ETIOLOGY 455 



1884, there was a small epizootic at Portland caused by 

 imported cattle. 



The most serious outbreak in the United States was in 

 igo2. The first herds affected were at Chelsea, Mass., in the 

 vicinity of the docks, to which place the infection was probably 

 carried from shipping. It is not known exactly how the infec- 

 tion was introduced, but it is highly probable that it came 

 through some one of the many possible channels other than 

 infected imported cattle. In this outbreak, the disease ap- 

 peared in Massachusetts, New Hampshire, Vermont and 

 Rhode Island. A total of 4.712 cattle were affected. The 

 comparative freedom of the United States from this disease is 

 attributed to the enforcement of rigid quarantine measures. 



§ 361. Etiology. The specific cause of foot and mouth 

 disease has not been clearly demonstrated. It has been shown, 

 however, that it is caused by a specific infection and that 

 every outbreak starts from some previous case or cases. The 

 virus is contained in the eruptions and given off from the 

 mouth and feet, causing its wide distribution. Loeffler and 

 Frosch have shown that the cause— presumably a germ of 

 some form-would pass through a Berkefeld filter. Later 

 Loeffler showed that it did not pass through the finer Kitasato 

 filter Animals may be infected directly by coming in con- 

 tact with the disease, or indirectly by being exposed to the 

 virus in stables, cars or other places recently occupied by 

 infected animals. It is stated that the virus is destroyed in a 

 short time by drying, but some writers maintain that it will 

 persist for several months. Penberthy states that under ordi- 

 nary circumstances the virus does not retain its effectiveness 

 lono- Animals that have passed through the disease may 

 carr'y the virus for several months. The infected matter may 

 be carried on the clothing or hands of human beings and thus 

 be transmitted to animals or men. Milk is often the carrier of 



the virus. 



The period of incubati07i xs s\iori, irom 2^ io 72 bours m 



inoculated cases. It may be longer than this. 



