Variant Surface Glycoproteins (VSGs) of Trypanosomes

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Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.

By Kelly Wahl

Trypranasomes are single celled eukaryotic parasites (?) that infect humans and livestock causing trypanosomiasis, more commonly as sleeping sickness in Africa and Chagas disease in the Americas. These parasites are usually introduced into the body via an arthropod vector. The tsetse fly (subgenus Glossina morsitans), transmits the strains Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense responsible for sleeping sickness through its bite. The kissing bug (subfamily : Triatominae) spreads Trypanosoma cruzi through its feces which enter the body through the mucosal membranes, or broken skin (bite marks or scratches).

Trypanosome Infection; Sleeping Sickness, and Chagas Disease

Sleeping Sickness

Stage one of T. brucei infection is the haemolymphatic stage. Parasites circulate and multiply by binary fission in the blood and lymph systems. infection with T. b. rhodesiense often begins as a sore called a chancre and is followed a week or two of headaches, fevers, and muscle and joint pain. Enlarged lymph nodes are common and some patients also present with a rash. T. b. gambiense infection shows the same symptoms but they are not as severe and last for a longer period of time.

The second stage of infection is neurological. The parasites have crossed the blood-brain barrier and are now multiplying in the central nervous system. classic symptoms include impaired motor skills, seizures, confusion, and changes in personality. A disrupted circadian rhythm where a patient lies awake at night but sleeps during the day is where this disease gets its namesake. Without treatment the nuerological problems associated with T. b. rhodesiense infection progress to coma and death within a few months. The progression of T. b. gambiense infection takes much longer and a person can take years to show neurological symptoms.

Chagas Disease

Chagas disease is similar to sleeping sickness in many ways. There is an acute stage when the parasite is circulating in the bloodstream and the initial site of infection swells and a patient may present with a fever or show no signs of infection. One of the classic signs of acute chagas infection is Romana’s sign, the swelling of the area around the eye where the conjunctiva (mucosal tissue around the eye) or a site near the eye was point of infection. Serious symptoms are rare in this stage of infection but are possible. They include heart failure, chest pain, seizures, or paralysis.

Unlike sleeping sickness, chagas disease only progresses to the chronic form of the disease in 20 to 30% or people infected. The remaining 70 to 80% of people infected remain asymptomatic for life and may never know they are infected. As the parasite replicates in the target tissues; cardiac muscle and digestive smooth muscle those infected show a variety of cardiac problems such as irregular heartbeat, blood flow disorders, issues with heart muscle function, and blood clots. As well as problems with the digestive tracts such as ulcers.