ETIOLOGY | LEISHMANIASIS IN DOGS

Etiology

Leishmaniasis is a group of infections caused by protozoan of the genus Leishmania. There are a variety of clinical forms. In nature all existing species of Leishmania are transmitted to humans and other mammals by the bite of infected females sandflies. Invertebrate hosts are restricted to species of hematophagous Phlebotomus (Order Diptera, Family Psychodidae, Sub-Family Phlebotominae), especially subspecies Lutzomyia longipalpis in the New World and genus Phlebotomus in the New World.
In the Americas, human leishmaniasis can be divided in two broad categories: cutaneous and visceral leishmaniasis. Cutaneous leishmaniasis has a large variety of forms which can be grouped in the following manner: cutaneous leishmaniasis, characterized by localized skin lesions which can heal spontaneously or become chronic lesions with disfiguring scars; mucocutaneous leishmaniasis, characterized by ulcerative lesions and destruction of the mucosa; diffuse cutaneous leishmaniasis, characterized by nodular lesions which are not ulcerative and disseminated. The visceral form of the disease is chronic and progressive and affects various organs, including spleen, liver, bone marrow, lymph nodes and skin.
The cycle of Leishmania involves a vertebrate host and Phlebotomus fly as a vector. In the mammalian host, Leishmania is an obligate intracellular parasite and exists in the amastigote form inside cells of the mononuclear phagocytic system. The amastigote forms are characterized as circular, about 5 microns in diameter, having a nucleus, kinetoplast and rudimentary flagellum. It multiplies by binary fission, repeatedly until the host cell is destroyed. Inside the gastrointestinal tract of the sandflies, the amastigote transforms into paramastigotes and promastigotes - elongated, flagellated, motile forms, which have a central nucleus and terminal kinetoplast.
The transmission of the disease to vertebrate hosts occurs predominantly by inoculation of the infective promastigote form during a bite of the sandfly. However, other possible routes included direct contact, transplacental, venereal and blood transfusions.

After inoculation in mammalian hosts, the infective promastigote attaches to macrophages through different cellular receptors, and it is then localized into a vacuole which fuses with lysosomes The parasite survives phagocytosis and undergoes different metabolic transformations, becoming amastigote forms, which lyse the host cells and then infect other phagocytic mononuclear cells.
Visceral leishmaniasis in humans is known as kala-azar, ,which means lethal disease in Hindu. In the Old World the etiologic agents are Leishmania donovani and Leishmania infantum and in the New World, Leishmania chagasi.

Leishmania Menu | Epidemiology