LARYNGOTRACHEITIS VACCINATION 17 



natural outbreaks birds die of asphyxiation due to the plugging of the larynx and 

 trachea. Properly vaccinated birds do not die because the larynx and trachea 

 are unaffected; yet the birds have the disease and immunity is developed the same 

 as in natural outbreaks. It should not be forgotten that as long as acute cases 

 and chronic carriers remain on the premises there is always danger of the spread 

 of the disease to susceptible birds. 



The conditions under which vaccination may reasonably be expected to be 

 successful are as follows: First, the virus from which the vaccine is made must 

 be virulent. This is indicated by the way the disease attacks the birds sacrificed 

 for vaccine. It should always kill some of them in three or four days after 

 inoculation or infection. Second, it is no use to vaccinate birds already sick with 

 infectious laryngotracheitis. If the disease is pretty well scattered through the 

 whole flock, field tests indicate that it is useless to vaccinate. Also, birds badly 

 infested with worms or in a run-down condition generally are poor risks for 

 vaccination. Under no circumstances should a flock be vaccinated against in- 

 fectious laryngotracheitis unless the disease is already present on the farm and there 

 is imminent danger of its spreading to susceptible birds. 



Preparation of Vaccine 



When it is desired to vaccinate chickens on the range, laboratory vaccine may 

 be used. Since it is difficult to prepare infectious laryngotracheitis vaccine in 

 the laboratory on a large scale, and at the same time maintain a satisfactory 

 degree of virulence in every batch, it is well to test such vaccines before use. 

 One way to do this is to isolate some birds from the main flock and inoculate 

 them intratracheally with the vaccine. If most of the birds come down with 

 infectious laryngotracheitis within three days and some of them die, the virulence 

 is satisfactory and the vaccine may be used. But if the vaccine should prove to 

 be unsatisfactory, the birds should be destroyed and the premises thoroughly 

 cleaned and disinfected taking special care not to let the disease reach the main 

 flock. The secret of success in vaccinating against infectious laryngotracheitis 

 is a satisfactory vaccine in the hands of an experienced worker. 



If infectious laryngotracheitis has already appeared in a small portion of the 

 flock and its virulence is satisfactory for immunization, then autogenous vaccine 

 should be used. Autogenous vaccine may be prepared as follows: Take a bird 

 that has just died or one that is very sick and kill it. Lay the dead bird on a 

 table, box, or barrel, on its back, and beginning at the beak slit open the skin 

 of the neck with a pair of scissors, exposing the windpipe to the wish-bone. Care- 

 fully dissect the windpipe from the other tissues, taking care to get as much of 

 it as possible. Now slit the windpipe open, beginning at the larynx and cutting 

 clear through to the other end; and, by means of a small knife — a paring knife, 

 a pen knife, or a scalpel — scrape the exudate from the exposed larynx and trachea 

 and put it in a bowl or mortar. After the desired amount of exudate has been 

 secured, grind or triturate it with a smooth stick or pestle, adding a little cold 

 water or a mixture of glycerine and saline until a thin, paste-like mass is formed. 

 This is the vaccine. If it has been properly prepared from birds sick or dead 

 of infectious laryngotracheitis, it should be more virulent than any that can be 

 purchased because it is fresh. Furthermore, it is autogenous, and should be 

 specific for the particular disease that the birds are affected with. In order to 

 get the best results, fresh vaccine should be made from the sick birds every two 

 hours, and any that is left over after vaccination destroyed. It will require 



