Entomology for Medical students

1. 1-3mm
• Members of class insecta,
order diptera
• 127 families, >85,000 species.
• Diptera - most important 18-22mm
vectors human disease.
 > 1 million deaths p.a.
1
1-1.5mm

2. Flies - blackfly 1-3m m
Family Simuliidae.
• Simulium damnosum, S. neavei - important vectors in Africa.
• Simulium ochraceum - important vector in New World
(Australia – New Zealand)
• Breeds close to fast moving water or water falls
– Eggs are laid on running water, larvae attach on submerged
structures e.g. rocks, trees & vegetation
– S. neavei in Africa occur on arthropods
2

3. Black fly
1-3mm
Effects on hosts.
Allergic reactions. "Blackfly fever"
Vector - Onchocerca volvulus – filarial nematode.
Vectors - Leucocytozoon spp. - "malaria" in birds.
3

4. Midges.
1-1.5mm
Effects on vertebrate hosts:
• Annoyance.
• Vectors of Acanthocheilonema perstans
-filarial parasite humans and other filarial
nematodes.
4

5. Tabanids
Order Diptera.
Suborder Brachycera
18-22mm
Family Tabanidae.
• ~ 4000 species
• Females intermittent parasites
• Males not parasitic
• Adults - large body (6-25mm long)
• Large eyes - facilitates host location
• Mouthparts - cut large wound, where they feed
from a formed pool of blood
5

6. (c). Flies - tabanids
& bacteria. 18- 22m m
Suborder Brachycera, Family Tabanidae.
• Mechanical vectors:
– Bacillus anthracis – anthrax.
– Francisella tularensis - tularemia – deerflies Chrysops spp.
• Blood loss
Important genera:
• Tabanus
6

7. Flies - tabanids
18-22mm
• Vectors Loa loa, - filarial nematode.
• “Eye worm“.
• Vectors for Chrysops spp. (deerflies).
• C. dimidiata - most important.
7

8. Flies - tsetse fly
Family Glossinidae, genus Glossina.
• Hosts & vectors of trypanosome protozoans.
• Trypanosoma brucei species complex.
• Sub-saharan Africa.
8

9. Flies - sandflies
Family Psychodidae
Phlebotomus & Lutzomyia species
• Vectors of Leishmania - protozoa
• Cutaneous leishmaniasis (L. tropica - Old World
• L. mexicana- New World)
• Mucocutaneous leishmaniasis (espundia) - L.
braziliensis
• Visceral leishmanisis (kala azar) - L. donovani
9

10. Sand fly
• Sand flies
• Phlebotomus & Lutzomyia
• Short mouth parts, pool feeders
• Only ♀♀ take blood
• Vector of Leishmania, bartonellosis
(bacterial) & sand fly fever (viral)
• Less than 5mm length, hairy body &
wings
• Old world species live in arid/semi-
arid conditions, new world species are
forest dwellers
• Epidemiological implication
• Have limited flight range close to
breeding sites
• Most active at twilight, night & shade
10

11. House fly
• Musca domestica
• Domestic flies act as mechanical vectors of
many diseases
11

12. Public Health importance
1. Nuisance
• Large numbers flies can be bring significant
nuisance by disturbing people during work
and at leisure.
• Flies soil the inside and outside of houses
with their feaces.
• They can also have a negative psychological
impact because their presence is considered a
sign of unhygienic conditions.
12

13. 2. Diseases
• Flies can spread diseases because they feed freely on
human food and filthy matter
• Flies pick up disease-causing organisms while
crawling and feeding
• Those that stick to the outside surfaces of the fly
may survive for only a few hours, but those that are
ingested with the food may survive in the fly’s crop
or gut for several days
13

14. Diseases that flies can transmit include enteric
infections (such as dysentery, diarrhoea,
typhoid, cholera and certain helminth
infections), eye Infections (such as trachoma)
14

15. • Triatomine Bugs
(Order Hemiptera,
Genus Triatoma)
• Fleas (Order Siphonaptera)
Human Flea (Pulex)
Rat Flea (Xenopsylla)
Cat Flea (Ctenocephalides)
Jigger Flea(Tunga)

16. Bugs
• Class: Insecta
• Order: Hemiptera
• Family: Cimicidae ( bed bugs )
• Family: Reduviidae
• Sub-family: Triatominae
• 15 genera with > 100 spp
• Panstrongylus, Triatoma, Rhodnius

17. Bed bugs
• Family: Cimicidae
• Blood sucking
• Temporary ectoparasites of birds and
mammals
• Human parasites:
– Cimex lectularis - main
– Cimex hemipterus
17

18. Morphology
• Oval, dorso-ventrally flattened, red-brown
bodies
• They are covered with short, stout hairs
• They are 5-7mm long, with females slightly
larger than males
• Head have prominent compound eyes.
• The proboscis is flexed backwards under the
head when not in use
• Legs terminate in a pair of simple claws
• Forewings reduced (hemielytra pads), hind wings
absent
18

19. 19

20. Habits
• They feed at night on humans or other
mammals
• A blood meal is essential to production
of eggs
• Conceal themselves during the day in
crevices of wooden beds, mattresses,
or under loose wallpaper.
• In search for hosts, they respond to
warmth & CO2, odours
20

21. Habits...
• Are easily transported in clothing and
baggage
• In cold weather they remain inactive in
hiding places
• They can survive starvation for over a
year
• Emit a characteristic odour from scent
glands
• Often found in dwellings with high rate of
occupant turnover – hotels, motels,
hostels, shelters & apartment complexes
21

22. Life Cycle
• Females deposit about 200 eggs in cracks
and crevices
• Eggs
– White, ovoid, about 1mm in length
– Have an operculum at the anterior end
– They are coated with transparent cement
– They hatch in 4-10days
– No hatching at 37⁰ or below 13⁰ C
• Incomplete metamorphosis
22

23. Life cycle...
• Nymph
– Yellowish-white to brown
– Passes through 5 or 6 moults before
becoming a sexually mature adult
• At 30⁰C, development from eggs to adult
takes 3 weeks
• The life span of the adult is 6-12 months
23

24. Medical Importance
• Sleep disturbance
• Biting nuisance
– The bite produces red, itching wheals
– Allergic symptoms – local or generalised urticaria and
asthma
• Transmission of diseases?
– Not believed to be a vector of disease
– As a mechanical carrier - Hepatitis B virus from human
to human. Virus from faeces could infect a person by
contamination of skin lesions or mucosal surfaces or by
ingestion of dust
24

25. Triatomine bugs
Family: reduviidae
Sub-family: triatominae
• Cone nose/assassin/kissing bugs
• Medically important, only found in americas
• Size: 1-4 cm long
• Elongated head
• Lateral 4- segmented antennae
• Eyes lateral

26. Tritomine bugs...
• Proboscis ventrad
• Two pairs of wings
• Basal fore wing thick/hardened, posterior wing
membrenous = heteroptera
• Lateral margins of abdomen visible dorsally

27. Triatomine bugs…
• Most are dull brown but some may have markings
• The shape of the head, position of the antennae
relative to the eyes: genera specific
• Hemimetabolous
• Eggs laid in/near host habitations: cracks on walls
etc

28. Life cycle…
• Eggs are laid in batches 100-800
• Hatch into wingless nymphs
• There are 5 nymphal instars, each requiring
blood
• N4 and N5 have rudimentary wings
• May take in blood up to 10x body weight
• Assassin?

29. Life cycle…
• Both nymphs and adults feed nocturnally
• Feed on exposed parts of the body: face, eyes,
nose, mouth - kissing
• Defecates during feeding
• Feed on humans, wild and domestic animals.

30. Life cycle…
• Development from egg to egg takes 3 months in lab
but may take 1-2 yrs in nature
• Vectors of T. cruzi:
• R. prolixus, P. megistus, T. dimidiata and T.
infestans
• Prevention and control
• Insecticide residual spraying, Insecticide treated
bednets, improved housing

31. Order Siphonaptera
• SIPHONAPTERA: Greek "siphon" (hollow tube) + "a"
(without) + "pteron" (wing); fleas are wingless and have
tube-like mouthparts for sucking blood
• Body hard, laterally compressed, and bristly
• Legs long with large coxae and 5-segmented tarsi
• Generally live as ectoparasites of mammals and birds.
• Fleas transmit various pathogens, including tapeworm and
bubonic plague.
• About 1,100 species of Siphonaptera in the world, 238 in
North America.
• 7 families of fleas based on characters of the head,
abdomen, and various bristles. Many characters are visible
only on specimens mounted on microscope slides.

32. Order Siphonaptera...
Pulicidae -- common fleas
Ischnopsyllidae -- bat fleas
Tungidae -- sticktight and chigoe fleas
Dolichopsyllidae --rodent fleas
Hystrichopsyllidae -- rat and mouse fleas
Malacopsyllidae -- malacopsyllid fleas
Vermipsyllidae -- carnivore fleas

33. Distribution
• Species and genera are distributed in East-Asian,
Central-Asian, West-American, Patagonian, Papuan
(New Guinean), and East-African zoogeographical
subregions.
• Forest foothills with temperate and subtropical climate
most favourable conditions for the fleas.

34. Morphology
• Shape of the head, flat body & prehensile claws
of legs help it to move easily through host’s
wool
• Length of jump some flea species attain ~32
cm, average body length being from 1 to 5 mm

36. Biology
• Fleas are obligatory blood feeders parasitizing warm-
blooded vertebrates. More than 94% of known species
are parasites of mammals and only about 5% of them
occur on birds
• Fleas have 4 phases of development - the egg, the free-
living larva, pupa and the imago
• The larvae is wormlike, legless & eyeless with biting
mouth parts. The larvae undergoes 3 instars. Prior to
pupation it empties the alimentary canal, and spin a
silken cocoon
• The majority of fleas are closely associated with the
host's home (nest, burrow etc), attacking the host for
feeding

37. Life cycle
• Adult flea jumps onto a host, gets a meal. A flea
bite becomes inflamed, itchy and swollen
• Once fed, the flea will mate and lay eggs. This
occurs in yards, houses, & on pets
• In the next two to three weeks, hundreds of eggs
will be laid in yard, house and on the host
• Eggs hatch into small larvae, which feed on
anything organic. Including dried blood, flea
faeces, animal hair.

38. Life cycle...
• The larva will feed for days, spin a cocoon and undergo
metamorphosis
• This stage is called the flea pupa. Its a worst stage
because of its resistance to control
• The cycle is completed when the flea pupa hatches out.
Hatching occurs when a host is close, will bite and the
cycle will start all over again

39. Medical significance
• Fleas transmit pathogens that cause disease in
humans and other animals.
• The Cat and Dog flea are intermediate hosts for a
tapeworm (Dipylidium caninum) that infects dogs, cats, and
humans
• The Rabbit flea spreads a myxomatosis virus within rabbit
populations
• Oriental Rat Flea is the primary vector of Yersinia pestis,
the bacterial pathogen for bubonic plague.
• The cat flea commonly infests dogs, dog flea may
infest cats; both species may bite humans

40. Medical significance...
• Sand flea/jigger, Tunga penetrans
• Infect humans, pigs, birds
• Adapted to intracutaneous attachment, larvae free living, adults
free living but after mating penetrate the hosts.
• Soft areas are preferred for penetration
• In the body attaches with mouth, swells and envelops itself
leaving a spiracle for breathing
• Irritations start when a flea is mature, scratching helps to release
eggs

41. Control
• Best stage to control is an egg
• Treating animal pets
• If the pet is an inside animal, treat the home and the pet
• If the pet is an outside animal, treat the pet & the area the pet has
access to
• Treat home areas when fleas suspected
• Application of repellents
• Keeping environments clean out of organic matter
• Sweeping, mopping floors
• Treating floors with insecticides; DDT, OPs, PY, Cb
• Burning off infested soils
• Flea trap to induce hatching of pupae

42. Control...
• Wearing good, intact shoes
• Daily inspection of areas of the feet (interdigital
clefts)

43. Other ectoparasites
Arachnid Vectors TICKS
• Soft Ticks
1. TICKS
Class: Arachnida
Soft Ticks (Ornithodorus) Order: Acarina
Family: Argasidae
Hard Ticks (Ixodes, Amblyomma, Genus: Ornithodorous
Rhipicephalus, Dermacentor)
General Characteristics
-tough leathery integument
2. MITES -flattened oval shape when examined
(Dematophagoides, Demodex, dorsally
Sarcoptes) -they lack the dorsal shield
-they need to be examined ventrally to
observe their capitulum or
• Lice (Order Phthiraptera) mouthparts.
– Head/Body Lice (Pediculus)
Crab Lice (Phthirus)
43

44. Ticks
• Ornithodoros spp. is the Ornithodoros populating in
most important soft tick Europe, Africa, Asia and
disease vector found Americas.
throughout the world
Life cycles
• Soft ticks have a
hemimetabolous life cycle,
eggs hatching six legged
larvae, which moult to eight
legged nymphs
44

45. • There are 5 - 7 larval instars • The duration of the life cycle
depending on the species depends on temperature, host
availability and species
• Each stage requiring a blood
meal to proceed except of Disease
Ornithodoros moubata • Soft Ticks are vectors for
serious disease including :
– Tick borne relapsing fever
• Adult females lay small egg (Borrelia duttoni)
batches following each blood – Rickettsial disease (Coxiella
meal burneti), and some arboviruses
45

46. Hard Ticks
• Class: Arachnida
• Order: Acarina
• Family: Ixodidae
• Genus: Ixodes, Amblyomma, Rhipicephalus,
Dermacentor
46

47. General Characteristics
• They are flattened when examined dorsally
• Characterized by the presence of a dorsal plate or
scutum, and a capitulum that projects beyond the body
outline
• The scutum regularly covers the entire dorsal area
• Ixodes spp. inhabit in Canada, Europe, Russia,
China, Japan and Australia
47

48. • Ixodes Adult male
showing the scutum
covering the whole length
of the body
• The capitulum is seen
protruding forward
beyond the body outline
48

49. Life Cycle
• Similar to that of Soft Ticks
• There is only one nymph stage in Ixodes, and
following several weeks of stasis the nymph
will metamorphose into an adult
49

51. Diseases
• Hard ticks transmit lyme disease, tick paralysis and
Rickettsiae
• Arboviruses that are responsible for encephalitis and
haemorrhagic fevers, tularaemia and Babesia microti
infection
51

52. Other medically important Hard Ticks
• Dog ticks
Wood ticks (Rhipicephalus) found in
(Dermacentor andersoni) coastal areas.
• Lone Star ticks
• Found in the (Amblyomma
mountainous west of mericanum) found in
North America; forests in SE USA
• The females of these
species causes tick
paralysis.
52

53. • Dermacentor variabilis • Amblyomma, male hard
tick.
53

54. • Both Dermacentor and Amblyomma transmit Rocky
Mountain Spotted Fever (Rickettsia rickettsia).
• Dermacentor transmit arboviruses responsible for
encephalitis and heamorrhagic fevers.
• D. variabilis is also responsible for spreading
tularaemia, Mediterranean Spotted Fever and
African Tick Typhus.
54

55. Control
• Improve sanitation
• Cementing floors to eliminate cracks and crevices
and facilitate cleanliness
• Where floors are not cemented should be kept out
of dust
• The floors and walls up to a height of about half a
meter should be spread or dusted with lindane
55

56. • With dust floor monthly application would be
necessary
• Other chlorinated hydrocabons, organophosphorus
compounds, carbomates or pyrethroids may be
used
56

57. Mites
• Class: Arachnida • General Characteristics
• Order: Acarina • Dematophagoides, is a
• Genus: Dematophagoides, common dust mite,
inhabit beds,
Demodex, Sarcoptes mattresses, carpets and
house dust
57

58. • They are motile
• They feed on residual
organic debris 0.3 mm
in length
• They have four long
legs, suckers and pincer
chelicerae
58

59. • Dermatophagoides are antigenic, even when dead
(fecal pellets are also allergenic)
• Associated with complex allergies & symptoms such
as asthma, conjunctivitis and dermatitis.
• A treatment involves removal of accumulated
antigens from mattresses and pillows
59

60. • Demodex have been implicated in dermatitis and
should be considered in chronic, therapy-resistant
cases of blepharitis (inflammation of eyelids)
• The role of this mite in ocular disease is uncertain
washing with soap and water is the most effective
method of prevention.
60

61. • The mite, Sarcoptes scabiei, lives
on human skin causes scabies
• It is small (larger female is 0.3-
0.4 mm), colorless and oval with
8 short legs
61

62. • Symptoms of Sarcoptes infection arise after 4-6
weeks post invasion
• Comprise a papular pruritic eruption at a site
often unrelated to the site of infestation;
symptoms of secondary infestations arise almost
immediately
62

63. • Persistent nodular scabies involve itchy
erythematous or scabbed nodules
• When the immune system is impaired, Norwegian
(crusted) scabies may develop
– This presents with erythema and hyperkeratosis but little
itching
63

64. Diagnosis
• Discovery of mites or eggs by epidermal shave
biopsy or superficial scraping
• Burrows are best seen on wrists and inter-digital
spaces
• They fluoresce under a Wood's lamp after
application of liquid tetracycline and alcohol;
alternatively ink may be used
64

65. Treatment and control
• Lindane lotion is the treatment of choice,
permethrin is another alternative
• Ivermectin has been recommended for
Norwegian scabies
• Malathion liquid can also be used, benzyl
benzoate is also active
65

66. • Malathion should be avoided in infants
• Lindane should be avoided in pregnancy, breast-
feeding and in young children
• Treatment is applied over the whole body
except the head and neck and washed off after
24 hours
66

67. • Normal laundering of bed linen and clothes is
recommended
• Household and sexual contacts should also be
treated
• Symptoms may continue after treatment
because of persisting antigens, Calamine lotion
may be used
– other problems include re-infestation and secondary
bacterial infection
67

68. Myiasis
• Infestation of the organs and tissues
of humans or animals by fly larvae that
for some period of time, feed upon the
living or dead tissues or the ingested
food of the host
• It is the condition in which larvae of
flies exist as parasites in bodies of
vertebrates

69. Myasis
• Myasis is caused when fly maggots
(larvae of dipterans) invade living tissue or
when they are harboured in the intestines
or bladder
• Clinically, maggots causing myasis attack
three parts of the bogy: Cutaneous tissue,
body cavities and gut lumen

70. Myasis
• Some spp of maggots cause subcutaneous myasis, invade sores
&wounds (wound myasis), burrow under the skin (dermal
myasis)
• Body cavity myasis: Nasal myasis, ocular myasis ear myasis,
myasis of the anus and vagina
• Intestinal myasis-Eggs/larvae of many spp are deposited on
food stuffs may survive the journey to intestinal tract. They
may persist for months producing severe anxiety, and intestinal
irritation

71. Myasis
• Accidental = Facultative Myiasis
• Obligatory Myiasis

72. Myasis
• A number of families of flies e.g. Calliphoridae, Sarcophagidae
and Oestridae are composed of flies that are have either
facultative or obligate parasitic larval forms
• Family: Calliphoridae
• Non- metallic flies e.g. Cordylobia anthropophaga(Tumbu fly),
Auchmeromya senegalensis (Congo floor maggot)
• Metallic flies screw worms e.g. Cochliomya hominivorax(New
World), Chrysomia spp (Old World)
• Blow flies e.g. Lucilia spp (green bottles), Calliphora spp

73. Myasis
Family Sarcophagidae(Flesh flies)
The two genera Sarcophaga and Wohlfahrtia are of medical
importance
Family Oestridae
Subfamilies: Oestrinae, Gasterophilinae, Hypodermatinae and
Cuterebrinae.
Oestrinae, Gasterophilinae, Hypodermatinae are obligatory parasites of
domestic animals
Cuterebrinae has six genera that cause myasis in rodents, monkeys and
livestock
-Dermatobia hominis causes obligatory myasis in people and animals
living in central and south America

74. Facultative Myiasis
• Cutaneous myiasis - usually around wounds
• Larvae normally found in meat or carrion occasionally adapt
to a parasitic existence
• Usually do not invade healthy tissues
• Typically blow flies: species of Calliphora (bluebottles),
Lucilia (greenbottles), Phormia, Sarcophaga and
Wohlfahrtia (flesh flies), Cochliomyia macellaria (secondary
screw-worm), and others

75. Forensic Entomology, 2001. Byrd and Castner, Eds.

76. Forensic Entomology, 2001. Byrd and Castner, Eds.

77. Forensic Entomology, 2001. Byrd and Castner, Eds.

78. Facultative Myiasis
• Enteric Myiasis - accidental ingestion
• 50 species reported - most Muscidae and
Sarcophagidae
• Passive transport of larvae - no development in host
digestive tract
• Severity depends on fly species, number, location
• Genera commonly involved: Musca, Fannia,
Muscina

80. Facultative Myiasis
• Rectal/Urogenital Myiasis – access to intestine via
anus; larvae feed on excrement
• Immature stages may be completed in rectum or
terminal part of intestine
• Can occur in humans under unsanitary conditions
• Primary genera - Fannia, Musca, Sarcophaga

82. Sarcophaga Species

83. Obligatory Myiasis
• Calliphorids (non-metallic):
⇒ Cordylobia anthropophaga - tumbu or mango fly (Africa);
larvae attach and burrow into skin leaving spiracles
exposed - boil-like swelling [cover with paraffin or oil to
extract]
⇒ Auchmeromyia senegalensis - Congo floor-maggot
(Africa); adult looks like tumbu fly, but larvae do not
remain attached; feed nightly from people sleeping on
the floor

84. Obligatory Myiasis
• Calliphorids (metallic):
⇒ Cochliomyia hominivorax - New World screw-worm;
eradicated from US and Mexico, but outbreaks possible
⇒ Chrysomya bezziana - Old World screw-worm
• Sarcophagids (flesh flies):
⇒ Wohlfahrtia magnifica - ear, eye, nose
• Oestrids (bot flies):
⇒ Gasterophilus, Hypoderma, Oestrus, Cuterebra sp., and
Dermatobia hominis (human bot fly)

87. Dermatobia hominis larva
(human bot fly)

88. Control of Myiasis Species
• Control or eradication of the fly population - through
environmental sanitation or chemical control
• Avoidance of infestation (mechanical control) - do not sleep
outdoors or on the ground during fly activity, dress or cover
wounds to avoid fly strikes, use screening
• Treatment of infestation (remove larvae - antibiotic follow-up)