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African trypanosomiasis

(Redirected from Human African Trypanosomiasis)
"Sleeping sickness" and "Sleep fever" redirect here. For other uses, see Sleeping sickness (disambiguation).
This article is about the human disease. For the disease affecting animals, see Animal trypanosomiasis.

African trypanosomiasis is an insect-borne parasitic infection of humans and other animals.[3]

African trypanosomiasis
Other namesSleeping sickness, African sleeping sickness
Trypanosoma forms in a blood smear
SpecialtyInfectious disease
SymptomsStage 1: Fevers, headaches, itchiness, joint pains[1]
Stage 2: Insomnia, confusion, Ataxia[2][1]
Usual onset1–3 weeks post exposure[2]
TypesTrypanosoma brucei gambiense (TbG), Trypanosoma brucei rhodesiense (TbR)[3]
CausesTrypanosoma brucei spread by tsetse flies[3]
Diagnostic methodBlood smear, lumbar puncture[2]
MedicationFexinidazole, pentamidine, suramin, melarsoprol, eflornithine, nifurtimox[3]
PrognosisFatal without treatment[3]
Frequency977 (2018)[3]
Deaths3,500 (2015)[4]

Human African trypanosomiasis (HAT), also known as African sleeping sickness or simply sleeping sickness, is caused by the species Trypanosoma brucei.[3] Humans are infected by two types, Trypanosoma brucei gambiense (TbG) and Trypanosoma brucei rhodesiense (TbR).[3] TbG causes over 92% of reported cases.[1] Both are usually transmitted by the bite of an infected tsetse fly and are most common in rural areas.[3]

Initially, the first stage of the disease is characterized by fevers, headaches, itchiness, and joint pains, beginning one to three weeks after the bite.[1][2] Weeks to months later, the second stage begins with confusion, poor coordination, numbness, and trouble sleeping.[2] Diagnosis is by finding the parasite in a blood smear or in the fluid of a lymph node.[2] A lumbar puncture is often needed to tell the difference between first- and second-stage disease.[2] If the disease is not treated quickly, it can lead to death.

Prevention of severe disease involves screening the at-risk population with blood tests for TbG.[3] Treatment is easier when the disease is detected early and before neurological symptoms occur.[3] Treatment of the first stage has been with the medications pentamidine or suramin.[3] Treatment of the second stage has involved eflornithine or a combination of nifurtimox and eflornithine for TbG.[2][3] Fexinidazole is a more recent treatment that can be taken by mouth, for either stage of TbG.[3] While melarsoprol works for both types, it is typically only used for TbR, due to serious side effects.[3] Without treatment, sleeping sickness typically results in death.[3]

The disease occurs regularly in some regions of sub-Saharan Africa with the population at risk being about 70 million in 36 countries.[5] An estimated 11,000 people are currently infected with 2,800 new infections in 2015.[6][1] In 2018 there were 977 new cases.[3] In 2015 it caused around 3,500 deaths, down from 34,000 in 1990.[4][7] More than 80% of these cases are in the Democratic Republic of the Congo.[1] Three major outbreaks have occurred in recent history: one from 1896 to 1906 primarily in Uganda and the Congo Basin, and two in 1920 and 1970, in several African countries.[1] It is classified as a neglected tropical disease.[8] Other animals, such as cows, may carry the disease and become infected in which case it is known as Nagana or animal trypanosomiasis.[1]

Signs and symptoms

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African trypanosomiasis symptoms occur in two stages: the hemolymphatic stage and the neurological stage (the latter being characterised by parasitic invasion of the central nervous system).[9][10] Neurological symptoms occur in addition to the initial features, and the two stages may be difficult to distinguish based on clinical features alone.[10]

The disease has been reported to present with atypical symptoms in infected individuals who originate from non-endemic areas (e.g. travelers). The reasons for this are unclear and may be genetic. The low number of such cases may also have skewed findings. In such persons, the infection is said to present mainly as fever with gastrointestinal symptoms (e.g. diarrhoea and jaundice) with lymphadenopathy developing only rarely.[11]

Trypanosomal ulcer

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Systemic disease is sometimes presaged by a trypanosomal ulcer developing at the site of the infectious fly bite within 2 days of infection. The ulcer is most commonly observed in T. b. rhodesiense infection, and only rarely in T. b. gambiense (however, in T. b. gambiense infection, ulcers are more common in persons from non-endemic areas).[10]

Hemolymphatic phase

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Incubation period is 1–3 weeks for T. b. rhodesiense, and longer (but less precisely characterised) in T. b. gambiense infection. The first/initial stage, known as the hemolymphatic phase, is characterized by non-specific, generalised symptoms[10] like: fever (intermittent), headaches (severe),[12] joint pains, itching,[9][10] weakness, malaise, fatigue, weight loss, lymphadenopathy, and hepatosplenomegaly.[10]

Diagnosis may be delayed due to the vagueness of initial symptoms. The disease may also be mistaken for malaria (which may in fact occur as a co-infection).[11]

Intermittent fever

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Fever is intermittent, with attacks lasting from a day to a week, separated by intervals of a few days to a month or longer.[9][10] Episodes of fever become less frequent over the course of the disease.[10]

Lymphadenopathy

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Invasion of the circulatory and lymphatic systems by the parasite is associated with severe swelling of lymph nodes, often to tremendous sizes.[9] Posterior cervical lymph nodes are most commonly affected, however, axillary, inguinal, and epitrochlear lymph node involvement may also occur.[10] Winterbottom's sign, the tell-tale swollen lymph nodes along the back of the neck, may appear.[9] Winterbottom's sign is common in T. b. gambiense infection.[10]

Other features

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Those affected may additionally present with: skin rash,[12] haemolytic anaemia, hepatomegaly and abnormal liver function, splenomegaly, endocrine disturbance, cardiac involvement (e.g. pericarditis, and congestive heart failure), and ophthalmic involvement.[11]

  •  
    Ulcer of human African trypanosomiasis[13]
  •  
    Typical fine-spotted pink rash of acute African trypanosomiasis on the skin of the abdomen ("trypanid rash")[14]
  •  
    Numerous spots of bleeding into the skin of the leg in a person infected with T. b. rhodesiense[14]

Neurological phase

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The second phase of the disease, the neurological phase (also called the meningoencephalic stage[10]), begins when the parasite invades the central nervous system by passing through the blood–brain barrier.[9] Progression to the neurological phase occurs after an estimated 21–60 days in case of T. b. rhodesiense infection, and 300–500 days in case of T. b. gambiense infection.[10]

In actuality, the two phases overlap and are difficult to distinguish based on clinical features alone; determining the actual stage of the disease is achieved by examining the cerebrospinal fluid for the presence of the parasite.[10]

Sleep disorders

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Sleep-wake disturbances are a leading feature of the neurological stage[9][15] and give the disease its common name of "sleeping sickness".[9][10][15] Infected individuals experience a disorganized and fragmented sleep-wake cycle.[9] Those affected experience sleep inversion resulting in daytime sleep[9] and somnolence,[10] and nighttime periods of wakefulness[9] and insomnia.[10] Additionally, those affected also experience episodes of sudden sleepiness.[10]

Neurological/neurocognitive symptoms

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Neurological symptoms include: tremor, general muscle weakness, hemiparesis, paralysis of a limb,[16] abnormal muscle tone, gait disturbance, ataxia, speech disturbances, paraesthesia, hyperaesthesia, anaesthesia, visual disturbance, abnormal reflexes, seizures, and coma.[10] Parkinson-like movements might arise due to non-specific movement disorders and speech disorders.[16]

Psychiatric/behavioural symptoms

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Individuals may exhibit psychiatric symptoms which may sometimes dominate the clinical diagnosis and may include aggressiveness, apathy,[10][16] irritability, psychotic reactions[16] and hallucinations, anxiety, emotional lability, confusion, mania, attention deficit, and delirium.[10]

Advanced/late disease and outcomes

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Without treatment, the disease is invariably fatal, with progressive mental deterioration leading to coma, systemic organ failure, and death. An untreated infection with T. b. rhodesiense will cause death within months[17] whereas an untreated infection with T. b. gambiense will cause death after several years.[18] Damage caused in the neurological phase is irreversible.[19]

Cause

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The life cycle of the Trypanosoma brucei parasites

Trypanosoma brucei gambiense accounts for the majority of African trypanosomiasis cases, with humans as the main reservoir needed for the transmission, while Trypanosoma brucei rhodesiense is mainly zoonotic, with accidental human infections.[20] The epidemiology of African trypanosomiasis is dependent on the interactions between the parasite (trypanosome), the vector (tsetse fly), and the host.[20]

Trypanosoma brucei

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Main article: Trypanosoma brucei

There are two subspecies of the parasite that are responsible for starting the disease in humans. Trypanosoma brucei gambiense causes the diseases in west and central Africa, whereas Trypanosoma brucei rhodesiense has a limited geographical range and is responsible for causing the disease in east and southern Africa. In addition, a third subspecies of the parasite known as Trypanosoma brucei brucei is responsible for affecting animals but not humans.[16]

Humans are the main reservoir for T. b. gambiense but this species can also be found in pigs and other animals. Wild game animals and cattle are the main reservoir of T. b. rhodesiense. These parasites primarily infect individuals in sub-Saharan Africa because that is where the vector (tsetse fly) is located. The two human forms of the disease also vary greatly in intensity. T. b. gambiense causes a chronic condition that can remain in a passive phase for months or years before symptoms emerge and the infection can last about three years before death occurs.[16]

T. b. rhodesiense is the acute form of the disease, and death can occur within months since the symptoms emerge within weeks and it is more virulent and faster developing than T. b. gambiense. Furthermore, trypanosomes are surrounded by a coat that is composed of variant surface glycoproteins (VSG). These proteins act to protect the parasite from any lytic factors that are present in human plasma. The host's immune system recognizes the glycoproteins present on the coat of the parasite leading to the production of different antibodies (IgM and IgG).[16]

These antibodies will then act to destroy the parasites that circulate around the blood. However, from the several parasites present in the plasma, a small number of them will experience changes in their surface coats resulting in the formation of new VSGs. Thus, the antibodies produced by the immune system will no longer recognize the parasite leading to proliferation until new antibodies are created to combat the novel VSGs. Eventually, the immune system will no longer be able to fight off the parasite due to the constant changes in VSGs and infection will arise.[16]

Vector

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Type Trypanosoma Distribution Vector
Chronic T. brucei gambiense Western Africa G. palpalis

G. tachinoides

G. fuscipes

G. morsitans

Acute T. brucei rhodesiense Eastern Africa G. morsitans

G. swynnertoni

G. pallidipes

G. fuscipes

 
Drawing of a tsetse fly from 1880

The tsetse fly (genus Glossina) is a large, brown, biting fly that serves as both a host and vector for the trypanosome parasites. While taking blood from a mammalian host, an infected tsetse fly injects metacyclic trypomastigotes into skin tissue. From the bite, parasites first enter the lymphatic system and then pass into the bloodstream. Inside the mammalian host, they transform into bloodstream trypomastigotes, and are carried to other sites throughout the body, reach other body fluids (e.g., lymph, spinal fluid), and continue to replicate by binary fission.[21][22]

The entire life cycle of African trypanosomes is represented by extracellular stages. A tsetse fly becomes infected with bloodstream trypomastigotes when taking a blood meal on an infected mammalian host. In the fly's midgut, the parasites transform into procyclic trypomastigotes, multiply by binary fission, leave the midgut, and transform into epimastigotes. The epimastigotes reach the fly's salivary glands and continue multiplication by binary fission.[23]

The entire life cycle of the fly takes about three weeks. In addition to the bite of the tsetse fly, the disease can be transmitted by:

  • Mother-to-child infection: the trypanosome can sometimes cross the placenta and infect the fetus.[24]
  • Laboratories: accidental infections, for example, through the handling of blood of an infected person and organ transplantation, although this is uncommon.
  • Blood transfusion
  • Sexual contact[25]

Horse-flies (Tabanidae) and stable flies (Muscidae) possibly play a role in transmission of nagana (the animal form of sleeping sickness) and the human disease form.[26]

Pathophysiology

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Tryptophol is a chemical compound produced by the trypanosomal parasite in sleeping sickness which induces sleep in humans.[27]

Diagnosis

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Two areas from a blood smear from a person with African trypanosomiasis, thin blood smear stained with Giemsa: typical trypomastigote stages (the only stages found in people), with a posterior kinetoplast, a centrally located nucleus, an undulating membrane, and an anterior flagellum. The two Trypanosoma brucei subspecies that cause human trypanosomiasis, T. b. gambiense and T. b. rhodesiense, are indistinguishable morphologically. The trypanosomes' length range is 14 to 33 μm; source: CDC.

The gold standard for diagnosis is identification of trypanosomes in a sample by microscopic examination. Samples that can be used for diagnosis include ulcer fluid, lymph node aspirates, blood, bone marrow, and, during the neurological stage, cerebrospinal fluid. Detection of trypanosome-specific antibodies can be used for diagnosis, but the sensitivity and specificity of these methods are too variable to be used alone for clinical diagnosis. Further, seroconversion occurs after the onset of clinical symptoms during a T. b. rhodesiense infection, so is of limited diagnostic use.[citation needed]

Trypanosomes can be detected from samples using two different preparations. A wet preparation can be used to look for the motile trypanosomes. Alternatively, a fixed (dried) smear can be stained using Giemsa's or Field's technique and examined under a microscope. Often, the parasite is in relatively low abundance in the sample, so techniques to concentrate the parasites can be used prior to microscopic examination. For blood samples, these include centrifugation followed by examination of the buffy coat; mini anion-exchange/centrifugation; and the quantitative buffy coat (QBC) technique. For other samples, such as spinal fluid, concentration techniques include centrifugation followed by examination of the sediment.[citation needed]

Three serological tests are also available for detection of the parasite: the micro-CATT (card agglutination test for trypanosomiasis), wb-CATT, and wb-LATEX. The first uses dried blood, while the other two use whole blood samples. A 2002 study found the wb-CATT to be the most efficient for diagnosis, while the wb-LATEX is a better exam for situations where greater sensitivity is required.[28]

Prevention

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See also: Tsetse fly § Control techniques
 
Capture devices for tsetse flies, on shore and on a boat in Africa. Efforts to prevent sleeping sickness.[29]

Currently there are few medically related prevention options for African trypanosomiasis (i.e. no vaccine exists for immunity). Although the risk of infection from a tsetse fly bite is minor (estimated at less than 0.1%), the use of insect repellants, wearing long-sleeved clothing, avoiding tsetse-dense areas, implementing bush clearance methods and wild game culling are the best options to avoid infection available for local residents of affected areas.[16]

In July 2000, a resolution was passed to form the Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). The campaign works to eradicate the tsetse vector population levels and subsequently the protozoan disease, by use of insecticide-impregnated targets, fly traps, insecticide-treated cattle, ultra-low dose aerial/ground spraying (SAT) of tsetse resting sites and the sterile insect technique (SIT).[30] The use of SIT in Zanzibar proved effective in eliminating the entire population of tsetse flies but was expensive and is relatively impractical to use in many of the endemic countries afflicted with African trypanosomiasis.[31]

A pilot program in Senegal has reduced the tsetse fly population by as much as 99% by introducing male flies which have been sterilized by exposure to gamma rays.[32][33]

Regular active surveillance, involving detection and prompt treatment of new infections, and tsetse fly control is the backbone of the strategy used to control sleeping sickness. Systematic screening of at-risk communities is the best approach, because case-by-case screening is not practical in endemic regions. Systematic screening may be in the form of mobile clinics or fixed screening centres where teams travel daily to areas of high infection rates. Such screening efforts are important because early symptoms are not evident or serious enough to warrant people with gambiense disease to seek medical attention, particularly in very remote areas. Also, diagnosis of the disease is difficult and health workers may not associate such general symptoms with trypanosomiasis. Systematic screening allows early-stage disease to be detected and treated before the disease progresses, and removes the potential human reservoir.[34] A single case of sexual transmission of West African sleeping sickness has been reported.[25]

Treatment

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The treatment is dependent on if the disease is discovered in the first or second stage of the disease. A requirement for treatment of the second stage is that the drug passes the blood-brain barrier.

First stage

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The treatment for first-stage disease is fexinidazole by mouth or pentamidine by injection for T. b. gambiense.[3] Suramin by injection is used for T. b. rhodesiense.[3]

Second stage

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Fexinidazole may be used for the second stage of TbG, if the disease is not severe.[35][3] Otherwise a regimen involving the combination of nifurtimox and eflornithine, nifurtimox-eflornithine combination treatment (NECT), or eflornithine alone appear to be more effective and result in fewer side effects.[36] These treatments may replace melarsoprol when available.[36][2] NECT has the benefit of requiring fewer injections of eflornithine.[36]

Intravenous melarsoprol was previously the standard treatment for second-stage (neurological phase) disease and is effective for both types.[2] Melarsoprol is the only treatment for second stage T. b. rhodesiense; however, it causes death in 5% of people who take it.[2] Resistance to melarsoprol can occur.[2]

Drug development projects. A major challenge has been to find drugs that readily pass the blood-brain barrier. The latest drug that has come into clinical use is fexinidazol, but promising results have also been obtained with the benzoxaborole drug acoziborole (SCYX-7158). This drug is currently under evaluation as a single-dose oral treatment, which is a great advantage compared to currently used drugs. Another research field that has been extensively studied in Trypanosoma brucei is to target its nucleotide metabolism.[37] The nucleotide metabolism studies have both led to the development of adenosine analogues looking promising in animal studies, and to the finding that downregulation of the P2 adenosine transporter is a common way to acquire partial drug resistance against the melaminophenyl arsenical and diamidine drug families (containing melarsoprol and pentamidine, respectively).[37] Drug uptake and degradation are two major issues to consider to avoid drug resistance development. In the case of nucleoside analogues, they need to be taken up by the P1 nucleoside transporter (instead of P2), and they also need to be resistant against cleavage in the parasite.[38][39]

Prognosis

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If untreated, T. b. gambiense almost always results in death, with only a few individuals shown in a long-term 15 year follow-up to have survived after refusing treatment. T. b. rhodesiense, being a more acute and severe form of the disease, is consistently fatal if not treated.[2]

Disease progression greatly varies depending on disease form. For individuals which are infected by T. b. gambiense, which accounts for 92% of all of the reported cases, a person can be infected for months or even years without signs or symptoms until the advanced disease stage, where it is too late to be treated successfully. For individuals affected by T. b. rhodesiense, which accounts for 2% of all reported cases, symptoms appear within weeks or months of the infection. Disease progression is rapid and invades the central nervous system, causing death within a short amount of time.[40]

Epidemiology

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Deaths per 100,000 population due to African trypanosomiasis by country in 2002[41]

In 2010, it caused around 9,000 deaths, down from 34,000 in 1990.[7] As of 2000, the disability-adjusted life-years (9 to 10 years) lost due to sleeping sickness are 2.0 million.[42] From 2010 to 2014, there was an estimated 55 million people at risk for gambiense African Trypanosomiasis and over 6 million people at risk for rhodesiense African trypanosomiasis.[43] In 2014, the World Health Organization reported 3,797 cases of Human African Trypanosomiasis when the predicted number of cases were to be 5,000. The number of total reported cases in 2014 is an 86% reduction to the total number of cases reported in 2000.[43]

The disease has been recorded as occurring in 37 countries, all in sub-Saharan Africa. It occurs regularly in southeast Uganda and western Kenya, and killed more than 48,000 Africans in 2008.[19] The Democratic Republic of the Congo is the most affected country in the world, accounting for 75% of the Trypanosoma brucei gambiense cases.[20] The population at risk being about 69 million with one third of this number being at a 'very high' to 'moderate' risk and the remaining two thirds at a 'low' to 'very low' risk.[5] The number of people being affected by the disease has declined. At this rate, sleeping sickness elimination is a possibility. The World Health Organization plans to eradicate sleeping sickness by 2030.[43][44]

Trypanosoma brucei gambiense[45] 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023
Angola 1498 2094 2406 1796 1274 2441 6726 8275 6610 5351 4546 4577 3621 3115 2280 1727 1105 648 517 247 211 154 70 69 36 35 19 18 79 30 33 174 44 52
Benin 0 0 2 1 0 0 0 0 0 20 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Burkina Faso 27 27 20 17 18 13 12 1 15 15 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0
Cameroon 86 69 21 3 20 21 17 10 54 32 27 14 32 33 17 3 15 7 13 24 16 15 7 6 7 6 6 5 7 17 2 11 7 11
Central African Republic 308 197 362 262 368 676 492 730 1068 869 988 718 572 539 738 666 460 654 1194 1054 395 132 381 59 194 147 124 76 57 86 39 44 110 104
Chad 20 221 149 65 214 315 178 122 134 187 153 138 715 222 483 190 276 97 196 510 232 276 197 195 95 67 53 28 12 16 17 15 18 7
Congo 580 703 727 829 418 475 474 142 201 91 111 894 1005 717 873 398 300 189 182 87 87 61 39 20 21 36 18 15 24 17 15 18 10 14
Côte d'Ivoire 365 349 456 260 206 326 240 185 121 104 188 92 97 68 74 42 29 13 14 8 8 10 9 7 6 3 0 3 2 1 0 1 0 0
Democratic Republic of the Congo 7515 5825 7757 11384 19021 18182 19342 25094 26318 18684 16951 17300 13816 11459 10339 10249 8013 8155 7318 7178 5624 5590 5968 5647 3205 2351 1769 1110 660 604 395 425 516 394
Equatorial Guinea 63 36 45 30 85 37 46 67 62 28 16 17 32 23 22 17 13 15 11 7 8 1 2 3 0 0 3 4 4 3 1 3 13 7
Gabon 80 45 33 80 61 20 32 11 6 38 45 30 26 26 49 53 31 30 24 14 22 17 9 17 10 9 10 9 16 8 11 18 21 12
Ghana 3 6 16 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0
Guinea 52 29 24 27 26 33 38 88 99 68 52 72 132 130 95 94 48 69 90 79 68 57 70 78 33 29 107 140 74 69 36 28 30 24
Mali 0 0 0 27 17 11 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Nigeria 24 0 0 0 0 0 0 0 0 27 14 14 26 31 10 21 3 0 0 0 2 3 2 0 0 0 1 0 0 0 0 0 0 0
South Sudan 67 58 28 62 69 56 157 737 1726 1312 1801 1919 3121 3061 1742 1853 789 469 623 373 199 272 317 117 63 45 17 12 17 11 15 10 30 50
Togo 2 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Uganda 2066 1328 2042 1764 1469 1062 981 1123 971 1036 948 310 604 517 378 311 290 120 198 99 101 44 20 9 9 4 4 0 1 2 1 0 0 0
Total 12756 10987 14088 16607 23266 23671 28736 36585 37385 27862 25841 26095 23799 19941 17100 15624 11372 10466 10380 9680 6973 6632 7091 6228 3679 2733 2131 1420 953 864 565 747 799 675
Trypanosoma brucei rhodesiense 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023
Ethiopia No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data 6 2
Kenya 91 8 4 2 1 0 2 5 14 22 15 10 11 0 0 0 1 0 0 1 0 0 2 0 0 0 0 0 0 0 0 0 0 0
Malawi 228 195 143 53 31 15 8 7 10 11 35 38 43 70 48 41 58 50 49 39 29 23 18 35 32 30 37 7 15 91 89 49 24 16
Mozambique 3 7 24 10 16 No data No data No data No data No data No data No data 1 No data 1 No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data No data
Uganda 1417 832 606 503 342 497 178 217 283 283 300 426 329 338 335 473 261 119 138 129 112 84 71 43 70 28 10 13 4 5 2 2 0 0
United Republic of Tanzania 187 177 366 262 319 422 400 354 299 288 350 277 228 113 159 186 127 126 59 14 5 1 4 1 1 2 3 3 0 3 1 1 1 1
Zambia 7 No data 4 1 1 1 3 No data No data 15 9 4 5 15 9 7 6 10 13 4 8 3 6 6 12 8 2 3 5 15 6 3 7 5
Zimbabwe No data No data No data No data 1 No data No data 9 No data No data No data No data No data No data No data 3 No data No data 0 3 2 4 9 1 3 3 1 1 0 2 0 0 0 0
Total 1933 1219 1147 831 710 935 591 583 606 619 709 755 617 536 552 707 453 305 259 187 154 111 101 85 115 68 52 27 24 116 98 55 38 24

History

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See also: Tsetse fly § History
 
In 1903, David Bruce recognized the tsetse fly as the arthropod vector.

The condition has been present in Africa for thousands of years.[46] Because of a lack of travel between indigenous people, sleeping sickness in humans had been limited to isolated pockets. This changed after Arab slave traders entered central Africa from the east, following the Congo River, bringing parasites along. Gambian sleeping sickness travelled up the Congo River, and then further east.[47]

An Arab writer of the 14th century left the following description in the case of a sultan of the Mali Kingdom: "His end was to be overtaken by the sleeping sickness (illat an-nawm) which is a disease that frequently befalls the inhabitants of these countries especially their chieftains. Sleep overtakes one of them in such a manner that it is hardly possible to awake him."[47]

The British naval surgeon John Atkins described the disease on his return from West Africa in 1734:[47]

The Sleepy Distemper (common among the Negroes) gives no other previous Notice, than a want of Appetite 2 or 3 days before; their sleeps are sound, and Sense and Feeling very little; for pulling, drubbing or whipping will scarce stir up Sense and Power enough to move; and the Moment you cease beating the smart is forgot, and down they fall again into a state of Insensibility, drivling constantly from the Mouth as in deep salivation; breathe slowly, but not unequally nor snort. Young people are more subject to it than the old; and the Judgement generally pronounced is Death, the Prognostik seldom failing. If now and then one of them recovers, he certainly loses the little Reason he had, and turns Ideot...

French naval surgeon Marie-Théophile Griffon du Bellay treated and described cases while stationed aboard the hospital ship Caravane in Gabon in the late 1860s.[48]

In 1901, a devastating epidemic erupted in Uganda, killing more than 250,000 people,[49] including about two-thirds of the population in the affected lakeshore areas. According to The Cambridge History of Africa, "It has been estimated that up to half the people died of sleeping-sickness and smallpox in the lands on either bank of the lower river Congo."[50]

The causative agent and vector were identified in 1903 by David Bruce, and the subspecies of the protozoa were differentiated in 1910. Bruce had earlier shown that T. brucei was the cause of a similar disease in horses and cattle that was transmitted by the tsetse fly (Glossina morsitans).[47]

The first effective treatment, atoxyl, an arsenic-based drug developed by Paul Ehrlich and Kiyoshi Shiga, was introduced in 1910, but blindness was a serious side effect.

Suramin was first synthesized by Oskar Dressel and Richard Kothe in 1916 for Bayer. It was introduced in 1920 to treat the first stage of the disease. By 1922, Suramin was generally combined with tryparsamide (another pentavalent organoarsenic drug), the first drug to enter the nervous system and be useful in the treatment of the second stage of the gambiense form. Tryparsamide was announced in the Journal of Experimental Medicine in 1919 and tested in the Belgian Congo by Louise Pearce of the Rockefeller Institute in 1920. It was used during the grand epidemic in West and Central Africa on millions of people and was the mainstay of therapy until the 1960s.[51] American medical missionary Arthur Lewis Piper was active in using tryparsamide to treat sleeping sickness in the Belgian Congo in 1925.[52]

Pentamidine, a highly effective drug for the first stage of the disease, has been used since 1937.[53] During the 1950s, it was widely used as a prophylactic agent in western Africa, leading to a sharp decline in infection rates. At the time, eradication of the disease was thought to be at hand.[citation needed][51]

The organoarsenical melarsoprol (Arsobal) developed in the 1940s is effective for people with second-stage sleeping sickness. However, 3–10% of those injected have reactive encephalopathy (convulsions, progressive coma, or psychotic reactions), and 10–70% of such cases result in death; it can cause brain damage in those who survive the encephalopathy. However, due to its effectiveness, melarsoprol is still used today. Resistance to melarsoprol is increasing, and combination therapy with nifurtimox is currently under research.[citation needed]

Eflornithine (difluoromethylornithine or DFMO), the most modern treatment, was developed in the 1970s by Albert Sjoerdsma and underwent clinical trials in the 1980s. The drug was approved by the United States Food and Drug Administration in 1990.[54] Aventis, the company responsible for its manufacture, halted production in 1999. In 2001, Aventis, in association with Médecins Sans Frontières and the World Health Organization, signed a long-term agreement to manufacture and donate the drug.[citation needed]

In addition to sleeping sickness, previous names have included negro lethargy, maladie du sommeil (Fr), Schlafkrankheit (Ger), African lethargy,[55] and Congo trypanosomiasis.[55][56]

Research

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The genome of the parasite has been sequenced and several proteins have been identified as potential targets for drug treatment. Analysis of the genome also revealed the reason why generating a vaccine for this disease has been so difficult. T. brucei has over 800 genes that make proteins the parasite "mixes and matches" to evade immune system detection.[57]

Using a genetically modified form of a bacterium that occurs naturally in the gut of the vectors is being studied as a method of controlling the disease.[58]

Recent findings indicate that the parasite is unable to survive in the bloodstream without its flagellum. This insight gives researchers a new angle with which to attack the parasite.[59]

Trypanosomiasis vaccines are undergoing research.

Additionally, the Drugs for Neglected Diseases Initiative has contributed to the African sleeping sickness research by developing a compound called fexinidazole. This project was originally started in April 2007 and enrolled 749 people in the DRC and Central African Republic. The results showed efficacy and safety in both stages of the disease, both in adults and children ≥ 6 years old and weighing ≥ 20 kg.[60] The European Medicines Agency approved it for first and second stage disease outside of Europe in November 2018.[61] The treatment was approved in the DRC in December 2018.[62]

Funding

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For current funding statistics, human African trypanosomiasis is grouped with kinetoplastid infections. Kinetoplastids refer to a group of flagellate protozoa.[63] Kinetoplastid infections include African sleeping sickness, Chagas' disease, and Leishmaniasis. All together, these three diseases accounted for 4.4 million disability adjusted life years (DALYs) and an additional 70,075 recorded deaths yearly.[63] For kinetoplastid infections, the total global research and development funding was approximately $136.3 million in 2012. Each of the three diseases, African sleeping sickness, Chagas' disease, and Leishmaniasis each received approximately a third of the funding, which was about US$36.8 million, US$38.7 million, and US$31.7 million, respectively.[63]

For sleeping sickness, funding was split into basic research, drug discovery, vaccines, and diagnostics. The greatest amount of funding was directed towards basic research of the disease; approximately US$21.6 million was directed towards that effort. As for therapeutic development, approximately $10.9 million was invested.[63]

The top funder for kinetoplastid infection research and development are public sources. About 62% of the funding comes from high-income countries while 9% comes from low- and middle-income countries. High-income countries' public funding is the largest contributor to the neglected disease research effort. However, in recent years, funding from high-income countries has been steadily decreasing; in 2007, high-income countries provided 67.5% of the total funding whereas, in 2012, high-income countries public funds only provided 60% of the total funding for kinetoplastid infections. This downwards trend leaves a gap for other funders, such as philanthropic foundations and private pharmaceutical companies to fill.[63]

Much of the progress that has been made in African sleeping sickness and neglected disease research as a whole is a result of the other non-public funders. One of these major sources of funding has come from foundations, which have increasingly become more committed to neglected disease drug discovery in the 21st century. In 2012, philanthropic sources provided 15.9% of the total funding.[63] The Bill and Melinda Gates Foundation has been a leader in providing funding for neglected disease drug development. They have provided US$444.1 million towards neglected disease research in 2012. To date, they have donated over US$1.02 billion towards the neglected disease discovery efforts.[64]

For kinetoplastid infections specifically, they have donated an average of US$28.15 million annually between the years 2007 to 2011.[63] They have labeled human African trypanosomiasis a high-opportunity target meaning it is a disease that presents the greatest opportunity for control, elimination, and eradication, through the development of new drugs, vaccines, public-health programs, and diagnostics. They are the second-highest funding source for neglected diseases, immediately behind the US National Institutes of Health.[63] At a time where public funding is decreasing and government grants for scientific research are harder to obtain, the philanthropic world has stepped in to push the research forward.[citation needed]

Another important component of increased interest and funding has come from industry. In 2012, they contributed 13.1% total to the kinetoplastid research and development effort, and have additionally played an important role by contributing to public-private partnerships (PPP) as well as product-development partnerships (PDP).[63] A public-private partnership is an arrangement between one or more public entities and one or more private entities that exists to achieve a specific health outcome or to produce a health product. The partnership can exist in numerous ways; they may share and exchange funds, property, equipment, human resources, and intellectual property. These public-private partnerships and product-development partnerships have been established to address challenges in pharmaceutical industry, especially related to neglected disease research. These partnerships can help increase the scale of the effort towards therapeutic development by using different knowledge, skills, and expertise from different sources. These types of partnerships have been shown to be more effective than industry or public groups working independently.[65]

Other animals and reservoir

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Main article: Animal trypanosomiasis

Trypanosoma of both the rhodesiense and gambiense types can affect other animals such as cattle and wild animals.[1] African trypanosomiasis has generally been considered an anthroponotic disease and thus its control program was mainly focused on stopping the transmission by treating human cases and eliminating the vector. However, animal reservoirs were reported to possibly play an important role in the endemic nature of African trypanosomiasis, and for its resurgence in the historic foci of West and Central Africa.[66][67]

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