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Trypanosomiases
Causative agent
- Trypanosomes are flagellate protozoans that inhabit the blood and tissues.
Distribution
- African trypanosomiasis (sleeping sickness) is found here and there in the countryside of tropical Africa. Epidemiologically two subspecies can be identified: a chronic West African type (causative agent Trypanosoma bruzei gambiense, 98% of cases) and an acute East African type (causative agent T. b. rhodesiense, 2% of cases).
- American trypanosomiasis, also known as Chagas disease (causative agent Trypanosoma cruzi), occurs in the primitive and rural areas of Central and South America.
African sleeping sickness
Transmission
- Spread by the bite of a tsetse fly. The source of infection is other humans, with T. b. rhodesiense also cattle and antelopes.
- Other possible routes of transmission: mother-to-child transmission during pregnancy, laboratory transmission, other insect vectors, sexual contact
Significance worldwide
- A significant decrease in the incidence has been achieved during the past decades; there are about 1 000 reported cases per year.
Signs and symptoms
- The chronic West African type has two stages.
- A reddish skin lesion (chancre) appears about a week after the bite of a tsetse fly, resolving spontaneously after several weeks.
- Haemolymphatic stage: after weeks or months, intermittent fever, headache, myalgia, lymphadenopathy (typically in the neck), rash, pruritus and oedema occur. Carditis is possible.
- Meningoencephalitic stage: CNS symptoms, including irritability, mental confusion, sleeping disorders and apathy (sleeping sickness), develop after several months or years.
- The disease progress is similar but faster in the East African type; the symptoms appear within 1 to 3 weeks.
Diagnosis
- In the acute phase: direct detection of trypanosomes in the chancre, in blood, in a lymphatic node or in tissue samples
- In the late phase: serological testing for specific antibodies (T.b. gambiense only), detection of trypanosomes in the CSF (the amount of leucocytes and proteins is often increased, but trypanosomes are only seldom found)
Treatment and prognosis
- Due to the rarity of the disease the treatment may be centralised in specialized hospitals.
- Pharmacotherapy is feasible in the early stage. The disease will often lead to death if left untreated. Even if treated, the mortality rate in the CNS stage is 10%, and the drugs have toxic adverse effects.
Prevention on individual level
- No vaccine is available.
- There is a risk of infection when travelling in rural endemic areas during the daytime. Prevention of tsetse fly bites: light-coloured, long-sleeved, long-legged clothing of tight weave fabric. Insect repellants have poor preventive effect against tsetse fly bites.
Chagas disease
Transmission
- In the faeces of a triatomine insect (also known as a kissing bug or assassin bug) as it bites a hole in the skin. The insects live in reed or straw-thatched roofs of dwellings and in wall cracks; they suck blood at night.
- Other possible routes of transmission: blood transfusion, mother-to-child transmission during pregnancy, laboratory transmission, organ transplantation, food contaminated with bug faeces
Significance worldwide
- Chagas disease is found in Central and South America. Approximately 6-7 million people are affected, and in some regions it is the main cause of death among the young and middle-aged.
- In non-endemic areas the disease is possible in immigrants from endemic areas. Isolated cases in travellers have been described in non-endemic countries.
Signs and symptoms
- The infection is lifelong.
- Initially, the infection is usually symptomless. Symptoms may develop in small children.
- A lesion (chancre, chagoma) may appear at the site of entry. If the faeces of the triatomine contaminates the eye, a typical unilateral eyelid swelling will develop (Romana's sign).
- After 1-2 weeks, the patient may develop fever and lymphadenopathy as well as myocarditis or meningoencephalitis.
- Over decades, the chronic infection may cause heart failure and cardiac conduction disorders, or dilatation of the oesophagus or colon (megaoesophagus or megacolon) due to a damage of the autonomic nervous system.
- Immunodeficiency may cause reactivation of the chronic infection.
Diagnosis
- In the acute phase: direct detection of trypanosomes in the blood
- In the late phase: serum antibodies
Treatment and prognosis
- Due to the rarity of the disease the treatment may be centralised in specialized hospitals.
- Pharmacotherapy is effective in the acute phase. In the later phase, medicines may have limited capacity to prevent the development of chronic infection and are associated with adverse effects.
- The mortality rate in the acute phase is 5-10%. In the chronic infection, 20-30% of the patients have cardiac, 10% gastrointestinal and 5% neurological symptoms. Cardiac complications are the most common cause of death.
Prevention on individual level
- No vaccine is available.
- Prevention of triatomine bites; careful selection of where to stay overnight
References
- Kennedy PG. Clinical features, diagnosis, and treatment of human African trypanosomiasis (sleeping sickness). Lancet Neurol 2013;12(2):186-94. [PubMed]
- Brun R, Blum J, Chappuis F, Burri C. Human African trypanosomiasis. Lancet 2010 Jan 9;375(9709):148-59. [PubMed]
- Bern C. Chagas' Disease. N Engl J Med 2015;373(5):456-66. [PubMed]
- Rassi A Jr, Rassi A, Marin-Neto JA. Chagas disease. Lancet 2010 Apr 17;375(9723):1388-402. [PubMed]