Night bites from pigeon ticks and mites: An underdiagnosed cause of anaphylaxis

Pigeons are being increasingly recognized as a troubling source of arachnid bites for humans in both the United States and Europe. This threat stems from urban pigeons roosting and nesting near human habitats and the ticks and mites that they carry.

Pigeon nests are commonly found on roofs, terraces, and window ledges. In the United States, pigeon mites lay eggs in the fibers of a pigeon’s nest. At night, these mites search for a blood meal and can make their way into human domiciles. Fortunately, these pigeon mites rarely spread disease, and their bite is limited to mild skin irritation and discomfort. Nevertheless, experts recommend that entryways—including doorways and windowsills—be treated with an EPA-registered miticide.

In Europe, the threat of illness spread by pigeons is more urgent. The European pigeon tick, or Argas reflexus, is a parasite hosted by urban pigeons. These ticks can bite humans, resulting in a gamut of reactions from local (eg, itching, erythema, and edema) to systemic (eg, IgE-mediated anaphylaxis).

Proper identification of pigeon tick bites as a possible differential diagnosis of anaphylaxis would improve medical care in Europe, according to a case study published in Allergy. Patients should be advised of steps that they can take to eradicate these pathogens from their living vicinities.

“Important clues for allergic symptoms related to A. reflexus bites are the occurrence of nocturnal reactions, previous local reactions on arms or legs highly suggestive of insect bites, and living in buildings where pigeons have their nests,” wrote authors, led by Giovanni Rolla, MD, Allergy and Clinical Immunology, Department Medical Sciences, University of Torino, Italy.

In the current case study, a 44-year-old man presented to the emergency department after a bout of nocturnal anaphylaxis. The patient awoke in the early morning with a diffuse erythematous rash, nausea, shortness of breath, and loss of consciousness.

First responders found the man confused and exhibiting diffuse erythema and wheals, along with angioedema of the lips and eyelids. The man’s vital signs included a heart rate of 120/min, a systolic blood pressure of 70 mm Hg, and an oxygen saturation of 90% on room air.

The first responders administered epinephrine 1:1000 0.3 mL IM. He was also administered supplemental oxygen on site, along with fluids, methylprednisolone 80 mg, and chlorpheniramine 10 mg intravenously.

After transfer to a local hospital, the patient’s condition resolved after 4 hours. The man was left with an area on his hand that was red, indurated, edematous, and pruritic.

On patient history, he recalled experiencing what he thought were bug bites on his hands in previous months. These bites occurred at night and were pruritic. During more focused follow-up questioning, the man said he lived under the roof of an old building where pigeons nested. The patient had no history of drug use, and he had not eaten anything unusual in the hours preceding the attack.

Laboratory tests showed increased serum tryptase levels, indicating severe anaphylaxis, which affected the skin, cardiovascular, and respiratory systems. He was treated for this condition, and after 24 hours, his serum tryptase levels fell back to within normal levels.

On the basis of the history and physical examination, Dr. Rolla and colleagues suspected that an insect bite was to blame for the patient’s symptoms. Skin prick tests and specific IgE levels to routine inhalant, food, and hymenoptera allergens were all negative. They then specifically tested for pigeon tick using extract and recombinant allergen in IgE immunoblot, experimental ImmunoCAP, and basophil activation. On IgE immunoblot, they noted two bands corresponding to Arg r 1, the major pigeon tick allergen.

Pest control was sent to the patient’s apartment, and the exterminators noted pigeon ticks in the building. Cracks in the patient’s masonry were fixed to stop the invasion of pigeon ticks and the patient was given an epinephrine auto-injector.

In addition to the current case study, Dr. Rolla and colleagues have documented 28 other similar cases of severe nocturnal anaphylaxis throughout Europe during the past 10 years. They suggested the following clues when diagnosing pigeon tick bites:

• Bites occurring at night during spring or summer
• Urban pigeons in the neighborhood
• Previous history of insect bites on the arms or legs
• People living in buildings where urban pigeons nest

The researchers suggested that allergy secondary to pigeon tick bite is underdiagnosed, and not included as part of the differential diagnosis, because of a dearth of necessary diagnostic reagents.

“The availability of rArg r 1 or A. reflexus tick extract for in vitro IgE diagnosis would greatly improve the diagnosis of patients with anaphylaxis of unknown etiology,” wrote the team.

Pigeon infestations are currently plaguing cities of Middle and Southern Europe. The investigators predicted that some cases of idiopathic anaphylaxis could be due to the pigeon tick.

“The identification of pigeon ticks as a trigger of anaphylaxis would greatly improve medical care and advice for these patients as the parasite can be exterminated by eradication measures to avoid further incidents,” the authors concluded.

Although the threat of bites from pigeon ticks and mites appears to be more serious in Europe than it is in the United States, minimizing the risk of such bites is a good idea in either locale. The presence of pigeon nests near apartments and other abodes can raise suspicion for the presence and identification of pigeon mites or ticks, with eradication or preventive strategies undertaken to minimize any risk to humans.