Leishmania

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

• Ingested by sand fly during feeding
  • Transforms in insect gut

• Multiplies and migrates to insect proboscis
  • Inoculated during feeding
  • Can be transmitted percutaneously if sand fly crushed on skin

• Invades macrophages and reverts to amastigote

• 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

• Involved in skin 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
  • In skin scraping or smears
  • In joint fluid, lymph node or bone marrow biopsies

Treatment and Control

• Chemotherapy
  • Prolonged treatment, expensive, suppresses infection
  • Does not cure infection

• Prevent sand flies biting
  • Collars, sprays containing insecticide with repellent effect

• 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