| Sucking louse | |
|---|---|
 | |
| Linognathus setosus (Linognathidae) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Psocodea |
| Suborder: | Troctomorpha |
| Infraorder: | Phthiraptera |
| Parvorder: | Anoplura Leach, 1815 |
| Families | |
| Synonyms | |
Siphunculata[1] | |
Sucking lice (knownscientifically asAnoplura) are aparvorder[2] of around 550species of lice. All sucking lice areblood-feedingectoparasites ofmammals. They can cause localized skin irritations and arevectors 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 calledpediculosis.Pediculus humanus is divided into two subspecies,Pediculus humanus humanus, or thehuman body louse, sometimes nicknamed "the seam squirrel" for its habit of laying of eggs in the seams of clothing, andPediculus humanus capitis, or thehuman head louse.Pthirus pubis (thehuman pubic louse) is the cause of the condition known ascrabs.
Sucking lice are classified as aparvorder called Anoplura, named by Leach in 1815. Anoplura belongs to theinfraorderPhthiraptera, which contains all lice, and is part of the largerorderPsocodea, which also contains booklice, barklice and barkflies. Acladogram showing the position of Anoplura withinPhthiraptera andPsocodea is shown below:[3]
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 smallproboscis that is usually kept inside of their head. Their color typically ranges between a mixture of yellow and white.[4] There are around 540 different species of Anoplura, and unlike the closely relatedMallophaga, sucking lice only parasitize mammals.[5]
Sucking lice bodies are typically oblong, with a flattened body and a head that is rounded in the front and smaller than the thorax.[6] The lice have anywhere from three to five separate thread–likeantennae on top of the end of the head that is used to help navigate their surroundings.[6] The head tends to slightly widen next to the antennae.[6] The antennae are composed of three to five equal sized joints that are used to aid in sensing their surrounding.[7] Thethorax contains two irregularly shaped triangular plates that help defend the insect's interior. Most sucking lice are no more than two millimeters in length.[6]
All sucking lice undergo a process of slowmetamorphosis, with three life stages of egg, nymph and adult.[8] 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.[9] Once a female louse matures, they will lay large amounts of small eggs (also known as nits) on the individual hairs of hosts.[9] Nits are usually between 0.3 and 0.8 millimeters long, and are often pale in color or nearly transparent.[10]
Sucking lice live exclusively on the outside of their hosts, making them consideredectoparasites.[11] The louse's proboscis consists of two distinct tubes, with the upper being called arostrum, and the lower being called astylet.[11] The lice will use their upper mouth piece to latch onto the skin with teeth–like structures, maintaining a firm hold during their feeding. The lower mouth piece consists of two stylets, also known as stabbers.[11] After the rostrum obtains a firm hold, the stylets will penetrate the skin with the serrated edges in a saw–like fashion. The louse will then regurgitate saliva through the proboscis inside of the body, before proceeding to suck the host's blood[12] in what has been described as a "pumping action".[11] Different species of sucking louse have specialised anatomy to helpparasitize on different mammals and to help survive various climates.[12]
Anoplura contains three species of lice that parasitize humans.[13] Anoplura body lice (Pediculus humanus humanus) typically carry the potential of causing skin irritation, and arevectors of multiple blood-born diseases.[14] Common symptoms of Anoplura body lice includerelapsing fever,trench fever andepidemic typhus.[14][15] Due to increased societal standards for hygiene, body lice in general is significantly less prevalent in developed regions.[15] During theAmerican Civil War, body lice were colloquially known as "seam squirrels" due to their tendency to lay eggs within the seams of soldier's clothes.[16][17] 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.[18] Cases of head lice are most common in children between the ages of 3 and 11.[19]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 ofPediculosis pubis.[19] Pubic lice are often mistaken assexually 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.[20]
Dogs can be affected by three individual species of Anoplura lice:Linognathus setosus, Heterodoxus spiniger andTrichodectes canis.[21] Dogs infested by lice show symptoms of discomfort such as rubbing, scratching and biting areas affected.[21] Coats of affected animals are often rough to the touch, and can become matted over time if left untreated.[22] Severe infestations of sucking lice can lead toanemia from the loss of blood as well.[22] Lice in dogs can only be contracted through either direct or indirect contact with another infested dog, and cannot be transferred across different species.[23]
Cats are not affected by Anoplura lice, rather they can only contract the speciesFelicola subrostrata, a type of chewing lice.[24][25]
Mostcattle 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.[26] Anoplura lice can only live off of the animal for a few days.[27] Female lice specialized to cattle tend to lay a single egg every day for around 2 to 3 weeks.[27] Similar to sucking lice in dogs, severe infestations can cause cattle to experience anemia, with newborn calves being particularly vulnerable.[26]
These 15families are generally recognized in the Anoplura:[5]
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Human lice and pediculosis | ||
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