African trypanosomiasis, also called sleeping sickness, is a fatal disease if left untreated. This disease is transmitted most of the time by the tsetse fly. African trypanosomiasis besides affecting humans, can also often affect hoofed animals, and domesticated animals such as dogs and cats. Besides being transmitted by the tsetse fly, this disease can also be transmitted from animals to humans. The etiologic agent of this disease is Trypanosoma spp., which is a protozoan parasite. (5) Trypanosoma spp.'s life cycle is similar in all the African varieties of the disease. The life cycle starts when a tsetse fly ingests blood from a host that is infected with trypomastigotes. The parasite reproduces in the gut of the fly, and makes its way to the salivary glands, where it transforms into metacyclic trypomastigotes. During feeding, the fly injects the cyclic trypomastigotes into the new host. The metacyclic trypomastigotes transform in the blood stream back to trypomastigotes. The trypomastigotes reproduce by asexual means in the blood stream of the host. (1) The cycle then starts all over again. In some instances, the disease is spread by mechanical factors. This means that there is no reproduction of the etiologic agent within the vector.
Identification of current infection of trypanosomiasis involves several types of tests. For example, inspection of chancre liquid and also lymph fluid can identify whether or not one has the disease. Also, a wet mount should be done to look for the motile trypanosomes. Making sure these preparations involve a concentrated version of the fluids ensures that there will be indeed something to observe. Concentration practices can involve the use of a centrifuge, then examining the fluid of the buffy coat. Another possible identification plan is currently being investigated. This involves the use of antigen detection. This could be particularly useful while the scientist is in the field. It should also be noted that transmission could occur by crossing the placenta from mother to fetus. (4)
One of the causative agents of trypanosomiasis, Trypanosoma brucei gambiense, was identified by Ford and Dutton in 1902. In 1903, David Bruce identified that the tsetse fly was the primary vector of this disease. It wasn't until 1906 that a basic treatment for the disease was starting to be used. The substance used, Atoxyl, is an arsenic compound. This substance is quite toxic, as proved in 1932 when "700 patients became blind after receiving the wrong dose of Atoxyl." (2) Due to this catastrophe, a Swiss chemist named Friedheim came up with the drug called melarsoprol, which finally in 1960 was used for treatment of trypanosomiasis. Melarsoprol was only used when the disease had progressed to the point where the central nervous system was being affected.
The first initial symptoms of sleeping sickness include high fever, headache, joint pain, weakness and general malaise. There can also be itching, especially at the point of inoculation. Eventually, the immune system of the host becomes weaker and weaker. As the progression of the disease occurs, symptoms become worse. The parasite can cross the blood brain barrier, and this is when the problems with the central nervous system begin. Confusion, coordination problems and other issues manifest. (3) If the disease is left untreated, the damage to the CNS is permanent. Endocrine problems, cardiovascular disorders, swelling (edema) and kidney problems persist. Finally, if left untreated, the disease causes coma and eventually death.
There are several ways in which the virulence of trypanosomiasis is increased. The means by which microbial virulence is increased is known as a process called "antigenic variation." Trypanosomes can become resistant to the host's immune system by altering their surface membrane. Also, a trypanosome "can express thousands of variants, multiplying with each new surface change."(2) Another way that virulence can be increased, although not a microbial factor, is by the changing weather patterns. Tsetse flies prefer humid weather conditions. When there is a particularly humid season, the tsetse fly will proliferate, causing more disease. Certain insecticides used to control the tsetse fly population sometimes are rendered useless, due to the tsetse fly becoming resistant. This is another way in which virulence is increased.
Treatment for trypanosomiasis depends on what stage the disease is in. Also, therapy will depend on which species of the parasite caused the disease. (3) At the present moment, there are still investigations being done to find an appropriate treatment for the sleeping sickness. If the disease has developed to the point of affecting the central nervous system, the drug still used for treatment is Melarsoprol. (2) One of the important criteria for trying to beat this disease is the current method for controlling it. Control of the disease is a multi million-dollar effort, and usually takes on three stages. The first stage consists of a "mobile medical surveillance" unit, which uses a variety of diagnostics to determine which stage of the disease the patients are in. (2) The second stage involves sending blood samples on a regular basis to a medical center to be analyzed, and treatment will presume if necessary. The last stage of control for this disease involves vector control. This can include not only spraying with insecticides, but also using traps and screens. Having screens on windows and doors is an easy, and cheap way to keep these menaces out of the home. Spraying of the tsetse fly is not only expensive, but also the insecticides used are thought by some to be a source of health problems as well. The active ingredient in the spray is called Endosulphan, known to be toxic. One very important method for controlling the tsetse fly is by game control. (5) The tsetse fly does not travel; they only stay on or near a particular herd of cattle, or sheep. Consequently, if we can control where these animals go, then spray or use traps in this general vicinity, then we have an effective means of eradication.
Currently, there is no effective vaccination against sleeping sickness. It is strongly recommended to wear protective clothing if going into an area where bites from the tsetse fly are possible. The tsetse fly can bite through light clothing, so it is recommended that one wears thick long sleeve shirts and pants to avoid a bite. The fly is attracted to either very bright, or very dark colors, so keeping clothes in a neutral shade, like khaki can possibly add to protection. Also, the fly is attracted to the dust that is caused by a moving vehicle, or a moving herd, so those who are visiting or working in a game park need to observe from a vehicle that offers protection in the form of windows.
In conclusion, this disease is a major problem to those who live in tropical areas of Africa. Without proper vaccines available, prevention calls for ongoing research. It is estimated that 25,000 new cases are reported each year in Africa. The tsetse fly is a tough opponent in this war, as they can express so many variations, which make them so difficult to eradicate completely. Hopefully, with the advancement of modern scientific techniques, we can find a vaccination that would be effective against this menacing disease.
References
1. "Life Cycle of Trypanosoma Spp." No author given. Accessed 5/4/02. http://www.biosci.ohio-state.edu/~parasite/lifecycles/trypanosoma_lifecycle.html
2. "Trypanosomiasis." No author stated. Accessed 5/2/02. http://www micro.msb.le.ac.uk/224/Trypano.html
3. "Trypanosomiasis, African." Last modified 10/29/01. No author given. Accessed 5/4/02. http://www.dpd.cdc.gov/dpdx/HTML/TrypanosomiasisAfrican.htm
4. "African Trypanosomiasis or Sleeping Sickness." March, 2001. No author given. Accessed 5/5/02. http://www.who.int/inf-fs/en/fact259.html
5. "Trypanosoma brucei (rhodesiense)." No author given. Accessed 5/1/02. http://www.medinfo.ufl.edu/year2/mmid/bms5300/bugs/rhodesie.html