Tarantula Spider Toxicity

Etiology

Tarantula venom contains a mixture of enzymes and nucleotides that can cause pain, tissue necrosis, and systemic reactions. However, severe sequelae are relatively rare. The more common mechanism of injury is related to cutaneous, pulmonary, and ocular irritation from urticating hairs. As a defense mechanism, tarantulas use their legs to dislodge hairs (or setae) from their abdomen, creating a cloud of urticating hairs. By traveling through the air, they are capable of making contact with the skin, eyes, and respiratory tract. Cutaneous exposure can cause intense pruritus, local histamine release, and in some cases, systemic reactions. Additionally, hairs can make contact with eyes from those who rub their eyes using their extremities that contain hairs from exposure. Severe injuries occur when hairs are inhaled, causing dyspnea and airway reactions, as well as when hairs make contact with the cornea, where they can become lodged and cause long-term complications.[3][4]

Epidemiology

Tarantula-related injury is a rare occurrence, with only 44 reports to the American Association of Poison Control Centers in 2018 and only 17 of those requiring evaluation at a healthcare facility. These were largely in adults and resulted in only minor injuries. These exposures are most commonly related to their popularity as pets.[5] Despite the known lethality of tarantula venom to insects and lab mice, there have been no reported human deaths due to toxicity from a tarantula bite. However, envenomation from certain species can still cause considerable discomfort.[6]

Toxicokinetics

Tarantula venom is fatal in lab mice. However, it has not been shown to be fatal in humans.[6] It contains a multitude of substances that can vary from one species to another. Some common components include but are not limited to:

• Polyamines
• Neurotransmitters
• Free amino acids
• Nucleotides
• Hyaluronidase

It is proposed that these components work synergistically with one another to propagate and spread the venom in order to enact a quick paralysis effect on prey.[6][7][8][9] In humans, the result is pain, local tissue necrosis, and in rare cases, severe muscle cramping.

More commonly, injury can occur from exposure to their urticating hairs, which can induce a local histamine reaction, causing irritation to the skin, eyes, and respiratory tract. These hairs have barbs along the shaft of the hair, which cause propagation deeper into tissue if not removed in a timely fashion. They can result in intense T-cell as well as IgE-mediated reactions. Anaphylaxis can occur in rare cases.[4]

History and Physical

While tarantulas are native to many areas of the world, their popularity as a pet leads to the majority of human exposures. Due to the conspicuous nature of the organism, patients will often report a history of known tarantula exposure, either by bite or exposure to the hairs. In the case of bite envenomation, patients will often complain of local symptoms, including pruritus, swelling, and mild to severe pain, lasting for several hours. Sometimes bites can be painless, and sometimes symptoms can be delayed over hours to days. Local tissue reaction may be seen, and depending on the species, local tissue necrosis may develop over hours to days.[10][11][12]

In the case of exposure to urticating hairs, the patient will often experience moderate-severe pain, pruritus, and erythema, which can last weeks. However, specific symptoms will depend on the site of exposure. Local symptoms previously mentioned are often associated with cutaneous involvement. If inhaled, rhinitis, cough, dyspnea, and wheezing can occur. Lastly, if there is ocular involvement, patients will often present with a painful, red, conjunctival injection due to corneal or scleral irritation, a reaction termed as ophthalmia nodosa. Later in the disease course, a granulomatous ocular disease may result.[3]

Although rare, patients may present with anaphylaxis to either the bite or hair exposure.[4]

Evaluation

There is no definitive laboratory test to diagnose a tarantula envenomation or exposure to their urticating hairs. Like other arachnid exposures and envenomations, most of the evaluation is performed with a thorough history and physical exam. The international standard for making a definitive diagnosis of a spider bite includes all three of the following:

1. An observation by the patient of the spider inflicting a bite.
2. The spider was caught and sent for identification by a qualified expert.
3. Symptoms associated with the bite, such as pain or discomfort.[10][13]

As tarantulas are such large, conspicuous spiders, it is often unnecessary to make the definitive diagnosis of a tarantula bite to make the presumed diagnosis. Often a reliable reported history of exposure should suffice.

It is important to thoroughly examine the wound or affected area. Often, a patient may suspect an arachnid envenomation but without a clear history of exposure. In these cases, an infection should be considered, especially if there are local signs such as fluctuance or purulent exudates at the wound site.

If the patient reports eye symptoms, such as pain or vision changes, or if the history provided is consistent with ocular involvement from urticating hairs, a slit-lamp exam should be performed to look for hairs embedded in the cornea or conjunctiva.

If the history is not entirely clear, it would be reasonable to perform basic laboratory bloodwork to help in diagnosing common mimics of tarantula exposures. This would include:

• Complete blood count
• Metabolic panel
• Wound culture (if applicable)

Treatment / Management

Treatment for tarantula bites or stings from their urticating hairs is mostly conservative and supportive. 

Skin

Pain can be treated with ice and analgesics. If the exposure occurred on a limb, elevating the limb can sometimes help. Itching can be treated with topical steroids, systemic antihistamines, or a combination of the two. Removal of urticating hairs using tape has been reported to reduce pruritus. Multiple applications of the tape can sometimes be necessary. Perform local wound care, and be sure to provide tetanus prophylaxis if necessary. Envenomations should be monitored for signs of secondary infection, but antibiotics are not routinely recommended for tarantula bites or hair exposure.  

Respiratory

Respiratory complaints should be treated with systemic antihistamines, bronchodilators, and corticosteroids. If symptoms progress to becoming severe, early airway management and pulmonary consultation are prudent.  

Ocular

An application of an eye shield can help prevent the patient from inadvertently rubbing the affected eye, which can worsen the damage. Ocular involvement, whether suspected or confirmed by slit lamp, should prompt an ophthalmology consultation as early removal of urticating hairs can reduce long-term complications, including ophthalmia nodosa. Topical steroids have been shown to reduce symptoms and aid in the resorption of hair without complication.[3] However, the decision to treat with ophthalmic steroids should be made in conjunction with an ophthalmologist consultant.(B3)

Systemic

In the rare case of anaphylaxis, treat as recommended for anaphylaxis of any etiologies.[14][15][16](B3)

Differential Diagnosis

The differential diagnosis hinges largely on the patient's history. Tarantulas are large, conspicuous spiders and are generally easily identifiable by adolescent and adult populations. However, one must also consider bites, stings, and exposures from other arthropods, including black widow spider bites, ant bites, and scorpion stings. Tissue necrosis secondary to envenomation can resemble cutaneous or deep space infections causing cellulitis, abscess, or necrotizing fasciitis. Local reactions due to urticating hairs can resemble contact dermatitis, urticaria, or systemic reactions such as anaphylaxis from other environmental sources. Ocular involvement can resemble keratitis or conjunctivitis acutely and can progress to resemble a granulomatous ocular disease of other etiology. Sometimes exposure to urticating hairs of other organisms, such as the spiny hairs of caterpillars, can cause similar reactions, including ophthalmia nodosa.[17]

Prognosis

Generally, the prognosis of tarantula envenomation is good, requiring only conservative management, including local wound care and pain control. Less commonly, more aggressive wound care, including debridement, may be necessary. Pain from a bite/envenomation can last for several hours. Pruritus associated with urticating hair exposure is usually self-limiting and responds to symptomatic treatment. In some cases, particularly in envenomation from species belonging to the rare Poeciltheria genus, delayed onset severe muscle cramping can occur and last up to three weeks.[11]

Complications

While in the acute setting, tarantula-related injuries can cause intense symptoms, but long-term complications are rare. Complications are largely a result of ocular injury from urticating hairs. In rare cases, long-term visual loss can occur after corneal injury associated with panuveitis, cataracts, and glaucoma.[3] Sometimes these hairs can penetrate deep into the eye and cause chronic irritation. This underscores the need for early opthalmology evaluation and removal of hairs to prevent deeper migration of the hairs and long-term complications in vision.