www.infonet-biovision.org - African Animal Trypanosomiasis / Nagana OLD

African Animal Trypanosomiasis / Nagana OLD

Common names:

Nagana / Tsetse Disease / Tsetse Fly Disease

General information on disease				Methods in tsetse and trypanosomiasis control
Tsetse biology				Information Source Links

General information on disease

Parasitic diseases that affect livestock are widespread in sub-Saharan Africa, particularly in arid and semi-arid areas. One of the most serious parasitic diseases is trypanosomiasis. This disease, which affects both human beings and livestock is transmitted by tsetse flies and covers approximately 10 million square kilometres in 38 African countries.

The tsetse flies transmit trypanosomes that affect human health, both directly through the sleeping sickness, and indirectly through the wasting diseases of livestock. The effect on livestock not only reduces the availability of meat and milk, but most particularly cattle and horses can not be used for transport and traction anymore. For agricultural communities, this means that only small areas can be tilled by hand. This leaves the communities vulnerable to food shortages.

African animal trypanosomiasis (AAT) is a disease complex caused by tsetse-fly-transmitted Trypanosoma congolense, T. vivax, or T. brucei brucei. African animal trypanosomiasis is most important in cattle but can cause serious losses in pigs, camels, goats, and sheep. Infection of cattle by one or more of the three African animal trypanosomes results in subacute, acute, or chronic disease characterized by intermittent fever, anemia, occasional diarrhea, and rapid loss of condition and often results in death. In southern Africa the disease is widely known as nagana, which is derived from a Zulu term meaning "to be in low or depressed spirits". (Foreign Animal Diseases)

The human-infective forms are subspecies of Trypanosoma brucei; they cause sleeping sickness or human African trypanosomiasis (HAT).

Host range:

Cattle, sheep, goats, pigs, horses, camels, dogs, cats and monkeys are susceptible to Nagana.

Symptoms:

Severity of disease varies with species and age of the animal infected and the species of trypanosomes involved. The incubation period is usually 14 weeks. The primary clinical signs are intermittent fever, anemia, and weight loss. Cattle usually have a chronic course with high mortality, especially if there is poor nutrition or other stress factors.

A presumptive diagnosis is based on finding an anemic animal in poor condition in an endemic area. The diagnosis has to be confirmed by demonstrating trypanosomes in stained blood smears or wet mounds. Other infections that cause anemia and weight loss should be ruled out by examining a stained blood smear.

In humans, the principal signs and symptoms of sleeping sickness are intermittent fever with enlarged lymph glands and spleen in the early stage, followed in the advanced or late stage by neurological symptoms and endocrine disorders.

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Tsetse biology

Tsetse are unique amongst important vectors, with a series of biological and demographic characteristics that make them very vulnerable to available control techniques. Their life cycle is unusual since they do not lay eggs. Instead, the female develops the egg and young larva within her uterus and lays the mature larva into shaded soil. The larva quickly burrows under the soil surface and pupates, and the adult emerges 20-45 days later depending on temperature (pupal development does not succeed below 17°C and above 32°C). Thus, each female produces only one offspring at a time. As a result, the tsetse population growth tends to be low. This means that even small increases in average daily mortality rate can cause a population to decline in number.

Tsetse are generally unable to fly for long periods. It has been argued that the flying time of tsetse is limited to about 15-30 minutes per day. At an average speed of 5 m/s the total distance flown per day would be between 4.5 and 9 km. The displacement in one day is estimated to be between 167m and 1.3km.

With these attributes - low reproductive rate and low dispersal capacity, combined with susceptibility to available insecticides - tsetse would appear to be highly vulnerable for well executed control measures. Indeed, past attempts to control tsetse were successful - until the tsetse control campaigns stopped. So when the control interventions were stopped, in most cases the controlled regions were left to reinvasion by tsetse from neighbouring areas.

This clearly shows the need for large-scale and community-based approaches.

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Methods in tsetse and trypanosomiasis control

Tsetse survival depends on detecting and encountering suitable hosts on which to feed. This can be used to design traps that mimic key features of host animals and attract tsetse so that they are then captured or killed. Trapping technology, which is often enhanced with attractant odours that attract and kill tsetse flies, is relatively simple and less polluting to the environment than insecticide application.

Tsetse trap

Insect specialists at icipe found out that tsetse flies are attracted to blue colour, prefer black cloth to land on and will use white colour as an orientation. According to this research findings, traps have been designed with blue/black/white cloth. To discourage theft, slits can be made in the blue cloth. To increase trap efficiency, cow urine is placed under the traps in plastic bottles. For a detailed description how to make a tsetse trap, see Technical brief on www.practicalaid.org (click here).

Trap densities: In the case of savannah species each fly may disperse up to 500 metres in a single day, so that with an average trap density of just four traps per km2, there is a high likelihood that each fly encounters at least one trap. However, species living in forests disperse little more than 5-10m per day, so that effective trap densities need to be very much higher.

Traps are relatively inexpensive and lend themselves to community participation. However, problems are experienced due to trap theft, vandalism, and damage by wildlife. To reduce theft of traps and vandalism requires at the very least a high degree of community education and awareness-raising. Such community awareness can be extended further to community participation, involvement of local people in control activities, and even community-based systems, such as management and financing.

More information on different models of tsetse traps available under http://www.vestergaard-frandsen.com/tsetse-brochure.pdf or http://www.vestergaard-frandsen.com/index.htm

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Information Source Links

Community-based Tsetse Fly Management through Use of Trapping Technology. Practical Action. The Schumacher Centre for Development and Technology. www.practicalaction.org Website to download technical brief
Foreign Animal Diseases, "The Gray Book". Online Version: www.vet.uga.edu
Kuzoe, F.A.S.; Schofield, C.J. / Strategic Review of Traps and Targets for Tsetse and African Trypanosomiasis Control. Special Programme for Research and Training in Tropical Diseases (TDR). UNICEF, UNDP, WorldBank, WHO.
Vestergaard Frandsen (Supplier of tsetse traps and other technologies for disease control in the tropics) www.vestergaard-frandsen.com

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