HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



in by the host and may be termed a commensal or food 

 robber. The host does not suffer because of the small 

 amount of food taken by the parasite. In some cases, how- 

 ever, the ciliates attack the intestinal wall and thus be- 

 come pathogenic. This attack may be slight, in which case 

 the host makes repairs as rapidly as the tissues are 

 injured, or may be severe, in which case symptoms of 

 balantidiosis ensue. Evidence that all individuals infected 

 with B. coli exhibit symptoms is furnished by Aguilar 

 (1926) who observed 40 cases at the Quirigua hospital 

 in Guatemala during the period from August 30 to 

 October 2, 1925; these 40 cases represented 10 per cent 

 of the admissions for these months. All 40 gave a history 

 of diarrhea and in 14 the stools contained pus or pus 

 and blood. Stovarsol was used in treating these patients 

 with apparently complete success. 



Although the attack on the intestinal wall by B. coli 

 may be very slight, every infected person is liable at some 

 time to exhibit clinical symptoms. These symptoms vary 

 in severity from diarrhea to dysentery which may be 

 continuous or characterized by apparent recovery and 

 subsequent relapse. The disease produced is known as 

 balantidiosis, balantidial dysentery or ciliate dysentery 

 and the symptoms have been described many times. 



Pathogenesis. The early pathological changes appear 

 to be due to irritation caused by penetration of the para- 

 sites into the tissues of the intestinal wall. This results 

 in hyperaemia of the mucosa. The ulcers are at first visi- 

 ble as minute reddened areas of the mucosa; as these 

 grow larger a necrotic area appears in the center. Later 

 the ulcers become undermined at the edges. When ex- 



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