Leishmania

Leishmania spp.
Kingdom	Eukaryota
Phylum	Euglenozoa
Class	Kinetoplastea
Order	Trypanosomatida
Family	Trypanosomatidae
Genus	Leishmania
Species	L. infantum, L. donovani, L.chagasi

Leishmania Life Cycle - Wikimedia Commons

Leishmania donovani in bone marrow cell - Dr. L.L. Moore, Jr.

L. tropica

Yutaka TsutsumiWikiMedia Commons

Overview

Leishmania spp. are intracellular parasites of macrophages from the same family as Trypanosoma spp.. These organisms parasitise human, dogs and wild animals throughout southern Europe, Africa, Asia and South America. The infection is transmitted by sandflies. Infection can cause both cutaneous and visceral disease. Three types of Leishmania spp. are described;

1. Hypoplaria - found in lizards that ingest the sandfly intermediate host. Development occurs in the hindgut of the fly.
2. Peripylaria - found in mammals and lizards, development occurs in the fore- and hindgut of the fly.
3. Suprpylaria - found only in mammals transmitted by the bite of a sandfly, development occurs in the fore- and midgut of the fly.

Recognition

Leishmania spp. are ovoid shaped parasites containing a rod shaped 'kinetoplast'. The kinetoplast is associated with a rudimentary flagellum that does not extened beyond the cell margin. The position of the kinetoplast changes as the parasite changes between life stages. Once ingested by a sand fly the parasite takes the promastigote form and the kinetoplast moves the the posterior of the cell.

Life Cycle

The life cycle of Leishamania spp. requires transmission between mammalian (and occasionally reptile) hosts by a blood sucking fly. The sand flies is the intermediate host, in the Old World the flies are of the genus Phlebotomus and in the New World they are of the genus Lutzomyia. The amastigote form which lacks a flagella is found in he vertebrate hosts macrophages. The amistgote is ingested by the sand fly whilst it feeds on the host, once ingested the Leishamnia will transform into the flagellated promastigote form in the insect gut. Replication by binary fission occurs in the insects gut followed by migration to the proboscis of the insect. The presence of Leishamnia in the insects proboscis allows innoculation of the next host on which the fly feeds with the Leishmania parasite. Crushing the sand fly on the skin of a mammal can allow percutaneous transmission. Once inside the vertebrate host the Leishmania will invade the hosts macrophages and having done this revert to the amastigote form.

Pathogenesis

Infection with Leishmania can produce either cutaneous or viscreal disease as the infected macrophages proliferate in foci. There is a very long incubation period from infection to pathology, which can take years and therefore many infected dogs either never become symptomatic or remain so for a long period of time.

• 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

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