Trypanosomiasis / Nagana
Scientific Name:Trypanosomiasis brucei
Local Names: Luo: tuo maugo, nyalolwe / Kamba: kamosu, ksiko / Kipsigis: kanyagat / Meru: mutombo / Gabbra: ghandi, ndukan, kando / Samburu: itikana, saar / Swahili: lotorobwo, ndorobo /Somali: agku, aino, angsulleh, attech, bargerish, dorobo, dukan, gandi, gindi, gundho, korbarar, malale, salaf, suuilleh / Turkana: edeke lo eidiit, lokipi, lotorob, tikana, lonyang / Maasai: Kububwuo, dorobo / English: Trypanosomosis/Trypanosomiasis
Common Names: Nagana, Surra, Dourine, Sleeping sickness
Description: Tse-Tse Fly transmitted disease
Host: Cattle, camels, pigs, donkeys, goats, sheep, horses, dogs and human
Tse-Tse Fly transmitted Trypanosomiasis is a parasite infection of cattle, camels, pigs, donkeys, goats, sheep, horses and dogs. It also affects humans as Sleeping Sickness. The disease occurs worldwide in tropical and sub tropical countries. It is caused by microscopically small blood parasites called Trypanasoma or, in short, Tryps. The major species are Trypanasoma congolense, Trypanasoma vivax, Trypanasoma brucei and Trypanasoma simiae.
In Kenya trypanosomiasis occurs where host, parasite and transmitting Tse-Tse flies occur together. This includes areas near Lake Victoria, Southern Kenya around Lake Magadi and the Nguruman Escarpment and the Mara, the Coastal areas and around Tsavo National Park. Transmission of T.vivax in cattle can sometimes be maintained in the absence of Tse-Tse flies through normal biting flies (Tabanids). This happens in areas bordering Tse-Tse infested zones where migrating infected cattle have introduced the Trypanosomes. - The cool Highlands and arid parts of North Kenya are free from Tse-Tse transmitted Tryps, except when infected animals are brought in from endemic areas.
In humans the disease is known as sleeping sickness.
Mode of Spread
The disease is transmitted in Africa by Glossina tsetse flies and in exceptional cases also mechanically by biting flies. Tsetse-transmitted trypanosomes are maintained in wild animals. Adult Tse-Tse flies are aggressive blood-suckers and seek out suitable hosts in daylight by sight and smell. Different fly species favour certain hosts. Warthog, eland, buffalo bushbuck, bushpig, duiker, certain reptiles and hippo are peculiarly sought out by certain flies. In these wild animals the disease is mild and symptomless and they act as reservoir hosts from which domesticated livestock can be infected.
|Adult Glossina Tsetse fly|
© John W. McGarry and the School of Vet Science in Liverpool
Animals are infected with trypansomes by the bite of an infected tsetse fly. Tsetse flies themselves become infected when they feed on an infected animal host: the ingested trypanosomes undergo a cycle of development in the fly lasting between 8 to 35 days before infective trypanosomes are produced. Once infected a fly is usually capable of transmitting trypanosomes for the rest of its life. Infection rates in wild populations of tsetse flies are normally low, varying from 1 to 20%.
All species of domestic animals are susceptible to infection but infections with tsetse fly transmitted Tryps are particularly important in cattle. African Zebus are fully susceptible to Tryps infection, but certain breeds of small hump-less West African dwarf-cattle i.e. the Ndama can be resistant.
Types of Tsetse Flies
Tsetse flies can be divided into three groups - forest, riverine and savannah. Trypanosomiasis becomes important when man and domestic livestock compete with wildlife and tsetse for graying land, or come into contact with tsetse as a result of other activities (e.g. cattle crossing into tste-tse infested riverine zones during drought).
Forest tsetse are of least importance as their habitat is frequently unsuitable for raising livesteock. Riverine tsetse are more important because they infest vegetation near essential water supplies. The most important are the savannah tsetse as the inhabit vast areas of land otherwise suitable for grazing animals. The flies prefer shade and have a limited flight distance. They tend to live along dry riverbeds, areas of thick bush and clumps of trees. From here they venture out during the day to feed on wild and domestic animals.
© John W. McGarry and the School of Vet Science in Liverpool
Biting flies are involved mainly in the transmission of T. evansi in camels which is transmitted by tabanid camel flies.
Tabanid flies are persistent, aggressive feeders, annoying the host so that feeding is often interrupted, thus ensuring that several new hosts may be bitten, increasing the possibility of multiple infections. Wildlife normally plays little or no part in the transmission of trypanosomiasis in camels.
Signs of Trypanosomiasis
Trypanosomes appear in the blood of infected animals from between 3 to 16 days after initial exposure, the time factor being dependant on the species of trypanosome. Trypanosomes vary in their grade of attack. Trypanosoma vivax can cause a severe, rapidly deadly disease with a characteristic haemorrhagic syndrome, Trypanosoma brucei in cattle can be quite mild, while Trypanosoma congolense varies in severity. Mixed infections can also occur.
The primary clinical signs are periodic fever, anaemia, and weight loss. In cattle it is a long-lasting (chronic) disease with a high mortality. Rapid onset severe (acute) infections occasionally occur, notably with T. vivax in cattle.
- Infected animals are usually tired and weak and are left behind by the rest of the herd. There is an intermittent fever. They appear sleepy, have rough, dull coats, progressive anaemia and lose condition.
- Superficial lymph nodes are usually enlarged and prominent, sometimes leading to a mistaken diagnosis of ECF.
- The animal has a foul smell that slme herders can recognize.
- There is a severe drop in milk production.
- There is a watery discharge from the eyes of sick animals, especially those infected with T. vivax, and the eyes of such animals are cloudy and blink a lot.
- Paleness of the gums, under the tongue and inside the eyes becomes visible after several weeks of infection.
- Pregnant animals abort or give birth to weak offspring while some animals become infertile.
The disease can become more severe due to accompanying factors like poor nutrition, stress and over working. Some animals recover very slowly without treatment while others become very sick, collapse and die after a few months.
The area, the presence of tsetse flies, the appearance of weak, anaemic, sleepy and tired, emaciated animals should be a warning sign that they may be infected with trypanosomiasis. Vets can check for trypanosomes by directly examining a fresh blood sample under the microscope. Tryps can also be seen in dried and stained blood smears, but chances of finding the tryps are lower than in fresh blood. If fresh liquid blood samples have overstayed, it can be difficult to see the Tryps under the microscope.
The use of small field centrifuges has helped greatly in Tryps diagnosis in the field. Other diseases can be confused superficially with trypanosomiasis, so demonstration of the parasite is most important. Hence the alerting of a skilled veterinarian is vital to obtain a diagnosis. ECF in acute cases, and worm infestations and malnutrition in chronic cases can be confused with trypanosmiasis.
Prevention and Control
Avoid fly-infested areas and minimize contact between livestock and wild animals.
- The use of insecticidal attractants in tsetse traps has considerably reduced tsetse fly numbers in the areas which they have been used, utilising the fact that tsetse flies are attracted to colours such as dark blue. These traps should be used wherever possible. Trapping technology is relatively simple and less polluting to the environment than insecticide application.
- Take animals to water when fly activity is low, flies are inactive at night – so crossing a river or watering in the dark is an option.
- Repel flies with smoke from smouldering cow dung.
- Seperate sick animals from healthy ones. The disease is not contagious but when cattle are together they attract flies, which may transmit infection.
- Use of less tryps sensitive breeds of cattle such as Orma Boran.
- Clear thick bush to reduce tsetse habitat.
- Use insecticidal pour-ons on cattle such as Cypertick and Ectomin (not organic and mostly useless).
- Frequent spraying and dipping of animals.
- Use preventative anti-Tryps drugs (called trypanocide or trypanocidals) such as Samorin and Suramin – one injection prevents Tryps infection for many weeks.
- Good nutrition, especially where exotic breeds are reared.
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 incease trap efficiency, cow urine is placed under the traps in plastic bottles.
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 www.vestergaard-frandsen.com.
No new drugs for either treatment or prevention have been developed for a very long time so it is vital to use those few that are available properly to avoid drug resistance. Most importantly animal bodyweights should not be underestimated. The following treatments can be used:
- Berenil, Norotryp, etc (Diminazine aceturate): other names Trypazen, Diminazen. Should be prepared by mixing 2.36 g of powder with 12.5 ml of clean water. The mixture should be given as injection at 3.5 mg/kg body weight in the muscle. This amounts to one sachet per 300 kgs bodyweight.
- Novidium (Homidium chloride or bromide): other trade name Ethidium. Can be prepared by mixing 1 tablet 250 mg in 10 litre of sterile clean water and used soon after mixing at 1mg/kg body weight injected deep into the muscle.
- Samorin or Trypamidium (Isometamidium chloride): other trade names Trypacide. It can be prepared by mixing 125 mg of powder in 12.5 ml of clean sterile water and ensuring that all the powder dissolves. Inject the mixture deep intramuscular injection into the neck or slowly intravenously and ensure that medicine goes into the vein. The mixture should be used within 2 days.
- Samorin can be used to prevent the disease, given at intervals of about 4 months. Check dose rate and give according to the correct body weight.
- Camels: Use Tryquin as Berenil can be toxic to camels.
Common Traditional Practices
Traditional practices have been recorded, but no official testing has been carried out to confirm of disapprove the efficacy. Therefore it is highly recommended for all communities to use the methods of control that have been tested and found effective in order to keep their livestock healthy and alive.