Centipede Envenomation

Etiology

Centipedes are usually active at night and prefer moist warm climates. Thus, presentations for centipede bites are more often occur during summer nights. Bites are often seen on the hands and feet. Bites to the feet are often due to centipede proclivity for hiding in shoes and due to people accidentally stepping on these arthropods while barefoot. Bites to the hands are more common in children or patients who attempt to handle the centipede.[1][2]

Epidemiology

Centipedes are found on every continent except Antarctica and are present in all 50 states in the United States of America. Overall, centipedes prefer warm climates, and so are more frequently found in the southern states of the USA, particularly in Hawaii.[4] Centipede bites are a fairly rare occurrence, and their bites are typically not considered life-threatening; this is likely due to the shy nature of centipedes and their preference for nocturnal activity. Further, while centipedes are very effective killers of their prey, the majority of centipedes are too small for their bites to cause significant morbidity to humans.

The majority of documented bites are from the Scolopendra family. These are the largest centipedes currently identified, reaching up to 12 inches in length. Their size likely reflects the amount of venom available for injection, which is the probable cause of more severe symptoms leading to presentation for medical care.

Studies have shown that between 1979 and 2001, only 6 deaths in the USA are attributable to centipede bites, compared to 1060 fatalities from bees, wasps, and hornets over the same time frame. Further, in these cases of mortality from centipede bites, the etiology of how the centipede venom caused death was not identified. Historically, three well-documented cases of death directly relating to centipede bites were from 1) a bite to the back of the throat that led to swelling and asphyxiation, 2) a death related to anaphylaxis after a bite, and 3) a child who was bitten on the scalp. Fortunately, while human mortality is rare, centipede bites may still cause severe pain and sometimes significant complications.[1][2][5]

Pathophysiology

Centipede venom is a pharmacologically diverse and potent substance. Venom can include bioactive proteins, peptides, and other small molecules.[6] These can have myotoxic, cardiotoxic, and neurotoxic effects. Currently, there are approximately 50 identified constituents of centipede venom, all with different properties to block or activate ion channels. The biochemistry of centipede venom is an area of recent exploration where much is still under investigation.

Centipede bites can have a wide range of symptoms, but the most commonly reported is localized pain. Victims describe the pain as an immediate, localized burning that ranges in severity, though most often reported as very severe. It also ranges in duration from 30 min to 3 days.[1][2][5][7]

Other localized effects may include erythema, bruising, and swelling. Sometimes these bites can bleed extensively and achieving hemostasis may be a challenge, even with pressure dressings. Local pruritus and paresthesia have also been noted. Some patients develop cellulitis or necrosis in the area of the bite.

Systemic effects are far less common, but when they do occur, they can have significant consequences. The most acutely dangerous systemic effect is anaphylaxis. Neurologic manifestations include headache, lethargy, anxiety, and vagotonia. Cardiovascular effects are rare, but case studies have reported hypotension, tachypnea, palpitations, vasospasm, and acute myocardial ischemia. Other systemic effects include fever, chills, nausea, lymphangitis, and rhabdomyolysis. Centipede bites also carry a risk for tetanus transmission.[8][9][10][11]

History and Physical

When a patient presents with a centipede bite, specific factors merit consideration. The first few questions seek to confirm the nature of the causative creature. The patient should describe the offender in as much detail as possible. Timeline is also significant to determine how long a patient should have monitoring for further symptoms. The size of the patient is a consideration; centipede venom is potent and dangerous, but compared to typical centipede prey, human size serves a protective factor from severe systemic symptoms. However, in infants and small children, the size differential is not as substantial or protective. It is also imperative to consider the patient’s history of allergies and other chronic medical problems, as this can provide a focus for observation of specific systemic effects. Tetanus immunization history is also important.  Finally, providers should inquire about systemic or non-dermatologic symptoms.

On physical exam, it is key to view the bite closely. A centipede bite consists of 2 bite marks. There is typically localized erythema or ecchymosis and swelling. Examine the patient closely for non-dermatologic symptoms, such as neurologic deficits or chest pain, as guided by patient symptoms.[2][3]

Evaluation

Local wound care is the primary management of uncomplicated centipede bites. Monitoring for systemic symptoms is recommended. If the patient complains of specific symptoms such as chest pain, work up for myocardial ischemia including troponins and EKG should be obtained. Imaging is not necessary for acute centipede bite.

Treatment / Management

Treatment of minor centipede bites is straightforward and includes:

1. Irrigating the site to reduce the risk of infection.
2. Apply ice packs as the cold elevates the pain threshold, impedes nerve conduction, and vasoconstricts vessels to prevent tissue edema.
3. Some patients report pain improvement with submersion of the extremity in hot water, as it is thought to denature any heat-labile toxins in the venom. However, some patients have also reported increased pain with hot water exposure.
4. Also recommended is systemic and local analgesia. In particular, local anesthesia with lidocaine at the bite site should provide significant relief.
5. If the patient has no tetanus vaccination within the past 5 years, update tetanus vaccination.
6. Though not universally recommended, select patients may benefit from antihistamines, corticosteroids, and anxiolytics.
7. Antibiotics are not typically warranted for prophylaxis, as infections are rare with proper wound care.

There is no specific antidote for centipede venom. If systemic symptoms occur, treatment is mainly supportive or related to the specific symptom. For example, anaphylaxis treatment will be the same as anaphylaxis related to any other allergen with epinephrine. In the case of myocardial ischemia, therapy will be similar to cardiac ischemia of any etiology (i.e., aspirin and percutaneous coronary intervention). In the case of delayed effects such as cellulitis or localized necrosis, antibiotics and wound debridement will be necessary.[2][12][11](B3)

Differential Diagnosis

• Spider bite
• Insect bite
• Scorpion evenomation
• Cellulitis

Prognosis

Overall, prognosis after centipede envenomation is excellent. Pain control is usually successful with appropriate analgesic measures. Systemic symptoms and even local complications are rare.

Complications

The following complications may accompany a centipede bite[9][10][11]:

• Cellulitis or abscess
• Local necrosis
• Myocardial ischemia
• Rhabdomyolysis
• Anaphylaxis