Introduction

• Leishmaniasis is a protozoal infection of man and animals.
• Cause: intracellular protozoan parasite of the genus Leishmania.
• Transmission is predominantly by sand-fly bites Sandfly. Congenital transmission has been described in dogs and transmission via contaminated blood transfusion has been described in dogs and humans.
• Several species of Leishmania infect animals and humans. Some species cause cutaneous infection in humans termed cutaneous leishmaniasis whereas other species cause infection of visceral organs in humans termed visceral leishmaniasis.
• Dogs and cats manifest a combination of cutaneous and visceral disease signs when infected with Leishmania infantum, the main cause of human visceral leishmaniasis in the Mediterranean region and South America.
• Other dermatotropic species of Leishmania that infect humans have also been described to cause cutaneous disease in cats.
• Signs: alopecia, focal crusty dermatitis, nodular dermatitis, and ocular disease are among the presenting signs, with discrete or widespread cutaneous lesions.
• Diagnosis: demonstration of the parasite in macrophages in skin biopsy Biopsy: skin, lymph node or bone marrow aspirates Fine-needle aspirate and serology or PCR PCR (Polymerase chain reaction) .
• Prognosis: clinical recovery following treatment is common in cats without severe kidney disease or immune-suppressive co-infection. Treated cats may remain carriers and clinical relapses may occur.

Pathogenesis

Etiology

• Leishmania is a genus of protozoa which are intracellular in their mammal host and extracellular in their sand fly vector.
• There are more than 20 different Leishmania species.
• Leishmania infection in cats has been described with 7 of these species to date, with L. infantum being the most severe cause of feline disease.
• Sand flies of the genus Phlebotomus are the principal vectors of leishmaniasis in the Old World. In the New World sand flies of the genus Lutzomyia are the principal vectors.
• No proven competent sand fly vector identified in the USA to date.

Predisposing factors

General

• An association was found between feline immunodeficiency virus (FIV) Feline immunodeficiency virus infection and Leishmania infection in cats.

Specific

• Being bitten by infected sand flies.

Pathophysiology

• The parasite occurs in the amastigote form in the vertebrate host and in the promastigote form in the sandfly vector and on culture Leishmania promastigotes.
• The promastigotes, inoculated into the vertebrate host by the sandfly vector, enter macrophages where they transform into amastigotes before multiplying.
• Infection and multiplication in cells of the monocyte/macrophage line leads to generalized lymphadenopathy and splenomegaly in the dog.
• Immune complex formation contributes to the pathological changes.
• Visceral leishmaniasis is a chronic wasting disease in the dog and cat.
• Female sand flies, feeding on an infected host, ingest amastigote laden macrophages  →  promastigotes form in the insect's gut and migrate to the proboscis.
• Promastigotes (flagellated forms) are inoculated into the feline host, enter macrophages and transform into amastigotes.
• They multiply in cytoplasmic vacuoles, and disrupt, the macrophages with the released parasite infecting other cells  →  lymphoreticular hyperplasia with generalized lymphadenopathy and splenomegaly.
• Visceral leishmaniasis is associated with dissemination of the amastigotes throughout the reticuloendothelial system - particularly the spleen, bone marrow, lymph nodes, liver and small intestine.
• The parasite can be detected in most organs and several tissues with specific predilection to the skin, bone marrow and lymph nodes of affected cats.
• Antibody response resulting from sustained antigen stimulation, results in immune complex formation and the development of lesions in the kidneys. A moderate to severe glomerulonephritis is commonly present.
• Local proliferation of the parasite in macrophages causes granulomatous lesions and subsequent development of chronic ulceration due to necrosis of overlying epidermis. Renal failure is often the immediate cause of death.

Timecourse

• Infection is chronic and the incubation period is long. In dogs it has been reported to last from 3 months to several years.

Epidemiology

• Leishmaniasis in cats has been reported from areas where the disease is endemic in humans and dogs.
• There are also reports of disease in non-endemic areas with cats that have been imported from endemic regions or have traveled to ones. For instance, feline cases have been diagnosed in non-endemic Switzerland in cats that were imported from Spain.
• Epidemiological studies have shown high infection rares in some endemic areas with a relative low incidence of clinical disease.
• Despite this, the number of feline clinical cases described from southern Europe is considerably lower than that of dogs from the same region.
• The sand fly vectors are most active at dawn and dusk.
• Sand flies have a limited flight range of about 3 km.
• Transmission can occur by blood transfusion.

Diagnosis

Treatment

Prevention

Outcomes