INFECTIOUS LARYNCiOTRACHEITIS CARRIERS 171 



when the temperature and relative humidity were comparatively low. The 

 conditions then prevailing were more favorable, and the virus was preserved in 

 a viable condition in one trial for six days and in another for nine days. All of 

 the virulent pieces of tissues and exudates had dried nut considerably, but not 

 enough to preserve them indefinitely. 



The location of the tubes in the litter and in the poultry house was important; 

 for the virus in the tubes placed in moist and sunny places, such as near the 

 drinking fountain and in front of the windows, lost its virulence in three days. 

 The virus in tubes buried in the corners, under the roosts, and under the laying 

 boxes remained virulent for longer periods. 



It was impossible to measure the contribution of other factors that may have 

 been involved in the partial desiccation and prolongation of the virulence of the 

 tissues and exudates in the test tubes. Possibly the dry, dusty litter absorbed 

 the moisture, and such aerobic bacteria and moulds as grow at low temperatures 

 removed some of the oxygen, thus making the atmospheric conditions favorable 

 for a partial preservation of the viruses used in those experiments. 



Practical Applications 



When infectious laryngotrucheitis has existed in a flock and the recovered 

 birds are kept for breeding purposes, there is reason to suspect that some of them 

 may be carriers, and it is very unwise to mix any of the pullets and cockerels 

 coming in from the range in the fall with the breeders. The two flocks should 

 be kept entirely separate. The old hens and roosters should be disposed of as 

 soon as the l)reeding season i^ over, and the premises which they have occupied 

 thoroughly cleaned and disinfected. In this way the cycle of infection as it occurs 

 on many poultry farms should be broken and the disease should disappear from 

 the premises. 



Terminal disinfection is important in poultry management and should 

 receive more attention than is ordinarily given to it. Terminal disinfection has 

 to do with cleaning up after an outbreak, or after disposing of birds among which 

 carriers are suspected. Before disinfection can be intelligently appled something 

 should be known about the virus, bacteria, or parasite it is desired to kill. It is 

 already known that infectious laryngotracheitis is caused by a filtrable virus 

 (Beach, 1930; Beaudette, 1930; Cibbs, 1931; Graham, Thorp and James, 1931). 

 Experiments show that this virus is easy to destroy outside of the bird. Ordi- 

 narily it does not live longer than 24 hours at 68° F. (20° C.) when exposed to light 

 and air, or 3 or 4 days when placed in an ice box. If moisture and air are re- 

 moved by means of a vacuum pump, and the dehydrated virus is kept in a sealed 

 desiccator just above the freezing point, its virulence is often maintained for 

 several months; but these conditions are unusual, and seldom, if ever, found in 

 a ])oultrv house. 



The virulence of the virus in tracheal exudates and i)ossibly in other secre- 

 tions from diseased birds may be prolonged in the litter of poultry houses in 

 winter. While factors responsible for this prolongation are not well understood, 

 it is (luitc likely that constant low temperature, low relative humidity, dry 

 environment, and overcrowding are largely responsil)!(' foi' tlic spread of the 

 disease in poultry houses. 



With these facts in mind it is possible to understand wiiy it is very difficult 

 to control infectious laryngotracheitis in winter. At this time of year the virus 

 is likely to be more resistant than it is at other seasons. The disinfectant is apt 



