Emerging infections: mimickers of common patterns seen in dermatopathology.

The following discussion deals with three emerging infection diseases that any dermatopathologist working in the northern hemisphere can come across. The first subject to be dealt with is gnathostomiasis. This parasitic disease is produced by the third larvarial stage of the parasite that in most patients is associated with the ingestion of raw fish. Epidemiologically, it is most commonly seen in South East Asia, Japan, China, and the American continent, mainly in Mexico, Ecuador, and Peru. Nowadays, the disease is also seen in travelers living in the developed countries who recently came back from visiting endemic countries. The disease produces a pattern of migratory panniculitis or dermatitis with infiltration of eosinophils in tissue. The requirements for making the diagnosis are provided, including clinical forms, common histological findings on skin biopsy as well as the use of ancillary testing. Buruli ulcer, a prevalent mycobacterial infection in Africa, is described from the clinical and histopathological point of view. The disease has been described occasionally in Central and South America as well as in developed countries such as Australia and Japan; Buruli ulcer has also been described in travelers returning from endemic areas. Clinically, the disease is characterized by large, painless ulcerations with undermined borders. Systemic symptoms are usually absent. Classical histological findings include a particular type of fat necrosis and the presence of abundant acid fast bacilli in tissue. Such findings should raise the possibility of this disease, with the purpose of early therapeutically intervention. Lastly, the infection by free living ameba Balamuthia mandrillaris, an emerging condition seen in the US and Peru, is extensively discussed. Special attention is given to clinical and histological characteristics, as well as to the clues for early diagnosis and the tools available for confirmation.