Difference between revisions of "Trypanosomosis"

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Revision as of 11:51, 3 June 2011

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


  • Myositis
    • Infrequent muscle lesions with mononuclear infiltrates
    • Dogs, cats and pigs are affected
    • Parasites lie between myofilaments
    • May cause fibre degeneration