Leishmania

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Leishmania Life Cycle - Wikimedia Commons
Leishmania donovani in bone marrow cell - Dr. L.L. Moore, Jr.
L. tropica - Yutaka Tsutsumi, M.D., Professor, Department of Pathology, Fujita Health University School of Medicine
  • Leishmania spp. are intracellular parasites of macrophages
  • Are closely related to Trypanosoma spp.
  • Cause diseases in humans, dogs and wild animals
  • Present in southern Europe, Africa, Asia and south America
  • Can cause both cutaneous and visceral diseases

Recognition

  • Ovoid shaped
  • Possesses a rod-shaped kinetoplast
  • Has a rudimentary flagellum which does not project beyond the cell margin
  • After the amastigote has transformed into a promastigote inside the sand fly, the kinetoplast is situated in the posterior of the body

Life Cycle

  • Transmitted by blood sucking sand flies
    • Phlebotomus spp. in the Old World
    • Lutzomyia spp. in the New World
  • The amastigote (morphological form) is found in vertebrate macrophages
  • Multiplies and migrates to insect proboscis
    • Inoculated during feeding
    • Can be transmitted percutaneously if sand fly crushed on skin
  • Multiplies by binary fission

Pathogenesis

  • Infection of vertebrate host
    • Produces foci of proliferating Leishmania-infected macrophages in skin (cutaneous) or internal organs (visceral)
  • Very long incubation period
    • Months to years
  • Many infected dogs are asymptomatic
  • Cutaneous form
    • Produces areas of ulceration on pinnae of ears, eyelids or on the lips
  • Visceral form causes chronic wasting condition
    • Generalised eczema
      • Loss of hair around eyes producing 'spectacle' effect
    • Intermittent fever
    • Generalised lymphadenopathy
  • Long periods of remission followed by recurrence of clinical signs is not uncommon in infections

Epidemiology

  • Disease dependent on sand fly vectors
    • E.g. Common in dogs around the Mediterranean coast, foci around southern Europe and around Madrid
  • Reservoirs of infection
    • E.g. Wild animals such as rodents and stray dogs
  • Mechanisms of transmission
    • sand fly bite
    • Rarely through direct contact
  • Leishmaniasis in British dogs
    • Susceptible to infection if exposed whilst abroad in endemic areas as have no immunity
    • No sand flies in Britain but dogs have become infected whilst in contact with infected imported animals

Diagnosis

  • Demonstrate Leishmania organisms

Treatment and Control

  • Chemotherapy
    • Prolonged treatment, expensive, suppresses infection
    • Does not cure infection
  • Destruction of infected and stray dogs
    • Sand flies biting infected dogs may spread the disease to other dogs, humans and wildlife
    • There is a slight possibility of transmission to humans by direct contact


In dogs

  • disseminated disease of the monocyte-macrophage system
  • protozoa; genus Leishmania
  • increased travel means clinincal disease may be acquired in endemic areas but now presents to veterinarians in non-endemic areas
  • lymph node aspirates contain macrophages with organisms