AFRICAN ANIMAL TRYPANOSOMIASIS By Sumbu Mbilika

African Animal Trypanosomiasis (AAT) is a parasitic disease that causes serious economic losses in livestock from anemia, loss of condition and emaciation. Many untreated cases are fatal. It is called nagana in livestock and other wild animals and African sleeping sickness in humans. AAT is found mainly in those regions of Africa where its biological vector, the tsetse fly, exists. One organism, Trypanosome vivax, has become established in South America, where it is transmitted by biting flies acting as mechanical vectors. Protecting animals from Trypanosomiasis is difficult in endemic areas, as bites from tsetse flies and a variety of other insects must be prevented.

Animals Affected

Trypanosomes can infect all domesticated animals; clinical cases have been described in cattle, water buffalo, sheep, goats, camels, horses, donkeys, alpacas, llamas, pigs, dogs, cats and other species. In parts of Africa, cattle are the main species affected, due to the feeding preferences of tsetse flies; in effect, they can shield other domesticated animals such as goats and pigs from the effects of Trypanosomiasis. More than 30 species in the wild or zoos, including ruminants such as white-tailed deer, duikers, antelope and African buffalo, as well as wild Equidae, lions, leopards, warthogs, capybaras, elephants, nonhuman primates and various rodents are also known to be susceptible to infection.

When an infected tsetse fly bites an animal, the parasites are transmitted in the saliva. Trypanosomes can also be spread by fomites and mechanical vectors including surgical instruments, needles, syringes and various biting flies including horse flies (Tabanidae family). The immune response is unable to completely eliminate trypanosomes and animals can become inapparent carriers and this includes the African Buffalo. These unapparent infections can be reactivated if the animal is stressed.

Signs and Symptoms

African Animal Trypanosomiasis symptoms occur in two stages. The first stage, known as the haemolymphatic phase, is characterized by fever, headaches, joint pains, and itching. Invasion of the circulatory and lymphatic systems by the parasites is associated with severe swelling of lymph nodes, often to tremendous sizes. Winter bottom's sign, the tell-tale swollen lymph nodes along the back of the neck, may appear. If left untreated, the disease overcomes the host's defences and can cause more extensive damage, broadening symptoms to include anaemia, endocrine, cardiac, and kidney dysfunctions. The second, the neurological phase, begins when the parasite invades the central nervous system by passing through the blood–brain barrier. The term 'sleeping sickness' in humans comes from the symptoms of the neurological phase. The symptoms include confusion, reduced coordination and disruption of the sleep cycle, with bouts of fatigue punctuated with manic periods, leading to daytime slumber and night-time insomnia. Without treatment, the disease is invariably fatal, with progressive mental deterioration leading to coma and death. Damage caused in the neurological phase is irreversible.

Treatment

All animals diagnosed with African Trypanosomiasis should receive treatment. The specific drug and treatment course depends on the type of infection. Medicine such as Pentamidine, is the recommended drug for first stage of infection. The other drugs such as suramin, melarsoprol, eflornithine, and nifurtimox are used to treat African trypanosomiasis. They further go one explaining that there is no test of cure for African trypanosomiasis. After treatment patients need to have serial examinations of their cerebrospinal fluid for 2 years, so that relapse can be detected if it occurs. The infection can also be treated with a variety of antifungal agents, including benznidazole and nifurtimox. Melarsoprol is another drug which is used for the treatment. Diminazene, homidium, isometadium, suramin, and melarsomine can all be used to treat infections. Resistance is increasing in endemic areas and recurrent treatments may be necessary. The use of trypanotolerant (animals resistant to the disease) breeds for livestock farming should be considered if the disease is widespread.

Control/Preventative Measures

Most trypanosomes are transmitted by tsetse flies and can only become established in areas where these vectors exist. If the outbreak is detected early, this organism might be eradicated by quarantines, movement controls and the euthanasia of infected animals. Trypanosomes cannot survive for long periods outside the host and disappear quickly from the carcass after death. Controlling arthropod vectors is important in preventing new infections. African Animal Trypanosomiasis can be controlled by reducing or eliminating tsetse fly populations with traps, insecticides and other means and by treating infected animals with anti-parasitic drugs. Animals given good nutrition and rested are more likely to recover rapidly than undernourished and stressed animals. No vaccines are available for Trypanosomiasis. Tsetse fly transmitted trypanosomes can be prevented by simply avoiding tsetse flies for example, by demarcation of tsetse fly free grazing, planning trek routes to avoid tsetse habitat and by transporting livestock in motorized vehicles. Indeed farmers and stockmen accrue a great deal of skill and local knowledge over this common-sense approach to the problem. In general, tsetse fly control is very costly and requires a high degree of management, organization and specialist expertise.

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