Parasitic Insects, Mites and Ticks: Genera of Medical and Veterinary Importance/Sucking lice

Female human head louse.jpg

Lice (Phthiraptera)[edit]

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Characters of lice[edit]

Lice are bugs that stay as obligate parasites; that’s, they’re all so specialised that they’ll solely feed and develop as parasites. Every feeding stage of the life-cycle takes repeated small meals. Lice are flattened dorso-ventrally, and by no means develop wings. On their hosts lice present a uninteresting floor and are coloured from pale yellow via to darkish brown.

Female human head louse.jpg
{Photograph} reveals a stay feminine Head-louse, genus Pediculus, that infests the scalp of people. Be aware its dimension in opposition to the strands of hair. (Photograph by Gilles San Martin).

Lice stay solely on their hosts; they crawl from one particular person host to a different when hosts are in shut contact. Some species are in a position to survive for a short while off their host. Females connect their eggs in rows onto hairs or feathers of their hosts. These glued eggs are known as nits and are simply acknowledged as an indication of louse infestation. Lice steadily lay small batches of huge eggs and their survival fee is excessive as they become nymphs. This good survival allows louse infestations to extend to excessive densities per host below beneficial situations, usually when hosts are housed shut collectively for lengthy intervals. Nonetheless, sparse infestations by lice usually trigger little or no indicators of illness.

Every species of louse is specialised for feeding on one species of host, or on a couple of intently associated species. This allows particular diversifications for digestion of blood and evasions of immune reactions by their hosts. These associations additionally simplify identification of those parasites. The Order Phthiraptera is assumed to have a number of origins, making their classification troublesome and different. (Older groupings of the lice included the blood-sucking Siphunculata and the skin-chewing Mallophaga). Nonetheless, lice converged throughout evolution, and for medical functions are simply grouped into these specialised to suck blood (sub-Order Anoplura), and people specialised to chew on pores and skin scales, hair or feathers. There are two sub-Orders of chewing lice, the Amblycera and the Ischnocera [1][2][3][4].


  • Stomach = Posterior a part of physique of bugs, containing intestine, gonads and different organs.
  • Bristle = A big thick sort of seta (6 on Pediculus).
  • Claw = Legs of most bugs and acarines finish in laborious sharp gripping organs (5 on Haematopinus).
  • Eye = Most bugs have distinguished eyes on their head, both compound eyes of many sensory items, or easy eyes of 1 sensory unit (2 on Pediculus).
  • Granuloma = Scar tissue, as typically types in pores and skin the place an insect or acarine has fed and made an infected wound.
  • Nit = Vernacular and medical time period for egg of a louse glued to hair or feathers of host (10 on Haematopinus).
  • Obligate = A type of parasitism the place the parasite can solely feed parasitically, in distinction to facultative parasitism the place the animal can optionally feed in a free-living or non-parasitic approach.
  • Paratergal plate = Hardened (sclerotized) plates on the lateral margins of belly segments of some lice (5 on Pediculus).
  • Pediculosis = Scientific time period for the illness state of heavy infestation with lice.
  • Pruritus = Itching.
  • Seta = A pivoted moveable extension of the physique wall of bugs and acarines (5 on Solenopotes).
  • Sclerotize = When a part of the physique wall of an insect or acarine turns into tanned and tougher than surrounding areas.
  • Spiracle = Opening in physique wall to permit respiration (Four on Pthirus).
  • Sternal plate = A sclerotized a part of the physique wall on the ventral floor of a louse (Eight on Linognathus).
  • Sucking = This time period is used to differentiate the anopluran lice, which suck up blood from their hosts with needle-like mouthparts, from the amblyceran and ischnoceran chewing lice, which haven’t any blood-sucking mouthparts (see Chewing lice ).
  • Tubercle = A hump formed protrusion of the physique wall (Four on Pthirus).

Characters of Sucking lice (Anoplura)[edit]

The mouthparts are skinny and lengthy for piercing, and are retracted when not in use. There aren’t any sensory palps. Antennae often consist of 5 segments. The thorax has its three segments fused collectively, with out apparent divisions. Spiracles are often seen dorsally; a pair on the thorax and one at either side of most belly segments. Eyes happen on some species, as a pair on their head. These lice parasitize many species of mammals.

Linognathus louse female ventral.jpg
{Photograph} reveals a feminine Linognathus louse from an infestation on cattle, displaying gripping of host hair, and descriptions of two eggs (arrowed). Be aware that the mouthparts of sucking lice are retracted inside the head between classes of blood feeding.
Linognathus louse feeding through skin.png
Diagram of feeding at pores and skin reveals a typical sucking louse penetrating dermal capillaries of host with lengthy advantageous mouthparts (proportions of louse to pores and skin usually are not drawn precisely).

Pediculus (Pediculidae)[edit]

Pediculus female dorsal.png

Characters: feminine, dorsal. 1- Width of head is the same as its size. 2- Antenna has 5 segments. 3- Eyes are distinguished. 4- Stomach is elongate, bulging centrally. 5- Stomach paratergal plates are distinguished. 6- Tibial spurs have small bristles.

The 2 species (or sub-species) P.humanus humanus, the Physique-louse, and P.humanus capitis, the Head-louse parasitize solely people [5][6].

Indicators and signs: Physique-lice reside and lay their eggs on clothes of people. They crawl onto their host’s pores and skin to feed on blood, leading to small localized infected and pruritic websites. Continual heavy infestations result in a thickening and added pigmentation of the pores and skin. Head-lice reside within the hair of the pinnacle and lay eggs (generally known as nits) on these hairs. These eggs or their empty circumstances are essentially the most simply seen signal of infestation. Irritation and pruritus outcome from these lice feeding. Infestations of people by Physique-lice are commonest both on people dwelling in extreme poverty, or on bigger teams of individuals compelled to crowd collectively below situations of social collapse, warfare or refugee camps [7].

Illness: The Head-louse isn’t identified to transmit any pathogens. Heavy infestations of the Physique-louse trigger the situation is named pediculosis, skilled actually as feeling awful. The Physique-louse transmits to people three species of micro organism: Rickettsia prowazekii inflicting epidemic or louse-borne typhus. [8]; Bartonella (previously Rochalimaea) quintana inflicting trench fever [9]; and Borrellia recurrentis inflicting louse-borne relapsing fever [10].

Pthirus (Pthiridae)[edit]

Pthirus female dorsal.png

Characters: feminine, dorsal. 1- Head is blunt anteriorly; eyes are current. 2- Fore-legs are skinny; mid- and hind-legs are stout. 3- Thorax is broad while stomach is slender and brief. 4- Stomach bears lateral tubercles and dorsal spiracles. 5- Mid- and hind-legs have massive claws which shut onto a tibial spur.

Hosts: The human Pubic-louse or Crab-louse, P. pubis, is particular for people. The opposite single species of this genus is particular for gorillas.

Signs and illness: Infestations are often confined to pubic hair however hair in axillae, eyebrows and beard might develop into infested. Pruritus is the most common symptom of infestation however spots of gray pigmentation of pores and skin might happen the place there may be persistent infestation. Pthirus pubis isn’t a vector of pathogens [11].

Haematopinus (Haematopinidae)[edit]

Haematopinus female dorsal.png

Characters: feminine, dorsal, claw and egg. 1- Level at which mouthparts protrude when in use. 2- Head is elongate. 3- Eyes are absent, however there may be an ocular level posterior to the antenna. 4- All legs are of comparable dimension. 5- All legs bear a big claw that closes onto a tibial spur. 6- Subsequent to the tibial spur is a tibial pad. 7- Stomach segments bulge laterally. 8- Stomach segments bear hardened (sclerotized) paratergal plates. 9- Physique is massive with distinct brown areas. 10- Egg glued by a feminine onto a hair of its host. Additionally: sternal plate on ventral aspect of thorax is massive and darkish.

Hosts: The one species of louse discovered on pigs is Haematopinus suis (Hog-louse); infesting the neck, flanks and insides of legs. Horses and different equids are infested by H. asini on their head, neck, again, brisket and between legs. Cattle are infested by H. eurysternus (Brief-nosed louse) which happens everywhere in the physique, and H. quadripertusus (Tail-louse) which infests the tail.

Indicators: These lice trigger irritation, pruritus, and dermal granulomas.

Illness. Piglets might undergo extreme anemia if closely infested. Biting-stress and misplaced manufacturing in pigs and cattle is induced. Additionally economically important losses to processors of leather-based hides could also be brought on by dermal granulomas on the feeding websites of those massive lice [12].

Linognathus (Linognathidae)[edit]

Linognathus female ventral.png

Characters: feminine, ventral. 1- Head is often elongate. 2- There is no such thing as a ocular level posterior to the antenna. 3- Fore-legs are smaller than the mid- and hind-legs; claw on the fore-leg types a smaller gripping mechanism than on the mid- and hind-legs. 4- Physique is darkish gray and these lice are medium sized. 5- Every phase of the stomach bears two rows of setae. 6- Stomach is with out paratergal plates. 7- Sternal plate on ventral floor of thorax is slender or absent.

Hosts: Cattle are infested by Linognathus vituli (Lengthy-nosed cattle louse) on their head, thorax and stomach. Sheep are equally infested by L. ovillus (Blue louse), while L. pedalis infests toes of sheep. Canines are infested by L. setosus and goats by L. stenopsis.

Indicators: Irritation, pruritus, dermal granulomas, and dermal induration are induced. Heavy infestations result in the hair-coat having a awful look: matted, staring and uninteresting. Sheep infested with L. ovillus might lose areas of wool attributable to mixture of irritation and protracted self-grooming. (Be aware that the feeding of those and related lice doesn’t outcome within the disruption and heavy scabbing of the pores and skin floor that’s the primary signal of infestation with psoroptic scab mites. Inspection by eye reveals intact pores and skin even when louse infestations are pretty heavy.)

Illness: Heavy infestation causes biting-stress, and anemia results in lack of manufacturing. Hides for leather-based manufacture are broken by granuloma formation at feeding websites of those lice [13].

Solenopotes (Linognathidae)[edit]

Solenopotes female ventral.png

Characters: feminine, ventral. 1- Head is with out eyes and ocular factors, and has a blunt profile. 2- Fore-legs are smaller than the mid-legs and hind-legs; they lack a tibial spur. 3- Stomach is with out paratergal plates. 4- Stomach spiracles are borne on tubercles. 5- Stomach segments bear one row of setae. 6- Sternal plate on the ventral floor of thorax is massive and darkish. Additionally: physique is small and gray.

Hosts: Cattle are infested by Solenopotes capillatus (Little blue louse) on their head, neck, shoulders, again and tail.

Indicators and illness: Irritation and pruritus, and the indicators listed above for Linognathus are induced. Results on host are much like these for Linognathus however this smaller louse is much less prone to trigger lousiness[14].

Polyplax (Polyplacidae)[edit]

Polyplax-female ventral.png

Characters: feminine, ventral. 1- Head is brief and blunt; eyes and ocular factors are absent. 2- Antennae are massive relative to dimension of head. 3- Fore-legs are small relative to mid- and hind-legs; they haven’t any tibial spurs. 4- Paratergal plates are current on the stomach. 5- Stomach segments bear two rows of setae. 6- Sternal plate on ventral floor of thorax is massive. Additionally: physique is small.

Hosts and Illness: Lice of this genus infest rodents. Such infestations might develop into an issue to pet rodents and in laboratory colonies.

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  1. Ledger, J.A. (1980) The Arthropod Parasites of Vertebrates in Africa south of the Sahara. Vol. IV Phthiraptera (Insecta). Johannesburg, South African Institute for Medical Analysis.
  2. Lane, R.P. & Crosskey, R.W. (eds) (1993) Medical Bugs and Arachnids. London, Chapman & Corridor. ISBN 0-412-40000-6.
  3. Lancaster, J.L. & Meisch, M.V. (1986) Arthropods in Livestock and Poultry Manufacturing. Chichester: Ellis Horwood Ltd. ISBN 0-85312-790-5.
  4. Value, M.A. & Graham, O.H. (1997) Chewing and Sucking Lice as Parasites of Mammals and Birds. Technical Bulletin 1849, Washington D.C., United States Division of Agriculture.
  5. Olds B.P., et al. (2012) Comparability of the transcriptional profiles of head and physique lice. Insect Molecular Biology 21: 257–68.
  6. Yong, Z., et al. (2003) The geographical segregation of human lice preceded that of Pediculus humanus capitis and Pediculus humanus humanus, Comptes Rendues Biologies, 326: 565–574.
  7. Buxton, P.A. (1947) The Louse; an Account of the Lice which Infest Man, their Medical Significance and Management (2nd ed.). London: Edward Arnold.
  8. McDade, J.E., et al. (1980) Proof of Rickettsia prowazekii infections in america. The American Journal of Tropical Drugs and Hygiene, 29(2),277-284.
  9. Brouqui, P., et al. (1999) Continual Bartonella quintana bacteremia in homeless sufferers. New England Journal of Drugs, 340:184-189 DOI: 10.1056.
  10. Cutler, S.J., et al. (1997) Borrelia recurrentis: Characterization and comparability with Relapsing-Fever, Lyme-associated, and different Borrelia spp. Worldwide Journal of Systematic Bacteriology 47, 958-968.
  11. Anderson, A.L. & Chaney, E. (2009) Pubic Lice (Pthirus pubis): Historical past, biology and remedy vs. information and beliefs of US school college students. Worldwide Journal of Environmental Analysis and Public Well being. 6: 592-600. doi:10.3390/ijerph6020592.
  12. Smith, H.M., et al. (1982) Parasitism amongst wild swine within the southeastern United States. Journal of the American Veterinary Medical Affiliation, 181: 1281-1284.
  13. Otter, A., et al. (2003) Anaemia and mortality in calves infested with the long-nosed sucking louse (Linognathus vituli Veterinary Document, 153:176-179.
  14. Grubbs, M.A., et al. (2007) Life cycle particulars of Solenopotes capillatus. Journal of Financial Entomology, 100: 619-621.

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