Canine leishmaniasis: Update in dogs (Proceedings)
• The protozoan of the genus Leishmania causes two types of disease - cutaneous or visceral. Organ systems affected include the skin, hepatobiliary, spleen, kidneys, eyes, and joints, or develop hemorrhagic diathesis.
• Dogs with Leishmaniasis in the United States fall into 2 categories:1. acquired the infection (usually caused by L. donovani infantum) overseas from around the Mediterranean basin, Portugal, and Spain, with sporadic cases arising from Switzerland, northern France, and the Netherlands. Dogs imported from endemic areas of South and Central American, and southern Mexico may be infected with L. donovani complex or L. braziliensis.
2. Endemic cases in Foxhounds populations (Feb 2000) in most states and even Canada. Thought not to be vector transmitted.
• Sandfly vectors (not in US) transmit flagellated parasites into the skin of a host, where it often localizes in the cat. In dogs, there is invariably spread of the parasite throughout the body to most organs, although renal failure is the most common cause of death. Incubation period: 1 mth - yrs.
• Virtually all dogs develop visceral or systemic disease, but 90% of dogs have cutaneous involvement as well. There is no sex or breed predilection (except Foxhounds in US!).
• Cats develop cutaneous disease (rare) with no sex or breed predilection.
• Historically, exercise intolerance, severe weight loss, anorexia are the main signs with diarrhea, vomiting, epistaxis and melena less common.
• Clinically, most dogs have lymphadenopathy, cutaneous lesions, and emaciation. Signs of renal failure (polyuria, polydipsia, vomiting) may be present. Neuralgia, polyarthritis, polymyositis, osteolytic lesions or proliferative periostitis are rare. Fever and splenomegaly occurs in about a third of dogs.
• Hyperkeratosis is the most prominent finding (excessive epidermal scale with thickening, depigmentation and chapping of the muzzle and footpads). Hair coat is dry, brittle with hair loss. Intradermal nodules and ulcers occur in some dogs. Abnormally long or brittle nails are a specific finding in some dogs.
• Cats usually develop cutaneous nodules.
• Differentiate visceral from systemic diseases including mycoses (blastomycosis, histoplasmosis), systemic lupus erythematosus, metastatic neoplasia, distemper, vasculitis.
• Cutaneous lesions need to be differentiated from other causes of hyperkeratosis including primary idiopathic seborrhea and nutritional dermatoses (vitamin A-responsive, zinc-responsive). Other causes (idiopathic nasodigital hyperkeratosis, lichenoid-psoriasiform dermatosis, epidermal dysplasia, and Schnauzer comedo syndrome) are rare and breed specific. Hyperkeratotic and nodular lesions caused by leishmaniasis are easily differentiated from other etiologies by finding organisms on skin biopsies.
• Hyperproteinemia with hyperglobulinemia (100% of cases) and hypoalbuminemia (95% of cases) is characteristic (differentiate from chronic ehrlichiosis and multiple myeloma).
• Proteinuria (85% of cases), high liver enzyme activity (55% of cases), thrombocytopenia (50% of cases), azotemia (45% of cases), and leukopenia with lymphopenia (20% of cases) are other findings.
• Coomb's test, antinuclear antibody test, and lupus erythematosus cell test may be positive.
• Serologic diagnosis is available – fluorescent antibody (Communicable Disease Center - CDC), or ELISA from other diagnostic laboratories (Cornell, North Carolina).
• Culture of skin, splenic, bone marrow, or lymph node biopsies or aspirates by the CDC although this takes a long time and is not practical.
• Cytologic and histopathologic identification of intracellular organisms in the above biopsies or aspirate specimens is the definitive test of choice.
• Cytologic examination of the lymph nodes and bone marrow is probably not as efficient as culture of the lymph nodes or bone marrow.
• PCR of bone marrow tissue particularly, but also lymph nodes is effective especially in heavily infected animals.
• A combination of diagnostic techniques (cytology, serology etc) is often needed to make a definitive diagnosis.