Immunohistochemical Detection of Leishmania Infantum in Formalin-Fixed, Paraffin-Embedded Sections of Canine Skin and Lymph Nodes

Canine leishmaniasis is a protozoal infection caused by Leishmania infantum which multiplies through the process of binary fission in macrophages of the skin and the reticulolymphoid organs (lymph nodes, bone marrow, etc.). The disease is transmitted to humans and animals by bloodsucking sandflies. Outside of America, 2 canine leishmaniasis is endemic in several countries around the Mediterranean basin, with an average prevalence 7 of from 20% to 40%; the growing international displacement of humans and their pets and the viral (acquired immunodeficiency syndrome: AIDS) and iatrogenic factors of immunodepression 1 have helped to increase the frequency and the distribution of the zoonosis. Clinical signs of the illness are numerous and varied: 6 generalized lymphadenopathy, cachexia, exfoliative dermatitis with scaling, hyperkeratosis, alopecia, and ulcers. The disease is extremely polymorphic, so observation of the organism in appropriate tissue samples and demonstration of serum anti-Leishmania antibodies are necessary to confirm the diagnosis. The differential diagnosis includes several immunologic skin diseases (pemphigus foliaceus, systemic lupus) and other scaling dermatoses of the dog (zinc-responsive dermatoses, necrolytic migratory erythema, etc.); hence, the veterinarian often performs a skin or lymph node biopsy. Unfortunately, skin biopsy results vary considerably: typical features 4,7 are inflammatory infiltrate of macrophages and lymphocytes, granulomatous perifolliculitis, and perivascular and diffuse dermatitis. Parasitic organisms are frequently not easily recognized and the examination of the hematoxylin and eosin (HE) sections is sometimes inconclusive. The purpose of this study was to evaluate two immunohistochemical techniques for the demonstration of Leishmania in skin and lymph node biopsies. Material consisted of formalin-fixed biopsies from 26 dogs examined in the Dermatology Department of the Veterinary School of Lyon (4 dogs) and the surgeries of veterinarians located in an area where leishmaniasis is endemic (22 dogs). The diagnosis of leishmaniasis was confirmed by serologic immunofluorescent assay. a Thirty-four skin biopsies were obtained from selected areas of the bodies of 26 dogs in apparently healthy (11 biopsies) or visibly abnormal areas (23 biopsies). Fifteen lymph nodes were obtained from 9 dogs that were euthanatized for medical reasons. All the samples were fixed in 10% neutral formalin and then embedded in paraffin using routine procedures. One section from each sample was stained with standard HE staining to identify the parasites in the infected cells, since it is a common pathological technique that is able to define subtle cellular differences if there are pathologic changes.