Case Report

Dermatology 2007;215:66–68 Received: October 9, 2006 DOI: 10.1159/000102037 Accepted: January 31, 2007

Outbreak of Tropical Rat Mite (Ornithonyssus bacoti) Dermatitis in a Home for Disabled Persons

a b a J. Baumstark W. Beck H. Hofmann

a b Department of Dermatology and Allergy Biederstein, Technical University, and Institute for Comparative Tropical Medicine and Parasitology, Veterinary Faculty, Ludwig Maximilians University, Munich , Germany

Key Words Introduction recognized in 1923 as an origin of human Tropical rat mite Ornithonyssus bacoti dermatitis in the USA. In Germany, O. ba- Tropical rat mite dermatitis Different mite species, generally found coti was first observed in the Hamburg sea- on animals and/or in their environment, port in 1931, a place indicating the ecto- may infest humans temporarily; such ar- parasite was carried across the world Abstract thropods should be considered as a possi- oceans along with infested ship rats or Five mentally handicapped individuals liv- ble cause of pruritic and erythematous skin mice, probably in the periods of sailing ves- ing in a home for disabled persons in South- reactions of unclear origin. The tropical rat sels [3–10] . According to experience in ern Germany were seen in our outpatient mite, Ornithonyssus bacoti, is an external Germany O. bacoti appears on wild and pet department with pruritic, red papules pre- parasite occurring on rats (Rattus norvegi- rodents more frequently than one might dominantly located in groups on the upper cus, Rattus rattus), mice (Mus musculus), expect [10] . Single case reports from differ- extremities, neck, upper trunk and face. gerbils (Meriones unguiculatus) and vari- ent parts of the world show the presence of Over several weeks 40 inhabitants and 5 ous other small mammals. Although rats this haematophagous pest arthropod also caretakers were affected by the same rash. are known to be the preferred hosts, infes- causing dermatitis in humans [2–10] . Inspection of their home and the sheds tation of 10 other species of small mam- nearby disclosed infestation with rat popu- mals has been reported. However, in case lations and mites. Finally the diagnosis of the principal animal host is not available, C a s e R e p o r t tropical rat mite dermatitis was made by the human beings may become the victim of identification of the arthropod Ornithonys- mite infestation. The relatively low host Five handicapped patients (4 male, 1 fe- sus bacoti or so-called tropical rat mite. The specificity might be the reason why labora- male; age: 22–57 years) living in a home for patients were treated with topical cortico- tory personnel was infested while handling disabled persons close to Munich were suf- steroids and antihistamines. After elimina- mice [1] . Little information is available fering from itching papules developing for tion of the rats and disinfection of the rooms about the distribution of tropical rat mite approximately 3 weeks. Physical examina- by a professional exterminator no new cases in wild and pet rodents in Europe. The pest tion of the patients revealed red papules of rat mite dermatitis occurred. The tropical arthropods live under tropical and temper- and seropapules, 1–2 mm in diameter, of- rat mite is an external parasite occurring on ate climate conditions. Therefore, its name ten surrounded by a pale halo, located in rats, mice, gerbils, hamsters and various oth- ‘tropical rat mite’ is misleading. O. bacoti groups or individually predominantly on er small mammals. When the principal ani- has been reported from all continents ex- the upper extremities, neck, upper trunk mal host is not available, human beings can cept the Arctic and Antarctic regions as a and face ( fig. 1 ). Some of the papules were become the victim of mite infestation. parasite on small wild, commensal, and excoriated due to scratching. Further Copyright © 2007 S. Karger AG, Basel laboratory mammals and rodents or on physical examination was unremarkable man. The first case report of tropical rat except for the skin lesions. No insects mite in humans from Australia is from could be found on the skin. According to 1913 [2] . Furthermore this arthropod was the accompanying social worker nearly 40

© 2007 S. Karger AG, Basel J. Baumstark 1018–8665/07/2151–0066$23.50/0 Department of Dermatology and Allergy Biederstein Fax +41 61 306 12 34 Biedersteiner Strasse 29 E-Mail [email protected] Accessible online at: DE–80802 Munich (Germany) www.karger.com www.karger.com/drm Fax +49 89 4140 3578, E-Mail [email protected] 1

Fig. 1. Pruritic papules on the right hand. Fig. 2. Tropical rat mite (O. bacoti) from the home of the disabled persons. 2

of 70 inhabitants and 5 of the employees Table 1. Classification of mites (Acari) [18] were affected by itching papules. The diag- nosis of insect stings was based on clinical Parasitic Acari findings. The treatment of the patients was Ixodidae castor bean tick directed towards symptomatic relief. Five Argasidae soft-bodied tick of them required oral antihistamines and Sarcoptidae sarcoptic mange mite a topical therapy with crotamiton lotion, Trombiculidae harvest mite and 1 patient in addition received topical Dermanyssidae poultry red mite corticosteroid and antiseptic ointment. Cheyletiellidae fur mite The home of the patients, the farm and Demodicidae follicle mite sheds located next to the home, where the garbage is stored in bins for collection, as Nonparasitic Acari well as the stable for domestic animals in- Tyroglyphidae storage mite cluding the storage room for feed were ex- Pyroglyphidae house dust mite amined. These locations are kept open and are often visited by the disabled. There we discovered distinctive signs of a big popu- lation of rats. Inside the sheds lots of mites could be detected in various places. By ex- amination of these mites with light mi- Discussion titis requires detection of the parasite, croscopy female and male adults of the which is more likely to be found in the en- species O. bacoti could be identified (fig. 2). All developmental stages of O. bacoti vironment of its host than on the hosts’ Compared to other gamasid mite species exclusively consume blood. Those para- skin itself. Therefore, most mites are found belonging to the Macronyssidae, tropical sites induce a nonspecific dermatitis by in and around the animals’ sleeping area rat mites show a variety of different mor- their mouth parts and saliva components; and nests, in the floor dust and in clothing phological characteristics. therefore, it is difficult to diagnose rat mite [8–11] . A professional exterminator was con- dermatitis unless the parasites are found. O. bacoti belongs to the phylum Ar- tracted to eliminate the rats in the garden In most cases, the mites are recognized thropoda, class Arachnida, order Acari and sheds. All rooms of the home were dis- only when they attack humans. In cases of and superfamily Parasitoidea (table 1). infected, the bedlinen were changed sev- pet rodent infestation or attacked small The life cycle of the tropical rat mite in- eral times and the garbage was collected mammals from household husbandries, cludes 5 developmental stages: egg, larva, and eliminated more frequently. After veterinary practitioners sometimes see O. protonymph, deutonymph and adult. The these interventions no more cases of trop- bacoti on the hosts’ integument or envi- entire life cycle takes as little as 11–13 days ical rat mite dermatitis occurred. ronment. The diagnosis of rat mite derma- under optimum environmental condi-

Tropical Rat Mite Dermatitis in a Home Dermatology 2007;215:66–68 67 for Disabled Persons tions; however, protonymphs can survive ical rat mites are much more hairy than coptes scabiei var. hominis, which burrow for 43 days and adults for up 63 days with- other mite species. The density of the hair tunnels into the skin of their host. How- out blood meal [10, 11]. Female mites reach coat of the abdomen is considerably higher ever, sometimes humans are also vulner- a size between 0.75 and 1.40 mm, males are in comparison to D. gallinae and O. sylvi- able to less frequently recognized forms of a little smaller [13] . Usually those external arum. There are remarkable differences in dermatitis caused by ectoparasites para- parasites can be seen with the naked eye the shape of the dorsal shield (scutum), sitic on various animals [15–18] . These when crawling, especially on white back- sternal and genital shield, position of the dermatoses are often misdiagnosed as grounds. The unfed mite is of a grey-white anus, number and location of various se- prurigo simplex, allergy, unspecific mos- colour and is rather active in movement, tae, etc. O. bacoti , in contrast to the other quito insect bites or bacterial folliculitis. but, after having engorged, it is darker, 2 mite species, shows a sharp caudal apex We believe that the proper identification of red-brown, and sluggish [11]. of the scutum, an oval genital shield with epizootic animal mites is important for The identification of the tropical rat a cranial positioned anus. further treatment. The presence of O. ba- mite requires special knowledge about the Case reports about tropical rat mite in- coti is indicative of a rat-infested environ- morphological characteristics of these ar- festation are rarely recorded in the human ment or infested small mammals in flats. thropods. At first sight, O. bacoti looks and veterinary literature, possibly because Identification allows the physician or vet- similar to Dermanyssus gallinae and Orni- of the difficulty of detection and accurate erinarian to advise the patient and/or pet thonyssus sylviarum . All 3 mite species are identification of this ectoparasite. Futher- owner on eliminating the origin. Of note, haematophagous external parasites with more, in contrast to other arthropod stings the correlation of systemic symptoms such the same physiology and developmental and bites [14] so far no systemic allergic as eosinophilia and IgE induction would behaviour, but the preferred hosts of D. reactions to tropical rat mite infestation be of interest to possibly identify typical gallinae and O. sylviarum are wild and do- have been reported. Dermatologists are features of rat mite bites. We hope the new mestic birds or bats. These bird-specific keenly aware of dermatoses associated aspects given here will draw attention to mites might also be transmitted onto hu- with mites; particularly when the pre- this subject. man skin and cause pruritic lesions. Trop- ferred host is man, as is the case with Sar-

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68 Dermatology 2007;215:66–68 Baumstark /Beck /Hofmann