Trypanosoma brucei is a microscopic, single-celled parasite responsible for a serious and often fatal human disease. It is a protozoan parasite and a significant public health concern in sub-Saharan Africa due to the debilitating illness it causes.
Understanding the T. brucei Parasite
Trypanosoma brucei is a flagellated protozoan, moving with a whip-like appendage. It exists as a species complex with two main human-infecting subspecies: Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense. These subspecies differ in disease progression and geographic distribution.
T. b. gambiense, found in West and Central Africa, causes a chronic disease form, with symptoms developing over months to years. Humans are its primary reservoir, though it can infect wildlife and domestic animals. In contrast, T. b. rhodesiense in East and Southern Africa leads to a more acute and rapid disease progression, often within weeks. Game animals and livestock are its main reservoirs, making it a zoonotic parasite.
The tsetse fly (genus Glossina) is the primary vector, transmitting T. brucei to mammalian hosts, including humans, through its bite. Inside the tsetse fly, ingested parasites develop in the midgut, then migrate to the salivary glands, transforming into metacyclic forms infective to mammals.
In the mammalian host, injected metacyclic forms become bloodstream forms, multiplying in blood and other body fluids. A unique feature of T. brucei is its ability to evade the host’s immune system by periodically changing its dense coat of variant surface glycoproteins, a process known as antigenic variation. This allows the parasite to persist in the host, contributing to chronic infections.
The Disease: African Trypanosomiasis
African Trypanosomiasis, or Sleeping Sickness, progresses through two distinct stages. The initial hemolymphatic stage involves parasites circulating in the blood and lymphatic system.
Symptoms include intermittent fever, headaches, muscle and joint pain, itchy skin, and swollen lymph nodes. A red sore (chancre) may develop at the tsetse fly bite site, more common with T. b. rhodesiense. This stage lasts months to years for T. b. gambiense but only weeks for T. b. rhodesiense.
The second, meningoencephalitic stage begins when parasites invade the central nervous system, leading to severe neurological symptoms. Patients may experience confusion, poor coordination, behavioral changes, and sleep cycle disruptions, including daytime insomnia and excessive nighttime sleepiness.
Without treatment, this stage is fatal, leading to tremors, slurred speech, seizures, coma, and death. In T. b. rhodesiense cases, death can occur from heart inflammation (myocarditis) within three to six months, even before overt neurological signs fully develop. Diagnosis involves detecting the parasite in body fluids like blood or lymph node aspirates using light microscopy. A lumbar puncture examines cerebrospinal fluid for trypanosomes and an elevated white blood cell count, confirming central nervous system involvement and disease stage.
Treatment and Prevention
Treatment for African Trypanosomiasis varies depending on the T. brucei subspecies and disease stage. Early diagnosis is important for more effective treatment outcomes and to minimize drug toxicity. Hospitalization is usually necessary, and patients often require follow-up examinations, including lumbar punctures, for up to two years to monitor for relapse.
First Stage Treatment
T. b. gambiense: Pentamidine (intramuscularly/intravenously) or fexinidazole (oral).
T. b. rhodesiense: Suramin (intravenously).
Second Stage Treatment
Drugs that cross the blood-brain barrier are required.
T. b. gambiense: Nifurtimox-eflornithine combination therapy (NECT) or eflornithine. Fexinidazole is an option for less severe cases.
T. b. rhodesiense: Melarsoprol, an arsenic-derived drug with severe side effects.
Prevention strategies focus on reducing contact with the tsetse fly and controlling fly populations. Personal protection measures include wearing long-sleeved shirts, long pants, and closed shoes made of thick fabric, as tsetse flies can bite through thin materials. Wearing neutral-colored clothing is also advisable, as tsetse flies are attracted to bright and very dark colors. Insect repellents have limited efficacy against tsetse flies.
Avoiding areas with high tsetse fly densities is another preventive measure. These flies often inhabit rural areas, woodlands, and dense vegetation, so staying on main paths and inspecting vehicles before entry can help. Vector control measures include the deployment of insecticide-treated traps and targets, which are cloth screens designed to attract and kill the flies. Treating livestock with insecticides also helps control fly populations. Active screening and surveillance in endemic areas are important for early identification of cases and disease control.