Pseudoscabies caused by Dermanyssus gallinae in Italian city-dwellers: a new setting for an old dermatitis

Dermanyssus gallinae (De Geer 1778; the red poultry mite or chicken mite; fig. 1) is the most common mite associated with feral pigeons (Columba livia).1,2 It is a nocturnal blood-sucking ectoparasite and stays on the bird to feed only. During the daytime, it is usually foundin close proximity to the nest (1). In the absence of its usual host, the red mite can also infest mammals and cause a non-specific dermatitis associated with intense itching in humans. Infestations are often misdiagnosed and inevitably lead to failures in treatment. Figure 1. Figure 1. Open in figure viewerDownload Powerpoint slide D. gallinae, female: an egg is visible within the abdomen. This report outlines the importance of the red mite associated disease in humans through the report of seven episodes of pseudoscabies caused by D. gallinae in Italian cities, from 2001 to 2007. All cases shared common features. Particularly, all the patients lived and/or worked in urban environments but had no contact with animals or poultry farms. In five of the cases, people were infested in their homes and in the remaining two cases at work. Abandoned pigeon nests were always found in close proximity to the rooms infested by the mites. Medical consultations failed to solve the human dermatitis, which returned when symptomatic treatment with antihistamines and corticosteroids stopped. Indeed, diagnoses were consistently generic, and even when skin lesions were attributed to acariasis, the possibility of an animal to human cross-infection was not considered. Our experience confirms that most dermatologists have difficulty identifying ectoparasitoses, such as those that arise within new or atypical conditions. This is probably the main reason why similar cases of gamasidosis are more difficult to recognize than classical ones occurring in rural areas. The cases reported here give new insights into the sanitary role of D. gallinae infestation for humans living in urban areas. They also underline the need for dermatologists to be more aware of this threat and more familiar with its presentation and management. The meaning of these mites in public health also stems from their role as potential allergens and reservoirs of pathogens.1,3–5 Red mite is able to survive for long periods without a blood meal. This can lead to recurrent episodes of pruritic dermatitis (as has been observed in occasionaly-used buildings i.e. holiday homes). Therefore, the long-lasting absence of the human host does not guarantee the elimination of the mite from the environment, and a period of more than 9 months is necessary.6 In conclusion, the differential diagnosis of non-specific dermatitis in people living in urban settings should always include pseudoscabies caused by D. gallinae, particularly when the lesions develop in spring and the patients live and/or work on the upper floors of buildings. When the clinical presentation is non-specific and the arthropod cannot be found in cutaneous lesions, the environmental anamnesis could be a useful tool to diagnose successfully pseudoscabies. Dermatologists should provide the patients with complete instructions on how to inspect the living quarters and identify the mite (i.e. shape, colour, size of the mite; nocturnal feeding habits; typical hiding places), if suspicious elements emerge. The successful identification of the mite is absolutely fundamental to manage the clinical episodes correctly: specimens should be collected from the environment and sent to the laboratory of entomology for further identification. The involvement of a veterinary parasitologist can also be useful for a rapid diagnosis. Nowadays, the increase of synanthropic animals carries a high risk of zoonotic diseases and requires the collaboration of physicians and veterinarians as well as public health care officials.