General | March 31, 2015 | Author: The Super Pharmacist
Ticks are blood sucking, external parasites that survive through feeding on the blood (hematophagy) on mammals, birds and occasionally reptiles and amphibians (1). They are the prominent vector of disease causing pathogens in animals, and second only to mosquitoes as vectors causing pathogens of disease in humans (2). There are an estimated 69 species of ticks globally that are capable of causing paralysis (3), with the most harmful in Australia being Ixodus holocyclus. It can cause paralysis in humans, cats, dogs, sheep, cattle, pigs and horses (4).
Historically tick paralysis in Australia has mainly been seen as a concern in veterinary medicine, although climactic conditions that result in tick densities reaching very high levels has resulted in the number of humans being bitten increasing significantly. Although it still occurs very rarely in humans, tick paralysis can be very serious if left untreated – if ticks are not removed the mortality rate resulting from respiratory paralysis is approximately 10%.
Tick paralysis is characterised by a number of symptoms including flu like symptoms, lymph node tenderness, headache, rash, weakness of the limbs, and an unsteady gait. As the tick engorges itself with blood, paralysis develops: as a result, undetected ticks will often result in prolonged debilitation.
There are several other illnesses associated with tick bites, including tick typhus (also known as Rickettsial spotted fever or Queensland tick typhus) which is characterised by headaches, rashes, swollen glands, and fever. It is rarely fatal and can be treated with common antibiotics. In Australia, it is found only in some parts of the Eastern coastline and Bass Strait Islands.
Lyme disease is another prevalent tick-borne virus, although it is found more commonly in the Northern Hemisphere with no medically confirmed cases in Australia since the late 1980’s.
Allergic reactions are the most serious complication associated with ticks, varying from mild swelling and itching to severe and life threatening anaphylactic reactions (5).
Tick bite allergy will typically occur rapidly on feeding or following removal of the tick, whereas paralysis usually only occurs after several days of blood engorging by an adult female tick (6).
The most effective method to prevent tick bites is to stay away from areas that are endemic. This is a particular important consideration for individuals who know that they will experience severe anaphylactic reactions to ticks. If individuals cannot avoid a tick-infested area, it is recommended that light clothes are worn (so that ticks can be easily identified), with an insect repellent containing 20% DEET or Picaridin applied to skin every couple of hours.
DEET based repellents are not suitable for young children. There are some guidelines suggesting that natural repellents, such as lemon and eucalyptus oil, do effectively prevent ticks from attaching (7), however such repellents are very rarely registered with national bodies responsible for testing its efficacy and safety as an insect repellent, and there remains limited evidence for its use. This could, however, simply be as a result of a very small evidence base for tick prevention.
It is recommended that ticks are removed as soon as they are identified on the body and it is crucial that this is done correctly to prevent any further infection or future tick-related harm. Whilst guidelines tend to vary slightly by country, the measures remain roughly the same:
Do not aggravate the tick at any stage with a substance such as methylated spirits, nor should it be touched or disturbed unduly as this will increase the likelihood of it injecting saliva into the skin and causing a potential allergic reaction.
More suitable aerosol repellents, containing pyrethrin or a pyrethroid, are an appropriate treatment option. Permethrin is also recommended. The aerosols act as both a narcotic and a toxicant, preventing the tick from injecting any saliva into the bloodstream. After being sprayed the tick can be removed, although the site on the body that has been bitten can often remain itchy and aggravated for several weeks afterwards.
The recommendation of DEET usage is based on a firm evidence base, with its efficacy tending to plateau at around 50% concentration. Most guidelines tend to recommend DEET products with a concentration of ≥20% due to the well evidenced long-term effects of its use on exposed skin (9). Permethrin also has a strong evidence base in regards to being a highly effective repellent of a number of potentially harmful animals such as ticks, chiggers and mosquitoes (10).
There is limited literature in the existing evidence base regarding treatment options for humans after a tick has been removed, with the majority of published studies focused on treatments in veterinary medicine. Only one study could be found suggesting that antibiotic prophylaxis should be administered to humans after ticks have been removed, although the rationale for doing so was not made abundantly clear (11).
Antibiotic prophylaxis is commonly used in the treatment of Lyme disease (12), although further research is required to see if such post-tick medication is required for paralysis that occurs as a result of a Ixodus holocyclus bite. Although antihistamines are regularly recommended for similar reactions, there is no available evidence regarding specific treatment options for ticks.
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