Back To CourseUExcel Microbiology: Study Guide & Test Prep
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Angela has taught college Microbiology and has a doctoral degree in Microbiology.
Let's play make-believe for a minute: You have just graduated college and sweet, old grandma has rewarded you by sending you on an African safari. While out viewing the giraffes, you're bitten on the arm by a big, nasty fly. That fly injects you with a parasite. Fortunately, your body quickly identifies the parasite and begins building up an immune cell army to kill it. Within two weeks, the army is fully assembled, but the parasite is nowhere to be found.
Instead, your body now has a new parasite that looks a bit like the original, but different enough that the army doesn't recognize it. Not a problem, you are more than capable of building up a new army, but after two more weeks, the parasite is, again, nowhere to be found. This arms race can go on almost indefinitely. To make matters worse, you can't seem to stay awake, sleeping throughout the day and night, and you just don't feel like yourself anymore. Eventually, you'll have to seek treatment, or you'll die!
This is not the plot of the latest medical thriller. In fact, it is the typical disease process associated with Trypanosoma. Trypanosoma brucei is a protozoan parasite that causes African sleeping sickness. The parasite is thin and crescent-shaped with flagella for motility. All Trypanosoma look indistinguishable, but two varieties exist that differ in the pace of the disease. The varieties are T. brucei gambiense and T. brucei rhodesiense. For this lesson, most of the information will apply to both varieties. Where there are distinctions, I will make them clear.
There is one major distinguishing characteristic of the Trypanosoma lifecycle that you need to remember: Trypanosoma can only be transmitted through the bite of an infected tsetse fly. This fly lives only in equatorial Africa. There have been no reported cases of human-to-human transmission of the infection. In Africa, very few tsetse flies actually harbor the parasite, but when the fly feeds on the blood of an infected organism, like a human, sheep, or cow, it picks up Trypanosoma.
The parasite reproduces by binary fission in the intestine of the fly before invading the salivary glands. It takes about three weeks from when the fly ingests the parasite until it reaches the saliva. Now, when the infected tsetse fly bites another organism, the Trypanosoma in the saliva are injected into the skin and invade the lymphatic vessels. From there, they invade the bloodstream and are pumped throughout the rest of the body, infecting all other bodily fluids, while increasing in number by binary fission. Eventually, the Trypanosoma invade the spinal fluid and infect the central nervous system. If you haven't already guessed it, this is bad.
Besides a very painful bite, a person bitten by an infected tsetse fly is in for some other unpleasant symptoms. Within one to three weeks, the bite will form a hard, red nodule that is swollen and painful. Then, the lymph nodes begin to swell, accompanied by fever, severe headaches and fatigue. Now, the disease earns its name, African sleeping sickness, because the infected person begins to sleep long hours during the day. This is accompanied by behavioral and personality changes, such as a decreased ability to concentrate, speak and walk, as the parasite begins to cause inflammation of the brain and spinal cord. The person begins to waste away before slipping into a coma with death to follow.
That sounds pretty bad, but the way this plays out can differ depending on which variety of Trypanosoma causes the infection. In people infected with T. brucei gambiense, the disease process, from infection to death, can take up to seven years. Usually, symptoms are mild and intermittent for months and don't lead to severe symptoms and death for about three years. In contrast, T. brucei rhodesiense causes a much more acute disease. Severe symptoms appear in a couple of weeks, with death coming within a couple of months.
In remote African villages, infection with Trypanosoma can seem pretty dire, but with access to medical care, Trypanosoma is easy to positively diagnose, even at the early stages. A doctor can look for Trypanosoma parasites microscopically in samples from the lymph nodes, blood or spinal taps. Their characteristic cell shape helps in identification. There are blood tests available, but in this case, visual identification is usually quicker, easier and all that is required.
If the diagnosis is positive, treatment is obviously required. African sleeping sickness is 100% fatal without treatment, and natural immunity will not occur. Remember how our African safari story included an immune systems arms race? Well, this is completely accurate. Trypanosoma can change its surface antigens to stay one step ahead of the immune system. By the time the immune system has made antibodies for those antigens, the Trypanosoma switches them up, rendering the antibodies useless. This also means that vaccinations are unlikely to be effective, and that reinfections are possible.
If caught early, Pentamidine can be used to eliminate Trypanosoma from the body with good success. If the disease has had a chance to spread to the brain, treatment requires drugs that can cross the blood-brain barrier to fully eliminate the parasite. These drugs are often more toxic and have more side effects. By this time, the patient requires hospitalization.
The treatment is not the end of the road, unfortunately. People that are treated for Trypanosoma need regular spinal taps for two years to ensure the disease has been fully eradicated.
Now, don't suddenly start obsessing over every bug bite just yet. The tsetse fly that spreads Trypanosoma only lives in Africa, and even in Africa it is only in 36 countries. Cases in the United States are rare, and always occur in people that have recently traveled to Africa. Within those 36 equatorial countries in Africa, however, the disease is quite severe. Estimates put new cases of sleeping sickness per year anywhere between 10,000 and 500,000. The range is so large because many cases go unreported and undiagnosed. It is estimated that there are 65,000 deaths from African sleeping sickness every year.
There are a couple of preventative measures. Clearing brush and tsetse fly breeding areas can reduce the fly population. People living and traveling in affected regions of Africa can wear insect repellent, cover exposed skin with medium-weight fabrics, and thoroughly clear buildings and vehicles of flies before use.
Let's review: The protozoal parasite Trypanosoma brucei causes African sleeping sickness in equatorial Africa. The disease is spread by the bite of an infected tsetse fly. The parasite spreads through the body via the blood and lymph, causing fevers, headaches and swollen lymph nodes. Eventually, the disease will spread to the brain, causing neurological problems, coma and death.
Finding Trypanosoma microscopically in blood, lymph and spinal samples is the accepted method of diagnosis. If caught early, the disease can be treated with Pentamidine. If neurological symptoms have developed, a drug that is capable of passing the blood-brain barrier is required, which can cause more side effects. Regular testing is required for two additional years to ensure the disease has been eliminated.
Due to the adaptive nature of the parasite, no natural immunity or vaccination can prevent infections. Clearing fly habitats, using insect repellents and covering exposed skin are the best methods available for preventing infection.
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Back To CourseUExcel Microbiology: Study Guide & Test Prep
28 chapters | 238 lessons