1. The Life Cycle of
Trypanosomiasis
Report by:
Veronica Baje
2. African Trypanosomes
• “African trypanosomes” or “Old World trypanosomes” are
protozoan hemoflagellates of the genus Trypanosoma, in the
subgenus Trypanozoon.
• Two subspecies that are morphologically indistinguishable cause
distinct disease patterns in humans: T. b. gambiense, causing
chronic African trypanosomiasis (“West African sleeping sickness”)
and T. b. rhodesiense, causing acute African trypanosomiasis (“East
African sleeping sickness”).
• The third subspecies T. b. brucei is a parasite primarily of cattle and
occasionally other animals, and under normal conditions does not
infect humans.
3.
4. Prevention and Control
There is no vaccine or drug for prophylaxis against African
trypanosomiasis. Preventive measures are aimed at
minimizing contact with tsetse flies. Local residents are
usually aware of the areas that are heavily infested and they
can provide advice about places to avoid.
• Wear long-sleeved shirts and pants of medium-weight
material in neutral colors that blend with the background
environment. Tsetse flies are attracted to bright or dark
colors, and they can bite through lightweight clothing.
• Inspect vehicles before entering. The flies are attracted to
the motion and dust from moving vehicles.
• Avoid bushes. The tsetse fly is less active during the hottest
part of the day but will bite if disturbed.
• Use insect repellent. Permethrin-impregnated clothing and
insect repellent have not been proved to be particularly
effective against tsetse flies, but they will prevent other
insect bites that can cause illness.
5. • Control of African trypanosomiasis rests on
two strategies: reducing the disease
reservoir and controlling the tsetse fly
vector.
• Because humans are the significant disease
reservoir for T. b. gambiense, the main
control strategy for this subspecies is active
case-finding through population screening,
followed by treatment of the infected
persons that are identified.
• Tsetse fly traps are sometimes used as an
adjunct. Reducing the reservoir of infection
is more difficult for T. b. rhodesiense, since
there are a variety of animal hosts.
• Vector control is the primary strategy in use.
This is usually done with traps or screens, in
combination with insecticides and odors
that attract the flies.
Editor's Notes
During a blood meal on the mammalian host, an infected tsetse fly (genus Glossina) injects metacyclic trypomastigotes into skin tissue. The parasites enter the lymphatic system and pass into the bloodstream . Inside the host, they transform into bloodstream trypomastigotes , are carried to other sites throughout the body, reach other body fluids (e.g., lymph, spinal fluid), and continue the replication by binary fission . The entire life cycle of African trypanosomes is represented by extracellular stages. The 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 . The cycle in the fly takes approximately 3 weeks. Rarely, T. b. gambiense may be acquired congenitally if the mother is infected during pregnancy.