Arthropods

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Arthropods

• Gregory L. Brower, D.V.M., Ph.D.
• Cell Biology and Anatomy
• School of Medicine
• Columbia, South Carolina

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Textbook Is Not Your Best Resource
Textbooks are at least 4 years out of date. Keep
abreast of current treatment regimes by
consulting Centers for Disease Control or World
Health Organization web sites. http//www.dpd.cdc
.gov/dpdx/
CDC or WHO www.afpmb.org/pubs/Field_Guide/field_g
uide.pdf
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Myiasis

• Burial of fly larvae in tissue
• Cochliomyia (New World Screw worm), Chrysomya
  (Old World Screw worm) Calliphora, Oestrus,
  Sarcophaga, Gastrophilus
• Distributed worldwide

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Myiasis Distribution

• Distribution worldwide
• Healthy or necrotic tissue
• mandibular hooks aided by proteolytic enzymes
• Gastrointestinal
• Urinary

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Screw WormGeographic Distribution
Chrysomya bezziana
Cochliomyia hominivorax
Cochliomyia hominivorax
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Chrysomya bezziana Old World Screw Worm
The Breast Journal Vol. 13 297-301, 2007
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Myiasis Symptoms

• Tissue damage and necrosis
• Secondary bacterial infections

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Myiasis Treatment

• Hygiene
• Avoid flies, especially on open wounds
• Debridement of wound
• Antibiotics only if secondary bacterial infection

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Myiasis
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Lice
Pediculus humanus capitis (head louse) P. humanus
humanus (body louse) Pthirus pubis (crab
louse) Worldwide distribution
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Lice Life Cycle
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Pediculus humanus capitis Head Lice

• Mostly children
• Crowded environment
• Adult (secondarily)
• Rarely affects African Americans
• Moderate to severe itching
• Fever
• Secondary infections

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Head Lice Old School Treatment

• 1 benzene hexachloride (Kwell)
• 0.2 pyrentins
• 2 pipronyl butoxide
• copper oleate may be as effective and less toxic
  than benzene hexachloride
• Good hygiene

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Head Lice Current Treatment
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Pediculus humanus corporis Body Lice

• Similar to head lice
• Affects all ages
• Associated with bad hygiene
• Dermatitis
• Primary vectors of
• Epidemic typhus
• Louse-borne relapsing fever
• Trench fever
• Treatment similar to head lice
• Cleanliness is preventive

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Phthirus pubis Pubic Lice

• Commonly referred to as crabs
• Transmitted sexually
• Infest coarse hair in pubic area in adults
• Pubic lice found on the head or eyelashes of
  children are indication of potential sexual
  exposure or abuse.
• Occasionally pubic lice may be spread by close
  personal contact or fomite transmission from
  clothing, bed linens, and towels that have been
  used by an infested person.

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Phthirus pubis Life Cycle
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Pubic Lice Diagnosis and Treatment

• Symptoms consist of severe itching of the
  infested area
• Diagnosed based upon finding lice (difficult to
  spot)
• Treatment similar to head lice
• 1 permethrin
• mousse containing pyrethrins and piperonyl
  butoxide
• Lindane in refractory cases

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Fleas Tunga penetrans

• Most fleas are ectoparasites, with the exception
  of Tunga penetrans (sand fleas, chigoe, Jigger,
  chique, etc.)
• Tropical and subtropical
• Female burrows under the skin, lays eggs and dies

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Fleas Tunga penetrans Life Cycle
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Tunga penetrans

• Tissue invasion and erosion
• Usually feet and toes are involved
• Severe pruritis and pain
• Auto-amputation can occur in severe cases
• Treatment consists of removal of fleas
  (surgically, if necessary)
• Shoes are protective

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Mites (Sarcoptes scabie)

• Cause of Scabies
• Worldwide distribution
• Typically associated with poor living conditions

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Mites (Sarcoptes scabie)

• Skin affected includes finger webbing, wrists,
  buttocks, interscapular, axilla, female breasts,
  genitalia and abdomen.
• Mite burrows under the skin and forms tunnels.
• Mite lays eggs in tunnels that hatch into larvae.
• Larvae mature, exit the tunnel and form new
  tunnels.

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Mites (Sarcoptes scabie)

• Diagnosis is based on characteristic rash.
• Application of ink to affected areas and wiping
  reveals burrows.
• Microscopic examination of skin scraping.

Photos courtesy of CDC and University of Iowa
Hardin Library for the Health Scienceshttp//www.
lib.uiowa.edu/Hardin/md/cdc/3810.html
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Mites (Sarcoptes scabie)
Crusted scabies occurs predominantly in patients
who are immunocompromised, elderly,
institutionalized, or bedridden.
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Mites (Sarcoptes scabie)

• Swab lesions with malathion or benzene
  hexachloride
• Topical steroid should be avoided
• Wash clothes in hot water

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Chiggers (Trombiculidae)

• Ectoparasites
• Eutrombicula sp.
• Leptotrombidium sp.
• Bites typically occur under tight clothing or on
  wrinkled skin
• ankles, wrists, thighs, groin and waist
• Feed on digested skin and lymph
• Digestive enzymes cause severe irritation
• occasionally fever

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Chiggers (Trombiculidae)

• Bite develops allergic response
• Larvae usually already detached
• Intense pruritis
• Secondary bacterial infections
• Local anesthetic to relieve irritation