Ticks
Is your dog ticked off?

Ticks - There are four stages within a tick's life cycle: Egg; Larva; Nymph; Adult

Larvae that hatch from the eggs are often referred to as the seed tick and differ from adults in that they only have six legs.  Larvai moult (shed their skin) and become eight legged nymphs.  Nymphs in turn moult to become adults.

Morphology

The kennel tick is yellowish to reddish-brown in colour with distinct, slightly convex eyes.  Three posterior grooves located towards the rear end) are present, which are well defined in the male kennel tick.  The male kennel tick's body-wall has a salmon pink colour.

Life Cycle

The Kennel tick is a three-host tick with dogs primarily being the hosts for all stages of development.  This means that the eggs hatch into larvae.  the larvae feed on one host and when engorged fall off to the ground where they moult into nymphs.  The nymphs ten feed on a seond host and when engorged fall off to the ground and moult into adults.  The adults in turn feed on a third host and when engorged fall off to the ground to lay eggs.  The engorged female kennel tick lays 3 000 to 5 000 eggs.

The kennel tick is well adapted to living in kennels and houses and the females may lay their eggs under the bedding of dogs or in cracks and crevices within kennels or walls.

Sites of attachment on host

Larvae are found on the stomach and sides, whereas nymphs are found on the ears and shoulders, and adults on the ears, neck and shoulders of dogs.  Adults and nymphs may also be found between the toes of dogs.

Disease transmission in dogs

The kennel tick is responsible for the transmission of:

• Ehrlichia canis in dogs, the cause of canine ehrlichiosis or tropical pancytopaenia
• Hepatozoon canis
• Tranmission of Babesia canis vogeli and possibly Babesia canis rossi.  Babesia canis vogeli most commonly causes subclinical infections in dogs.  Babesia canis rossi is therefore of most importance as it frequently causes severe and life-threatening diseases in dogs.

The glossy brown tick has a very dark, shiny and black or reddish-brown scutum (a chitin plate in the exoskeleton of hard-bodies ticks) there are 4 definite longitudional rows of large punctuation on the scutum.

Life Cycle

The glossy brown tick is a three-host tick and the adults are found on dogs, but also on large carnivores, zebras, wathogs, rhinoceroses and cattle.  The immatures occure on rodents.

Signs of attachment on host

The adult ticks are found on the head and shoulders of dogs.

Disease transmission in doges

It doesn't appear to be involved in disease transmission in dogs.

Morphology

The yellow dog tick has short mouthparts giving the capitulum (head-shaped part) a triangular appearance.  The scutum is yellow and has numerous small punctuations.  Eyes are absent.

Life Cycle

The yellow dog tick is a three-host tick and the adults occur on dogs, cats and larger carnivores.  The immatures are  found on rodents.

Sites of attachment on host

The yellow dog ticks are most commonly found on the head, neck and shoulders of dogs, but in severe infestations they may be found all over the body of the dog.

Disease transmission in dogs

The yellow dog tick is the major factor for Babesia canis rossi.

Morphology

The bont-legged tick is a two-host tick.  With two-host ticks, the larvae and the nymphs feed on the same host and the engorged immatures fall off to the ground where they moult into adults.  The adult ticks then feed on a second host and when engorged fall off the host and the engorged female then lays between 5000 and 15000 eggs.  The adult ticks are occasionally found on dogs, but are more commonly found on cattle, sheep, goats, horses and large wild herbivores.  The immatures on found on scrub hares, ground birds and rodents.

Importance in dogs

When these ticks infest dogs, they tend to cluster on one site and can cause severe skin necrosis (death of cells or tissues).

Tick control entails both environmental control as well as control on the dog itself.  Environmental control may involve the following

• Keeping grass cut short
• Use an approved acaracide in the kennels
• Regular washing of bedding

The following active ingredients are used in tick control products for dogs:

• Organophosphors and carbamates

  These actives inhibit acetylcholinesterase that is a neurotransmitter (a chemical substance that transmits nerve impulses across a synapse, the junction between two nerve cells.) As a result it induces muscular contractions followed by paralysis in the tick.  Although these actives were once very popular due to their prolonged action, their use has declined because of their low margin of safety.

   

• Pyrethrins and pyrethroids
  These actives disrupt sodium and potassium ion transport in nerve membranes, which results in spontaneous depolarization and neuromuscular blockade.  Synthetic pyrethroids generally have a greater potency and residual effect.

   

• Formamidines
  This active inhibit monamine oxidase.  The only veterinary approved formamidine is amitraz.

   

• Phenylpyrazoles
  It has a broad spectrum insecticidal and acaracidal activity.  Fipronil binds to y-aminobytyric acid receptors, and thereby inhibits the flux of chloride ions into nerve cells of the parasite, resulting in hyperexcitability.

   

• Nitroquanadines
  These act on nicotinic acetylcholine receptors on the postsynaptic membrane causing CNS (central nervous system) impairment and death.

   

• Macrocyclic lactones
  Currently selamectin is the only approved semisynthetic avermectin developed specifically to control both internal and external parasites in cats and dogs.  Its exact mode of action is controversial.  It is believe that it bind to glumate-gated chloride channels in the parasite's nervous system, resulting in an increased permeability and an influx of chloride ions into the nerve cell.  This inhibits nerve activity, resulting in paralysis. 

Remember to protect your beloved dog against ticks and tick-borne diseases by regularly applying topical ectoparasitcides according to the package insert of the relevant product, or as prescribed by your veterinarian.  And don't forget environmental control!  Effective tick control lies in the combination of environmental control as well as apply topical ectoparasiticides on dogs.