550 Protozoa of the Digestive and Urogenital Tracts 



Giardia lamblia 



Stiles 



This flagellate, described by Lambl in 1859 as Cercomonas intesti- 

 nalis, probably was first seen by Leeuwenhoek in 1681. Although the 

 organism is often referred to as Giardia iy-itestinalis, Lambl's name had 

 already been used for a parasite of Amphibia and the correct specific 

 name is Giardia lamblia. Nuclear division and fission have been de- 

 scribed (101). 



The flagellate (Fig. 11. 3, D, E) measures 9-21 x 5-lltj.. The body is 

 flattened dorso-ventrally with a rather convex dorsal surface and a more 

 flattened ventral surface, the anterior part of which forms a concave 

 "sucker." Two flagella emerge from the posterior pole, while three other 

 pairs extend from the lateral and anterolateral surfaces. The paired 

 axostyles, which may appear fused in stained preparations, extend to 

 the posterior end of the body. Two parabasal bodies, sometimes fused 

 together, lie near the axostyles in the posterior third of the body. 



The cysts (Fig. 11. 3, F, G) measure 8-14x6-10[j, and may contain 

 2-16 nuclei, axostyles, parabasal bodies, and fibrils which are possibly 

 flagellar axonemes. The cyst is the stage most commonly found in stool 

 examinations, since the flagellated forms are discharged primarily during 

 attacks of diarrhea. 



Although it was suspected, at one time, that rodents may serve as 

 reservoirs, this suspicion has not been confirmed. Experimental infection 

 of rats has been reported (8), but such infection has been temporary and 

 has not led to production of cysts. 



Flagellosis 



The effects of flagellate infections have been evaluated primarily 

 by correlating clinical observations with incidence of infection. On such 

 a basis, there is no evidence that Retortomonas intestinalis and Tricerco- 

 monas intestinalis are harmful. Chilomastix mesnili has been associated 

 with abnormal stool frequency often enough to arouse suspicion, but 

 there is no reason for considering this species a serious parasite. 



Pentatrichomonas hominis has been found in diarrheic patients (150) 

 and "Pentatrichomonas ardin-delteili" was first observed (44) in patients 

 with dysentery and later in cases of dysentery and chronic diarrhea (105). 

 Therefore, it is often assumed that P. hominis is occasionally a causative 

 or contributary factor in digestive disturbances. Invasion of tissues — 

 agonal (110) and possibly postmortem (176) — has been reported, but 

 probably does not occur in the usual infection. 



Infection with Giardia lamblia is frequently correlated with digestive 

 disturbances, although there is no invasion of tissues. Heavy infections 

 might interfere with normal absorption, since the flagellates adhere to 



