The Blood Flagellates 585 



desiense is a more virulent strain of T. gambiense (17), and there have 

 been suggestions that the two types are interconvertible (26). 



T. gambiense (Fig. 12.2) measures 10-40[x in length and contains a 

 small spherical kinetoplast. Three forms have been described: slender 

 flagellates with a long flagellum, intermediate forms with a short flagel- 

 lum, and broad forms with no "free flagellum. It has been suggested that 

 such polymorphism is correlated with sexual phenomena, but the evi- 

 dence is inconclusive (Chapter II). In man, trypanosomal stages appear 

 in the blood, where they undergo fission. Eventually the flagellates may 

 get into the cerebrospinal fluid, the invasion often bringing on "sleeping 

 sickness." 



Glossina palpalis is the major vector, but G. tachinoides is important 

 in some parts of West Africa. The fly sucks the trypanosomes into the gut 

 along with a meal of blood. For a few hours, at least, the trypanosomes 

 apparently remain unchanged. If conditions are favorable, the flagellates 

 survive and undergo fission, but only a small percentage of the tsetse flies 

 actually become infected after ingesting T. gambiense. After about two 

 weeks, the digestive tract contains many slender trypanosomes. The 

 infection gradually extends into the foregut and some of the flagellates 

 usually reach the salivary glands by the end of the third week. Here 

 the trypanosomes become attached, change into the crithidial stage 

 (Fig. 12.2) and divide rapidly for two or three days. The flagellates then 

 develop into metacyclic trypanosomes infective for the vertebrate host. 

 The insect phase of the cycle lasts from three to five weeks, depending 

 upon environmental conditions. 



In the transfer from tsetse fly to vertebrate, two methods are possible: 

 mechanical transfer of the flagellates shortly after ingestion; and cyclic 

 transfer, in which the flagellates pass through developmental stages in the 

 vector before they are again infective for the vertebrate. Within a day or 

 so after ingestion, completion of the insect cycle becomes essential for 

 infection of the vertebrate. 



The life cycle of T. rhodesiense is quite similar to that of T. gambiense. 

 However, the insect phase of the cycle — in the usual vector, Glossina 

 morsitans — requires only about two weeks for completion. 



Symptoms and pathology. In Gambian sleeping sickness, the bite of 

 an infected fly often causes a local irritation Avhich normally disappears 

 after a few days. Following an incubation period, ranging from tw^o 

 weeks to a year or more, an irregular recurrent fever usually is the first 

 noticeable symptom. Although the fever is sometimes mild, temperatures 

 of 105-106° may be observed. After a time, physical weakness becomes 

 marked and other symptoms include anemia, rapid pulse, severe head- 

 aches, enlargment of the cervical lymph glands ("Winterbottom's sign"), 

 and loss of weight. Itchy skin eruptions are fairly common, although less 

 noticeable in natives than in foreigners. Enlargement of the liver and 



