Variant Surface Glycoproteins (VSGs) of Trypanosomes

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Trypanosomes

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 (95% of reported cases) and Trypanosoma brucei rhodesiense (5% of reported cases) responsible for sleeping sickness through its bite. The kissing bug (subfamily : Triatominae) spreads Trypanosoma cruzi when its feces 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.

Treatment

Symptomatic trypanasome infection is usually fatal if left untreated. While there is no vaccine or prophylactic drugs to prevent T. brucei infection there are drugs available for treatment a recent infection as well as cases that have already become symptomatic. The earlier the diagnosis is made the easier it is to manage symptoms with less toxic drugs that target the parasite outside of the central nervous system. once the infection has become symptomatic strong drugs with much higher toxicity must be used to cross the blood-brain barrier and attack the parasite in the CNS. If the infection has progressed to this point it is likely that a lengthy hospital stay is required to clear up infection.

Why Are Trypanosomes of Public health and Economic Interest?

African trypanosomiasis is of public health and economic importance for a number of reasons. Besides affecting humans, trypanosomes also infect domesticated cattle making cattle sick with disease called Nagana and hindering economic development in affected areas. Animals also serve as reservoirs to the parasites, most importantly T. b. rhodesiense making it difficult to eradicate the parasite in a given area. These parasites are only found within the tsetse flys’ geographic range, sub-Saharan Africa and have devastating economic effects on the people infected because of the length of infection and the nature of those infected. Those who rely on farming, fishing, and hunting are most at risk to be bitten by an infected tsetse fly and are also commonly the breadwinners in poor, rural populations.