African Sleeping Sickness Global Impact

Quick Facts

Human African Trypanosomiasis (HAT), also known as African Sleeping Sickness is a parasitic disease that is transmitted through the bite of an infected tsetse fly. The early stages of the disease can include flu-like symptoms and in some cases can include heart abnormalities. During the advance stages of the disease, the parasites enter the brain leading to encephalitis, coma and death. HAT is 100% fatal if left untreated. Most of the exposures to the tsetse fly and therefore the parasite occur in rural populations, which are poor and lack adequate health systems. Currently treatments rely on medications that are toxic, painful, expensive and are becoming ineffective due to parasite resistance. Thus, due to limited health care and poor treatment options, infection typically results in death. Development of effective, safe treatments is desperately needed for this devastating disease.

What is it?

Trypanososma brucei is a parasitic protozoan. When an infected tsetse bites an animal or human to take a blood meal, T. brucei parasites (trypomastigotes) in the fly's saliva enter first the lymphatic system and then the blood system. Parasites replicate in blood cells, eventually causing cell rupture to allow release of parasites back into the blood stream to infect new cells. Eventually parasites breach the blood-brain barrier and infect the brain, leading to irreversible neurological damage, coma and death.

African Trypanosomiasis Life Cycle

Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense

The parasite passes back and forth between the tsetse fly and a mammalian host. Stages 2–4 take place in the host and stages 6–8 in the fly; stages 1 and 5 are the fly’s blood meals that carry the parasite between them. After stage 8, the cycle begins again at stage 1.

1. Stage 1: Tsetse fly takes a blood meal and injects parasites

   Infective stage

   Transmission: fly to host

   

   The infected fly injects metacyclic trypomastigotes into the skin.

2. Stage 2: Parasites transform in the host

   In the mammalian host

   

   Injected metacyclic trypomastigotes transform into bloodstream trypomastigotes, which are carried to other sites.

3. Stage 3: Parasites multiply in body fluids

   In the mammalian host

   

   Trypomastigotes multiply by binary fission in various body fluids, such as blood, lymph, and spinal fluid.

4. Stage 4: Trypomastigotes circulate in the blood

   Diagnostic stage

   In the mammalian host

   

   Circulating trypomastigotes are present in the blood during the acute phase; they are usually undetectable in the latent phase.

5. Stage 5: Tsetse fly takes a blood meal and ingests parasites

   Transmission: host to fly

   

   The fly ingests bloodstream trypomastigotes while feeding on an infected host.

6. Stage 6: Parasites transform in the fly’s midgut

   In the tsetse fly

   

   Bloodstream trypomastigotes transform into procyclic trypomastigotes in the fly’s midgut. Procyclic trypomastigotes multiply by binary fission.

7. Stage 7: Parasites leave the midgut

   In the tsetse fly

   

   Procyclic trypomastigotes leave the midgut and transform into epimastigotes.

8. Stage 8: Parasites multiply in the salivary gland

   In the tsetse fly

   

   Epimastigotes multiply in the salivary gland and transform into metacyclic trypomastigotes, ready to be injected at the fly’s next blood meal.

   Cycle continues at stage 1

Stage 1: Bite: fly infects host

Stage 5: Bite: host infects fly

Key

• Blue arrows and borders: stages in the mammalian host
• Red arrows and borders: stages in the tsetse fly
• Violet: the fly’s blood meals (stages 1 and 5), which pass the parasite between fly and host

Source: adapted from the CDC DPDx African trypanosomiasis life cycle.

Where does it occur?

African Trypanosomes are endemic in 36 countries located in sub-Saharan Africa, putting approximately 60 million people at risk for this disease. The parasite can infect both humans and domesticated live stock (sheep, cattle, horses, cattle, dogs, pigs), thus impact both the health and economic development of these countries. It is estimated that up to 70,000 people are infected annually, and without early treatment the disease is usually fatal.