CHAPTER VI. 

 INFECTIOUS DISEASES DUE TO PROTOZOA. 



PIROPLASMOSES. 



Definition. — Piroplasms are one-celled protozoa which 

 assume various shapes, some of them pear-, some round-, 

 and some ring-shaped. When introduced into the body of a 

 susceptible animal they enter the red blood corpuscles which 

 cells they destroy, leading to anemia, hemoglobinemia, and 

 icterus. Piroplasms are transmitted from the infected to the 

 susceptible animal by insects known as ticks. In the tick 

 they probably pass through an evolutionary stage. The most 

 important pathogenic piroplasms and the piroplasmoses they 

 produce are the following: 



(a) Piroplasma bigeminum, causing Texas fever. 



(b) Piroplasma parvum, causing East African fever of 

 cattle. 



(c) Piroplasma- equi, producing biliary fever of horses. 



(d) Piroplasma ovis, causing so-called malarial fever of 

 sheep. 



(e) Anaplasma marginale, producing gall sickness of 

 cattle. 



Relationship of the Tick to Piroplasviosis. — Animals become 

 infected when on pasture from being bitten by ticks. These 

 insects, of which there are a great many varieties, belong to 

 the group Ixodinse and the family Ixodidae. From a patho- 

 logical standpoint the most important belong to the genus 

 boophilus and the genus ixodes. The ticks become fully 

 developed either on the animal which serves as host (Texas 

 fever) or they leave the host as nymphs (East Coast fever), 

 or both as larvae and nymphs (European piroplasmosis).' 

 The most important varieties are the following: 



(a) Ixodes ricinus (European piroplasmosis). 



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