Sleeping sickness, also known as Human African Trypanosomiasis (HAT), is caused by Trypanosoma brucei rhodensiense in Eastern Africa and Trypanosoma brucei gambiense in Western Africa. Both protozoan species are morphologically identical, but have drastically different epidemiological features. Several species of hematophagous glossina, commonly known as tsetse flies, are the vectors of these related diseases, and are responsible for cyclical transmission of the parasitic protozoan between numerous vertebrate hosts. Both forms of sleeping sickness affect the central nervous system. The term “sleeping sickness” is derived from the West African form of trypanosomiasis, primarily because invasion of the cerebrospinal fluid and brain after infection of the blood is often delayed, resulting in symptoms of extreme fatigue that can last for several years before the severe phase of the disease sets in; toxemia, coma and death. In contrast, the typical East African form of trypanosomiasis is characterized by rapid and acute development of the disease, and untreated patients can die within weeks or months of infection.
Saturday, November 20, 2010
What Are The Symptoms?
For West African Trypanosomiasis:
- Fever
- Severe Headache
- Irritability
- Fatigue
- Swollen Lymph Gland
- Aching Muscles and Joints
- Weight Loss
- Body Rash
- Fever
- Rash
- Swelling Around the Eyes and Hands
- Severe Headache
- Fatigue
- Aching Muscles and Joints
- Swollen Lymph Glands On the Back of the Neck
- Infection of the Nervous System
- Personal Changes
- Loss of Concentration
- Confusion
- Slurred Speech
- Seizures
- Difficulty In Walking and Talking
- Sleeping Long During the Day, but Having Trouble At Night
Where Does This Happen?
The earliest recorded major epidemics of sleeping sickness took place in Uganda and Congo between 1896 and 1908, where roughly 500,000 people were estimated to have died in the Congo Basin, and approximately 300,000 died in Busoga, Uganda. With the Rift Valley transecting the country, Uganda is in the precarious position of having foci of both forms of diseases which resulted in two other major epidemics of sleeping sickness - one in the late 1940's and another in 1980. Throughout West Africa, smaller epidemics of sleeping sickness rapidly spread from Senegal to Cameroon during the 1920's, and died down by the late 1940's.
What Causes It?
There are 31 species and subspecies of tsetse flies under the genus Glossina, family Glossinidae, and order Diptera. Although the tsetse flies can be found over some 9 million squared kilometers of the African continent, presence of glossina populations throughout the continent are far from continuous. In general, the Sahara and Somali Deserts limit the populations in the north, extending across the entire continent from Senegal in the west to southern Somalia in the east. Tsetse populations are denser in West and Central Africa, and are found more at irregular intervals to the East and down to the borders of the Kalahari and Namibian Deserts in Southern Africa. Unlike other insects, there are no seasonal interruptions in the life cycles of tsetse flies. Below The diagram further explains the involvment of the tsetse fly in the process of infection of African Trypanosomiasis.
Life Cycle Of the Vector
Unlike most insect species that produce large quantities of eggs, fertilized female tsetse flies “give birth” to one larva. A typical female tsetse fly will produce one full grown larva approximately every 9-10 days depending on temperature and humidity. A single egg will hatch and develop to a third-stage larva in the uterus of the female fly, where it is nurtured and supplied with nutrients. This reproductive process is known as adenotrophic viviparity . This form of reproduction ensures the higher degree of survival of each offspring, but is also the reason why reproductive rates are considerably low in tsetse fly populations. Larviposition takes place when the third-instar larva is deposited onto a suitable site, usually soil or sand depending on the species, and the larva burrows down to its optimum depth to become a pupa. Usually an adult fly will emerge after the puparial period which varies according to temperature but on average is around 30 days at 24°C. Longevity of the adult fly varies greatly according to seasonal factors. For the general tsetse population to increase, it is critical that the average female lifespan exceed 36 days. During perfect conditions, female flies can live as long as 3 months, producing as much 10 offspring during her lifetime.
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| Anatomy Of A Female Tsetse Fly |
Life Cycle Of Human African Trypanosomiasis
African trypanosomes are extracellular organisms, both in the mammalian and insect
host. Infection in the human host begins when the infective stage, known as the metacyclic
stage, is injected intradermally by the tsetse fly. The organisms rapidly transform into blood-stage trypomastigotes (long, slender forms), and divide by binary fission in the
interstitial spaces at the site of the bite wound. The buildup of metabolic wastes and cell
debris leads to the formation of a chancre.
What Should I Do?
Today, there are only a handful of active drugs available for treatment of human African Trypanosomiasis. No significant development has been made over the last 2 decades. The current line of treatment is problematic for many reasons: firstly, the drugs are harmfully toxic requiring extensive hospitalization. Secondly, regular follow-ups to check for relapse are essential but difficult in many of the areas where sleeping sickness is endemic.
Drugs Available For Treatment Of HAT
- Suramin
- Pentamindine
- Melarsoprol
- Eflormithine
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