Sucking louse

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Sucking lice (known scientifically as Anoplura) are a parvorder<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> of around 550 species of lice. All sucking lice are blood-feeding ectoparasites of mammals. They can cause localized skin irritations and are vectors of several blood-borne diseases.

At least three species or subspecies of Anoplura are parasites of humans; the human condition of being infested with sucking lice is called pediculosis. Pediculus humanus is divided into two subspecies, Pediculus humanus humanus, or the human body louse, sometimes nicknamed "the seam squirrel" for its habit of laying of eggs in the seams of clothing, and Pediculus humanus capitis, or the human head louse. Pthirus pubis (the human pubic louse) is the cause of the condition known as crabs.

ClassificationEdit

Sucking lice are classified as a parvorder called Anoplura, named by Leach in 1815. Anoplura belongs to the infraorder Phthiraptera, which contains all lice, and is part of the larger order Psocodea, which also contains booklice, barklice and barkflies. A cladogram showing the position of Anoplura within Phthiraptera and Psocodea is shown below:<ref name="deMoya2021">Template:Cite journal</ref> Template:Clade

CharacteristicsEdit

Sucking lice are typically flattened and wingless, with sharp claws on their legs that are used to attach themselves to hair or human clothing. All sucking lice suck blood through a small proboscis that is usually kept inside of their head. Their color typically ranges between a mixture of yellow and white.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> There are around 540 different species of Anoplura, and unlike the closely related Mallophaga, sucking lice only parasitize mammals.<ref name=":8" />

Sucking lice bodies are typically oblong, with a flattened body and a head that is rounded in the front and smaller than the thorax.<ref name="bulletin-1883">Template:Cite book</ref> The lice have anywhere from three to five separate threadTemplate:Ndashlike antennae on top of the end of the head that is used to help navigate their surroundings.<ref name="bulletin-1883" /> The head tends to slightly widen next to the antennae.<ref name="bulletin-1883" /> The antennae are composed of three to five equal sized joints that are used to aid in sensing their surrounding.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The thorax contains two irregularly shaped triangular plates that help defend the insect's interior. Most sucking lice are no more than two millimeters in length.<ref name="bulletin-1883" />

Life cycleEdit

All sucking lice undergo a process of slow metamorphosis, with three life stages of egg, nymph and adult.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The entire process of Anoplura's growth occurs whilst on their host, however they are able to survive for small periods of time in outside environments.<ref name=":0">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Once a female louse matures, they will lay large amounts of small eggs (also known as nits) on the individual hairs of hosts.<ref name=":0" /> Nits are usually between 0.3 to 0.8 millimeters long, and are often pale in color or nearly transparent.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Feeding methodEdit

Sucking lice live exclusively on the outside of their hosts, making them considered ectoparasites.<ref name="lapage-1951">Template:Cite book</ref> The louse's proboscis consists of two distinct tubes, with the upper being called a rostrum, and the lower being called a stylet.<ref name="lapage-1951" /> The lice will use their upper mouth piece to latch onto the skin with teethTemplate:Ndashlike structures, maintaining a firm hold during their feeding. The lower mouth piece consists of two stylets, also known as "stabbers".<ref name="lapage-1951" /> After the rostrum obtains a firm hold, the stylets will penetrate the skin with the serrated edges in a sawTemplate:Ndashlike fashion. The louse will then regurgitate saliva through the proboscis inside of the body, before proceeding to suck the host's blood<ref name="aspinall-2006">Template:Cite book</ref> in what has been described as a "pumping action".<ref name="lapage-1951" /> Different species of sucking louse have specialised anatomy to help parasitize on different mammals and to help survive various climates.<ref name="aspinall-2006" />

EffectsEdit

In humansEdit

Anoplura contains three species of lice that parasitize humans.<ref>Template:Cite journal</ref> Anoplura body lice (Pediculus humanus humanus) typically carry the potential of causing skin irritation, and are vectors of multiple blood-born diseases.<ref name=":1">Template:Cite journal</ref> Common symptoms of Anoplura body lice include relapsing fever, trench fever and epidemic typhus.<ref name=":1" /><ref name=":2">Template:Cite journal</ref> Due to increased societal standards for hygiene, body lice in general is significantly less prevalent in developed regions.<ref name=":2" /> During the American Civil War, body lice were colloquially known as "seam squirrels" due to their tendency to lay eggs within the seams of soldier's clothes.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite book</ref> Anoplura head lice (Pediculus humanus capitis) is significantly more common than pubic or body lice, with studies reporting an infestation rate between 3.6% and 61.4% from countries in North and South America.<ref>Template:Cite journal</ref> Cases of head lice are most common in children between the ages of 3 and 11.<ref name=":3">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Pthirus pubis (also known as pubic lice or crabs) is a species of sucking lice that affects the genitals of humans, and is the cause of Pediculosis pubis.<ref name=":3" /> Public lice are often mistaken as sexually transmitted infections due to frequently being contracted through sexual contact, however they are only considered parasites as they can be spread through non-sexual methods such as sharing blankets or towels.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In other animalsEdit

Dogs can be affected by three individual species of Anoplura lice: Linognathus setosus, Heterodoxus spiniger and Trichodectes canis.<ref name=":4">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Dogs infested by lice show symptoms of discomfort such as rubbing, scratching and biting areas affected.<ref name=":4" /> Coats of affected animals are often rough to the tough, and can become matted over time if left untreated.<ref name=":5">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Severe infestations of sucking lice can lead to anemia from the loss of blood as well.<ref name=":5" /> Lice in dogs can only be contracted through either direct or indirect contact with another infested dog, and cannot be transferred across different species.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Cats are not affected by Anoplura lice, rather they can only contract the species Felicola subrostrata, a type of chewing lice.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref>

Most cattle species can be affected by sucking lice, with certain lice species being specially adapted to their preferred cattle and unable to be transferred across any other species.<ref name=":6">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Anoplura lice can only live off of the animal for a few days.<ref name=":7">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Female lice specialized to cattle tend to lay a single egg every day for around 2 to 3 weeks.<ref name=":7" /> Similar to sucking lice in dogs, severe infestations can cause cattle to experience anemia, with newborn calves being particularly vulnerable.<ref name=":6" />