Is Wolbachia complicating the pathological effects of Dirofilaria immitis infections? L. Kramer a, * , F. Simo ´n b , F. Tamarozzi a , M. Genchi c , C. Bazzocchi c a Dipt. di Produzioni Animali, Universita ` di Parma, 43100 Parma, Italy b Laboratorio de Parasitologı ´a, Facultad de Farmacia, Universidad de Salamanca, Spain c Dipt. di Patologia Animale, Igiene e Sanita ` Pubblica Veterinaria, Universita ` di Milano, Italy Abstract Human and animal parasitic filarial nematodes, which often are the cause of severe disease, harbor intracellular bacteria of the genus Wolbachia (Rickettsiaceae). It is thought that these bacteria play an important role in the pathogenesis and immune response to filarial infection. In order to determine the possible role of Wolbachia in heartworm disease, dogs naturally infected with Dirofilaria immitis were studied for specific antibody response to Wolbachia surface protein (WSP). Antibody subclasses were analyzed to determine immune response polarization. Dogs that died from heartworm disease were necropsied, and various organs were studied by immunohistochemistry to determine whether Wolbachia-derived molecules were present in tissue from infected dogs. Humoral response to the WSP was present in all infected dogs and appeared to be predominantly of the Th1-type. Several organs, including lung, liver, and kidney, contained positive-staining cells for WSP, confirming that the canine host does come into contact with Wolbachia-derived molecules. # 2005 Elsevier B.V. All rights reserved. Keywords: Wolbachia; Heartworm; Dirofilaria immitis 1. Introduction Human and animal parasitic filarial nematodes, which are often the cause of severe disease, harbor intracellular bacteria of the genus Wolbachia (Rick- ettsiaceae). It is thought that these bacteria play an important role in the pathogenesis and immune response to filarial infection (Bandi et al., 2001). In adult Dirofilaria immitis, Wolbachia is present in the hypodermal cells of the lateral chords; the cytoplasm of some of these cells is filled with Wolbachia and resemble insect bacteriocytes. Wolba- chia is also present in the ovaries of female worms and in developing embryos but has not been demonstrated in the male reproductive apparatus (Sacchi et al., 2002). Several studies have investigated the humoral response to Wolbachia-derived molecules from the Wolbachia of D. immitis. Infected cats have circulat- ing anti-Wolbachia surface protein (WSP) antibodies, as shown by Western blot analysis. Humans living in D. immitis-endemic areas have circulating anti-WSP www.elsevier.com/locate/vetpar Veterinary Parasitology 133 (2005) 133–136 * Corresponding author. Present address: Dipartimento di Produ- zioni Animali, Facolta ` di Medicina Veterinaria, Universita ` di Parma, Via del Taglio 8, 43100 Parma, Italy. Tel.: +39 0521 032776; fax: +39 0521 032770. E-mail address: kramerlh@unipr.it (L. Kramer). 0304-4017/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.vetpar.2005.04.011