CONTINUING MEDICAL EDUCATION Pet Hamsters as a Source of Rat Mite Dermatitis CPT Naomi B. Creel, MC, USA; COL Mark A. Crowe, MC, USA, Ret; Gary R. Mullen, PhD GOAL To understand the causes of rat mite dermatitis OBJECTIVES Upon completion of this activity, dermatologists and general practitioners should be able to: 1. Explain the role of mites as human pathogens. 2. Recognize the symptoms of mite bites. 3. Discuss treatment options for rat mite dermatitis. CME Test on page 440. This article has been peer reviewed and is accredited by the ACCME to provide continuing approved by Michael Fisher, MD, Professor of medical education for physicians. Medicine, Albert Einstein College of Medicine. Albert Einstein College of Medicine designates Review date: May 2003. this educational activity for a maximum of 1 This activity has been planned and implemented category 1 credit toward the AMA Physician’s in accordance with the Essential Areas and Policies Recognition Award. Each physician should claim of the Accreditation Council for Continuing Medical only that hour of credit that he/she actually spent Education through the joint sponsorship of Albert in the activity. Einstein College of Medicine and Quadrant This activity has been planned and produced in HealthCom, Inc. Albert Einstein College of Medicine accordance with ACCME Essentials. Drs. Creel, Crowe, and Mullen report no conflict of interest. The authors report no discussion of off-label use. Dr. Fisher reports no conflict of interest. Rat mite dermatitis is characterized by pruritic woman with rat mite dermatitis who developed papules in a patient exposed to the tropical rat this eruption after exposure to her pet hamster. mite Ornithonyssus bacoti. We report a case of a Mites were collected from the hamster and iden- tified as O bacoti. Reported sources of rat mites, as well as avian mites and other mites that bite Accepted for publication April 18, 2003. humans, are reviewed. Dr. Creel is from the National Capital Consortium Dermatology Cutis. 2003;71:457-461. Residency Program, Walter Reed Army Medical Center, Washington, DC. Dr. Crowe is from the Department of Dermatology, Madigan Army Medical Center, Tacoma, Washington. Dr. Mullen at mite dermatitis is a pruritic eruption in is Professor, Department of Entomology and Plant Pathology, humans caused by bites from the tropical rat Auburn University, Alabama. R mite Ornithonyssus bacoti. Other biting mite The opinions expressed are those of the authors and should not species that have been reported to cause a similar be construed as official or as representing those of the Army dermatitis in humans include Dermanyssus gallinae Medical Department or the Department of Defense. Reprints: CPT Naomi B. Creel, MC, USA, 6900 Georgia Ave, (red mite or poultry mite), Ornithonyssus sylviarum Dermatology Service, Room 1J, Walter Reed Army Medical Center, (northern fowl mite), and Ornithonyssus bursa Washington, DC 20307 (e-mail: [email protected]). (tropical fowl mite).1-6 The eruptions caused by VOLUME 71, JUNE 2003 457 Rat Mite Dermatitis Figure 1. Excoriated erythem- atous papules on the wrist. these mites are clinically indistinguishable. Initial debility, anemia, decreased reproduction, and case reports of mite dermatitis identified the death in small animals, suggesting that it may have sources of these mites to be rat-infested homes or contributed to the hamster’s death. bird nests around the home.1-6 Rat mite dermatitis also was reported in a patient who had contact Comment with mite-infested laboratory mice.7 More recently, Mites are arthropods in the class Arachnida, which avian mite dermatitis was reported in patients who includes ticks, spiders, and scorpions. The arachnids had mite-infested pet gerbils.8 This report describes are characterized by 4 pairs of legs and 2 body regions, a patient with rat mite dermatitis acquired from a a cephalothorax and an abdomen. Mites and ticks pet hamster. Based on the variety of mites and are further classified in the subclass Acari. Mites of sources of infestations, mite dermatitis may be medical importance can be grouped by their pathol- more common than generally thought. ogy in humans.9 House dust mites (Dermatophagoides and Euroglyphus ssp) cause respiratory allergies, Case Report whereas human follicle mites (Demodex spp) infest A 48-year-old healthy woman presented with a hair follicles and associated sebaceous glands. complaint of pruritic papules on the wrists (Figure 1) Neither group of mites causes cutaneous lesions in and waist for several weeks. History revealed she the form of bites or burrows. The scabies mite maintained a small menagerie of animals including (Sarcoptes scabiei) is a primary human parasitic mite horses, dogs, cats, and hamsters. She was informed in which the adult mite burrows and feeds on skin that her skin lesions were most likely the result of cells. Chiggers (family Trombiculidae) and common insect bites and she should evaluate her animals animal mites bite humans but do not reside on and their environment for evidence of infestation. humans as a primary host. Many mite species are She returned 2 days later and reported that her opportunistic, often feeding on various hosts they hamster had died the previous day. When she went encounter.10 The common animal mites that bite to bury it, she noticed numerous red specks in its humans include several avian mites, the rodent mites, fur. She placed the hamster in a plastic bag in the and fur mites of rabbits (Cheyletiella parasitivorax), freezer until she could bring it in for examination. dogs (Cheyletiella yasguri), and cats (Cheyletiella Examination of the hamster (Figure 2) revealed blakei). Mites infesting grain, hay, and straw occa- numerous red mites (Figure 3). The patient’s symp- sionally cause dermatitis in humans. toms resolved over the following few weeks. The The usual hosts of the tropical rat mite O bacoti mites were identified as the tropical rat mite are the brown rat (Rattus norvegicus) and the black O bacoti. No necropsy was performed on the ham- rat (Rattus rattus). This mite is yellow to dark red, ster, and a specific cause of death was never deter- when blood-fed, and ranges in size from 0.75 to mined. This mite ingests blood and can cause 1.4 mm. It will feed on humans when its rodent hosts 458 CUTIS® Rat Mite Dermatitis Figure 2. Deceased pet hamster with numerous red mites in its fur. Figure 3. Red mite from the hamster was identified as Ornithonyssus bacoti (magnified from original size of 1.5 mm). are killed or abandon their nests.11-16 O bacoti also cracks in buildings. It feeds on the host nocturnally infests mice and hamsters in research laboratories.7 for 1 to 2 hours at a time, and may live up to The common avian mites D gallinae, O sylviarum, 8 months without a host. O sylviarum and O bursa and O bursa occur on both domestic and wild bird spend their entire life cycle on the host. The mites species, including chickens, ducks, pigeons, spar- will leave the host and bite humans in close prox- rows, canaries, starlings, robins, tiger finches, and imity, especially in heavily infested quarters. The doves.1 D gallinae has been identified on commensal Ornithonyssus species live only 2 to 3 weeks without and laboratory rodents, and in one case it was found a host.9 on a farm dog.17-19 The species are similar in size and Mite bites typically produce urticarial, pruritic appearance, but differ in their life cycle. The adult papules on the skin. These papules result from an mite of these species ranges in color from brown to inflammatory cutaneous reaction to mite saliva as it red and in size from 1 to 3 mm. D gallinae lives most takes a blood meal. Clinically, the bites are nonspe- of its life cycle off the hosts in nests, crevices, and cific, but pruritus is the most consistent feature. The VOLUME 71, JUNE 2003 459 Rat Mite Dermatitis lesions may be vesicular, urticarial, eczematous, or tions, drug hypersensitivity reaction, and neuroder- any combination of these. Secondary lesions such as matitis should be considered. persistent nodules, postinflammatory hyperpigmen- Treatment focuses on reducing or eliminating tation, excoriations, and secondary infection may be problem mites in infested areas, often requiring present. The bites tend to occur in asymmetric involvement of veterinarians and pest control groups, most commonly on the abdomen and agencies. In the case of D gallinae, which does not extremities. Often a patient presents with a combi- live on the host, acaricides must penetrate into nation of these clinical features, but denies a history crevices and cracks in buildings.21 Both the host of any “bites.” and the area of infestation must be treated to exter- On pathologic examination, the lesions are non- minate O sylviarum and O bursa. Elimination of specific mild arthropod reactions with superficial and rats and removal of their nests are important for mid-dermal perivascular infiltrate. Eosinophils may controlling O bacoti.22 Patients may be treated with be present. The epidermis may be mildly spongiotic. antihistamines and topical corticosteroids for The diagnosis of mite dermatitis should be con- symptomatic relief. The dermatitis is self-limited sidered in unexplained pruritic dermatitis. The when the exposure is eliminated. rodent and avian mites are rarely found on the Two important mite-borne diseases of humans human host because the mites leave after feeding. are tsutsugamushi disease (scrub typhus) and rick- History of exposure can include bird handling, ettsialpox, caused by the rickettsial organisms bird nests or roosts near the home, rat infestations, Orienta tsutsugamushi and Rickettsia akari, respectively. pets, and occupational exposure to laboratory In the case of tsutsugamushi disease, chiggers are the rodents.