VPA 221: Veterinary Entomology and Acarology (1+1)

EFFECT ON HOST

Direct effect

• Ticks injure animals by their direct biting process.  The bite is painful and it annoys the host espceially cattle and dogs.  The effect is termed 'tick worry' and this has an adverse impact on production of infested animals
• The wounds caused by the tick bites predispose the host to blow fly strike
• Ticks suck blood and heavy infestation results in anaemia due to heavy loss of blood.  In hard ticks the females are heavy feeders and one tick can consume 0.2 to 2 ml of blood - in calves 500 ticks can kill the animal.  Soft ticks such as Ornithodorus sp. sucks 1-2 ml of blood at a time and kills the animal following an overnight infestation
• Ticks damage the hide , there is inflammation, swelling, ulceration and itching.  Dermatitis results due to the tick bite especially the longirostrate ticks.  The hide is affected and becomes unfit and is treated as third quality.  It is often condemned.  The marking on the leather due to the tick bite is referred to as white spot leather

Indirect effect

• Transmission of Babesia spp., Theileria spp., Anaplasma spp., Ehrlichia spp.

Tick paralysis

• Caused by 46 species of ticks in 10 genera including Argasids and Ixodids
• Host: Livestock, pets and man
• It is an ascending motor paralysis induced by substances introduced into host with the saliva when ticks attach and feed
• Toxic substances
  • Proteinaceous material produced by salivary gland and secreted into saliva
  • Some say it produced by ovaries-Ixovotoxin
  • Holocyclotoxin- Ixodes holocyclus inhibits secretion at neuromuscular junctions
• Tick
  • Female
  • Sometimes nymphs
• Incidence- depends on
  • Number of ticks
  • Period of feeding
  • Area fed
• Clinical signs
  • Disruption of motor co-ordination
  • Brief incubation- 5-7days
  • General malaise, loss of appetite, headache, vomiting
  • 1^st paralysis of lower extremity, flaccid paralysis (hind limbs)
  • Locomotor ataxia - erratic wobby gait
  • Muscular weakness
  • Lack of ankle, knee, or abdominal reflexus
  • Paralysis ascends affects forelimbs - upper body – neck head- collapse - death - flaccid tetraplegia
  • Decreased sensory perception
  • Paralysis of chest muscles leads to respiratory failure
  • Patient is in co-ordinated, unable to move arms / legs, sit upright, difficulty in speaking, chewing, swallowing
  • In young children, death occurs in 24-48 hrs
  • Tick when removed, recovery is seen– total recovery immediate to several weeks except in Ixodes holocyclus.
  • In dogs preceding all these symptoms, inflammation and conjunctivitis of eye,keratitis and cardiac abnormalities
• Treatment
  • Phenoxybenzamine HCl
  • Alpha adrenergic blocking drug

Tick bite allergies

• IgE mediated immediated Hypersensitivity reaction
• Occurs early during tick attachment and feeding
• Small large local reaction (View image...)
• Systemic- shock like symptoms
• Unsual allergic reaction- nausea, diarrhoea, vomiting, edema and erythema

Tick toxicosis

• Associated with soft tick – Ornithodoros savignyi – trembling, frothy saliva, gnashing of teeth, sometimes foreleg paralysis
• H. truncatum - sweating sickness which occurs in sheep, goat, pigs even dogs which occurs in S,G,P, even dogs
• Female while feeding increase incidence summer.
• Fever, anorexia, hyperaemia, hyperaesthesia of skin and mucous membrane, salivation, lachrymation and moist eczema
• No paralysis- cracked skin- screw worm.
• 75% mortality
• Symptoms within 4 days of tick attachment
• Immune for 4 years
• Toxin
  • Unknown
  • Epitheliotrophic

Anaemia

The Indirect effects include the vector potentiality of each tick which is given under each genera of ticks dealt with