48 



THF. HIMOFLACELLATES 



fly takes 15 to 35 days, and the flies are 

 not infective until the metacyclic trypano- 

 somes have appeared in the salivary glands. 



This type of development, in which the 

 trypanosomes are found in the anterior 

 part of the vector and are introduced by 

 its bite, is known as development in the 

 anterior station to contrast it with devel- 

 opment in the posterior station or hindgut. 

 In the latter, exemplified by the lewisi 

 group, infection is by contamination with 

 feces. 



In addition to the cyclical transmis- 

 sion described above, T. briicei may oc- 

 casionally be transmitted mechanically by 

 tsetse flies or other biting flies. In this 

 case, the trypanosomes remain alive in 

 the proboscis for a short time and are 

 transferred to a new host if the fly bites it 

 soon enough after having bitten an infected 

 one. 



mrtacjclic 



crithUiat* 



Fig. 3. Simplified life cycle of Trypano- 



sotna briicci. (From Noble, 1955) 



Pathogenesis : The signs and patho- 

 genesis of the trypanosomoses of domestic 



animals are more or less similar. Dif- 

 ferent hosts are affected to different de- 

 grees. Horses, mules and donkeys are 

 very susceptible to T. briicei. Affected 

 animals have a remittent fever, edema- 

 tous swellings of the lower abdomen, gen- 

 italia and legs, a watery discharge from 

 the eyes and nose, and anemia. The ani- 

 mals become emaciated altho their appe- 

 tite is good. Muscular atrophy sets in, 

 and eventually incoordination and lumbar 

 paralysis develop, followed by death. The 

 course of the disease is 15 days to 4 

 months, and untreated animals rarely re- 

 cover. 



The disease in sheep, goats, camels 

 and dogs is also severe. The signs are 

 much the same as in horses. In the dog, 

 fever may appear as shortly as five days 

 after infection, and the parasites often 

 cause conjunctivitis, keratitis and blind- 

 ness. 



The disease is usually more chronic 

 in cattle. There is remittent fever with 

 swelling of the brisket, anemia, gradual 

 emaciation, and discharge from the eyes 

 and nose. The animals may survive for 

 several months. Swine are more resistant 

 than cattle and usually recover. 



Following infection, the trypanosomes 

 appear first in the blood and lymph, caus- 

 ing fever, edema, anemia, etc. and only 

 later on are they able to invade the central 

 nervous system, causing incoordination, 

 paralysis and meningo-encephalitis. 



The exact way in which they act to kill 

 their victims is unknown, altho several 

 theories have been advanced. It is known 

 that they have a high glucose metabolism, 

 and one theory was that they rob the body 

 of glucose so that death is due to hypo- 

 glycemia. In experimental animals, life 

 can be prolonged by feeding glucose and 

 shortened by injecting insulin. This 

 theory, however, has been discredited. 



It is known that the serum potassium 

 level increases in trypanosomosis, and 

 another theory was that the effects are due 

 to the high potassium level. However, the 

 latter is a result of the disease and not a 



