African Trypanosomiasis and Tsetse Flies Essay

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BIOLOGY COURSEWORK
Nagana Disease (Specifically Trypanosomiasis Brucei)
The problem
The Tsetse fly (genus Glossina), a blood-feeding fly found in sub-Saharan Africa, is the main vector of the parasite protozoon trypanosome. As tsetse flies feed on animals (such as camels, cows and horses which are all susceptible to the disease) and humans they transmit trypanosomes into their blood stream. These trypanosomes cause a various forms of African Trypanosomiasis, which can be fatal to both humans and animals. In humans it is more commonly known as sleeping sickness and in animals its common name is Nagana (meaning “to be in low or depressed spirits” 1). Conservationists have referred to the tsetse fly as the “savior of Africa” because its presence has stopped farms and domesticated animals taking over the habitats of wild animals (interview with Natalie McComb). This is because most wild animals are not affected but these trypanosomes. Trypanosomiasis Brucei, which I will concentrate on in this study, is an acute form of Nagana disease. With initial symptoms of anemia, lethargy, diarrhea, fever and loss of appetite it is an extremely weakening disease. 2

Typanosomiasis brucei has three sub-species. Table 1 shows the scientific classification of Trypanosomiasis brucei. T. brucei brucei (one of these sub-species) is transmitted through the salivary gland of the tsetse fly, when the fly bites it injects saliva before it can start sucking blood and therefore it efficiently transfers the trypanosomes into the blood stream of its prey. 3

Table 1: scientific classification of Trypanosoma brucei
Scientific Classification

Kingdom:
Excavata
Phylum:
Euglenozoa
Class:
Kinetoplastea
Order:
Trypanosomatida
Genus:
Trypanosoma
Species:
T. brucei
Sub-species
T. b. brucei

T. b. gambiense

T. b. rhodesiense

Nagana disease can have detrimental effects on inhabitants of areas where livestock are susceptible to Nagana. The disease can be fatal within weeks 4 and if it not fatal then it can cause severe decreases in milk production and growth of cows. This can have terrible economic effects on the surrounding villages and families as a result of lack of income due to lack of animal produce, this also leads to lack of supplies to families reliant on the surrounding herd for meat and milk. It can also put horses out of work for weeks or months leading to loss of profit. Nagana disease must be controlled. There are several drugs that can be given to animals infected with Trypanosomiasis brucei brucei, which is the main solution for the disease however the tsetse fly population must also be managed and, in places where possible, eradicated.

Solutions
Chemotherapy
This is the use of drugs that can help to cure an already infected animal from the disease. Trypanocides (drugs which kill/inhibit development of trypanosomes) treat the disease by disrupting or stopping enzymes or metabolic pathways that lead to the formation of Trypanosomiasis. Trypanosomes affect the animal by “overwhelming” 5 their immune system and in order to overcome the disease completely they must have plenty of rest, food and water aswel as being administered the appropriate curative drugs.

Biologists try to find drugs that have minimal side effects meaning that the host cells are affected as little as possible. These are hard to find and as a result most drugs do have some negative effects and many drugs affect different animals in varying ways. For example Quinapyramine (one of the drugs used to treat T. brucei) is hardly toxic to dogs however has been known to cause fatality in pigs due to very high levels of toxicity. 5

Chemoprophylaxis
These are drugs used for prevention of diseases. They last longer in the animals system and therefore protect the animal for a longer period of time. These are administered at regular set intervals so that the concentration of the drug in the animals’ body fluid never drops below the curative
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