Tropical Rat Mites (Ornithonyssus Bacoti) – Serious Ectoparasites

DOI: 10.1111/j.1610-0387.2009.07140.x Review Article 1

1 Tropical rat mites (Ornithonyssus bacoti) – 2 3 4 serious ectoparasites 5 Wieland Beck1, Regina Fölster-Holst2 6 (1) Pfizer GmbH Animal Health, Berlin, Germany 7 (2) Department of Dermatology, Venereology and Allergy, University of Schleswig-Holstein, Campus Kiel, Germany 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 JDDG; 2009 • 7:1–4 Submitted: 16.3.2009 | Accepted: 24.4.2009 23 24 Keywords Summary 25 • tropical rat mite In Germany there is limited information available about the distribution of the 26 • epizoonosis tropical rat mite (Ornithonyssus bacoti) in rodents. A few case reports show 27 • man that this hematophagous mite species may also cause dermatitis in man. 28 • rodents Having close body contact to small rodents is an important question for 29 • dermatitis patients with pruritic dermatoses. The definitive diagnosis of this ectopara- 30 sitosis requires the detection of the parasite, which is more likely to be found 31 in the environment of its host (in the cages, in the litter or in corners or cracks 32 of the living area) than on the hosts’ skin itself. A case of infestation with trop- 33 ical rat mites in a family is reported here. Three mice that had been removed 34 from the home two months before were the reservoir. The mites were detect- 35 ed in a room where the cage with the mice had been placed months ago. 36 Treatment requires the eradication of the parasites on its hosts (by a veterinar- 37 ian) and in the environment (by an exterminator) with adequate acaricides 38 such as permethrin. 39 40 41 42 Introduction tropical rat mite from other mite species nymphs: 0.5-0.7 mm). Females, who live 43 The tropical rat mite (Ornithonyssus ba- (O. bacoti: very hairy, D. gallinae and O. up to 70 days, lay 90-120 eggs 2-3 days 44 coti) (Figure 1), whose developmental syviarum:few hairs; O. bacoti: caudally after a single blood meal in various nests 45 stages feed on the blood of their hosts, pointed dorsal plate, D. gallinae: cau- in the environment, not on the skin sur- 46 belong to the family Macronyssidae. dally rounded dorsal plate, O. sylviarum: face of the host. After another 1-4 days 47 They are frequently confused with red dorsal plate with a conical end; O. ba- larvae hatch form the eggs. The entire 48 bird mites (Dermanyssus gallinae) or coti: anal plate with cranial anus, D. gal- developmental cycle lasts 11-16 days at 49 the Nordic bird mites (Ornithonyssus linae and O. syviarum: anal plate with normal room temperature and at a rela- 50 sylviarum), which also belong to the caudal anus). A specialist for medical tive humidity of 75-80 %. 51 Macronyssidae and possess similar mor- arachno-entomology should be con- Just as most representatives of the 52 phologic characteristics. An exact differ- sulted. The fully engorged female Or- Macronyssidae tropical rat mites are ac- 53 ential diagnosis is essential especially in nithonyssus bacoti can easily be seen with tive at night and seek dark hiding places 54 view of possible epizoonoses, as only so the naked eye on its host or in the litter during the daytime. At night the para- 55 can the origin or reservoir of the parasites or in hiding places (adult mites: 0.6-1.1 sites search for their preferential hosts 56 be determined. Certain morphologic mm). The developmental stages, i. e. (especially wild rodents [Norway rat, 57 structures (e. g. hairiness, caudally eggs, larvae and nymphs can usually be house rat and mouse] and pet rodents 58 pointed scutum [dorsal plate], typical recognized with the help of adhesive tape that are offered for sale in pet stores 59 form of the anal plate with a cranial stripping under the microscope (eggs: [gerbil and hamster] to feed on blood. If

60 DDG09094 anus) allow for differentiation of the 0.3-0.4 mm, larvae 0.3-0.4 mm, suitable preferential hosts are unavailable

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Figure 2: Close skin contact to small mammals, e. g. rats, facilitates transmission of skin parasites, Figure 1: Tropical rat mite (Ornithonyssus e. g. tropical rat mites. 20 bacoti), Note: sharp caudal apex of the scutum 21 and hairy body surface (200 ϫ). 22 23 or in the case of close human-animal after finding mites in the living or work- 24 skin contact, the mites can occasionally ing environment. Research on the etiol- 25 infest humans. The sale and distribution ogy usually is restricted to an inquiry of 26 of small rodents without elimination of the patient; on-site inspection as well as 27 ectoparasites as well as litter and feed examination of living quarters are rarely 28 from breeding and sales cages contribute performed. Recently infestations with 29 considerably to the spread of these tropical rat mites have increasingly been 30 parasites [1]. Further, free-roaming cats observed in Germany and other Euro- 31 that catch affected rodents also con- pean nations [1]. Adequate control 32 tribute to the spread of these parasites to measures demand an exact parasitologi- 33 pet owners. cal species determination to clarify the 34 As infestation with tropical rat mites of- etiology and detect the mite reservoir. 35 ten occurs with very close bodily contact Ornithonyssus bacoti affects primarily 36 between human and affected animal, wild rodents such as rats and mice in 37 children with pets are particularly ex- Germany. In private households even 38 posed (Figure 2) [1, 2]. Sometimes even well-cared for small mammals are possi- 39 people who have no pets in their home ble reservoirs [7]. In the 11 registered 40 and no other contact with animals are cases of human infestation with tropical 41 also infested. In such cases wild rodents rat mites in Germany, all could be attrib- 42 can serve as a reservoir for the mites. As uted to the appearance of parasite in the 43 the mites have a large radius of action, living quarters [8]. Due to the difficult Figure 3: Cutaneous lesions of the mother. 44 they are entirely capable after a blood diagnosis of this pathogen and the sus- Multiple excoriated papules, partly urticarial, on 45 meal to leave their preferential hosts and pected number of unrecognized infesta- the upper extremity. 46 enter buildings and living quarters [3-6]. tions, a much greater distribution of this 47 People visited upon by the tropical rat mite species than assumed to date is clinically similar to an ictus (arthropod 48 mite develop pruritic insect bite-like cu- probable. An affected family will now be bite) reaction. While the father and 49 taneous lesions. At the visit of the physi- presented. daughter had only few lesions on the 50 cian the patient is usually unaware of the forehead and dorsa of hands, respec- 51 cause. As the parasites are active at night Case report tively, the mother displayed multiple 52 and the blood meal on the skin of the A married couple and their adult daugh- acute and chronic lesions especially on 53 host lasts maximally 20 minutes, they ter present in the outpatient service of the limbs (Figure 3). To exclude prurigo 54 usually cannot be detected on the skin the Department of Dermatology, Kiel, simplex subacuta or a pruriginous 55 [4, 5]. The primarily consulted physician because of pruritic cutaneous lesions. dermatitis, skin biopsy was performed 56 will therefore usually consider cutaneous These have been present for weeks and confirming the clinical diagnosis of ictus 57 lesions to be a result of allergies, fungal various topical agents including gluco- reaction. Animal contact, especially pets, 58 infections or bacterial infections. Suspi- corticosteroids have hardly led to im- was denied. The family, who only 59 cion of a parasitic cause only dawns after provement. Dermatologic examination recently had moved into a new building, 60 unsuccessful symptomatic therapies or shows excoriated papules and urticae, was instructed to carefully inspect their

JDDG |8˙2009 (Band 7) © The Authors • Journal compilation © Blackwell Verlag GmbH, Berlin • JDDG • 1610-0379/2009/0708 Reaction of ictus by tropical rat mites Review Article 3

1 as vector for various diseases is unknown. seven cases the tropical rat mite Ornitho- 2 In the literature infestations of rodents nyssus bacoti, in four cases the Nordic 3 and humans, too, with Ornithonyssus ba- bird mite Orntihonyssus sylviarum, in 4 coti manifesting clinically as ictus reac- four further case species identification 5 tions have been reported [1-16]. As it is a was not possible [8]. 6 parasite active at night, predominantly For elimination various acaricides in 7 skin regions not covered by tight cloth- spray form can be employed. Well-suited 8 ing are affected. When primary hosts are are most “flea sprays” containing perme- 9 lacking, for example after elimination of thrin and piriproxyfen [17, 18]. The par- 10 rats or in cases of heavy infestation of asites can survive for a time without a 11 Figure 4: Dust lice (Psocoptera), a common small pets, the parasites can expand their live host without a blood meal. Details 12 arthropod in flats with high humidity and radius of activity and temporarily infest on the exact time are lacking. In the case 13 mildew, e. g. behind wallpaper (600 ϫ). humans. Exactly this was observed in a presented here Ornithonyssus bacoti 14 medical student in Munich, Germany survived for weeks in the conduit pipes 15 [4, 5] who kept no pets and had attacks after rodent elimination in the back yard 16 living quarters for possible parasites and of pruritus predominantly in the night. before people in the second floor were 17 to reconsider their history of animal con- A search for parasites was successful. infested. According to our own observa- 18 tact. Several days later we received a After the veterinarian identified the trop- tions tropical rat mites can survive up to 19 small package with insects which were ical rat mite an on-site inspection and 6 months without a blood meal [1]. 20 microscopically identified as book or inquiry of other tenants were performed. Increasingly, especially if small rodents 21 dust lice (Psocoptera) (Figure 4). These Not only in the apartment of the student are held as pets, infestation with animal 22 insects that often occur in new buildings but in the apartment of other tenants ectoparasites, especially tropical rat 23 play a medical role, as type 1 allergies who also had pruritic cutaneous lesions, mites, should be considered in the differ- 24 eliciting rhinitis and asthma, but can be a mass infestation with Ornythonyssus ential diagnosis. To verify the parasitosis 25 excluded as the cause of the cutaneous le- bacoti was found. An exact evaluation possibly infested animals should be 26 sions. During a telephone call two weeks revealed that cutaneous lesions appeared in examined by a veterinarian to identify 27 later the mother continued to complain temporal association with extermination and eliminate skin parasites. Even with a 28 of highly pruritic cutaneous lesions. She of rodents in the back yard of the house. negative history of animal contact, the 29 also reported on mice that the daughter From here masses of mites, due to the careful inspection of the living quarters 30 had held in her room up to three months lack of the main hosts, obviously found for parasites is prudent, as the described 31 previously. As symptoms persisted even their way along vertical conduit pipes in case demonstrates. <<< 32 without the mice, she had not consid- their search for new mammals (“blood 33 ered this information important. We rec- donors”) into the apartments of the ten- Conflicts of interest 34 ommended to examine the room and es- ants. The mite plague was eliminated by None. 35 pecially the exact place where the cage an extermination with the use of perme- 36 with the mice had stood for the presence thrin. 37 of parasites. The content of the next Another route of transmission is by pets. 38 package brought the solution: Ornitho- As these are usually kept in adequate Correspondence to 39 nyssus bacoti. After adequate extermina- hygienic conditions, a massive infesta- Prof. Dr. Regina Fölster-Holst 40 tion with permethrin sprays, symptoms tion by tropical rat mites is an exception. Department of Dermatology, Venereology 41 did not recur. When suspected, it is always advisable to and Allergy 42 have a veterinarian carefully examine University of Schleswig-Holstein, 43 Discussion animals, cages and litter. In a family of Campus Kiel 44 In the USA the tropical rat mite was first five who kept two gerbils and a hamster Schittenhelmstr. 7 45 described as he nosogenic agent of a hu- massive numbers of tropical rat mites D-24105 Kiel, Germany 46 man dermatitis in 1923. In Germany were discovered in the litter of the gerbils Tel.: +49-431-597-1596-1579-1501 47 Ornithonyssus bacoti was first discovered [2]. While the hamster and the parents Fax: +49-431-597-5349 48 on infested ship rats in the port of Ham- showed no signs or symptoms, all E-mail: 49 burg in 1931 and may possibly have children (wheals, excoriated papules) [email protected] 50 spread from here to new areas of distri- and both gerbils (uneasy, superficial 51 bution [9]. As the pathogen is cos- excoriations on the head, ears and neck) References 52 mopolitic and is found in tropical as well were affected. Parasite control on the 1 Beck W, Pantchev N. Parasitäre 53 as moderate climate zones the name animals and in the environment was able Zoonosen. 1. Auflage. Hannover: 54 tropical rat mite is misleading for the to completely eliminate the invading Schlütersche, 2009; S. 92–99. 55 uninitiated and may suggest that this mite population. 2 Beck W. Massenbefall mit der Tropi- 56 skin parasite does not even occur in Mid- In recent years among the mites sent in schen Rattenmilbe, Ornithonyssus 57 dle Europe. According to our own obser- for diagnostics from human living quar- bacoti (Acari: Macronyssidae), beim 58 vations about 80 % of wild rodents in ters in Berlin and the state of Branden- Gerbil - Erfahrungen zur Therapie mit 59 Germany are infested by this parasite burg in 15 cases mites of the genus Selamectin (Stronghold®). Kleintier- 60 [4, 5]. If the tropical rat mite plays a role Ornithonyssus were identified, of these in prax 2002; 47: 607–613.

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