L4: Medical Entomology Flashcards
What is the classification of arthropods?
Class insecta and class arachnida
What are the characteristics of class Insecta?
Body:
Wings:
Legs:
Head, thorax, abdomen
Present or absent
Three pairs (Hexapoda)
What are the characteristics of class Arachnida?
Body:
Wings:
Legs:
- Cephalothorax, abdomen - one mass
- Absent
- Four pairs (Octopoda)
What is the medical importance of arthropods?
- Arthropods as disease agents:
- Dermatitis by the insect bite e.g., lice, mosquitoes.
- Inoculation of poisons e.g., ticks.
- Tissue invasion Sarcoptes scabiei (Scabies), larvae of flies (myiasis).
- Entomophobia: abnormal fear when seeing an arthropod (e.g., Spiders). - Arthropods as vectors for transmission of diseases agents, by:
- Mechanical transmission (Passive carrier), e.g. Typhoid fever by Musca fly.
- Biological transmission (Part of its Life cycle), e.g. Plague by Fleas
What are the general characters of mosquitos?
ο One pair of wings.
ο The female mouth is adapted for piercing & sucking of blood. Male feed on nectar.
ο Complete metamorphosis [Egg (on water surface) β> Larva (aquatic) β> Pupa (aquatic) β> Adult].
What is the medical importance of mosquitos? ( female transmits)
ο Human malaria (Anopheles spp.)
ο Lymphatic filariasis (Culex spp.) (elephantiasis is due to Normal mosquito)
ο Yellow fever, dengue fever (Aedes aegypti)
What are the methods of control of Mosquitos?
ο Physical control: Elimination of breeding places, bed nets, wire screening of doors and windows.
ο Biological control: Natural enemies such as frogs, Gambusia affinis fish.
ο Chemical control: Insecticides (Paris green as poison for larvae, DDT), repellants (Citronella oil).
What are the general characters of flies (Musca domestica)?
ο The adult fly is 6-10 mm long, grey in color. One pair of wings.
ο Mouth parts are soft, retractile, adapted for lapping and sucking fluids.
ο Complete metamorphosis [Egg (on ground) β> Larva β> Pupa β> Adult].
What is the medical importance of flies?
- Mechanical transmission of Viruses, Bacterial & Parasites disease (e.g., protozoa cyst & helminths eggs).
- Accidental myiasis.
What are the methods of control of flies?
ο Health education and sanitation.
ο Fly nets.
ο Insecticides e.g. DDT & Pyrethrum.
What are the general characters of lice (pediculus spp.)?
ο Small insect 2-4 mm, wingless. Permanent ectoparasites.
ο Mouth parts are adapted for piercing and sucking blood in all stages.
ο Incomplete metamorphosis [Egg β> Nymph β>Adult]
What are the names of lice infesting man?
ο Pediculus humanus capitis (head louse).
ο Pediculus humanus corporis (body louse).
ο Phthirus pubis (pubic louse): sexually transmitted parasite.
What is the medical importance of lice?
- Head Lice (more common) cause itching and dermatitis (NOT known to transmit pathogens but stimulates its invasion).
- Pediculosis (vagabondβs disease) by all types: severe dermatitis, skin becomes thickened hyper-pigmented skin.
- Vector of diseases (body louse): as ο Epidemic typhus.
ο Epidemic relapsing fever. ο Trench fever.
What are the methods of treatment and control of lice?
ο Heath education and good hygiene. Frequent bathing.
ο Topical pediculicides (Permethrin lotion 1%, Benzyl alcohol).
ο Oral ivermectin.
ο Wet combing of hair (to remove eggs). Washing clothes and bed lining in boiled water
What are the general characters of fleas?
ο -Small, bilaterally compressed. Brown in color, with no wings.
ο -Mouth is adapted for piercing and sucking of blood.
ο - Complete metamorphosis (Egg β> Larva β> Pupa β> Adult).
What is the medical importance of fleas?
1- Plague:
- It is an acute severe bacterial disease.
- Fleas act as vectors and transmit them to humans;
- It is an acute infectious disease caused by bacteria (Yersinia pestis) which is transmitted from human or rats to human by fleas.
- e.g., Pulex irritans (Human flea), Xenopsylla cheopis (rat flea).
2- Endemic typhus feve (Rickettsial infection). Fleas act as vectors and transmit them to humans.
3- Flea dermatitis: Itching due to biting followed by a 2ry bacterial infection.
What are the methods of control of fleas?
- Sanitation: Vacuuming of carpets and furniture.
- Boiling of cloths and linings.
- Application of insecticides as Pyrethrins or Insect growth regulators sprays for indoor and infested pets.
- Flea traps
What are the general characters for ticks?
- The body is one mass sac-like.
- The mouth is adapted for piercing and sucking. (In all stages)
- Metamorphosis is gradual (Egg β> Larva (6L)β> Nymph (6L)β> Adult)
. - Ticks are classified into 2 families:
ο Ixodidae (hard ticks). ο Argasidae (soft ticks).
What is the Medical importance of ticks?
- Diseases transmitted by ticks:
a) Bacterial diseases: e.g., Lyme disease.
b) Viral disease: e.g., Viral meningoencephalitis fever.
c) Protozoal diseases: e.g., Texas cattle fever. - It causes Dermatitis.
- It causes Tick Paralysis.
- It is produced by some toxins in the saliva of the tick;
- it produces a blockage of the neuro-muscular junctions of the spinal cord. (When it is near the CNS)
- Paralysis disappears after the removal of the causative tick.
What is the treatment and control of tick paralysis?
- By the removal of the tick after covering the tick with ether or gasoline oil.
- Control: Spraying insecticides on the floors, in cracks in the walls
What are the important members of mites causing diseases to man?
- Sarcoptes scabiei.
- Demodex folliculorum.
- House dust mites (HDMs).
What are the general characters of Sarcoptes scabies?
- It is a small mite (200-450 ΞΌm), grey (like flies) in color, oval in shape (itch mite).
β’ It has 4 pairs of legs as adult & nymph
and 3 pairs of legs as larva.
- Skin disease, worldwide, increase in poor hygiene & over-crowded areas.
- Mouth is adapted for tearing the tissues.
- Metamorphosis is gradual like lice and ticks (Egg Larva Nymph Adult).
What is the habitat of Sarcoptes scabiei and its life cycle?
ο Skin: It lives in intracutaneous tunnels of thin skin between fingers, wrist, back of the hands, elbows, axillae, breast, umbilicus, back, bends of the knee, groin, buttocks, and external genitalia.
ο The head and neck are not affected.
ο The female burrows tortuous tunnels in the skin epidermis and deposits eggs.
ο both larvae and nymph are found in hair follicles.
ο Maturity occurs after two weeks from the deposition of the eggs
ο The larvae and nymphs move freely over the skin and are found in hair follicles.
What is the mode of infection by Sarcoptes scabiei?
By contact with an infected person or contaminated clothes and sexual contact.
