GIARDIA INTESTINALIS 125 



The cysts usually form around single animals which then proceed 

 to divide into two or more individuals. The commonest condi- 

 tion is that of two parasites lying with their anterior ends at 

 opposite ends of the cyst (Fig. 33D). 



According to Wenyon, Giardia is a very persistent flagellate, 

 often keeping an individual infected for years. It is sometimes 

 noticeably pathogenic, causing intermittent diarrhea in which 

 blood and mucus is passed, swarming with parasites. Between 

 such attacks the infected person passes apparently normal stools, 

 with only the cysts of Giardia in them. An active increase of 

 parasites accompanied by attacks of diarrhea is likely to occur 

 after exposure to weather, irregular diet, or other weakening 

 conditions. Many cases of dysentery and diarrhea in British 

 soldiers invalided home from Gallipoli were found to be due to 

 Giardia infection. The acute symptoms last from one to six 

 months, after which the symptoms practically disappear for a 

 variable length of time. Strangely enough there is always 

 spontaneous improvement upon a change to a cooler climate. 



Giardia infections are extremely difficult to get rid of, and 

 some infections seem to survive every attempt at treatment. 

 They do not respond to emetin, though they are sometimes 

 destroyed by beta-naphthol. The latter drug in combination 

 with bismuth salicylate has been found successful in some cases. 

 Escomel in Peru uses a method of dieting followed by calomel 

 and castor oil and claims to rid his patients of the parasite by the 

 third day. The difficulty experienced in expelling these para- 

 sites is probably due to their habit of lodging themselves in the 

 digestive glands outside the main passage of the intestine, where 

 it is difficult for drugs of any kind to reach them. 



Like other intestinal protozoans, Giardia is transmitted in the 

 encysted state with polluted food and water. Stiles has shown 

 that flies play an important role in the spread of the infection, 

 carrying the cysts on their feet from open privies and depositing 

 them on human food. By capturing flies known to have fed on 

 Giardia-mieciQd material and shaking them up in distilled water, 

 Stiles was able to recover Giardia cysts from them, thus prov- 

 ing as a fact what had long been beheved without definite 

 proof. 



