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antipodi
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Wed Apr 05, 2006 1:17 pm
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 Australian Poisonous Insects
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Australian Poisonous Insects
Of all the thousands of Australian spiders, arthropods and insects, only three have bites which alone are capable of causing death - the funnel-web spider (and related atrax species), the red back spider and the paralysis tick.
In most other spider or insect bites, rest and elevation, local application of ice packs and lotions, simple analgesics and antihistamines are all that is required.
In some patients, anaphylactic reactions may occur after insect bites, and these may be life threatening.
Spider Bites
The Sydney funnel web (and a few related atrax species) is unquestionably the most dangerous spider in Australia; the red back and the paralysis tick are the only other two arachnids with potentially fatal bites.
The AVRU has a page on spider identification with some nice photos and a description of their behaviour. The Australian Reptile Park pioneered funnel web venom milking and is the sole supplier of venom to CSL for antivenom production, and they now have a specific spider exhibit. If you capture a live funnel web please take it to one of their funnel-web collection points. Their comprehensive information about important Australian spiders makes fascinating reading.
Sydney Funnel Web (Atrax robustus)
This is one mother of a spider!
It is a large (6-7 cm), black, aggressive, beautiful looking spider with massive fangs. These are large and powerful enough to easily penetrate a fingernail. When disturbed it tends to rear up on its hind legs, a defensive posture that exposes the fangs. They don't jump. During a bite the spider firmly grips its victim and bites repeatedly; in most cases the experience is horrific. The venom is highly toxic. Before an effective antivenom was developed, significant bites usually resulted in severe symptoms and death was not uncommon.
The Sydney funnel web spider is mostly found near Sydney (from Newcastle to Nowra and as far west as Lithgow but sightings have been reported as far north as Brisbane. Related species are found along the eastern coast of New South Wales.
The venom of the slightly smaller male spider is five times as toxic as the female. This is unfortunate, as male funnel webs tend to roam about, particularly after heavy rain in summer, and often wind up indoors. The primary toxic component is atraxotoxin, which alone can cause all the symptoms. The venom also contains hyaluronidase and other components (GABA, spermine, indole acetic acid). For some strange reason, human beings (and other primates and monkeys) are particularly sensitive to the venom, whereas toads, cats and rabbits are almost unaffected!
Atraxotoxin causes acute massive release of neurotransmitters at autonomic and neuromuscular junctions with associated uncontrolled autonomic hyper-reactivity and muscle twitching, followed about 2 hours later by neurotransmitter depletion and weakness.
Symptoms
The bite is usually immediately painful, and if substantial envenomation occurs, symptoms commence usually within a few minutes. They include, progressively:
* Piloerection, sweating, muscle twitching (facial and intercostal, initially), salivation, lacrimation, tachycardia, and then (fairly rapidly) severe hypertension.
* Vomiting, airway obstruction, muscle spasms, writhing, grimacing, pulmonary oedema (of neurogenic or hypertensive origin), extreme hypertension.
* Unconsciousness, raised intracranial pressure, widely dilated pupils (often fixed), uncontrolled twitching, and death unless artificial ventilation is provided.
After about 2 hours the muscle fasiculations and most symptoms start to subside, and are replaced with insidious but profound hypotension, primarily due to severe cardiac failure.
First Aid:
The pressure immobilisation technique MUST be commenced as soon as possible. Any delay risks the rapid onset of systemic symptoms. There have been no reports of deaths when effective first aid had been instituted.
The patient should immediately be evacuated to a medical facility capable of managing the envenomation. Treatment will require giving antivenom, providing artificial ventilation, and invasively monitoring the patient. Bandages MUST NOT be removed prematurely.
There is evidence that the venom may inactivated by prolonged localisation.
Medical Management
Institute intravenous access, adequate monitoring (iv, SpO2, non-invasive or arterial BP) and obtain antivenom BEFORE removing first aid bandages! An apparently well patient may suddenly deteriorate when they are removed.
The moment symptoms or signs of systemic toxicity develop, the antivenom should be administered intravenously. Supportive management, including oxygen, iv atropine, antihypertensives and sedation is usually required even if the antivenom is given. If the antivenom is administered early, the clinical situation is unlikely to get out of control.
Management of severe envenomation involves:
* Airway control (intubation), administration of muscle relaxants, hyperventilation.
* Invasive monitoring.
* Gastric drainage (to prevent acute gastric dilation occurs).
* Atropine iv to control cholinergic hyperactivity.
* Sedation - benzodiazepines.
* Anti-adrenergic agents early to control hypertension; later, inotropic agents and volume support - may require swan-ganz monitoring if difficult to manage.
* Antivenom administration - one to two ampoules intravenously, slowly. May be repeated, according to response, at 10 to 15 minute intervals.
The antivenom is a highly purified rabbit IgG immunoglobulin and is highly effective; it should be given as soon as signs of significant envenomation are seen. Prophylactic adrenaline is not required, nor steroids, and there have been no reports of adverse reactions following its use.
Occasionally bites from the mouse spider or other atrax species may develop similar symptoms; if these are severe enough it may be useful to try funnel web antivenom.
Red Back (Latrodectus mactans hasselti)
The adult female red back is about 2-3 cm long, quite black, with a distinctive red stripe on its abdomen. The male is much smaller and considered harmless. Neither are aggessive. Here's some general info from the Australian Museum.
Red back venom contains neurotoxins, but works very slowly. Fatalities, even from untreated bites, are rare.
The bite is immediately painful; the pain may involve the whole limb. Sweating is common, starting only on the affected limb. Systemic envenomation usually results in headache, nausea, vomiting, abdominal pain, pyrexia, hypertension and in severe cases, paralysis. Untreated, the symptoms worsen over a 24 hour period and may take weeks or months to resolve.
The pressure and immobilisation technique is NOT recommended as local pain may become excruciating. It may be relieved by the application of ice packs.
The red back specific anti-venom is reliable and is given to around 250 cases each year. It should be withheld unless signs of systemic envenomation develop, and if none occur with 24 hours is usually not required. However, if administration is delayed, it is still effective in relieving symptoms up to 10 days after the bite.
Antivenom may be given intramuscularly, because of the small volume involved. Adrenaline need not be given beforehand, unless the patient has prior exposure to equine antivenom or antitoxin or has an allergy to equine protein, in which case steroids should be given for four days as well.
White Tail
The white-tailed spider (Lampona cylindrata), and bites from some other spiders, such as the common black window or house spider (Badumna species), the cupboard or brown spider, and (in the US)the brown recluse (Loxosceles reclusa) and hobo spiders (Tegenaria agrestis), have been infrequently implicated in the development of the so-called necrotising arachnidism syndrome, in which a near-painless bite progresses to painful cutaneous blistering and inflammation which may progress into intensely cyanotic lesions, occasionally resulting in substantial recurrent local tissue necrosis with a deep rolled ulcer involving fat and skin and exposing muscle. Amputation has been required for severe necrosis, and ulcer recurrence may last for years.
The precise cause is unknown, however it appears to be due to locally acting necrotising toxin (the recluse venom alone causes necrosis), probably in association with secondary infection. Approximately 25% of cases are associated with skin cultures positive for staphlococci . Strep pyogenes or mycobacterium ulcerans have been causatively implicated, however new evidence suggests that mycobaterium ulcerans may not play a significant role in the syndrome.Treatment depends on severity.
If an area of redness and blistering develop, the limb should be elevated and the patient rested. No drug treatments, including antibiotics, have been clearly shown to be effective at this stage. Blisters may be cultured and a microbiologist needs to be involved to look for mycobacteria as well as other bacteria. Antibiotics should be administered on positive culture or on reasonable suspicion of secondary infection, however poor clinical response is to be expected. Lesions ahould be carefully observed; it may be a good idea to photograph them daily, and the patients temperature and general condition should be observed and recorded.
Should the situation deteriorate, the skin may start to look mottled or pale or bluish, or the redness and swelling may spread widely. This is unusual, but if it happens the patient needs admission to hospital. Ruling out serious secondary infection is advisable; this may include skin biopsy. The role of empirical antibiotic therapy is unclear. Should gangrene and/or skin necrosis occur surgical management may be appropriate, however early aggressive surgical therapy is not advocated. Hyperbaric Oxygen and Dapsone have been shown to be of benefit, mostly on data from treatment of experimental brown recluse venomation of animal models. It is probably worth discussing severe cases with the Venom Research Unit of the University of Melbourne. The AVRU site provides information about white tail spider bites and necrotising arachnidism. They are conducting a research sudy of necrotising arachnidism. "If you live in Australia, have been bitten recently (in the last few days) by a spider and have the spider that bit you, AVRU would like to hear from you. Please contact AVRU during office hours, or by mail or email, for further information about the study."
There has been some difficulty in clearly identifying the offending spider in cases of necrotising arachnidism. Convalescent serum (stored at -20C) may be tested against known spider venom components.
Other spiders
Always try to catch the spider for identification. The AVRU has a page of photos and information and a spearate page on the mouse spider. The Australian museum has factsheets on the trapdoor, mouse, white-tail, wolf, black house, huntsman, sac, orb-weaving and other spiders as well as information about their role in the environment.
Only the funnelweb and redback are known to cause death from envenomation. Other spider bites usually cause local pain, which may be relieved by ice packs or simple analgesics and antihistamines may help swelling and itching. Vague constitutional symptoms such as dizziness, headache, etc usually do not require specific treatment.
The pressure-immobilisation technique is inappropriate for bites from spiders other than the funnel web and related atrax species. It should be applied when the spider has been clearly identified as a funnel-web, there are signs of systemic envenomation, or as a precaution when there is reasonable doubt that the spider causing the bite may have been a funnel web.
The huntsman is a common large spider along the east coast of Australia. One of my favourites! I actually had a big one fall into my lap off the sun shade of my car while driving down the freeway once! They are quite harmless, though when they wander indoors or get lost inside cars it can be frightening. Don't kill them, just get them outside again.
Ticks
The Australian paralysis tick (Ixodes holocyus) is widely distributed in south eastern coastal temperate regions. It secretes a neurotoxin in its saliva that causes a progressive, and occasionally fatal, paralysis. Sometimes a severe hypersensitivity reaction may occur. Often the tick goes unnoticed until weakness or ataxia develop, and then is found during an ensuing search (don't forget to look behind ears etc!). Occasionally localised paralysis of facial muscles occur, but more commonly there is progressive ascending flaccid paralysis affecting the lower limbs first. Other grass ticks can be a real nuisance at times, causing really itchy bites.
Prevention is better than cure. If you know you are going into tick areas, wear long, light-coloured trousers and tuck them inside tight socks. If you look out for ticks crawling up the outside of your trouser legs you can brush them off before they get inside.
First Aid
Removal of the tick can be achieved in many different ways. Never grip the the sac and pull! This may squeeze more venom in, or break it off leaving the head and 'torso' firmly stuck, which is likely to get infected. These days most people recommend gripping the tick as near to the head as possible with a very pointy pair of tweezers or forceps. Ordinary eyebrow tweezers are not much good because the points are too wide. You can make eyebrow tweezers much more useful by filing the tips away to a sharp point. For larger ticks I personally like making a 'loop' or 'noose' from a piece of cotton thread with a single throw knot (half of a reef knot). This is placed at the base of the body, then slowly and gently closed until it won't slip over the body. Then I gently pull on the free ends of thread with a 'to-and-fro' rocking motion until the whole tick comes out. Nothing entertains children more than seeing the little wriggling legs of the removed tick - except the satisfaction of finally squishing them!
Ticks usually have a firm hold on you once they have dug in. Additionally, there can be quite a lot of swelling around them. This can make them difficult to remove, and so many people have sought means to induce them to 'let go' by themselves, or at least to cause them to 'relax their grip'. These have included putting ti-tree oil, metho, turps, kero or similar on the tick, or spraying with insecticide, or even touching the tick with a lighted match. Not all at the same time! Any of these are potentially hazardous to the patient because they can induce spasm in the tick and may cause it to inject more venom (as well as the possibility of skin reactions or burns). There are no scientific studies to actually test if any of these manouevers are more helpful than just pulling it out alive. The US Centres for Disease Control recommends against doing any of these things.
I received an e-mail from a person in the US who suggested thoroughly coating the tick with vaseline for 10 minutes. Ken Markham has tried this and says that it works well so long as the tick is completely and totally covered. Even then you sometimes need to wait up to 2 hours. Ken says that sfter 30 minutes to 2 hours they just back out by themselves. If you are a patient person, and can fully coat the tick, this is probably the best option. Insects breathe by drawing air in from the sides of their bodies and can survive for a long time without any air at all.
Sharyn Powlseland from Far North Queensland recommends avoiding physical disturbance of the tick if possible, then applying several drops of 100% Ti-Tree oil and waiting 20 minutes - or until the legs no longer wriggle once prodded - before pulling it out.
It's hard to know if the tick would prefer to be ripped out alive or to be asphyxiated or anaesthetised first! My personal preference is to cover them in with a cotton wool ball soaked in methylated spirit (alcohol) for 15 minutes. This should gradually anaesthetise the tick and sterilises the area; I think they seem a little easier to pull out that way. If you have lots of small ticks, just pull them out alive, as there will be too many to soak in alcohol. When they are small and have not 'dug in' too far they are easy to pull out.
Whatever you do, make sure you kill them afterwards.
If the patient has developed severe symptoms, apply the pressure and immobilisation technique until they can receive antitoxin.
I've received an e-mail from a farmer with a lot experience with bites from both paralysis and grass ticks. He has also experienced similar bites mostly around the ankles and at times over the body, without being able to discover the cause, and is wondering if ticks in their 'nymph' stages might also be the culprit. If someone knows the most likely cause for his bites, or if indeed tick nymphs can bite, I'd be grateful for an email.
Medical treatment.
An effective antivenom is prepared from the serum of chronically infested dogs. This should be administered intravenously to all patients with signs of systemic envenomation.
Airway support and ventilation may occasionally be required; equally rarely desensitisation of hypersensitive individuals.
Sharyn Powlseland from Far North Queensland recommends taking a homeopathic remedy called 'Ledum' as soon as possible after tick bite to 'help the immune system to deal with the venom and the body to cope and heal.' Additionally she recommends taking 'large doses of Vit C, Vit E and B5(pantothenic acid)within the first 48 hours'.
Severe persistant itching can be a problem. First exclude or treat infection. Severe cases may require short-course systemic steroids.
More info? Scotland Island News have a great practical article on ticks, their life-cycle and bite minimisation strategies. There is a great deal of information at Tickalert, an excellent Australian site, and more on the AVRU tick information pages.
Bees, wasps, ants and other arthropods
These bites, no matter how painful, are only potentially lethal in patients with allergy to the venom of the insect concerned. In these patients, a bite should be considered a medical emergency. The pressure and immobilisation technique should be applied and the patient immediately brought to a hospital. Anaphylaxis should be treated promptly with adrenaline, airway support, colloids, etc.
Bee stings should be scraped off, rather than pulled out, to avoid squeezing further venom from the attached sac into the patient.
Ice packs applied to the bitten area may reduce local pain. If severe, antihistamines, oral analgesics, and even steroids may be required.
The AVRU provides indentification and first aid information for arthopods and their bites. Factsheets on other insects are also available from the Australian Museum.
_________________
Antipodi
May one day man and Animals live together in harmony and peace
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