TRYPANOSOMOSIS (Nagana)

Trypanosomosis, or Sleeping Disease is an infection affecting both animals (cattle, sheep, goats, horses and donkeys) and humans. The disease mainly occurs in areas where Tsetse flies inhabit. Tsetse flies infest 10 million square kilometers and affect 37 countries, mostly in Africa, where it is known as ‘Nagana’. It is the most economically important livestock disease of Africa, as it can have a devastating impact on rural areas as it continues to be a serious threat to livestock production and sustainable rural development. In Botswana, Trypanosomosis is usually transmitted from one animal to another through blood lymph and other fluids of infected animals by blood sucking tsetse flies- Glosina morsitans centralis which is confined to the Okavango Delta and Kwando/Linyati rivers in Ngamiland and Chobe districts. The disease can also be spread by biting flies like Tabanas, Stomoxys and Hippobosca species as well as through the needle during inoculations. Wild animals and chronically infected animals can act as carriers.

 

Symptoms
Symptoms often begin to show 8- 24 days after infection. The most important clinical sign is non-regenerative anemia.

The major clinical signs are:

  • intermittent fever
  • anemia
  • edema
  • apathy (lack of interest, enthusiasm, have a dull mood)
  • pale mucous membranes
  • ocular discharge
  • teary
  • enlarged lymph nodes
  • abortion
  • decreased fertility
  • loss of appetite, body condition and productivity( as a wasting disease, affected animals are chronically unproductive in terms of milk, meat, manure and traction with mortality rates possibly being high)
  • occasionally there is diarrhoea and cachexia
  • early death in acute forms
  • progressive emaciation (being abnormally thin and weak) and eventual death in chronic forms often after digestive and/or nervous signs

Diagnosis

  • Blood samples are taken and detection of blood trypanosomes in the blood is done
  • Standard serological tests are done at the National Veterinary Laboratory.
  • Clinical signs like enlargement of the lymph nodes, progressive anemia and constant body weight loss are indicators of the disease.
  • History of increase in the number of tsetse flies in the district can also raise alarm on the disease.

Treatment and Prevention

  • At present no vaccine is available.
  • If detected early, Trypanosomosis can be treated with trypanocidal drugs for therapeutic and prophylactic purposes.
  • Therapeutic drugs for cattle include diminazene aceturate (Berenil), homidium chloride (novadium) and homidium bromide (ethidium). Prophylactic drugs for cattle include homidium chloride, homidium bromide and Isometamidium (Samorin or Trypamidium). Berenil is not well tolerated by horses.
  • However the effectiveness of these drugs is now questionable following years of use, causing resistance and now various strains of Trypanosomosis occur.
  • Another area of control that has been studied is to eradicate the tsetse flies which transmit the disease.
  • The most common of the procedures that have been developed are:

Aerial spraying with Endosulfan on tsetse habitat to reduce their numbers.

Odour-bait technique (OBT) using Deltamethrin: these are essentially cloth screens (blue/black) mounted on metal frame. To a tsetse fly the simple device looks and smells like a host animal, but is lethal following the slightest contact

Sterile Insect Technique (SIT): Sterile male tsetse flies are released.in this way the population of these flies is reduced.

Destruction of tsetse habitat and alteration of vegetation so that it becomes unsuitable for tsetse flies.

  • However, these methods are costly and require a high level of management, organization and specialist expertise.
  • Good husbandry and use of trypanotolerant (trypanosome resistant) breeds of animals can be the better option.