Leishmaniasis is an infectious disease of people and wild and domestic animals throughout temperate, subtropical and tropical regions of the world.
Old World
Leishmania donovani complex- Causative agent of visceral leishmaniasis in Africa, India, South America and Mediterranean countries. Transmitted by sand flies (Phlebotomus spp).
Leishmania tropica complex- Causative agent of cutanious leishmaniasis in Asia, west Africa and Mediterranean countries. Sandfly transmitted.
New World
Leishmania braziliensis complex. Parasites in this group produce cutanious lesions or mucocutanious lesions. I is most common in Central and South America with some reportings in U.S. There may be numerous wildlife reservoirs. The cutanious form of the disease, usually manifested by single ulcerated lesions on the ears is most common. Knowledge of leishmaniasis is important to the clinician since infections can cause clinical disease in dogs and cats and because these animals are reservoirs for the organism in some locations.
In the Americas, parasites of the L. donovani complex are considered primarily viscerotropic but also produce primary cutanious lesions in humans and canines. Parasites of the L. braziliensis complex produce cutaneous lesions manifested by single ulcerated lesions on the ears.
Since leishmaniasis is an obligatory intracellular parasite, host defenses are dependent on T lymphocyte activity. T. lymphocyte regions in the lymphoid organs become depleted and B cells proliferate in response to infection. Without T cell support, macrophages can not kill the amastigotes and the parasite proliferates. Proliferation of B lymphocytes, histocytes and macrophages result in a lymphadoneopathy and hepatosplenomegaly. Exuberant B lymphocyte generates a large amount of circulating immune complexes (CIC) which deposit on walls of blood vessels causing a vasculitis, polyarthritis and glomerulonephritis. In canines, CIC deposition in the kidneys results in renal failure which is the main cause of death in leishmania infected dogs. Cats are rarely clinically affected.
The primary clinical findings are cutanious involvement although dermatologic abnormalities in the absence of other signs of disease are rare. Weight loss and muscle atrophy are the most common signs of visceral involvement.
Diagnosis is based on finding amastigotes free or in macrophages in giemsa-stained smears from lymph nodes or bone marrow (below). Biopsy material from liver or skin is also useful as is serologic testing (IFA, CF, ELISA). Serology is often used to verify the presence of antibody but does not prove or disprove active disease. Since dogs rarely spontaneously eliminate the parasite, a positive titer should indicate current infection.
Canine leishmaniasis is resistant to therapy. Most clinicians feel that the dog never will eliminate the infection and that retreatment will be necessary. The drugs of choice arepentavalent antimonials.
It should be remembered that leishmaniasis is a public health concern (zoonotic) and care should be taken in both handling and treating canine cases.