coat is thickest

• Debilitated animals are often predisposed as they cannot groom properly

Cattle

• One chewing louse
  • Bovicola bovis

• Several sucking lice
  • E.g. Linognathus vituli

• Most lice have a preferred predilection site on the body

• Some lice will gather in clusters

• Causes
  • Ill-thrift
  • Anaemia
  • Down-graded leather

Sheep

• One chewing louse
  • Damalinia ovis

• Two sucking lice
  • Lignognathus spp.
    • The 'foot louse' and the 'face louse'

• Causes fleece damage

Pigs

• One sucking louse
  • Haematopinus suis
  • Large 5mm louse which is easily visible on the skin
  • Common to the UK
  • Overseas it is a vector of African swine fever virus and rickettsiae

Horses

• One chewing louse
  • Damalinia equi

• One sucking louse
  • Haematopinus asini

• Mainly found in the mane and tail but can spread over the body

Dogs

• One chewing louse
  • Trichodectes canis

• One sucking louse
  • Linognathus setosus

• Neglect is usually associated with heavy infestations

Cats

• One chewing louse
  • Felicola

Poultry

• Several species of chewing lice
  • Lipeurus spp. are the most pathogenic
    • The 'wing louse' and the 'head louse'
  • Menacanthus spp. are also pathogenic
    • Lays its eggs in clusters around the cloaca

• No sucking lice

Control

• Few insecticides will kill lice eggs on the animal

• Two treatments are needed to kill nymphs emerging from eggs at the time of the initial treatment and those that will emerge 2-3 weeks later
  • At two week intervals
  • Or a product with a two week residual activity can be used

• Sucking lice are more susceptible to systemic insecticide treatment than chewing lice

• Resistance to insecticides may become a problem so alternating the chemicals used and avoiding pour on treatments (which have a greater risk of resistance developing) should be considered