Trypanosomosis

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

• In donkeys:
  • T. brucei in skin infections

Epidemiology

• Vector distribution
  • Tsetse flies found in riverine, savannah and forest habitats
  • Up to 20% flies infected
  • Flies infected for life

• 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

• Tsetse fly control
  • Spraying and trapping

• 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