African and American Trypanosomiasis
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Direct answer
African and American trypanosomiasis are protozoan infections caused by Trypanosoma brucei subspecies and Trypanosoma cruzi, respectively. African sleeping sickness is spread by the tsetse fly, while American trypanosomiasis (Chagas disease) is spread by reduviid, or triatomine, bugs. The exam-critical distinction is that African disease reaches the central nervous system in its late stage, whereas Chagas disease causes cardiomyopathy and megaoesophagus in the chronic phase.
What you must remember
- Gambiense form: Trypanosoma brucei gambiense causes chronic sleeping sickness in West and Central Africa and accounts for most cases.
- Rhodesiense form: Trypanosoma brucei rhodesiense causes acute sleeping sickness in East Africa, with faster progression.
- Vectors: Tsetse flies (genus Glossina) transmit African disease, and reduviid bugs transmit Chagas disease through their faeces.
- Winterbottom sign: Enlarged posterior cervical lymph nodes are a classic clue to the gambiense infection.
- Romaña sign: Unilateral, painless periorbital oedema is a feature of acute Chagas disease.
- Chronic Chagas: Cardiomyopathy, megaoesophagus and megacolon arise from chronic inflammation and denervation of the gut.
- Staging: Trypanosomes in CSF, or more than 5 white cells per microlitre, define late-stage African disease.
- Drugs: Benznidazole or nifurtimox treat Chagas disease, while late-stage African disease needs drugs that cross the blood-brain barrier.
Following the parasite from bite to brain
African trypanosomes multiply in blood and lymph before they invade the central nervous system. The stage decides which drug is safe, so staging is tested as often as the vector.
- Bite and chancre: A tsetse bite may leave a small, often unnoticed chancre, and parasites then spread through blood and lymph.
- Haemolymphatic stage: Intermittent fever, headache, lymphadenopathy and splenomegaly appear as trypanosomes multiply, with posterior cervical nodes classically enlarged. Early symptoms are vague, so a travel or residence history from an endemic area matters.
- Neurological stage: Parasites cross the blood-brain barrier, causing sleep-wake reversal, personality change and progressive coma if untreated. Without treatment this stage is fatal.
- Diagnosis: The card agglutination test for trypanosomiasis (CATT) screens for gambiense disease and is cheap enough for field surveys. Microscopy of lymph node aspirate, blood or CSF then confirms infection.
- Drug choice by stage: Suramin or pentamidine treats early disease, depending on species. Late gambiense disease is treated with nifurtimox-eflornithine combination therapy (NECT) or oral fexinidazole, while melarsoprol, an arsenical with serious toxicity, is reserved for late rhodesiense disease.
Where the exam tries to catch you
Most errors come from mixing up the vector, the stage and the organ damage of the two forms.
- Trap: Choosing tsetse fly as the vector for American trypanosomiasis Correct: Chagas disease is transmitted by reduviid bugs whose faeces carry Trypanosoma cruzi.
- Trap: Linking Romaña sign to African disease Correct: Romaña sign belongs to acute Chagas disease after conjunctival inoculation.
- Trap: Starting melarsoprol without staging Correct: CSF examination must come first, because melarsoprol is toxic and is reserved for late disease.
- Trap: Relying on blood microscopy for chronic Chagas Correct: parasites are scanty in the chronic phase, so serology is the usual tool.
Frequently asked questions
Which vector transmits African sleeping sickness?
The tsetse fly, genus Glossina, transmits African trypanosomiasis in sub-Saharan Africa. Infected flies inoculate trypomastigotes during a blood meal, and the infection then spreads through the blood and lymph.
What is Winterbottom sign in African trypanosomiasis?
Winterbottom sign is enlargement of the posterior cervical lymph nodes in African trypanosomiasis, most typically in the gambiense form. It is an early clinical clue that appears during the haemolymphatic stage of the disease.
Which drug is used for early stage African trypanosomiasis?
Early African trypanosomiasis is treated with suramin for rhodesiense disease and pentamidine for gambiense disease. Late-stage disease needs drugs that cross the blood-brain barrier, namely NECT or fexinidazole for gambiense and melarsoprol for rhodesiense, per current WHO guidance.
How is chronic Chagas disease diagnosed?
Chronic Chagas disease is diagnosed by serology, with two different tests such as ELISA and indirect haemagglutination used to confirm the result. Parasites are scanty in the chronic phase, so blood microscopy is usually negative.
Why does Chagas disease cause megaoesophagus and megacolon?
Megaoesophagus and megacolon in Chagas disease result from destruction of enteric ganglion cells during the chronic phase. The resulting denervation produces dilated and dysmotile oesophagus and colon.