Host-Parasite Specificity in the Coccidia of Mammals

The problem of host-parasite specificity in the coccidia undoubtedly ranks next to that of therapeutics from an economic and medical standpoint. Man is concerned to know whether or not he may be infected with the coccidioses which are so abundant among his domestic animals or household pests. For the sake of his domestic animals, he inquires whether or not the disease which is so devastating among his cattle is identical with the infection among the rats and rabbits, and also whether the flying birds such as sparrows carry a coccidial organism which is infective to poultry. In other words, it is important to know whether or not certain animals can act as biological or mechanical vectors of coccidiosis in man or his domesticated animals. The importance of this question is even greater from a purely scientific point of view. Granted that there is such a phenomenon as specificity between host and parasite, to what extent does it prevail and by what mechanism does it operate? Many assertions have been made regarding host-parasite specificity in the coccidia, especially those that infect man, and some experimental work has been done. The assertions have been based on morphological resemblances, and on the fact that certain parasites occupy similar tissues in different hosts.