68 HORSE, SWINE AND POULTRY DISEASES 



the treatment of it by means of continued exposure to a high tem- 

 perature for a certain length of time, which weakens the virus to 

 such an extent that it is only capable of producing a very mild and 

 not dangerous attack of anthrax in the animal in which it is inocu- 

 lated, and thus protects the animal from inoculation of <a stronger 

 virus. The production of this virus, which is carried on in some 

 countries at the expense of the government and is furnished at a 

 small cost to the farmers in regions where the disease prevails, in 

 this country is made in private laboratories only. (Spl. Rpt. Horse, 

 Dept. Agr., 1911; F. B. 79; Ark. E. S. 96; Del. Col. E. S. 20, 32, 

 37, 90; La. E. S. 44; S. Dak. E. S. 36; Okla. E. S. 27.) 



INFECTIOUS ANEMIA ( SWAMP FEVER). 



This disease which in horses is also known by a number of 

 other names, as swamp fever, American surra, malarial fever, ty- 

 phoid fever of horses, the unknown disease, no-name disease, plains 

 paralysis, and pernicious anemia, has recently been the subject of 

 much investigation. The cause of the disease has now been defi- 

 nitely determined as an invisible virus, which is capable of passing 

 through the pores of the finest porcelain filters, like the infection 

 of foot-and-mouth disease, rinderpest, hog cholera, and similar dis- 

 eases. The disease is most prevalent in low-lying and badty drained 

 sections of the country, although it has been found in altitudes as 

 high as 7,500 feet on marshy pastures during wet seasons. There- 

 fore proper drainage of infected pastures is indicated as a preven- 

 tive. It is also more prevalent during wet years than in dry seasons. 

 It usually makes its appearance in June and increases in frequency 

 until October, although the chronic cases may be seen in the winter, 

 having been contracted during the warm season. 



Cause. It has been conclusively proven that infectious anemia 

 is produced by an invisible, filterable organism which is transmissible 

 to horses, mules, and asses by subcutaneous inoculation of blood se- 

 rum. The virus which is present in the blood may be transmitted to 

 a number of equines in a series of inoculations by injecting either 

 the whole blood, the defibrinated blood, or the blood serum which has 

 been passed through a fine filter, thus eliminating all the visible 

 forms of organismal life, including bacteria, etc. This virus has 

 also been found to be active in the carcass of an affected animal 

 twenty-four hours after death. 



Following the injection of the infectious principle there is a 

 period of incubation which may extend from ten days to one and 

 one-half months, at the end of which time the onset of the disease 

 is manifested by a rise of temperature. If uncomplicated, the in- 

 fection runs a chronic course, terminating in death in from two 

 months to one and one-half years, or even longer. The probability 

 of the virus being spread by an intermediate host, such as flies, mos- 

 quitoes, internal parasites, etc., is now receiving careful investiga- 

 tion. From experiments already conducted it appears that this dis- 

 ease, formerly supposed to be confined to Manitoba and Minnesota, 

 is more or less prevalent in Kansas, Nebraska, Colorado, Wyoming, 

 Montana, North Dakota and Texas. 



