Cause
Sleeping sickness occurs when the parasite Trypanosoma brucei gambiense (West Africa) or Trypanosoma brucei rhodesiense (East Africa) is introduced into the body following a bite by a tsetse fly that had itself become infected by biting humans or animals harboring the parasite.
Tsetse flies are found only in sub-Saharan Africa, and only some species transmit the parasite. Male and female tsetse flies feed exclusively on blood – on average every three days – and act as a vector for transmitting the parasite to humans and livestock.
Trypanosome transmission is restricted to specific rural ecological foci. Sleeping sickness does not occur in all the areas inhabited by tsetse flies, possibly because of the complexity of parasite development in tsetse flies and the relatively low rate of infection, even in endemic areas.
Symptoms
During the first stage of the disease, the parasites in the bloodstream cause a range of general symptoms that make it hard to diagnose, such as fever, headaches, tiredness and inflammation of the lymph nodes. If the disease remains untreated, the parasites infect the central nervous system, and it is during this second stage that characteristics of the sleep/wake cycle appear. This deterioration of the central nervous system is invariably fatal if left untreated.
98% of sleeping sickness cases are caused by Trypanosoma brucei gambiense, which results in chronic infection – sufferers can be infected for several months or even years without exhibiting excessively severe symptoms. When symptoms are eventually linked with the disease, it is often already at an advanced stage and the central nervous system is already affected.
Epidemiology
There have been several sleeping sickness epidemics in Africa: in 1900, 1920, and most recently an epidemic which ended in the late 1990s.
The prevalence of the disease currently varies from one region to the next, although more than 70% of reported cases since 2011 have been in the Democratic Republic of the Congo. Some countries have reported no cases for more than a decade.
Sustained efforts have led to a reduction in the number of cases since the 90s. In 2018, only 997 new cases have been identified, but the actual number of cases could be higher. Social instability and/or lack of access make it hard to establish an accurate overview of the situation.
70 million people are at risk of sleeping sickness in 36 sub-Saharan African countries.
Treatment
The type of treatment depends on the parasite species and how advanced the disease is, but the earlier the diagnosis, the better the prognosis.
The drugs used during the first stage – pentamidine for Trypanosoma brucei gambiense and suramin for pour Trypanosoma brucei rhodesiense – have few side effects and are relatively easy to administer.
Treatment in the second stage is more complex and the drugs are more toxic as they have to cross the blood-brain barrier. Melarsoprol (derived from arsenic) is effective against Trypanosoma brucei rhodesiense but kills 5% of patients from encephalopathy. The combination of nifurtimox and eflornithine (NECT) is effective and recommended for advanced chronic forms of Trypanosoma brucei gambiense. Fexinidazole, a shorter and effective oral therapy is available since 2020 for both stages of Trypanosoma brucei gambiense and acoziborole, a single oral treatment currently in clinical trials, could lead to the elimination of the disease targeted by the WHO for 2030.
Statistics and data: WHO
May 2021