Medical Entomology: Insect Attacks & Lice

Medical Entomology

• Medical entomology studies insects that attack living and dead vertebrates.

Modes of Attack and Consequences

• Insects attack through stinging, urticating, and biting which leads to nuisance and can cause allergies.
• Insects can cause infestations and vector diseases.
• Delusory parasitosis is a phobia related to insects.

Order Phthiraptera: Parasitic Lice

• Lice have chewing and sucking mouthparts and undergo hemimetabolous development.
• Lice are wingless ectoparasites of vertebrates that are dorso-ventrally flattened.
• Lice have stout legs with strong grasping claws and tend to be host-specific.
• There are over 3000 species of lice worldwide.

Chewing Lice

• Chewing lice possess mandibular mouthparts.
• Chewing lice feed on feathers and dander or skin.

Sucking Lice

• Sucking lice possess sucking mouthparts.
• Sucking lice feed on the blood of a host.
• Hematopinus siris is the Hog Louse.
• Echinophthirius horridus is the Seal Louse.
• Pediculis humanus capitis is the head louse.
• Pediculus humanus corporis transmits rickettsia typhus, which caused more wartime casualties than combat.
• Pediculus humanus corporis is transmitted through crushed lice or feces scratched into the skin.
• Pediculus humanus capitis and P.h.corporis are morphologically similar but ecologically differentiated.
• P.h.corporis feeds on the lower body and lives in clothing.
• mtDNA and nDNA sequences indicate body lice originated in Africa around 72,000 +/- 42,000 ybp.
• Humans were likely naked for longer than previously believed.

Order Siphonaptera: Fleas

• Fleas have mandibulate mouthparts as larvae and haustellate mouthparts as adults.
• Fleas undergo holometabolous development and have laterally compressed bodies.
• Fleas have caudally-directed setae and spines.
• Resilin aids in jumping.
• Fleas are not as host-specific as lice.
• There are 2380 species of fleas worldwide.
• Ctenocephalides canis is the dog flea.
• Xenopsylla cheopis, the Oriental Rat flea, is the primary vector of Yersinia pestis, the agent of plague.

Plague

• Plague spread through Europe during the Black Death (1346-1353).

Order Diptera: True Flies

• Fly larvae have chewing mouthparts, while adults have sucking, lapping, or biting mouthparts.
• Flies undergo holometabolous development and use forewings for propulsion.
• Hindwings are modified as halteres.
• There are over 150,000 species of flies worldwide.
• Glossina transmits trypanosomiasis.
• Female Glossina give birth to mature larva.

Infestation (Myiasis)

• Female flies deposit eggs or larvae into living or dead tissue.
• Larvae develop within the host and emerge before the puparial stage.

Oestridae: Bot Flies, Warble Flies

• Adults are robust and hairy, resembling bees.
• Adults lack mouthparts or have vestigial mouthparts.
• Larvae are endoparasites of mammals.
• Cuterebra abdominalis is the rabbit bot fly.
• Dermatobia hominis is a Human Bot Fly or Torsalo.
• Dermatobia hominis glues its eggs to a carrier fly.

Infestation Sites

• Infestation sites include under the skin and, rarely, in the nostrils or scrotum.

Remedies

• Remedies include pins, cigarette smoke, Vaseline, camphor, and surgery.

Forensic Entomology

• Colonization of vertebrate corpses occurs in a predictable succession.
• Forensic entomology assists with estimating the elapsed time since death.
• It also provides clues about environmental circumstances at the time of death.

Succession of Colonization

• Fresh corpses attract blow flies (Calliphoridae).
• Drier corpses attract drosophilid flies, cheese skipper flies (Piophilidae), and rat-tailed maggots (Syrphidae).
• Dry corpses attract dermestid beetles and clothes moths (Tineidae).