24-8 MASS. EXPERIMENT STATION BULLETIN 257 



The Use of the Cutaneous Vaccine in a Flock Infected with Fowl Pox 



Late in Septenilber, 1928, attention was called to a small flock of Rhode 

 Island Reds that was affected with fowl pox to a slig'ht degree. It was de- 

 cided to vaccinate cutaneously all birds in the flock in order to stay the 

 spread of the infection if possible. The flock was located within walking 

 distance of the College, and periodic pers,onal observations of the results of 

 the vaccination could be made. All the birds, confined in three separate 

 units, were vaccinated and observations made of the results as follows: 



Unit 1. 



According to information received from the owner, the infection had 

 started in this snuall unit, consisting of a pen of 17 hens and 1 cock. Fowl 

 pox had never been present on the premises. Its source of introduction into 

 the flock could not be traced. Eight of these birds showed tj^ical lesions 

 of fowl pox of a severe form, which apparently had been present for about 

 one week. All 18 birds were vaccinated cutaneously with the standard vac- 

 cine on September 26. Those birds showing lesions of pox demonstrated no 

 follicular reaction whatever, while those not showing lesions responded to 

 the vaccination with a slight follicular swelling, which was not followed by 

 scab formation. This SiWeUing appeared on the third day but was not present 

 on the eighth day after vaccination. The infection in this pen entirely dis- 

 appeared by October 23. 



Unit 2. 



This unit consisted of 125 pullets confined to an open yard about 75 feet 

 distant from unit 1. These birds were vaccinated cutaneously on September 

 26, at which time they were moved from the yard to a laying house, closely 

 adjoining unit 1. At the time of vaccination all birds were closely examined 

 and three were found with slight, miimature lesions of pox. It was evident 

 that they had but recently become infected. About 90 per cent of the birds 

 showed a slight follicular swelling in three days and a more pronounced 

 swelling seven days after vaccination. On the thirteenth day the swellings 

 were most prominent, and the first evidence of follicular scab development 

 was noticed. No additional infection developed in this pen, and on October 

 23 the birds were well into production. 



Approximately 10 per cent of these birds, including the three infected 

 ones, failed to show any follicular reaction following vaccination. There was 

 little probability tliat they had acquired iniiiiunity through a previous, un- 

 noticed infection. They might have been non-susceptible or naturally immune 

 to the disease. However, it appeared probable that these birds were fairly 

 well advanced in the stage of incubation at the time they were vaccinated 

 and sufficient cutaneous resistance had developed to prevent the vaccine from 

 "taking". But in such cases one would expect to see a few minor pox lesions 

 develop. 



Similar results were obtained later in the year. White Leghorn cockerels 

 were obtained for experimental purposes from a flock in which several cases 

 of pox had existed. It was known that these birds had been in contact with 

 the infected ones but had never shown lesions of the disease. When cutane- 

 ously vaccinated they failed to react with the development of swollen follicles 

 and follicular scabs. The explanation of these results requires further in- 

 vestigation. 



