Mites of Medical Importance

1. MITES of medical importance

2. MITES (Acari)
• Free-living
• Predacious
• Parasitic (endo/ecto)
• Sexes are separated
• How can non-ixodid mies
be distinguished from
ticks?

3. Mites (Acari) - division
• Non-ixodid mites (mites)
- minute size (about 1 mm)
- absence of hypostome
- life span: days or weeks
- generation time: days or
weeks
• Ixodid-mites (ticks)
- size mm to cm
- presence of hypostome
- life span: months or years
- generation time: months
to years

4. Mites- body division
• Gnathosome (capitulum)
- Anterior structure
including the mouthparts
such as pincer-like
chelicerae and pedipalps
- hypostome (optional)
• Idiosome
- sac-like structure
- enclose: alimentary
canal, reproductive
organs, nervous system
- Eight legs in adults
- Hexapod larva

5. Fot. A-D: Gnathosome: 1- hypostome 2- pedipalp 3- chelicera

6. Effects on Humans and Animals
• Dermatitis or other tissue damage.
• Loss of blood or other tissue fluids.
• Transfer of pathogenic agents.
• Strong allergic reactions: asthma, rhinitis, oculorhinitis,
eczema ($10 billion each yr.)
• Livestock: skin damage as much as $45 million worth
each year.

7. General Life Cycle
• Egg
• Hexapod larva
– May or may not feed
• Nymph
– May or may not feed.
– Protonymph, Deutonymph, Tritonymph
• Adults (♀♂)
– May take one or several meals

8. Acariasis
• Infestation with mites (or ticks)
• Some possible sites of infestation:
– Respiratory passages and lungs
– External, inner and middle ear
– Nasal passages
– On and in the skin
– GI tract

9. Sarcoptidae
“Scabies Mites”
• Sarcoptes scabiei
var hominis
• Also called the “itch
mite” of humans
• It causes the “Seven
Year Itch” or
“Norwegian Itch”
• Not Vectors of any
disease

10. Distribution
• Worldwide
• All races and socioeconomic classes
• All climates
• 300 million cases annually!

11. Sarcoptes scabiei (female)

12. Behavior
• The female mite dissolves the stratum corneum of the
epidermis with proteolytic secretions and burrows
downward (initially in thinner skin)
– Bend of knee and elbow
– Webbing between fingers and folds of the wrist
– Genitalia and buttocks
– Breasts
– Head (Norwegian scabies).

13. Life Cycle

15. Recognition of Scabies
• Females narrow twisting tunnels
• Feces in tunnels may be visible through
skin
• Severe itching (reaction to proteins)
• Genital lesions
• Large rashes on body
• Sores on body from scratching
• Patients often dirty

16. Sarcoptes scabiei
• The head,
• face and neck,
• palms and soles
often are involved in
infants and very young
children, but usually not
in adults and older
children

17. Transmission
• Spread by ovigerous female mites
through:
– Personal (prolonged close) contact
– Occasionally by infested sheets (rare)
– Touching or shaking hands (unlikely)
– Sexual activity
– Among children (outbreaks)
– Mites can survive 24-72 hours off host

18. Scabies Rash

19. Rash Continued
• First time: 3-6 weeks incubation
• Second time: 2-4 days (reinfection)
• Development of severe pruritus
– Scratching at night, after hot baths
• Secondary infection
– Boils
– Pustules
• Norwegian Crusted Scabies: (rare)

20. Crusted scabies - massive infestation with
Sarcoptes scabiei var. hominis
Rare and severely debilitating
disease characterized by
infestation of the skin with up to
millions of Sarcoptes scabiei
mites, and the development of
hyperkeratotic skin crusts*
* hypertrophy of the cornea or the horny
layer of the skin
Because they are infested with large numbers of mites
(up to 2 million), VERYCONTAGIOUS.

21. Norwegian scabies on a foot of an AIDS
patient.

22. Unusual scalp crusted scabies in human with T-cell lymphotropic virus 1
(HTLV-1) infection
A: A flower-like nucleated T cell in the peripheral blood smear from the patient. B: Pathology of
marrow biopsy revealed lymphomatous involvement in marrow space. C, D: Crusted scaly
lesions at the scalp and posterior auricular skin fold (arrow). E: Microscopic examination of a
scraping (Lai et al. 2011)

23. Norwegian scabies in a renal transplant patient
(Sampathkumar et al. 2010)

24. Figures 2a & 2b. Crusted lesions over elbow and back of the
malnourished young adult patient (Subramaniam et al. 2010)

25. The hand of a 51-year-old woman with systemic lupus erythematosus,
showing cutaneous greasy eruptions caused by Norwegian scabies
(Chan et al. 2009)

26. Crusted (Norwegian) scabies
• Crusted (Norwegian) scabies is a severe form of scabies that can
affect immunocompromised people, or persons who have
conditions that prevent them from itching and/or scratching (spinal
cord injury, paralysis, loss of sensation, mental debility).
• It is seen often in patients with systemic diseases such as leprosy,
systemic lupus erythematosus, rheumatoid arthritis and leukemia
• It is characterized by vesicles and thick crusts over the skin that can
contain many mites. Itching (pruritus) may be absent because of a
patient’s altered immune status or neurological condition.

27. Diagnosis
• Scraping laterally across the skin with a blade,
taking care to avoid bleeding
• Ink on skin
• Infestation
– Most 1-15 adults
– Avg. 11 adults
– 3% have more than 50
– More than 1000! (Norwegian)

28. Microscopic image of skin scrapings showing scabetic mites (A), eggs and
fecal pellets (B, arrows).

29. Treatment (topical)
• Lindane lotion for 12 hours (neurotoxicity)
– Don’t shower first!
– Shower first, treat later (Norwegian)
• Sulphur Preparations (Mitigal)
– 1 treatment 100% effective, but mild dermatitis
• Modern acaracide (insecticides)
– 5% permethrin cream (low mammalian toxicity)
– 1% aqueous malathion (relatively low human toxicity.)

30. The Left Elbow of a Patient with AIDS before and after Treatment for Scabies.
The patient had heavily crusted elbows before treatment (Panel A), but was cured
of scabies six weeks after the initial visit (Panel B).
She required three doses of oral ivermectin and topical treatment with 5 percent
permethrin cream (Meinking et al. 1995)
A B

31. Trombiculidae
• Around 3000 spp.
Worldwide.
• 20 spp. Medically
important (attack
people) e.g.
Trombicula sp.

32. US distribution of chiggers - other areas
also have focally high populations
The Culprit
Larval
chigger mite

33. • Egg  Larvae (parasitic stage)  2 nymphal stages  Adult.
• Require humidity and a vertebrate host for larval stage
• Non-burrowing
• Tissue feeders: digestive enzymes in the saliva, secreted into host
break down cells and make surrounding tissue harden. As the mite
feeds longer, the saliva seeps farther down, digesting more tissue,
and therefore causing the stylosome to penetrate to lower layers of
skin.
– Reaction around chigger

34. Medical Importance
• Stay on host a couple of days.
• Itching occurs 3-6 hours after exposure.
• More severe due to intense irritation.
• Treatment:
– Bathing
– Antiseptic

36. Chigger Protection
• Stay out of areas where chiggers are likely to be present
including woodlots, pastures, roadside ditches or other areas
with tall grasses and weeds. Chiggers are especially
common in moist low-lying areas.
• Wear loose-fitting clothing and avoid sitting or reclining on
the ground when camping, picnicking or working outdoors.
• Apply a repellent containing DEET (N,N-diethyl-meta-
toluamide) to shoes, socks and trousers before entering
chigger-infested areas.

37. Chigger Protection
• Immediately after possible exposure to chiggers take a bath,
thoroughly scrubbing the body with hot soapy water. This will kill or
dislodge many of the chiggers.
• When bites begin to itch, apply alcohol, followed by one of the non-
prescription local anesthetics. A baking soda paste, calamine lotion
or product such as "After-Bite" also will help reduce discomfort.
• Avoid scratching bites since this only increases irritation and may lead
to secondary infection of the bite.
• Eliminate tall grasses and weeds. Chiggers also can be reduced by
spraying infested plants with carbaryl (Sevin).

38. Animal derived Mites
Dermanyssus gallinae
(Chicken mite)
Ornithonyssus bacoti
(Tropical rat mite)

39. Chicken mite
• Ectoparasite of chickens and
many other wild and domestic
birds
• Temporary parasite of human
• Important vector of Q-Fever,
• And many viruses causing
different types of encephalitis
and encephalomyelitis
Tropical rat mite
• Ectoparasite of rats and many
other wild and domestic
rodents
• Accidental pest to human
• Vector of Q-fever,
• Plague,
• Tularemia
• Recurrent fever

40. Medical importance
• Nymphal stages and
adults feed on animals
and humans
• Painful bites may cause
severe dermatitis and
produce sleepless nights
while they leave nests
invading homes (stress)

41. Demodicidae
“Follicle Mites”
• Tenth to a fourth of a mm
long.
• 2 species:
– Demodex folliculorum
– Demodex brevis

43. Demodecosis hominis  5 m/cm2
• Very common
• Chronic skin disease: mainly the face (T-zone)
• Primary 8-15% secondary 30-40% of the face
• 20% of individuals age 10-20 years is infested
• 100% of the aged have them
• Saprophytic mites are benign except when they invade the dermis,
causing dermatitis
– Acne rosacea
– Chronic blepharitis
– Invade living tissue (rare).

44. Demodecosis hominis
Figure 1 and 2. Demodecosis: numerous
erythematous, dome-shaped papules are
distributed on the face and neck;
a few month history of pruritic skin eruption

45. Blepharitis is an inflammation of the lash follicles at
the eyelid margins due to excess growth in lash
follicles of bacteria normally present on the skin.
The eye with blepharitis

46. Factors predisposing to the disease
• Reduced immunity (chemotherapy, AIDS)
• Metabolic disorders
• Incorrect diet

47. Pyroglyphidae
“House-Dust Mites”
• 2 species we are
concerned with:
Dermatophagoides
pteronyssinos (European
House Dust Mite)
Dermatophagoides
farinae (American
House Dust Mite)

48. Biology
• Dust:
– Prefer mattress dust
– Find in dust samples
– Find in furniture and carpets
• More abundant in older homes
• Humidity:
– 75% relative humidity is optimum.
– 40-50% relative humidity is minimal.
• Not common in more arid parts of the globe.

49. Biology Continued
• Females lay 1-3 eggs/day.
• Eggs hatch after 6-12 days.
• Egg  Larvae  Nymph (2 instars) Adult.
• Life cycle takes 3-4 weeks
• Adults live for 1-2 months.
• Typically 300 mites per/gram of house dust.
– Under ideal conditions (5000 mites/gram dust)
– Record (15,600 mites/gram dust)
– Above 100 mites/gram dust is considered a risk.

50. Allergies
• The exoskeleton and body parts have a common
antigen.
• People who are allergic to dust are also allergic to
mites.
• Have been linked to respiratory disease such as
asthma.
• Treatment/Control
– Severe allergy: can receive a series of injections
(desensitizing vaccine)
– Enclose mattress and pillows with plastic covers
– Wash bedding above temp 550C or dry-cleaning
– Leave electric blanket switched on max for 6 hours or
more during the day and vacuum-clean.

52. Interesting Facts
• House dust mites cause 25% of all allergies and
50% of all asthmatic diseases are traceable to
house dust mites.
• Exposure to house-dust-mite allergen in early
childhood is an important determinant in
asthma development

53. Areas at highest risk for dust mite problems.

54. Ixodid mites - hard ticks

55. ●During blood meal, ticks insert its hypostome into skin.
Its insertation produces an inflammatory reaction of the perivascular
tissues of skin with local edema, thickening and may complicated by
secondary bacterial infection.
● Adults may also enter ear canal causing complication due to enlarged
size after sucking blood, which make it difficult to remove

57. Biology
• life cycle: egg, larva,
nymph, adults
• every active stage feed to
moult or reproduce
• the female after feeding
drop off to lay eggs
(thousands)
• feeding period several
days
• life span from several
months to 3 years

58. Ixodes scapularis female
before feeding …and after the blood meal

59. Ixodid mites - soft ticks

60. Biology
• life cycle: egg, larva, 2-8
nymphal stages, adults
• every active stage feed to
moult or reproduce
• the female after feeding
drop off to lay eggs
(many times)
• feeding period 0,5-1,5 h
(except larva)
● Life span up to 20 years

61. Adult females of certain species (about 50) of hard and
soft ticks secrete neurotoxin in their saliva (made by
ovaries), inoculate it during biting especially in occipital
region.
In the US disease in human is associated with:
Dermacentor andersoni
Dermacentor variabilis
Amblyomma americanum
Ixodes scapularis
Ixodes pacificus
Otobius megnini
Tick paralysis

62. The disease manifests itself as a progressive,
ascending, flaccid motor paralysis that is due to
blocking of neuromuscular transmission.
Clinical manifestations:
I.P: 5-6 days
Rapid onset of:
malaise, vague pains, lassitude, irritability, tingling
sensation in extremities ( lips and face), low or no
fever

63. Clinical manifestations:
In a few a hours an ascending flaccid
paralysis starts:
Difficulty in walking, inability to stand
slurred speech, and diplopia
Death occurs from respiratory paralysis.
Diagnosis:
Clinical manifestations and recovery of ticks
Treatment:
Removal of the tick by gentle movement by
forceps after application of ether or alcohol,
not to miss anchoring mouthparts. Rapid
complete recovery if the paralysis is not in
advanced

64. Lyme disease rash
without central clearing

65. Erythema migrans (EM) rash characteristic
of Lyme disease

66. Multiple
Rashes
• Reaction as
bacteria move
through body
• Not caused by
multiple tick bites

67. Multiple
Rashes

68. LB Symptoms
If left untreated, the infection spreads and can result in
facial palsy (partial paralysis of muscles in one or both sides of the
face), meningitis,
heart palpitations
and severe joint pain.
These symptoms usually resolve in a few weeks but after several
months about 60% of patients will get severe joint swelling and arthritis.
A small minority may also get neurologic symptoms (tingling of the
extremities, shooting pains, numbness)