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Spiders are a type of eight-legged creature called arachnids and are distinct from other insects. A spider bite is also referred to as arachnidism. Not all spider bites are dangerous; however, bites of some poisonous varieties of spiders can be serious and associated with drastic complications if left untreated. The two most dangerous poisonous spiders that bite humans are brown recluse spiders and black widow spiders. If unsure of which spider caused the bite, it is advisable to seek urgent medical assistance at the nearest emergency department. Spider bites can occur outdoors in forested areas or wilderness but are also possible indoors in closed, damp, dusty spaces that do not receive much sunlight as spiders often lay eggs here.

Although it may not be possible to identify the spider that caused the bite, any information that can be provided to the healthcare workers can aid the treatment of the patient. Two of the most dangerous and poisonous spiders are described below:

  • Black widow spider: Black spherical body with eight legs and two reddish triangular markings usually joined to form a reddish hourglass shape on the underside of the spider.
  • Brown recluse spider: Tan, light to dark brown coloured spherical body with eight legs. A typical dark violin-shaped marking is present on top of the round brownish body.
  1. Recognising spider bites
  2. What to do in case of a spider bite
  3. Medical treatment for a spider bite

Not all spider bites have major signs and symptoms. Some common features to expect following a spider include:

  • Pain at the spider bite site
  • Burning sensation in the area of the spider bite site
  • Swelling on spider bite site
  • Blistering on spider bite site
  • A blister surrounded by a bruise or reddish skin colour (similar to a bull’s-eye). The blister may rupture and form a skin ulcer that later scars.
  • Blisters can rupture and ooze pus or blood
  • An itchy papule or wheal may develop and persist for several days around the site of the spider bite
  • Allergic reactions of the skin on or around the site of the spider bite
  • Hives (urticaria), which are itchy, raised welts found on the skin

Signs and symptoms of a possibly poisonous spider bite:

Signs and symptoms of severe allergic reaction or anaphylaxis:

  • Sudden and severe swelling around eyes and lips
  • Swollen tongue
  • Bluish colouration of the lips or fingernails
  • Sensation of constricting airways and/or difficulty breathing
  • Respiratory or breathing problems
  • Shortness of breath
  • Laboured breathing
  • Wheezing
  • Not breathing
  • Choking
  • Noisy breathing
  • Noisy breathing that ceases and is followed by an absence of any breath sounds
  • Drooling saliva
  • Generalised edema or swelling of the body
  • Hives or urticaria rash
  • Intense distress
  • Itching in the throat or mouth

Any indication of a poisonous spider bite or severe allergic reaction, or anaphylaxis, requires immediate medical assistance at the nearest healthcare facility.

Following are the first aid steps to take following a spider bite:

  • Try to calm the patient. 
  • Clean the spider bite site with water and soap thoroughly. Gentle scrubbing is recommended.
  • After cleansing the site, apply a clean ice pack or clean cloth dipped in cold water to the spider bite site for at least 15 minutes every hour. This will reduce or prevent the bite from becoming swollen and painful. This should be done till the pain and discomfort become manageable.
  • An antibiotic ointment, like neosporin, should be applied to the spider bite to prevent bacterial infection.
  • If the pain or discomfort is too much, over-the-counter painkillers like NSAIDs (such as paracetamol) should be taken.
  • If a wheal (raised circular lesion) that radiates outward from the site of the spider bite appears, antihistamine medicines like levocetirizine should be taken.
  • If intense itching occurs, an oral antihistamine (like levocetirizine) should be taken.
  • Spider bites usually resolve on their own without complications, provided the spider was non-poisonous and proper wound care was carried out to prevent infection. However, it is possible for other deadly signs and symptoms to appear with poisonous spider bites or anaphylaxis. In such cases, the patient should be taken to a hospital immediately.

If bitten by a spider, your doctor may prescribe you drugs to relieve pain and muscle spasms. Antivenom may be given in moderate to severe cases presenting with full-body cramps may be needed. The spider bite wound should be cleaned with betadine (povidone-iodine) solution three times a day and then soaked in sterile salt water (normal saline). Surgical wound repair may be required in more severe cases.

Hospitalization may be required for people younger than 16 or older than 60 and for people with high blood pressure, heart disease or severe symptoms.

In the case of a minor spider bite, an antibiotic ointment like neosporin should be applied daily at the site. Antihistamines should be taken in case of minor skin reactions and itching.

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