INFECTIOUS DISEASES. 569 



The cases of navel ill resulting from infection before birth can not 

 well be guarded against. By keeping mares, advanced in pregnancy, 

 in good physical condition, the fetus will be expelled immediately 

 upon the opening of the uterine cavity. 



Once the infection of the navel cord has set in, the cord should not 

 be ligated but should be washed in a disinfectant solution and a 

 veterinarian called for the subsequent treatment. 



INFECTIOUS ANEMIA OR SWAMP FEVER. 



By John R. Mohlee, V. M. D., Assistant Chief, Bureau of Animal Industry. 



Infectious anemia of horses, known also by a number of other 

 names, as swamp fever, American surra, malarial fever, typhoid 

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

 sis, and pernicious anemia, has recently been the subject of much in- 

 vestigation. The cause of the disease has now been definitely deter- 

 mined 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 diseases. The 

 disease is most prevalent in low-lying and badly drained sections 

 of the country, although it has been found on marshy pastures dur- 

 ing wet seasons in altitudes as high as 7,500 feet. Therefore proper 

 drainage of infected pastures is indicated as a preventive. It is 

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

 makes its appearance in June and increases in frequency until Oc- 

 tober, although the chronic cases may be seen in the winter, having 

 been contracted during the warm season. 



Cause. — It has been conclusively proved 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 defibrihated blood, or the blood serum which has 

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

 visible forms of organismal life, including bacteria, trypanosoma, 

 piroplasma, etc. This virus has also been found to be active in the 

 carcass of an affected animal 24 hours after death. 



Following the injecticn.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 mani- 

 fested by a rise of temperature. If uncomplicated, the infection 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, mosquitoes, inter- 

 nal parasites, etc., is now receiving careful investigation. 



