independent

Monday 18 November 2019

Blood-sucking parasites that command respect

Ticks are a tiny but resilient enemy.
Ticks are a tiny but resilient enemy.

Pete Wedderburn - Animal Doctor

Most people have a strong aversion to ticks, but to me, they are the most appealing of all parasites. I have a great deal of respect for these hardy, super-adaptable spider-like creatures. They've been around for a long time: even dinosaurs had ticks. And they'll be around when humans are extinct.

As part of a research project as a young vet, in Africa, I put ticks in a deep freeze to preserve them for examination by a specialist. A month later, when I thawed them out, they woke up and crawled around.

Ticks hide in the undergrowth of meadows and forests, attaching to passing animals, plunging their tiny, drill-like mouth parts into the skin, locating a tiny blood vessel, and sucking blood. They swell up with blood, changing from the size of a lentil to a large pea. Once they are full, they fall off the animal, landing back in the undergrowth, spending 90% of their lifetimes off the animals that they feed from.

Tick life cycles involve eggs, then three stages, larvae, nymphs, then finally, the adult. All stages suck blood. The ticks fall off the animals in between each stage. It takes between two days and two weeks for a tick to fill with blood, depending on the life stage (adults take longest because they are biggest). Adult male ticks do not swell up with blood and may not even attach to animals at all. Adult females lay hundreds of eggs when they fall off, and the eggs then hatch into young larvae, and so the cycle continues. 

Ticks used to have spring and autumn peaks (so-called "rises") but in recent years, due to the changing climate, they have become active all summer too.

Ticks cause two issues for pet owners. First, the direct harm by the ticks themselves, and second, the diseases that they can carry.

In general, the direct harm is minimal: they cause a minor irritation. Sometimes, the tick bite wound can become infected, causing a painful abscess, especially if the tick is brushed off or carelessly removed, breaking off the tiny mouthparts and leaving them embedded in the skin. If a high number of ticks attach, the bloodsucking can cause anaemia due to blood loss (similar to an animal bleeding from a wound for days on end). And with some exotic tick species (not seen in Ireland) there is a nasty neurological condition of dogs called Tick Paralysis caused by salivary neurotoxins produced by the ticks (similar to snake venom).

The diseases carried by ticks are a much more serious problem. When they suck a blood meal, ticks also inject small amounts of tissue fluid and saliva from their own bodies, and this often includes  disease-causing micro-organisms.

In Ireland, the most common tick species is the castor bean tick, Ixodes ricinus, which attaches to reptiles, birds and mammals. This is the tick most commonly seen on dogs. Cats are more likely to have a different species, known as the hedgehog tick or Ixodes hexagonus. Both of these ticks also affect reptiles, birds and farm animals. Other species of tick are far less common in Ireland.

Farm animals can be affected by three common tick borne diseases: Louping ill (a brain disease caused by a virus, mostly affecting lambs), Anaplasmosis (known as tick-borne fever, caused by a bacterial infection from ticks), and Babesiosis (or redwater), seen in cattle. Babesiosis doesn't affect dogs in Ireland, but the canine version is common in some Eastern European countries. Some imported dogs in Ireland have been reported to bring this disease back with them.

The biggest worry for Irish pet owners is a tick borne disease that can affect humans as well as dogs: Lyme Disease, caused by bacteria called Borrelia burgdorferi. This causes arthritis, as well as heart disease and kidney problems,in dogs, and in humans. While still rarely diagnosed in dogs, this has become increasingly common in humans in recent years, with about 300,000 cases in the USA each year and another 200,000 seen in Europe. The increase is thought to be caused by higher tick populations due to climate change, as well as increased levels of human activity in tick-infested territory, because of the popularity of outdoor activities (including dog walking). Studies have found no correlation between dog ownership and risk of Lyme Disease infection, and infected dogs pose little or no direct risk to humans. The risk to humans comes from direct contact with ticks, so if a dog comes home with lots of ticks, their human is also likely to get ticks themselves, and they should be aware of this disease.

The risk of infection of dogs with Lyme Disease can be reduced significantly by prompt removal of the tick, and the use of routine preventative products that rapidly kill or repel ticks is the safest approach. These come as tablets, to be given once a month or every 3 months, as well as topical insecticides like spot-on drops or collars. Owners should also check their dog for ticks at least every 24 hours, removing any ticks using a simple "twist and pull" action, with a specially designed remover like the O'Tom Tick Hook. Ticks should be handled with care, using gloves, and disposed of safely (e.g into fire, or squashing while inside plastic bag then into bin). I respect ticks, but I still see them as an enemy!

Wexford People

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