Ask The Expert - Ticks
Ticks are notorious vectors of human and animal diseases.
They transmit a greater variety of infectious organisms than any other group of blood sucking arthropods, second only to mosquitoes in their public health and veterinary importance.
A range of protozoal, viral, bacterial and fungal pathogens are spread by ticks and they can cause severe and sometimes fatal illnesses because of proteins injected in their saliva.
Hard ticks are by far the worst group, containing 650 species that infest mammals, birds and reptiles. Only the female engorges with blood. They are slow feeders which attach to the host and imbibe blood over several days with mating occurring on the host.
Soft ticks are a diverse group with around 170 species. Both males and females from this group engorge and they are rapid feeders becoming replete in only a few hours.
The lifecycle is dependent on the species. It may be a single host, 2 host or even 3 host lifecycle which contains four distinct stages; egg, larva, nymph and adult.
Egg
The female drops off the vertebrate host and seeks shelter to lay a single large batch of eggs, after which she dies. Typically, a batch contains several thousand brown globular eggs. The gene’s organ applies a waterproof wax coating to each egg for protection in the environment.
Depending on environmental conditions, eggs take from 2 weeks to several months to hatch out as hexapod (six legged) larvae.
Larvae
Larva has neither spiracles nor a tracheal system, so water loss is solely through the cuticle. When the larvae gets on to a host it attaches and feeds for several days only dropping off when engorged. Many larvae take refuge in moist layers (e.g. mulch) and they absorb moisture from the atmosphere, surviving without a meal for long periods.
Nymphs
Larvae digest the bloodmeal and then moult into an octopod (8 legged) nymph which has spiracles and a tracheal system. They must find a new host.
Nymphs feed from 4 to 8 days on the host before they drop off and find a suitable place to moult into the adult stage.
Adults
New adults must locate a suitable host. Females attach to the host but do not feed until mating has occurred. The male feeds but does not engorge. Engorged females drop off the host, digesting the bloodmeal on the ground, then lay eggs in large batches, often several thousand at a time.
To overcome adverse conditions, diapause (a resting stage) can occur at any stage of the lifecycle pre or even post feeding.
Host Finding Behaviour
Where there is no vegetation cover, ticks detect hosts by ground vibrations and emerge from their burrows to move towards the host.
When vegetation exists, larvae accumulate in large numbers near the tips of grasses and similar plants. As a host passes by, the ticks drop onto it from their elevated position. Ticks have no eyes so they rely on sensory organs to locate the host, but they are very strong climbers.
Attachment
A tick pierces the skin with its chelicerae and inserts the barbed hypostome to secure to the host. In brevirostrate ticks, cement secreted during the first 24 hours spreads over the surface of the host’s skin. Over the next 96 hours, extra cement penetrates and fills the lesion, attaching the tick firmly. The paralysis tick Ixodes Holocyclus is longirostrate and secretes no cement.
Feeding and Water Elimination
During engorgement, the body weight of a tick increases about 200 times. ½ to 2/3 of the water content of ingested blood is eliminated before feeding ceases. Final weight of an engorged tick is about 240mg. The excess fluid is eliminated via salivation and is passed back into the host. This saliva also contains anticoagulants, weak hydrolytic enzymes and pharmacological agents.
Tick Paralysis – the dangers of ticks
First recorded in Australia in 1843, it affects the lower limbs, ascending to the torso, upper limbs and the head region within a few hours. 46 different species in 10 genera have been associated with paralysis. Most important paralysis causing ticks are I.holocyclus in Australia and D. andersoni & D. variabilis in North America.
Paralysis is associated with female feeding and the first symptoms occur 5 to 7 days after attachment. A single female tick can paralyse and kill an adult human due to holocyclotoxin which is secreted by specific cells in the salivary glands.
Effective Treatment for Ticks
The treatment of ticks needs to be thorough. Use knowledge of where to locate them at each stage of the lifecycle. Protecting your pets is essential in high density tick areas of Australia and some excellent on-animal treatments are available.
Removing infestations from a pet’s environment is very important.
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