Immune responses in farm workers after exposure to Bacillus thuringiensis pesticides

Although health risks to pesticides containing Bacillus thuringiensis (Bt) have been minimal, the potential allergenicity of these organisms has not b een evaluated. Therefore, a health survey was conducted in farm workers bef ore and after exposure to Bt pesticides. Farm workers who picked vegetables that required Bt pesticide spraying were evaluated before the initial spra ying operation (n = 48) and 1 and 4 months after (n = 32 and 20, respective ly). Two groups of low- (n = 44) and medium- (n = 34) exposure workers not directly exposed to Bt spraying were also assessed. The investigation inclu ded questionnaires, nasal/mouth lavages, ventilatory function assessment, a nd skin tests to indigenous aeroallergens and to a variety of Bt spore and vegetative preparations. To authenticate exposure to the organism present i n the commercial preparation, isolates from lavage specimens were tested fo r Bt genes by DNA-DNA hybridization. Humoral immunoglobulin G (IgG) and imm unoglobulin E (IgE) antibody responses to spore and vegetative Bt extracts were assayed. There was no evidence of occupationally related respiratory s ymptoms. Positive skin-prick tests to several spore extracts were seen chie fly in exposed workers. In particular, there was a significant (p < 0.05) i ncrease in the number of positive skin tests to spore extracts 1 and 4 mont hs after exposure to Bt spray. The number of positive skin test responses w as also significantly higher in high (p < 0.05) than in low- or medium-expo sure workers. The majority of nasal lavage cultures from exposed workers wa s positive for the commercial Bt organism, as demonstrated by specific mole cular genetic probes. Specific IgE antibodies were present in more high-exp osure workers (p < 0.05) than in the low and medium groups. Specific IgG an tibodies occurred more in the high (p < 0.05) than in the low-exposure grou p. Specific IgG and IgE antibodies to vegetative organisms were present in all groups of workers. Exposure to Bt sprays may lead to allergic skin sens itization and induction of IgE and IgG antibodies, or both.