Ticks

PARASITES ARACHNIDA

Introduction

Ticks are ectoparasites which live by hamatophagy on the blood of mammals, birds and sometimes reptiles and amphibians. Ticks are of considerable veterinary importance, particularly in warmer climates where they can cause substantial economic losses through decreased productivity and disease. They are also also important in human medicine as they cause Lyme Disease and tick-bourne encephalitis/meningoencephalitis.

Ticks decrease productivity by causing fleece and hide damage, preventing animals from feeding (tick worry), ascending motor paralysis and anaemia. Infestation can also lead to secondary infection from blowfly and screw-worms leading to strike.

The soft ticks are only of importance in warmer climates, whereas the hard ticks cause significant problems in both warmer and temperate climates.

Morphology

• Mouthparts
  • Sensory organs for locating a feeding site called palps
  • Chelicerae for puncturing the skin
  • The hypostome pushes through the wound made by the chelicerae where backwards pointing teeth lock the mouthparts into the skin
    • Dorsal groove in the hypostome permits the flow of tick saliva and host blood

Hard Ticks

• Hard, chitinous covering over dorsal surface called the scutum
  • Unique to hard ticks
  • Males have a scutum which covers the entire body surface
  • Females have a scutum which only covers a small area behind the head

• Prominant biting mouthparts

• Festoons ('pie crust edging') around the posterior body margins

• Enamel coloured patches on scutum are present on ornate ticks

• Female hard ticks may swell up to three times their normal size when taking a blood meal

Soft Ticks

• No scutum

• Mouthparts are not visible from dorsal surface

• Feed little and often as cannot swell as much as hard ticks

Feeding

• Ticks stand upright

• Chelicerae cut through skin creating a pool of blood

• Hypostome is inserted deep into the skin

• Mouthparts are cemented into place

• Ticks feed continuously

• Tick saliva flows into host
  • Histamine blocking agents to minismise the host inflammatory response
  • Anticoagulents to ensure the free flow of blood
  • Cytolysins to enlarge the feeding lesion
  • Vasoactive mediators, enterases and carbohydrate splitting enzymes to increase the vascular permeability, facilitating feeding
  • Paralytic toxins

• Host tissue is broken down leaving a zone of necrosis creating a feeding lesion

Links

• Skin infections pathology