Serial IgE levels in allergic farmers related to the mite content of their hay

Summary Asthma and allergic rhinitis in farmers has been shown to be associated with the large numbers of ‘storage mites’ present in stored hay (Cuthbert et al., 1979). During the year July 1977 to June 1978, studies were undertaken to compare the IgE levels to specific storage mites in the sera of five farming and one control subject, with the numbers of mites present in their hay. Samples of hay were collected at monthly intervals and the total number of mites per gram of hay in each sample recorded. Species were identified and approximate estimates of the number of two of these, Tyrophagus longior and Acarus farris, were made for two of the farms Crook and Queenalia, respectively. Blood samples were also taken at monthly intervals from all the subjects and assayed by radioallergosorbet test for specific IgE to five storage mite species and to the house-dust mite (Dermatophagoides pteronyssinus). Mite numbers, both in respect of total counts and specific estimates, showed a rapid increase to a peak during the month of October with a subsequent fall in November and a partial recovery in December, after which numbers tended to even out. Only two of the farmers showed consistently raised levels of specific IgE to any of the storage mite species and these tended to follow the fluctuations of the mite numbers during the months to January 1978, after which one farmer (J.M. from Crook) showed a fall in his positive IgE titre to T. longior, whilst the other (W.W. of Queenalia) who was positive to A. farris showed a sudden rise in titre to this species. High titres to the house-dust mite (D. pteronyssinus) were recorded in the sera of three of the farmers. One farmer (J.M.) whilst giving a persistently high titre of IgE to T. longior, gave only a low one of less than twice normal to Tyrophagus putrescentiae, demonstrating a specificity of sensitization to the more commonly occuring of two of the species of a single genus.