638 PIROPLASMOSIS 



and nothing is known of the further history of the parasite within the 

 insect except that the eggs in the ovary may become infected, so that 

 insects developed from these can carry infection to animals. Frequently 

 when an animal has passed through an attack of a piroplasmosis it is 

 immune to the disease, and with regard to this immunity in certain cases 

 very interesting facts have been observed. For instance, the condition 

 may not be associated with the disappearance of the parasite from the 

 blood of the immune animal, and the latter may thus be a source of 

 danger to other non-immune animals with which ticks harboured by it 

 may come in contact. 



The following are the chief piroplasmata causing disease in animals : 

 (i) Piroplasma bigeminum. This was first described by Theobald Smith 

 and is the cause of Texas or red- water fever, a febrile condition associated 

 with hffimoglobinuria, which occurs in the Southern States of America, 

 the Argentine, South and Central Africa, Algeria, various parts of 

 Northern Europe, and in Australia. The organism gets its name of 

 bigeminum from the fact that it is often present in the red cells in pairs, 

 which may be attached to one another by a fine thread of protoplasm ; 

 this probably results from the complete separation of two individuals 

 being delayed after division has occurred. Infection is here spread by 

 the tick boophilus bovis, and some of the characteristics of the disease 

 epidemiologically are explained by the fact that this insect goes through 

 all its moultings on the same individual host. (2) Piroplasma parvum. 

 This organism was discovered by Theiler in the blood of cattle suffering 

 from African East Coast fever, a disease closely resembling Texas fever, 

 which prevails endemically in a narrow strip along a long extent of the 

 east coast, and which occurs epidemically inland. As its designation 

 implies, the organism is small, and it is also attenuated. Its insect host 

 is the tick rhipicephalus appendiculatus, and it may be noted that this 

 tick drops off the animal on which it may be feeding when it is about to 

 go through one of its several moultings. It can thus carry an infection 

 much more quickly and widely through a herd than can the carrier of 

 ordinary red-water fever. It may be said that in England there occurs a 

 red-water fever also associated with the presence of a piroplasm in the 

 blood, but the relationship of this organism to the other varieties has not 

 yet been fully worked out. (3) Piroplasma equi. This organism gives 

 rise to biliary fever in horses, another South African disease, and it is 

 carried by the tick rhipicephalus evertsii. In this disease Theiler made 

 the interesting observation that when the blood of a donkey which had 

 recovered from the disease was injected into a horse, the latter suffered a 

 slight illness only, although the organisms were present in the blood 

 injected. Such a fact is of importance, as attenuation of virulence in 

 pathogenic protozoa seems, so far as our present knowledge goes, a not 

 very common event. (4) Piroplasma canis. This causes a piroplas- 

 mosis occurring in dogs. 



With regard to the pathology of infection by piroplasmata we know 

 nothing. The diseases are often extremely fatal, carrying off nearly 

 every individual attacked, but we do not know the nature of the changes 

 originated. 



