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Ticks, Mites (Chiggers), and Cyclops - Park's SPM

Source: Park's Textbook of Preventive and Social Medicine

TICKS AND MITES (Acarina)

Ticks and mites form one of the largest and most important orders (Acarina) of the phylum Arthropoda. They are ectoparasites of vertebrate animals and all suck blood.

TICKS

Ticks are of two kinds: hard ticks (Ixodidae) and soft ticks (Argasidae).
Morphology:
  • Oval body, not distinctly separated into head, thorax, and abdomen
  • Four pairs of legs; no antennae
  • Hard ticks: covered dorsally by a chitinous shield called the scutum (covers entire back in males; only anterior portion in females)
  • Soft ticks: scutum absent; head lies ventrally and is invisible from above
  • Males are generally smaller than females
Habits:
  • Hard ticks: feed both day and night; cannot stand starvation; always found on hosts
  • Soft ticks: feed at night; can withstand starvation for several months; hide in cracks and crevices during daytime
Common hard ticks in India: Dermacentor, Haemaphysalis, Hyalomma, Rhipicephalus, Boophilus Important soft tick: Ornithodorus moubata (transmits relapsing fever)

Fig. 12 - Hard Tick

Hard tick - oval body with 4 pairs of jointed legs and visible capitulum (head) at the anterior end with scutum on dorsal surface

Fig. 13 - Soft Tick

Soft tick - heavily sclerotized, dark oval body with 4 pairs of legs; no scutum visible on dorsal surface; head hidden on ventral side

Life History of Ticks (4 Stages)

StageDetails
EggHard ticks: hundreds-thousands at one time (then female dies). Soft ticks: batches of 20-100 over long period. Hatch in 1-3 weeks.
Larva3 pairs of legs. Waits on grass/herbage for host. After blood meal, drops off and moults to nymph. Lasts 3-13 days.
Nymph4 pairs of legs, no genital pore. Blood suckers. Soft ticks have 5 nymphal stages.
AdultHard ticks: egg to adult ~2 months. Soft ticks: 9-10 months. Adults live 1 year or more.

Public Health Importance

Hard ticks transmit:
  • (a) Tick typhus (Rocky Mountain Spotted Fever)
  • (b) Viral encephalitis (e.g., Russian Spring-Summer Encephalitis)
  • (c) Viral fevers (e.g., Colorado Tick Fever)
  • (d) Viral haemorrhagic fevers (e.g., KFD in India)
  • (e) Tularaemia
  • (f) Tick paralysis
  • (g) Human babesiosis
Soft ticks transmit:
  • (a) Q fever
  • (b) Relapsing fever
  • (c) KFD
The tick attaches by burrowing its rostrum into the skin to suck blood, while secreting saliva containing a neurotoxin. Disease is transmitted trans-stadially (larva and nymph can also transmit) and by transovarian transmission through successive generations.

Comparison: Hard vs Soft Ticks

FeatureHard Ticks (Ixodidae)Soft Ticks (Argasidae)
ScutumCovers entire back (male); small anterior portion (female)Absent
HeadAnterior endVentral; not seen from above
SpiraclesBehind IV coxaBetween III and IV coxa
EggsHundreds/thousands at one sittingBatches of 20-100 over long period
Nymphal stagesOneFive
HabitsCannot stand starvation; feed night and dayCan stand starvation for a year or more
DiseasesTick typhus, viral encephalitis, haemorrhagic fever, tularaemia, tick paralysis, babesiosisRelapsing fever
Key speciesDermacentor andersoni, Haemaphysalis spinigeraOrnithodorus moubata

MITES (Chiggers)

Mites resemble ticks - 4 pairs of legs, body not well demarcated into head, thorax and abdomen. Two mites of public health importance:
  1. Trombiculid mite (chigger mite)
  2. Itch mite (Acarus scabiei / Sarcoptes scabiei)

TROMBICULID MITES

Spider-like arthropods. Important species: Leptotrombidium deliense and L. akamushi - vectors of scrub typhus in Asia and South Pacific.

Life Cycle of Mite (4 Stages)

StageDetails
EggLaid singly; hatch in ~1 week
LarvaVery small, pale orange, 3 pairs of legs. Attacks vertebrate hosts (rodents/man). After blood meal drops to ground; lasts 1-2 weeks
NymphBrick-red, 4 pairs of legs; lives on vegetable juices; lasts 1-3 weeks
AdultMale lives in soil; 4 pairs of legs (first pair largest); lives ~6 months

Fig. 14 - Life Cycle of a Mite (Eggs, Larva, Adult)

Mite life cycle diagram showing eggs (small round clusters at top), larva (hairy 6-legged form, left), and adult (8-legged form, right) labeled clearly

ITCH MITE (Sarcoptes scabiei)

  • Just visible to the naked eye; measures 0.4 mm
  • Body shaped like a tortoise - rounded above, flattened below
  • No demarcation into cephalothorax or abdomen
  • Body surface has folds and short bristles
  • Two pairs of legs in front, two pairs behind
  • Front legs: end in long tubular suckers
  • Hind legs: end in long bristles
  • Males have suckers on all legs except 3rd pair (distinguishes from female)
The female burrows into the epidermis causing scabies (itch).

Fig. 15 - Itch Mite (Sarcoptes scabiei)

Itch mite ventral view showing rounded tortoise-shaped body, 4 pairs of stubby legs with suckers on front pairs and bristles on hind pairs, and central mouth parts
Life history of itch mite:
  • Egg: Female lays up to 30 eggs (2-3/day) within burrows in stratum corneum; hatch in 3-4 days
  • Larva: Three-legged; leave burrows, bore into hair follicles; mature in ~3 days
  • Nymph: Develop into adults in 6-8 days
  • Adult: Full life cycle egg to adult = 10-15 days; adults live 1-2 months
Scabies - Mode of spread: (1) Close contact - sleeping in same bed, children playing, nursing infested persons; (2) Contaminated clothes and bed linen.
Sites of lesion: Hands and wrists (63%), extensor aspect of elbows (10.9%), axillae, buttocks, lower abdomen, feet and ankles, palms (in infants), breasts (women), genitals (men).
Control of ticks and mites:
  • Insecticidal: DDT, chlordane, dieldrin, lindane, malathion (1-2 lbs/acre)
  • Environmental: Fill cracks/crevices; reduce wild rodent hosts
  • Personal protection: Protective clothing with insect repellents (indalone, DEET, benzyl benzoate); regular self-examination in tick-infested areas

CYCLOPS (Water Flea)

Cyclops is a crustacean present in most collections of fresh water.
Morphology:
  • Tiny arthropod, not more than 1 mm in length
  • Just visible to the trained eye
  • Pear-shaped, semi-transparent body
  • Forked tail (furca)
  • 2 pairs of antennae
  • 5 pairs of legs
  • One small pigmented eye (hence "Cyclops")
  • Swims with characteristic jerky movements
  • Average life: ~3 months

Fig. 16 - Cyclops

Cyclops (water flea) line illustration showing pear-shaped segmented body, prominent 2 pairs of antennae at top, 5 pairs of swimming legs, bilateral egg sacs (ovisacs) on lower thorax, and forked tail (furca) at bottom

Public Health Importance

  1. Dracunculiasis (Guinea-worm disease): Cyclops is the intermediate host. Man acquires infestation by drinking water containing infected cyclops harboring the larvae of Dracunculus medinensis.
  2. Fish tapeworm (Diphyllobothrium latum): Cyclops also acts as one of the intermediate hosts (rare in India).

Control of Cyclops

MethodDetails
Physical - StrainingStraining water through fine cloth removes cyclops
Physical - BoilingKilled at 60°C; useful for individual prophylaxis
Chemical - Chlorine5 ppm destroys cyclops and guinea-worm larvae (excess must be dechlorinated)
Chemical - Lime4 g per gallon of water
Chemical - Abate (OMS-786)Organophosphorus insecticide; 1 mg/litre effective
BiologicalBarbel fish and gambusia fish feed on cyclops (used successfully in Karnataka)
Permanent solutionPiped water supply or tube wells; abolition of step wells
Source: Park's Textbook of Preventive and Social Medicine, Chapter on Arthropods of Public Health Importance (pp. 882-885)
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