220 PATHOGENIC BACTERIA OUTSIDE THE BODY 



cholera, distemper, roup, influenza and other carriers are 

 common. Carriers furnish the explanation for many of the 

 so-called "spontaneous" outbreaks of disease among men 

 and animals. 



(f) In this class come the "accidental carriers" like flies, 

 fleas, lice, bed-bugs, ticks and other biting and blood- 

 sucking insects, vultures, buzzards, foxes, rats and carrion- 

 eating animals generally; pet animals in the household, etc. 

 Here the animals are not susceptible to the given disease 

 but become contaminated with the organisms and then 

 through defilement of the food or drink, or contact with 

 individuals or with utensils pass the organisms on to the 

 susceptible. Some biting and blood-sucking insects transmit 

 the organisms through biting infected and non-infected ani- 

 mals successively. The spirilloses and trypanosomiases seem 

 to be transmitted in this way, though there is evidence 

 accumulating which may place these diseases in the next 

 class. Anthrax is considered in some instances to be trans- 

 mitted by flies and by vultures in the southern United States. 

 Typhoid transmission by flies is well established in man. 

 Why not hog-cholera from farm to farm by flies, English 

 sparrows, pigeons feeding, or by turkey buzzards? Though 

 this would not be easy to prove, it seems reasonable. 



Preventing contact of such animals with the discharges 

 or with the carcasses of those dead of the disease, destruc- 

 tion of insect carriers, screening and prevention of fly breed- 

 ing are obvious protective measures. 



(d) In this class come certain diseases for which particu- 

 lar insects are necessary for the parasite in question, so that 

 certain stages in its life history may be passed therein. The 

 most certain means for eradicating such diseases is the 

 destruction of the insects concerned. Up to the present no 

 bacterial disease is known in which this condition exists, unless 

 Rocky Mountain spotted fever and typhus fever shall prove 

 to be due to bacteria. Such diseases are all due to protozoa. 

 Among them are Texas fever, due to Piroplasma bigeminum 

 in this country which has been eradicated in entire districts 

 by destruction of the cattle tick {Margaropus annulatus). 



Piroplasmoses in South Africa among cattle and horses, 



