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Charles Moore
Charles Moore

Biting Louse

There are two main kinds of lice in the order Phthiraptera. These are the biting lice, which are most often found on birds, and the sucking lice, which are mostly found on mammals. The scientific name of the order comes from the Greek phtheir (louse) and aptera (wingless).

biting louse

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Sucking lice (Siphunculata) have long oval bodies, and their heads are smaller than those of biting lice. Their scientific name comes from the Latin word siphunculus, which means little pipe or siphon.

Nearly every mammal species can be infested by a sucking louse - even seals and walruses have them! These 'marine lice' all belong to the family Echinophthiriidae, and they can exist for long periods under water by taking a layer of air down with them between their specially modified body hairs, or by breathing air trapped in the host's body hair.

One of the best known lice is Pediculus humanus - the human louse - which has two distinct races. The race capitis may be found in the hair on the head, and their eggs, stuck to hairs, are termed nits. These can be very difficult and time consuming to remove - this is where the term 'nit-picking' came from.

Of these two human lice, the head louse is more common, and sometimes there are outbreaks of head lice infestation in schools. Head lice can survive any amount of washing and combing, so they are not associated with lack of hygiene. Luckily, whilst head lice can be irritating, they do not carry disease.

The horse biting louse (Werneckiella equi) is a common global equine ectoparasite. To our knowledge, benzoyl(phenyl)urea insecticides (triflumuron, diflubenzuron) commonly used as sheep lousicides, have not been evaluated for efficacy against W. equi. The aim of this study was to determine louse control efficacy, general wellness and dermal safety following triflumuron application as a backline pour-on to horses. Two efficacy trials using 25 adult naturally infested lousy horses, and a dermal safety trial using 10 adult louse-free horses were conducted over a 14-month period. Lousy animals were selected by assessment of their lice status prior to treatment. For the efficacy trial, the triflumuron product was applied at a dose of 2.5mg triflumuron per kg bodyweight (1 mL product per 10 kg bodyweight). For the safety study, triflumuron was applied at a 3x clinical dose of 7.5 mg triflumuron per kg bodyweight (3 mL product per 10 kg bodyweight). In our first efficacy trial, 100% lousicidal efficacy was achieved by day 44 post-treatment. In our second trial, no lice were identified on horses by day 71 post-treatment. In the safety trial, no adverse effects were seen. Results of this study demonstrate that the off-label, experimental pour-on application of triflumuron at 2.5 mg/kg bodyweight is convenient, highly effective and safe (at 3x the clinical dose) for the treatment of the horse biting louse, W. equi.

The prevalence and severity of cockle, a sheep pelt defect characterised by raised lumps, was assessed on lambs that were either louse-infested (Bovicola ovis) or louse-free at birth. Assessments were made on pickled pelts, 10 months after the lambs had entered the trial. Lambs kept free of lice did not develop cockle, whereas the defect was common in lambs (about 90%) that were infested with lice. There was a direct correlation between louse scores and cockle, high louse scores being associated with a more severe degree of cockle. The results give support to the strong causal relationship between B. ovis and cockle, but questions such as the minimum number of lice needed to cause cockle and the time required for cockle to develop still need to be answered.

The Mallophaga are a possibly paraphyletic[1] section of lice, known as chewing lice, biting lice, or bird lice, containing more than 3000 species. These lice are external parasites that feed mainly on birds, although some species also feed on mammals. They infest both domestic and wild mammals and birds, and cause considerable irritation to their hosts.[2] They have paurometabolis or incomplete metamorphosis.[3][4]

Female lice are usually more common than males, and some species are parthenogenetic, with young developing from unfertilized eggs. A louse's egg is commonly called a nit. Many lice attach their eggs to their hosts' hair with specialized saliva; the saliva/hair bond is very difficult to sever without specialized products. Lice inhabiting birds, however, may simply leave their eggs in parts of the body inaccessible to preening, such as the interior of feather shafts. Living louse eggs tend to be pale whitish, whereas dead louse eggs are yellower.[4] Lice are exopterygotes, being born as miniature versions of the adult, known as nymphs. The young moult three times before reaching the final adult form, usually within a month after hatching.[4]

Phthiraptera lice are members of Psocodea (formerly Psocoptera), the order that contains booklice, barklice and barkflies. Within Psocodea, lice are within the suborder Troctomorpha, and most closely related to the family Liposcelididae.[25] The oldest confirmed fossil louse is a bird louse, Megamenopon rasnitsyni, from Eckfelder Maar, Germany, which dates to the Eocene, around 44 million years ago.[26] Saurodectes vrsanskyi from the Early Cretaceous (Aptian) Zaza Formation of Buryatia, Russia, has also been suggested to be a louse, but this is tentative.[27]

Nearly 5,000 species of louse have been identified, about 4,000 being parasitic on birds and 800 on mammals. Lice are present on every continent in all the habitats that their host animals occupy.[29] They are found even in the Antarctic, where penguins carry 15 species of lice (in the genera Austrogonoides and Nesiotinus).[30] The oldest known record of the group is Megamenopon rasnitsyni from the Eocene of Germany, but it is essentially a modern form, belonging to Amblycera, so the group as a whole likely has an origin in the Mesozoic.[26]

The mitochondrial genome of the human species of the body louse (Pediculus humanus humanus), the head louse (Pediculus humanus capitis) and the pubic louse (Pthirus pubis) fragmented into a number of minichromosomes, at least seven million years ago.[34] Analysis of mitochondrial DNA in human body and hair lice reveals that greater genetic diversity existed in African than in non-African lice.[33][35] Human lice can also shed light on human migratory patterns in prehistory. The dominating theory of anthropologists regarding human migration is the Out of Africa Hypothesis. Genetic diversity accumulates over time, and mutations occur at a relatively constant rate. Because there is more genetic diversity in African lice, the lice and their human hosts must have existed in Africa before anywhere else.[35]

Robert Hooke's 1667 book, Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses with observations and Inquiries thereupon, illustrated a human louse, drawn as seen down an early microscope.[39]

In 1935 the Harvard medical researcher Hans Zinsser wrote the book Rats, Lice and History, alleging that both body and head lice transmit typhus between humans.[42] Despite this, the modern view is that only the body louse can transmit the disease.[43]

The human body louse Pediculus humanus humanus has (2010) the smallest insect genome known.[46] This louse can transmit certain diseases while the human head louse (P. h. capitis), to which it is closely related, cannot. With their simple life history and small genomes, the pair make ideal model organisms to study the molecular mechanisms behind the transmission of pathogens and vector competence.[47]

Robert Burns dedicated a poem to the louse, inspired by witnessing one on a lady's bonnet in church: "Ye ugly, creepin, blastid wonner, Detested, shunn'd, by saint and sinner, How dare ye set your fit upon her, sae fine lady! Gae somewhere else, and seek your dinner on some poor body." John Milton in Paradise Lost mentioned the biblical plague of lice visited upon pharaoh: "Frogs, lice, and flies must all his palace fill with loathed intrusion, and filled all the land." John Ray recorded a Scottish proverb, "Gie a beggar a bed and he'll repay you with a Louse."In Shakespeare's Troilus and Cressida, Thersites compares Menelaus, brother of Agamemnon, to a louse: "Ask me not what I would be, if I were not Thersites; for I care not to be the louse of a lazar, so I were not Menelaus."[54]

Most lice with public health and veterinary relevance have a global distribution, as they are associated with hosts that are also widely dispersed. Their global distribution is mediated by humans via tourism, transport, and the trade of pets and livestock. A particularly interesting louse is Heterodoxus spiniger which was originally a parasite of marsupials in Australia, later switched to dingoes, and from these moved to domestic dogs. The species is now spread worldwide in various carnivores, including domestic dogs [3].

Anoplura are important parasites of both humans and animals. In humans, louse infestation is known as pediculosis if caused by head or body lice, and as pthiriasis if caused by pubic lice. Pediculosis is a contagious parasitic infestation, transmitted from human-to-human by close contact or, in body lice, via infested clothes or bed linen. The most common louse infestation in humans is pediculosis capitis (caused by Pediculus humanus capitis), particularly affecting school children between three and 11 years, and clinically manifesting as scalp pruritus [4]. It is estimated that head lice infest more than 100 million people worldwide [5]. Pediculosis corporis (caused by Pediculus humanus humanus) is a major public health concern, mainly occurring in crowded human communities, such as refugee camps or shelters for homeless, where hygiene is poor and clothes or linen are not washed regularly [4]. At homeless shelters in Europe, the prevalence of body lice can reach over 20% [6]. The clinical signs of body lice infestation include intense pruritus and cutaneous rash, associated with allergy to the bites. In chronic infestations, the skin becomes thickened [5]. Pubic lice, Pthirus pubis, cause pubic pruritus. 041b061a72




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