Sensitivity to human, bovine and avian PPD's and their relation to tuberculosis in East Anglia

Abstract

The results of multiple puncture tuberculin testing with human, bovine and avian PPD's of 15.682 school children living in fourteen districts of East Anglia are reported. The districts are divided into those that are mainly urban in environment and those that are rural. The incidence of sensitivity to human PPD is greatest in the urban districts and that to bovine and avian PPD's is greatest in the rural districts. The distribution of bovine sensitivity is different from that of avian sensitivity. Evidence is presented suggesting that there has been a greater prevalence of tuberculous disease and infection caused by the bovine type tubercle bacillus than by the human type bacillus in rural areas, whereas in urban districts there has been a greater prevalence of respiratory tuberculosis and infection due to the human type than to the bovine type tubercle bacillus. The incidence of reactions to human, bovine and avian PPD's has been related to the incidence of tuberculous disease: respiratory, non-respiratory and all forms, between 1950 and 1959 in each district. There is a good relationship between the incidence of tuberculosis and the incidence of reaction to human and bovine PPD's. The incidence of reaction to human PPD is particularly related to the incidence of tuberculosis (all forms) and of respiratory tuberculosis; and the incidence of reaction to bovine PPD to the incidence of non-respiratory tuberculosis. There is no apparent relationship between avian sensitivity and tuberculous disease. Evidence based on this study that supports a non-tuberculous cause of tuberculin sensitivity is as follows: there are those who react only to avian PPD or give larger reactions to avian than the human and bovine PPDs; avian sensitivity has a different distribution from human and bovine PPD sensitivity in different districts; the incidence of avian sensitivity does not correlate with the incidence of tuberculous disease; small human and bovine reactions do not correlate with tuberculous disease and are possibly heterologous cross-sensitivity caused by a non-tuberculous infection. It is concluded that the incidence of sensitivity to human PPD is the best index of the amount of tuberculosis in the community. In districts suspected or found to have had bovine type tuberculous infection, comparative tuberculin testing with human and bovine PPDs will give an indication of the relative incidence of the two types of tuberculous infection. Comparative tuberculin testing with human and avian PPDs will give an indication of the amount of tuberculous infection and non-tuberculous tuberculin senstivity in the population. A coincidental finding, the result of changing the technique of Heaf testing, suggests that the use of three or more PPDs concurrently, has a non-specific enhancing effect upon latent tuberculin sensitivity of the host.