834 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



This coccidium is parasitic witliin the epithelial cells of the intestine and within 

 the epithelium lining the bile ducts. Adult, aSexual forms measure from 20/i to 

 Soii in diameter and they produce from 30 to 200 merozoites. The merozoites infect 

 other epithelial cells where they may again multiply asexuaUy or they may develop 

 into male and female forms destined to multiply sexually. One of the micro- 

 gametes, produced by a microgametocyte, fertilizes a macrogamete and an oocyst 

 is developed. Within the oocyst a number of sporoblasts form, which contain two 

 spores each. The oocysts are passed with the fseces and if they are ingested by a 

 suitable host the spores are set free. When the cyst reaches the intestine, the 

 sporozoits are liberated, and a new infection is commenced. 



Since the cells parasitized by the coccidia are destroyed, it is evi- 

 dent that a severe infection may do a great deal of harm and interfere 

 with the functions of both intestine and liver. The disease may be 

 limited by making it impossible for uninfected animals to come into 

 contact with the droppings of infected stock. 



Avian ,Coccidiosis 



Coccidium infection is of frequent occurrence among birds and es- 

 pecially those of domestic varieties without causing serious symptoms. 

 It is k?iown, however, to cause severe epidemics in certain species, 

 and when present in milder form should be regarded as antagonistic 

 to health. Entamoeba meleagridis the organism of "Black head" in 

 turkeys from its pecuHar relationship to the tissues has been erroneously 

 regarded as a form of coccidium. 



H^MOSPORiDiA (Danilewsky emend. Schaudinn) 



The most important parasites of this order are those, belonging to 

 the Genus Plasmodium, which cause malaria in man. Organisms 

 similar to these are parasitic in the red blood cells of higher apes and 

 monkeys. Proteosoma and Heemoproteus are two genera parasitic 

 in the red blood cells of birds. It was the study of these avian 

 parasites which led to the discovery of the way in which malaria is 

 transmitted by the bite of the mosquito. 



Plasmodium (Marchiafava and Celli) 



At least three species of this genus are parasitic in m.a,Ji: Plasmodium 

 vivax (Grassi and Feletti), the cause of tertian malaria, Plasmodium mal- 

 aria (Laveran), causing quartan malaria, and Plasmodium falciparum 

 (Welsh), which causes aestivo-autumnal malarial fever. 



