BS3030 – Biology of Parasitic Diseases
Trypanosoma brucei parasites and sleeping sickness
Human African trypanosomiasis
HAT; also known as sleeping sickness – vector-borne parasitic disease
Caused by trypanosomes transmitted by infected tsetse flies and is endemic in 36 sub-
Saharan African countries
People most exposed live in rural areas and depend on agriculture, fishing and hunting
T. b. gambiense causes chronic infections (>98% of reported cases)
T. b. rhodesiense causes acute infecions and fast-progressing disease (fatal w/out treatment)
Diagnosis and treatment is complex and requires specifically skilled staff
Sustained control efforts have reduced number or new cases
Disease pathology and clinical symptoms
Bite of infected fly parasite multiplies in the lymph and the blood of the person bitten,
causing unspecific symptoms; headaches, fever, weakness, joint pain and lymphadenopathy
(swelling of lymph nodes around neck)
May not show signs of illness immediately (weeks-months)
Over time the parasite crosses the blood-brain barrier infects CNS
Known as neurological or meningo-encephalic stage; obvious signs and symptoms; changes
in behaviour, confusion, sensory disturbances, poor coordination, abnormal tone and
mobility, ataxia (lack of voluntary muscle movements), seizures, coma and death
Vector biology, infection, and disease transmission
Trypanosomiasis is transmitted to humans and animals by blood-sucking tsetse flies of the
genus Glossina – both male and female flies can transmit infection
Not all species are recognised as vectors of sleeping sickness; tsetse flies are found on the
African continent south of Sahara
Wild and domestic animals can host these parasites and may represent a reservoir of
infection for the flies
Blood transfusion, accidental lab infection and mechanical and sexual transmission occur but
minimal epidemiological impact
, A perpetual cycle of infection
-- parasite in fly salivary glands (metacyclic trypamastigote)
-- flagellum in rear end
-- change into blood stream trypamastigote, can initiate cell division (metacyclic cannot)
-- many are able to survive in the blood and replicate rapidly
-- everywhere in circulation; remain in the blood
-- at some point they transform into stumpy form; shorter; known that this form tend to be the ones
better taken up by flies
-- blood stream ones back in flies transform to procyclin trypamastigotes
Disease burden
Important public health and socio-economic problem w risk of large-scale epidemics –
difficult to control and costly
Sleeping sickness 36 sub-Saharan countries – many live in remote rural arease with limited
access to health services
Disease surveillance, diagnosis and treatment is challenging – many more cases than
reported
War and poverty important factors that facilitate transmission
Estimated 300,000 – 500,000 new infections each year
~100,000 people disabled by the disease
Trypanosoma brucei parasites and sleeping sickness
Human African trypanosomiasis
HAT; also known as sleeping sickness – vector-borne parasitic disease
Caused by trypanosomes transmitted by infected tsetse flies and is endemic in 36 sub-
Saharan African countries
People most exposed live in rural areas and depend on agriculture, fishing and hunting
T. b. gambiense causes chronic infections (>98% of reported cases)
T. b. rhodesiense causes acute infecions and fast-progressing disease (fatal w/out treatment)
Diagnosis and treatment is complex and requires specifically skilled staff
Sustained control efforts have reduced number or new cases
Disease pathology and clinical symptoms
Bite of infected fly parasite multiplies in the lymph and the blood of the person bitten,
causing unspecific symptoms; headaches, fever, weakness, joint pain and lymphadenopathy
(swelling of lymph nodes around neck)
May not show signs of illness immediately (weeks-months)
Over time the parasite crosses the blood-brain barrier infects CNS
Known as neurological or meningo-encephalic stage; obvious signs and symptoms; changes
in behaviour, confusion, sensory disturbances, poor coordination, abnormal tone and
mobility, ataxia (lack of voluntary muscle movements), seizures, coma and death
Vector biology, infection, and disease transmission
Trypanosomiasis is transmitted to humans and animals by blood-sucking tsetse flies of the
genus Glossina – both male and female flies can transmit infection
Not all species are recognised as vectors of sleeping sickness; tsetse flies are found on the
African continent south of Sahara
Wild and domestic animals can host these parasites and may represent a reservoir of
infection for the flies
Blood transfusion, accidental lab infection and mechanical and sexual transmission occur but
minimal epidemiological impact
, A perpetual cycle of infection
-- parasite in fly salivary glands (metacyclic trypamastigote)
-- flagellum in rear end
-- change into blood stream trypamastigote, can initiate cell division (metacyclic cannot)
-- many are able to survive in the blood and replicate rapidly
-- everywhere in circulation; remain in the blood
-- at some point they transform into stumpy form; shorter; known that this form tend to be the ones
better taken up by flies
-- blood stream ones back in flies transform to procyclin trypamastigotes
Disease burden
Important public health and socio-economic problem w risk of large-scale epidemics –
difficult to control and costly
Sleeping sickness 36 sub-Saharan countries – many live in remote rural arease with limited
access to health services
Disease surveillance, diagnosis and treatment is challenging – many more cases than
reported
War and poverty important factors that facilitate transmission
Estimated 300,000 – 500,000 new infections each year
~100,000 people disabled by the disease
