African Trypanosomiasis Flashcards
Which 2 organisms are responsible for African trypanosomiasis in humans?
Trypanosoma Brucei Gambiense - T.b.gambiense
Trypanosoma Brucei Rhodesiense - T.b.rhodesiense
Are T.b.gambiense and T.b.rhodesiense morphologically different?
No - they are morphologically identical
What is African trypanosomiasis also known as?
Sleeping sickness
What proportion of African trypanosomiasis is caused by T.b.gambiense?
90%
What is the vector of African trypanosomiasis?
The Tetse fly
What is the incubation period of T.b.gambiense?
Months-years
What is the incubation period of T.b.rhodesiense?
3 days-3 weeks
How do T.b.gambiense and T.b.rhodesiense differ in terms of disease progression?
Rapidity/progressivity - T.b.rhodesiense causes a more acute disease, whereas T.b.gambiense tends to cause more protracted disease
What are the features of the Tetse fly?
- Wings that fold like scissors
- ‘Hatchet Cell’ appearance on folded wings
- Preference for biting large objects and moving objects
- Painful bite
- Preference for dark colours - tend to bite light-skinned individuals through dark clothing
How many new cases of African sleeping sickness are there per year?
100,000
Where in Africa does T.b.gambiense tend to occur?
Mostly the central rift valley of Africa - >70% of cases occurring in the DRC
Where in Africa does T.b.rhodesiense tend to occur?
Mainly in East Africa - particularly Tanzania and Uganda
Which type of Tetse flies tend to be the vector for T.b.gambiense?
G (glossina).palpalis
G.tachinoides
G.morsitans
Which type of Tetse flies tend to be the vector for T.b.rhodesiense?
G (glossina).morsitans G.pallidipes G.fuscipes G.swynnertoni G.tachinoides (in SW Ethiopia)
What is the type of trypanosomiasis that only effects domestic wild animals?
T.Brucei.Brucei
How often do Tetse flies blood feed?
Every 2-3 days
What is Winterbottom’s Sign?
Prominent LNs in the posterior triangle of the neck
What is the primary stage of African trypanosomiasis?
Trypanosomal chancre - red and inflamed local reaction at site of bite (not a guaranteed sign)
African trypanosomiasis caused by which organism is more likely to cause a trypanosomal chancre?
T.b.rhodesiense
What is the secondary stage of African trypanosomiasis?
Blood and LN involvement
What are the signs and Sx of secondary stage African trypanosomiasis caused by T.b.gambiense?
Low-grade/recurrent fever Bachkache/headache Tachycardia Circinate erythema rash Transient facial oedema Cervical lymphadenopathy (more so ++ that T.b.rhodesiense) Anemia monocytosis Liver ad spleen enlargement
What are the signs and Sx of secondary stage African trypanosomiasis caused by T.b.rhodesiense?
High/persistent fever Chills Headache Facial oedema Serous effusion - pleural/pericardial Myocarditis Bone pain Hepatitis Purpura Lymphadenopathy
In which stage of the disease does death most often occur in T.b.rhodesiense?
Secondary stage
What is the most common cause of death in T.b.rhodesiense?
Cardiac failure
What is the tertiary stage of African trypanosomiasis?
CNS involvement
How does the parasite gain access to the CNS?
- Across the choroid plexus
2. Transcytosis across endothelial cells
What are the signs and Sx of tertiary African trypanosomiasis caused by T.b.gambiense?
Thick, adherent dura
Oedema and dilated ventricles
Generalised leptomeningitis
Progressive encephalitis (accounting for the characteristic affect on sleep/wake pattern)
Dementia
Focal signs uncommon
CSF is turbid with increased cells and protein
What are the signs and Sx of tertiary African trypanosomiasis caused by T.b.rhodesiense?
Death has usually occurred by this stage
But if CNS involvement does occur, it tends to cause a rapidly progressive encephalitis, coma, followed by death
What may happen if Tx is given by the time disease has progressed to CNS involvement, but that treatment is delayed?
Persistent intellectual impairment
What is a characteristic histological sign of African trypanosomiasis?
Presence of moruluar cells in the brain and other organs
What may it be important to do before treating African trypanosomiasis?
Any co-existing infection/anaemia - many advocate routine use of anti-malarials/anti-helminths before/alongside use of specific treatments
Which drug can be used as a prophylactic agent in T.b.gambiense (but NOT T.b.rhodesiense)?
Pentamidine
What is the 1st line treatment for T.b.gambiense that hasn’t crossed the BBB?
Pentamidine IV or IM
Why should pentamidine ideally be given IV?
To avoid painful local reactions
What are the side effects of pentamidine?
Syncope
Low BP
Hypoglycaemia
What is an alternative treatment for T.b.gambiense?
Nifurtimox + eflorinithine
What is the 1st line treatment for T.b.rhodesiense that hasn’t crossed the BBB?
Suramin IV
What are the side effects of suramin?
Fever, proteinuria, nausea, idiosyncratic anaphylaxis
What drug can be used in T.b.gambiense ONLY when there has been CNS involvement?
Eflorinithine IV
What drug can be used in both types of African trypanosomiasis?
Metarsoprol IV
What is metarsoprol and what is it’s side effects?
Trivalent arsenic compound - a serious encephalopathy in 2-10% with a fatality rate of approx. 50%
What can be done to reduce the risk of developing the serious encephalopathy associated with metarsoprol?
Prophylactic steroids
Why may using eflorinithine treatment be more preferable to metarsoprol in T.b.gambiense?
Much better side effect profile - GI upset and anaemia (but is more expensive)
When can full cure assumed?
Only when a 2 year F/U has occurred
How can African trypanosomiasis be diagnosed?
- Gland puncture
- Blood film - stained or unstained (more difficult to detect T.b.gambiense in blood in later stages of infection)
- CSF (in CNS infection ) - either presence of trypanosomoes OR by cells >5mm OR increased protein. LP for CSF should only be taken after a few drug doses to reduce risk of X-infection from blood if infection not already in CSF
- CATT (circulating antigen agglutination trypanosome test) - 30 minute result, finger-prick test - can only be used in T.b.gambiense
What is the host reservoir in T.b.gambiense?
Humans
What is the host reservoir in T.b.rhodesiense?
Antelope types species - esp. bushbucks
How do Tetse flies become infective?
- Takes blood meal on infective host that has trypanomastigotes
- The trypanomastigotes then penetrate the peritrophic tube lining of the Tetse’s fly’s midgut, then the ectoperitrophic space where they multiple by fission, then moving to the proventriculus
- Then travel to the salivary glands where they becomes epimastigotes
- 20 days after initial blood meal, trypanomastigotes are present again within the salivary glands, making the Tetse fly infective fo the rest of it’s life (a few months)
Why do epidemics of T.b.gambiense tend to occur, but not epidemics of T.b.rhodesiense?
T.b.rhodesiense has a more acute progression, leading to death, and therefore there is never a large enough human reservoir to infect Tetse flies, unlike T.b.gambiense which has a chronic course, providing a large reservoir
In what habitat do the Tetse flies that act as a vector for T.b.gambiense tend to live?
In the shaded protection of forrest tunnels near waterways - why women, more involved in water collection, tend to be more commonly infected in T.b.gambiense
In what habitat do Tetse flies that act as a vector for T.b.rhodesiense tend to live?
Although they breed in/near water - they traverse the forrest widely up to the fringe of the savannah - in search of the animals on which they feed - why men - hunters or honey collectors, tend to me commonly infected
Then how is the T.b.gambiense Tetse fly vector controlled?
Clearance of the dense undergrowth of the forrest tunnels (loss of shade)
Then how is the T.b.rhodesiense Tetse fly vector controlled?
Forrest margin pushed back 1-2km from habitation
What are the other vector control methods?
- Use of insecticide (requires knowledge of where Tetse flies settle)
- Fly trapping methods
