THE HEMOFLAGELLATES 



47 



In the discussion which follows, each 

 trypanosome species is taken up separ- 

 ately, but special attention is paid to 

 T. briicei and T. criizi as representatives 

 of different types. 



TRYPANOSOMA BRUCEI 

 PLIMMER AND BRADFORD, 1899 



Synonym : T. pecaudi. 



Disease : Trypanosomosis, nagana. 



Hosts : Horse, mule, donkey, ox, 

 zebu, sheep, goat, camel, pig, dog, and 

 many wild game animals. Antelopes are 

 the natural hosts of T. brncei and serve 

 as reservoirs of infection for domestic 

 animals. Experimental attempts to infect 

 man have failed (Ashcroft, 1959a). 



Location : Blood stream, lymph, 

 cerebrospinal fluid. 



Geographic Distribution : Widely dis- 

 tributed in tropical Africa between 15^ N 

 and 25° S latitude, coinciding with the dis- 

 tribution of its vector, the tsetse fly. 



Prevalence : T. brucei is one of the 

 commonest and most important parasites 

 of domestic animals in Africa. It has pre- 

 vented the raising of livestock in vast 

 areas. 



Morphology : Polymorphic, with 

 slender, intermediate and stumpy forms. 

 Undulating membrane conspicuous. Ki- 

 netoplast small, subterminal. Slender 

 forms average 29 /i in length but range up 

 to 42 (i; posterior end usually drawn out, 

 tapering almost to a point, with kineto- 

 plast up to 4jj, from posterior end, with a 

 long, free flagellum. Stumpy forms stout, 

 averaging 18 ju in length with a range of 

 12 to 26 /i; posterior end broad, obtusely 

 rounded, with kinetoplast almost terminal; 

 free flagellum typically absent. Interme- 

 diate forms average 23 jj. in length; body 

 of medium thickness, with blunt posterior 

 end; moderately long free flagellum al- 

 ways present. A fourth form with a 

 posterior nucleus often appears in labor- 

 atory animals. 



Life Cycle : When it is first intro- 

 duced into the body, T. bnicei multiplies 

 in the blood and lymph by longitudinal 

 binary fission in the trypanosome stage, 

 being particularly common in the lymph 

 glands. Later the trypanosomes pass into 

 the cerebrospinal fluid and multiply here 

 and between the cells of the brain. Leish- 

 manial forms have also been reported 

 from the heart muscle of infected monkeys 

 (Noble, 1955). 



The vector is a tsetse fly of the genus 

 Glossina. T. brucei is generally trans- 

 mitted by members of the iiiorsifans group 

 of this genus, i.e., G. uiorsilaiis, G. 

 sivynnertoni and G. pallidipes. Both males 

 and females feed on blood and act as vec- 

 tors. Only a small percentage of the tsetse 

 flies which feed on an infected animal be- 

 come infected, most being apparently re- 

 sistant. In experimental studies, 10% or 

 less become infected, while less than 1% 

 of wild flies caught in endemic areas are 

 infected. 



When ingested by a tsetse fly, T. bru- 

 cei localizes in the posterior part of the 

 midgut and multiplies in the trypanosome 

 form for about 10 days. At first the try- 

 panosomes are relatively broad, up to 

 35/i long, with a kinetoplast about halfway 

 between the posterior end of the body and 

 the nucleus, with a less pronounced undu- 

 lating membrane than the blood form, and 

 with a free flagellum. On the 10th to 12th 

 day, slender forms appear and migrate 

 slowly toward the proventriculus, where 

 they are found on the 12th to 20th days. 

 They then migrate forward into the esopha- 

 gus and pharynx, thence into the hypopharynx 

 and finally into the salivary glands. Here 

 they attach themselves to the walls by their 

 flagella or lie free in the lumen, and turn 

 into the crithidial form. These multiply 

 further and then transform into the meta- 

 cyclic trypanosome form, which is small, 

 stumpy, and may or may not have a short 

 free flagellum. 



The metacyclic trypanosomes are the 

 infective forms. They are injected into the 

 blood with the saliva when the fly bites; up 

 to several thousand may be introduced by 

 the bite. The whole life cycle in the tsetse 



