Infection with Leishmania spp. (Leishmaniosis)

Infection often stays silent for a long time. Dogs that progress typically show enlarged lymph nodes, weight loss, lethargy and skin disease: exfoliative dermatitis, alopecia, ulcers, nodules and overgrown, abnormally curved nails (onychogryphosis). Eye lesions include blepharitis, conjunctivitis, keratoconjunctivitis and uveitis. Nosebleeds, lameness from arthritis, fever, vasculitis and increased thirst and urination may follow as the kidneys fail. Laboratory work often shows non-regenerative anaemia, high globulins with low albumin, proteinuria and azotaemia.

Leishmaniosis is caused by protozoan parasites of the genus Leishmania (family Trypanosomatidae); in dogs the main species is L. infantum (synonym L. chagasi). A sand fly bite delivers the parasite, which then multiplies as amastigotes inside macrophages of the reticuloendothelial system. Whether infection is contained or progresses depends on how well macrophages kill the parasite, steered by T lymphocytes and cytokines; many dogs stay subclinically infected, and immunosuppression or concurrent disease can tip them into illness. In canine disease the parasite spreads through lymph nodes, spleen, bone marrow and skin, producing a chronic viscero-cutaneous syndrome. Circulating immune complexes deposit in the kidney, causing glomerulonephritis and proteinuria that can end in chronic renal failure.

Only female phlebotomine sand flies transmit the parasite: Phlebotomus in Africa, Asia and Europe, and Lutzomyia in the Americas. The disease is therefore limited to where these vectors live, and endemic areas have been expanding. Dogs are the main reservoir of zoonotic visceral leishmaniosis caused by L. infantum, which is endemic in more than 70 countries across southern Europe, Africa, Asia and the Americas; resistant, symptom-free dogs can exceed half of the infected population. Cats, equids, cattle, wild canids, hares and rabbits are also infected. Blood transfusion, vertical and venereal transmission are proven non-vector routes. In temperate areas transmission is confined to warm months. In urban areas of the Middle East, cutaneous disease from L. tropica is maintained by humans rather than animals. WOAH lists the disease.

In dogs the commonest signs overlap with ehrlichiosis and babesiosis, other vector-borne infections, and intestinal helminth infections. Because the picture is non-specific, the diagnosis rests on finding the parasite in lymph node, bone marrow, spleen or skin samples, on PCR, or on serology (IFAT or ELISA), interpreted alongside history and clinicopathological findings.

Skin, lymph nodes, spleen, bone marrow, liver, kidneys (glomeruli), eyes, joints, blood vessels, nails, nasal mucosa

Protect dogs from sand fly bites with repellent spot-ons or insecticide-impregnated collars, keep them indoors during the sand fly season, and reduce sand fly habitat; canine vaccines are authorised in Europe and Brazil.

Depends on stage: good in mild disease, guarded to poor in severe disease, poor with advanced kidney involvement. Treatment brings clinical improvement but not parasitological cure; chronic renal failure is the main cause of death.