COCCIDIA 585 



en; oval oocysts, 29.5-33.5/u by 20-23^; spores 18.8/* by 8m; sporo- 

 zoites club-shaped; sporulation in four to six days at 28°C. (Ray, 

 1945). 



Genus Isospora Schneider. Oocyst produces two spores, each con- 

 taining four sporozoites. Avian Isospora (Boughton, Boughton and 

 Volk, 1938). 



/. hominis (Rivolta) (/. belli Wenyon) (Fig. 251, e, /). This is the 

 sole coccidian parasite of man known up to the present time. Its life 

 cycle is unknown, but most probably the schizogony, gametogenesis 

 and sexual fusion occur in the intestinal epithelium. Oocysts have 

 only been seen in the stools of infected persons. 



The oocyst is asymmetrically fusiform; 20-33^ by 10-16/*; wall is 

 made up of two membranes which are highly resistant to chemicals; 

 when voided in faeces, the contents either fill up the oocyst or appear 

 as a spherical mass, composed of refractile granules of various sizes; 

 nucleus appears as a clear circular area; when the faecal specimen 

 is kept in a covered container at the room temperature, the proto- 

 plasmic mass divides into 2 spherical sporoblasts in about 24 hours 

 each sporoblast develops in another 24 hours into a spore (10-16^ 

 by 7-10m) containing 4 sporozoites. Further changes take place when 

 the oocyst finds its way into the human intestine in contaminated 

 food or water. 



/. hominis has been observed in widely separated regions, but ap- 

 pears not to be of common occurrence. As to its effect on the human 

 host, very little is known. Connal (1922) described the course of an 

 accidental oral infection by viable mature oocysts, as follows: The 

 incubation period was about six days, the onset sudden, and the 

 duration over a month. The cure was spontaneous. The symptoms 

 were diarrhoea, abdominal discomfort, flatulence, lassitude, and loss 

 of weight. During the first three weeks of the illness no oocysts were 

 found, but then oocysts appeared in the stools for nine days. On the 

 10th day they were not seen, but reappeared on the 11th and 12th 

 days, after which they were not found again. The acute signs of ill- 

 ness abated within one week of the finding of the oocysts. The faeces 

 contained a large amount of undigested material, particularly fat 

 which gave it a thick oily consistency, showing signs of slow gaseous 

 formation. 



Matsubayashi and Xozawa (1948) found six cases of infection in 

 Japan. A volunteer ingested some 3000 oocysts. Eight days later 

 diarrhoea developed, followed by a rise of temperature above 39°C, 

 which lasted for 10 days. On the following day, the diarrhoea sub- 

 sided, but later returned and was especially pronounced on the 17th 



