2. Human African Trypanosomiasis: Sleeping Sickness in Sub-Saharan Africa
Matthew Malone
3/9/2012

3. Learning Goals
Understand the causes, risk factors, and modes of transmission for Human African Trypanosomiasis (HAT)
Know the role of armed conflict in the rise of infection rates throughout Africa
Use past HAT outbreak patterns and causes to understand the implications for future infection

4. The Problem
Multiple HAT outbreaks have occurred over the last century.
Armed conflict in Africa has escalated disease rates in recent years.
Continued displacement of populations may cause many more outbreaks.
Displacement widens the geographic disease spread.
There have been three major HAT epidemics in Africa over the past 100 years. The first epidemic, which took place between 1896 and 1906, largely affected equatorial Africa and caused the death of approximately 800,000 people.4 The second epidemic took place between 1920 and 1940 and caused colonial powers to invest in control and surveillance programs that almost eradicated the disease by the 1960s.4 The third epidemic, which occurred in 1970, was a direct result of the civil conflicts and the breakdown of HAT control and surveillance activities that took place after the advent of independence in most countries where HAT was endemic.4,5 This epidemic saw its peak in the late 1990s.
Social upheavals, population movements, and wars, combined with lack of awareness and poverty, have caused the disease to spread and evolve across sub-Saharan Africa. These risk factors still exist today, and for this reason, future epidemics are still very possible. In order to prevent future epidemics, steps must be taken to eliminate these factors or, at least, greatly minimize them.

5. Causal Agents Caused by the protozoan Trypanosoma Brucei
Has three subspecies:
Trypanosoma brucei gambiense
Trypanosoma brucei rhodesiense
Trypanosoma brucei brucei (animals only)
Human African Trypanosomiasis is caused by Trypanosoma Brucei which is a protozoan. It has three different subspecies which are Trypanosoma brucei gambiense (95% of all infections), Trypanosoma brucei rhodesiense, and Trypanosoma brucei brucei (under normal conditions does not infect humans). Trypanosoma brucei gambiense is usually associated with the chronic form of the disease and Trypanosoma brucei rhodesiense is usually associated with the acute form of the disease. T.b. rhodesiense is more virulent than T.b. gambiense and is less prone to cause large epidemics.1 This observation has been validated by the fact that there have been much less outbreaks caused by T.b. rhodesiense over time than outbreaks caused by T.b. gambiense.
Picture: Trypanosoma Brucei
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6. Vector Biology The vector for HAT is the tsetse fly Biological Vector
Inhabits rural areas
Bites during daytime hours
Both males and females are capable of carrying and transmitting the disease.
The vector for HAT is the tsetse fly. Although the tsetse fly is a biological vector, mechanical transmission through other blood-sucking insects is possible.2 There is less epidemiological data concerning this type of transmission. The flies only bite during daytime hours, and both male and female flies are capable of carrying and transmitting the disease.6 In eastern Africa the flies inhabit woodland areas and thickets throughout the savannah, and in western Africa the flies inhabit forests and vegetation along streams.6 Tsetse flies are the main means of transmission for HAT. However, mother to child infection has been seen as trypanosomes can cross the placenta and infect the fetus.6 Reports of accidental contamination via pricks from contaminated needles have also been reported.6
Pic: Tsetse fly
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7. Vector Biology Cont’d Tsetse flies belong to the genus Glossina
Glossina contains 3 subgroups
Glossina (includes G. morsitans group)
Nemorhina (includes G. palpalis group)
Austenina (includes G. fusca group)
Tsetse flies all belong to the genus Glossina. This genus consists of three subgroubs: Glossina (includes G. morsitans group), Nemorhina (includes G. palpalis group), Austenina (includes G. fusca group).1 For a species of Glossina, its vectorial capacity is determined by two factors.
Pic: Tsetse fly
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8. Vectors of T.b. gambiense G. palpalis & G. tachinoides groups
Vector Biology Cont’d
Vectors of T.b. gambiense
G. palpalis & G. tachinoides groups
Vectors of T.b. rhodesiense
G. morsitans, G. swynnertoni, & G. pallidipes groups
For a species of Glossina, its vectorial capacity is determined by two factors. These factors are the ability to become infected while feeding on a vertebrate host, and the ability to subsequently support the development of the infection and transmit trypanosomes to a different vertebrate host.1 Following these criteria, the G. palpalis group and the G. morsitans group are the only groups that contain species and subspecies that are vectors of T.b.gambiense.1 G. palpalis palpalis in forest areas and G. palpalis gambiensis in savannah areas (both are species of the G. palpalis group) are very proficient vectors species of T.b. gambiense in West and Central Africa.1 The vectors of T.b. rhodesiense are different from those of T.b gambiense. This strain is mostly transmitted by G.m. morsitans and G.m. centralis in East Africa (except Uganda and Kenya), G. pallidipes in eastern and southern Africa, and G. swynnertoni in Kenya and Tanzania.1 These species are all savannah species of the G. morsitans group.
Pic: Species and Subspecies of Glossina that are vectors for T.b. gambiense and T.b. rhodesiense
Source: Pepin J., Meda H. The epidemiology and control of human African trypanosomiasis. Adv Parasitol, 49 (2001), pp. 71–132

9. T.b. gambiense T.b. rhodesiense Reservoirs
For T.b. gambiense, the main reservoir of infection is humans, although both wild and domestic animals have also been seen to harbor the infection. For T.b. rhodesiense, the main reservoir for infection is cattle. However, other domestic animals (dogs, pigs, and sheep) and many game animals (warthogs, bushbuck, hartebeest, lions, zebras, impala, waterbuck, and hyenas) also carry the infection.1
Left Pic: People Walking
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Right Pic: Cattle
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10. Transmission Cycle Pic: HAT Transmission Cycle
Source: Simarro P., Jannin J., Cattand P. Eliminating human African trypanosomiasis: where do we stand and what comes next? PLoS Med. 5, e55 (2008), pp. 174–180

11. Civil Disturbance/War Cattle Movements
Risk Factors
Civil Disturbance/War
Cattle Movements
Population Movements/Migrations (Refugees)
Reduced Health Program Financing
Rural Living Environment
Tsetse flies are only found in sub-Saharan Africa. Within sub-Saharan Africa, there are multiple different risk factors that make some populations much more susceptible to acquiring HAT than others. Populations living in rural areas are the most at risk for becoming infected, as these areas are where tsetse flies are mostly found.2 Within rural areas, the populations most at risk for becoming infected are those that depend on agriculture, animal husbandry, fishing, or hunting.2 These activities heighten the exposure of those populations to tsetse flies and increases the probability that they will be bitten and contract HAT.
HAT was very nearly eradicated in many Sub-Saharan countries around the 1960s, but in recent years, as mentioned in the background, there has been a resurgence of HAT cases in several countries. There are several factors that contribute to both HAT resurgence and the onset of epidemics. These factors include civil disturbance, war, reduced health financing, dismantling of disease control programs, cattle movements, and population movements/migration (includes refugees).3 Population movement are especially significant in the transmission and spread of the disease because when large groups of people migrate from one area to another, trypanosomes are circulated from high-incidence to low-incidence areas, causing more susceptible populations to be at increased risk of acquiring infection.1
Pic: Central African Soldiers
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12. Case Study: Uganda HAT Outbreak
Began in the late 1980s and persisted through 2005
Refugees migrated from Uganda to Zaire and Sudanacquired infection
Refugees migrated back to Uganda accompanied by infected Sudanese refugeesspread infection
A case study that exemplifies the impact of migrations on disease spread and the onset of epidemics is the recent outbreak of HAT that has been observed in northwestern Uganda. This outbreak began in the late 1980s and persisted through Refugees migrated from Uganda to Zaire and Sudan, where they acquired infection. Years later, these refugees migrated back to Uganda accompanied by infected Sudanese refugees.1
Pic: African Refugees
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13. Case Study Cont’d
Pic: Sleeping Sickness in south-eastern Uganda,
Source: Berrang-Ford L, Martin O, Maiso F, Waltner-Toews D, McDermott J (2006) Sleeping sickness in Uganda: revisiting current and historical distributions. Afr Health Sci 6: 223–231

14. Epidemiology
In 1986, it was estimated that approx. 70 million people lived in areas conducive to disease transmission
HAT affects 36 countries in sub-Saharan Africa
According to the World Health Organization, HAT causes ~40,000 deaths in Africa annually
HAT occurs in 36 sub-Saharan African countries where over 50 million people are at risk for becoming infected.8 Currently, it is estimated that over 50,000 people within these countries are actually infected.9 HAT has been the leading cause of mortality in many different villages in the Democratic Republic of Congo, Angola, and Southern Sudan during epidemic periods.2 During these periods, the prevalence of HAT reached 50% and the disease caused more deaths than HIV/AIDS.2
Top Pic: Trypanosoma brucei gambiense
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Bottom Pic: Trypanosoma brucei rhodesiense
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15. 1998: ~40,000 reported cases; >250,000 actual cases
Epidemiology Cont’d
The total amount of reported HAT cases has decreased substantially over time.
1998: ~40,000 reported cases; >250,000 actual cases
2004: ~18,000 reported cases; between 50,000 and 70,000 actual cases
2010: ~7,000 reported cases; ~30,000 actual cases
Cases involving T.b. rhodesiense are much rarer than those involving T.b. gambiense.
The estimated amount of cases of HAT in Africa has changed drastically over time due to the escalation and cessation of epidemics. Between 1998 and 2004, the total amount of reported HAT cases, including both strains of the disease, fell from approximately 37,991 to 17,616, and the estimated number of actual cases was between 50,000 and 70,000.2 In 2009, the number of reported cases had dropped to 9, This marked the first time in five decades that the number of reported cases had fallen below 10,000. In 2010, 7,139 cases were reported, and the current estimated number of actual cases is 30,000. 2

16. Epidemiology Cont’d
Exact numbers for the amount of cases of the disease are hard to acquire due to the large amount of underreporting that occurs. For example, in 1998, almost 40,000 cases were reported but reports suggested that there might have been around 300,000 undiagnosed cases.2 In addition, there is more epidemiological data available for HAT caused by T.b. gambiense than for HAT caused by T.b. rhodesiense since HAT caused by T.b. rhodesiense is much rarer.
Pic: Trypanosoma brucei gambiense comparison between population placed under active surveillance and new cases
Source: Brun R., Blum J., Chappuis F., Burri C. Human African trypanosomiasis. Lancet (2009), pp. 148–159

17. Geographical Distribution
1998- World Health Organization states that there are over 200 active foci of HAT between latitude 15 degrees north and 15 degrees south (“tsetse belt”).
T.b. gambiense is mostly found in western and central Africa.
Over 95% of the cases of human infection found in the Democratic Republic of Congo, Angola, Sudan, Central African Republic, Chad, and northern Uganda.
T.b. rhodesiense is found mostly in eastern and southern Africa.
Over 95% of the cases of human infection occur in Tanzania, Uganda, Malawi, and Zambia.
T.b. rhodesiense is sometimes referred to as East African sleeping sickness because it is found mostly in eastern and southern Africa. Over 95% of the cases of human infection occur in Tanzania, Uganda, Malawi, and Zambia.6 T.b. gambiense is sometimes referred to as West African sleeping sickness because it is mostly found in western and central Africa. Over 95% of the cases of human infection are found in the Democratic Republic of Congo, Angola, Sudan, Central African Republic, Chad, and northern Uganda.6 Both forms of the disease have been major causes of depopulation of large tracts of fertile land in Africa.8 In 1998, the World Health Organization stated that there were over 200 active foci of HAT that were located between latitude 15 degrees north and 15 degrees south.1

18. Geographical Distribution Cont’d
According to a 2001 research article, Uganda was the only country where both T.b. gambiense and T.b. rhodesiense could be found without any overlap.1 This same article stated that the Democratic Republic of Congo was the country with the most severe HAT epidemic and that Angola was the country with the second highest amount of HAT cases. These observations are still seen today, although the number of HAT cases has declined a considerable amount over time. In 2010, the Democratic Republic of Congo was the only country in Africa to report over 500 new cases annually.2 Angola, Chad, Sudan, Central African Republic, and Uganda have all declared between 100 and 500 new cases annually.2 Cameroon, Congo, the Ivory Coast, Guinea, Malawi, United Republic of Tanzania, Gabon, Nigeria, Zambia, and Zimbabwe have been reporting less than 100 cases annually.2 Benin, Botswana, Burkina Faso, Burundi, Ethiopia, Gambia, Ghana, Guinea Bissau, Kenya, Liberia, Mali, Mozambique, Namibia, Niger, Rwanda, Senegal, Sierra Leone, Swaziland, and Togo have reported no new cases in over 10 years.2
Pic: Map of Africa Showing the Epidemiological Status of Countries Considered Endemic for the Disease
Source: Simarro P., Jannin J., Cattand P. Eliminating human African trypanosomiasis: where do we stand and what comes next? PLoS Med. 5, e55 (2008), pp. 174–180

19. Geographical Distribution/Conflict
The resurgence of HAT in several countries has been attributed to conflict and/or war.
Cases of HAT have been seen to occur significantly more often in countries where there is conflict, internationalized civil war, and/or high political terror.
The resurgence of HAT in several countries has been attributed to conflict and/or war. Conflict has also caused HAT cases to keep arising in regions that have low resources and in regions that are politically unstable.10 Cases of HAT have been seen to occur significantly more often in countries when there is conflict, internationalized civil war, and/or high political terror.10

20. Geographical Distribution/Conflict Cont’d
Pic: HAT incidence by conflict severity (a) and political terror scale (b)
Source: Berrang-Ford L., Breau L. Conflict and human trypanosomiasis. Soc. Sci. Med. (2010), pp. 398–407

21. Geographical Distribution/Conflict Cont’d
Forced population movement increases transmission.
Migration causes trypanosomes to circulate from high-incidence to low-incidence areas.
Conflict causes breakdown of control measures and surveillance, increasing disease spread
The fact that many conflicts still exist in Africa today is a cause for concern because these conflicts can potentially cause more outbreaks of HAT by putting reservoirs for infection in more contact with disease vectors. Conflict has been shown to cause problems for countries’ disease surveillance and control programs, and as long as conflict still exists, another HAT epidemic is very possible .
Pic: African Soldiers Attacking Protesters
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22. References
1. Pepin J., Meda H. The epidemiology and control of human African trypanosomiasis. Adv Parasitol, 49 (2001), pp. 71–132
2. Human African trypanosomiasis (sleeping sickness). Available at Accessed March 8, 2012.
3. Smith D., Pepin J., Stich A. Human African trypanosomiasis: an emerging public health crisis. Br Med Bull, 54 (1998), pp. 341–355
4. Brun R., Blum J., Chappuis F., Burri C. Human African trypanosomiasis. Lancet (2009), pp. 148–159
5. Simarro P., Jannin J., Cattand P. Eliminating human African trypanosomiasis: where do we stand and what comes next? PLoS Med. 5, e55 (2008), pp. 174–180

23. References Cont’d
6. Parasites- African Trypanosomiasis (also known as Sleeping Sickness). Available at Accessed March 8, Berrang-Ford L, Martin O, Maiso F, Waltner-Toews D, McDermott J (2006) Sleeping sickness in Uganda: revisiting current and historical distributions. Afr Health Sci 6: 223– Kuzoe FAS. (1993) Current situation of African trypanosomiasis. Acta Trop. 54: MacGregor P., Matthews K. New discoveries in the transmission biology of sleeping sickness parasites: applying the basics. J. Mol. Med., 88 (2010), pp. 865–871

24. References Cont’d
10. Berrang-Ford L., Breau L. Conflict and human trypanosomiasis. Soc. Sci. Med. (2010), pp. 398–407