Trypanosoma

Trypanosoma cruzi
CDC/Dr. Myron G. Schultz, WikiMedia Commons

T. cruzi in monkey heart
Dr. L.L. Moore Jr., WikiMedia Commons

Triatoma infestans the Kissing bug - WHO Wikimedia Commons

Chagas endemic zones 2005 - 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

• 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

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