Leishmania

From WikiVet English
Jump to navigation Jump to search


Infectious agents and parasitesWikiBugs Banner.png
PARASITES
PROTOZOA



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
  • 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

Trypanosoma

Trypanosoma cruzi - CDC/Dr. Myron G. Schultz
T. cruzi in monkey heart - Dr. L.L. Moore, Jr.
T. cruzi Life Cycle Diagram - Wikimedia Commons
Triatoma infestans the Kissing bug - WHO Wikimedia Commons
Chagas endemic zones 2005 - Wikimedia Commons
N'dama - Trypanotolerant West African Bos taurus - Wikimedia Commons
  • Protozoal parasites found in the blood and tissues of vertebrates
  • Worldwide distribution
  • Causes sleeping sickness in humans
  • Particularly seen in sub-Saharan Africa
    • Affects cattle production
    • Causes Nagana (Wasting disease)
  • Divided into two groups depending on the mode of development in the insect vector
    • Salivarian
      • Multiply in the foregut and proboscis
      • Transmitted via inoculation during feeding
      • Transmitted by Tsetse flies
      • Also known as anterior station development
    • Stercorarian
      • Multiply in the hindgut
      • Infective form migrates to the rectum
      • Transmitted via contamination of wounds with insect faeces
      • Also known as posterior station development
  • All Trypansomes except for T. equiperdum have arthropod vectors
    • T. equiperdum is a venereally transmitted disease
  • Non-cyclical transmission can also occur
    • Mechanical transmission
    • Transferred by interrupted feeding from one host to another
    • Usually transmitted by biting flies, e.g. Tabanidae and Stomoxys

Recognition

  • Elongated, spindle shaped protozoa
  • Between 8 and 39 μm in length
  • Flagellate
    • Flagellum runs the length of the body attached to the pellicle which forms an undulating membrane
  • Kinetoplast present which contains the DNA of the single mitochondrion

Life Cycle

  • Undergo morphological transformations in intermediate host before becoming infective for the next host
  • Blood-sucking flies ingest trypanosomes whilst taking a blood meal from an infected animal
    • Trypanosomes multiply first in the gut of the fly
  • Salivarian trypanosomes are transmitted by Tsetse flies
    • Trypanosomes pass forward to the salivary glands where they transform into the infective stage
    • Inoculated with saliva when Tsetse fly next feeds on a host
  • Stercorarian trypanosomes are transmitted by triatomid bugs, tabanids and keds
    • Trypanosomes pass back to the rectum
    • Next host is infected when skin wounds are contaminated with infected insect faeces

Pathogenesis

  • Salivarian
    • Causes wasting disease in cattle (nagana)
    • Sleeping sickness in humans
  • Stercorarian
    • T. cruzi most important in veterinary medicine
      • Occurs in South America
      • Infects armadillos, possums and humans
      • Causes Chagas' Disease
    • Transmitted by a triatomid (kissing) bug
    • Chronic infections are often fatal causing heart failure
    • Non-pathogenic species are transmitted by tabanids and keds
      • T. theileria and T. melophagium
  • Enlarged lymph nodes and spleen
    • Causes lymphoid exhaustion
    • Associated with plasma cell hypertrophy and hypergammaglobulinaemia
      • Due to an increase in IgM
    • With infections of increased duration, the lymph nodes and spleen shrink due to exhaustion of their cellular elements
  • Anaemia
    • Red blood cells are removed from circulation (haemolytic)
    • Is a cardinal feature of the disease
  • Degeneration and inflammation of multiple organs
    • E.g. Skeletal muscle, myocardium and CNS

Clinical Signs

  • In ruminants:
    • Anaemia
    • Enlargement of the lymph nodes
    • Progressive loss of body condition
    • Fever and appetite loss occur during parasite peaks
    • Chronic disease usually terminates in death of the animal if untreated
    • Can cause abortion, infertility and decreased growth in herds
  • In horses:
    • Acute or chronic infections of T. brucei
    • Oedema of the limbs and genitalia
  • In pigs:
    • T. congolense infections are mild or chronic
    • T. simiae infections are hyperacute usually leading to death from pyrexia in a few days
  • In dogs and cats:
    • T. brucei and T. congolese
    • Acute infections
    • Fever, anaemia, myocarditis, corneal opacity
    • Occasionally neurological signs present, such as increased aggression, ataxia and convulsions

Epidemiology

  • Vector distribution
  • Parasite virulence
    • Some parasitaemic animals survive for long periods of time
      • E.g. T. brucei and T. congolense
      • Increases the opportunity for infection of flies
    • Some trypanosomes kill their host in 1-2 weeks
      • E.g. T. vivax
      • Decreases the chances of fly infection
    • Trypanosomes avoid host immune defences by altering glycoprotein coat (surface antigen) before host antibody response
      • Antigenic variation can occur many times over several months causes relapsing parasitaemia
  • Host response
    • Trypanotolerant wild animals remain parasitaemic for prolonged periods without showing clinical signs of disease
      • Cause lasting reservoirs of infection
    • Most domestic livestock are susceptible to trypanosomosis
    • Some local breeds of sheep, goats and cattle are trypanotolerant
      • E.g. Bos indicus

Diagnosis

  • Demonstrate trypanosomes in blood
    • Giemsa stained smears
    • Fresh blood films
      • Motile trypanosomes
    • Haematocrit tube
      • Motile trypanosomes at the plasma/buffy coat interface

Control

  • Prophylactic drug treatment
    • Change drug group periodically to decrease the chances of resistance occurring
    • May lead to protective immunity but livestock will still be susceptible to heterologous challenges
  • Barrier fences and buffer zones
    • Separate livestock and wild animals
  • Trypanotolerant livestock

Other trypanosomes

  • Mechanically transmitted by biting flies
    • E.g. Surra affecting horses and camels in North Africa, Asia and South America
    • T. equinum in South America
    • T. evansi in Asia
  • Venereally transmitted
    • E.g. Dourine
      • Transmitted by T. equiperdum
      • Causes genital and abdominal oedema, emaciation and CNS signs
      • Affects horses and donkeys in Africa, Asia, Central and South America
  • Non-pathogenic species occur in the UK
    • In sheep caused by T. melophagium
    • In cattle caused by T. theileri