Caterpillar Envenomation Clinical Presentation

While the history of exposure related temporally to the onset of signs and symptoms may be clear, the diagnosis can be challenging. Maintain a high index of suspicion when patients present with unexplained acute dermatitis, rhinitis, conjunctivitis, or wheezing during months when caterpillars are numerous. In some regions of the world, the diagnosis becomes clear when clusters of seemingly unrelated cases start to present.

Onset of acute dermatitis due to hair exposure may immediately follow exposure or may be delayed 8-12 hours.

Intense pruritus, local pain or soreness (less common), and erythematous raised rash, blisters, and bruising at the site may occur. ^{[7, 8]} Skin necrosis has occurred following prolonged exposure to toxic hairs. With most toxic caterpillars, systemic symptoms are unusual in the absence of respiratory exposure.

Respiratory exposure may precipitate acute rhinitis, tearing, cough, dyspnea, respiratory distress, wheezing, and chest pain. This syndrome may need to be differentiated from the rare case of anaphylaxis.

Ocular exposure may initiate an acute conjunctivitis with severe pain, tearing, and redness. Visual acuity can be reduced as inflammation progresses.

Stings by venomous caterpillars result in immediate, localized, severe, burning pain, which can radiate proximally and be severe enough to inhibit movement of the extremity (pseudoparalysis). Redness and swelling with slight bruising may occur at the site. Over the first few days, the patient may note the development of small blisters, which can become hemorrhagic. Local findings, including pain, may persist for several days.

Systemic complaints may occur within minutes of the sting, although they usually occur within 2 hours. These complaints include headache, dizziness, restlessness, nausea and vomiting, malaise, swollen or tender lymph nodes, muscle spasms, rapid heart rate, and, in exceptional cases, altered mental status. Systemic symptoms usually resolve in 24 hours.

Following stings by some of the New World caterpillars in the family Saturniidae, which contain a fibrinolytic component to their venoms, patients may note scattered bruising (onset in 8-72 h) and bleeding from any of a number of sites (eg, gingival bleeding, hematuria). Intracranial bleeding and acute renal failure (rarely chronic renal failure) are possible complications. Coagulopathy can last 2-5 weeks.

There are several reports of stings from the puss caterpillar, Megalopyge opercularis, to an upper extremity causing severe pain that radiates to the chest and/or abdomen. ^{[9, 10]}   In the case of a 4-year-old female with a M opercularis sting to the second finger, clinicians initially suspected appendicitis due to the clinical symptoms before the sting was discovered. ^[11]

Local findings include erythematous papules that tend to congregate around the face, neck, trunk, arms, wrists, and hands and may become confluent; vesicles; local purpura; or ecchymosis.

Systemic signs may include a low-grade fever. ^[12] Anaphylaxis is reported. ^[13]

Findings of respiratory exposure include acute rhinitis, tearing, respiratory distress, and wheezing.

Ocular exposure can result in acute conjunctivitis. Following penetration of the cornea, findings include keratitis, ^[14] acute uveitis, ophthalmia nodosa, ^[15] and retinochoroiditis.

Local findings from stings can include erythema, edema, small petechiae or hemorrhagic papules, vesicles, bullae, and pseudoparalysis of the extremity because of pain. Following M opercularis stings, the site may take on a gridlike pattern matching the distribution of the creature's spines.

Systemic findings from stings can include restlessness, lymphangitis, oropharyngeal edema, lymphadenopathy, muscle spasms, tachycardia, altered mental status (unusual), seizures, and hypotension. ^{[16, 17]}

The wounds or dermatitis that follow exposures to irritant or toxic caterpillars and moths can become secondarily infected, which can lead to scarring and permanent dysfunction. The risk is increased when hairs or spines are retained or in patients with severe pruritus that leads to excessive scratching. In rare cases, necrosis can result from prolonged exposure to caterpillar or moth setae.

The first case reported of a sting by the white flannel moth caterpillar (Norape ovina) in the family Megalopygidae had a similar course of symptoms and resolution as other stings from the more commonly reported stings from the puss caterpillar in the same family. This particular patient reported a sting at the site that was treated conservatively at home, and he never sought medical care. This patient had resolution of the pain in under an hour and the burning sensation resolved within a day. A discoloration remained at the site of the sting for over 2 months. ^[18]

Ocular exposures can cause development of keratitis, acute uveitis, retinochoroiditis, endophthalmitis, and ophthalmia nodosa in the setting of retained hairs that tend to migrate into the eye. The ultimate outcome may be permanent blindness.

An uncommon but very concerning complication following caterpillar or moth exposures is the development of anaphylaxis in sensitized individuals.

Following stings by some of the New World caterpillars in the family Saturniidae, which contain a fibrinolytic component to their venoms, patients may note scattered bruising (onset in 8-72 h) and bleeding from any of a number of sites (eg, gingival bleeding, hematuria). ^{[19, 20, 21]} Intracranial bleeding and acute renal failure (rarely chronic renal failure) are possible complications. ^[22] Coagulopathy can last 2-5 weeks.