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United States Department of Agriculture

Agricultural Research Service

Title: A Review of the Mammalian Safety of Bacillus Thurngiensis-Based Insecticides

Author
item Siegel, Joel

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2000
Publication Date: January 20, 2001
Citation: Siegel, J.P. 2001. A review of the mammalian safety of bacillus thurngiensis-based insecticides. Journal of Invertebrate Pathology. Volume(17):13-21.

Interpretive Summary: The United States Environmental Protection Agency between the years 1961 and 1995 registered 177 insecticidal products containing viable Bacillis Thuringiensis (BT). Numerous laboratory studies have demonstrated that BT and BT products are non infectious and are toxic to mammals only at a dose equal to or less than 100 million colony forming units (cfu) per mouse (a human equivalent based on weight of >100 billion cfu). In contrast, as few as three vegetative cells of the mammalian pathogen B. anthracis can kill mice (a human equivalent of >one thousand cfu). There are only two literature reports of BT infection in man between the years 1997 and the present, but all infected individuals had experienced either extensive burns or a blast injury which predisposed them to infection. Two epidemiology studies conducted during large-scale aerial spray campaigns that utilized BT insecticides found no evidence of increased illness. Some recent papers have expressed concern about the production of B.cereus enterotoxins by BT isolates. These enterotoxins cause diarrhea or vomiting in man (depending on the enterotoxin). Laboratory studies found no evidence of illness in rats and sheep fed BT products, nor have epidemiology studies found increased incidence of diarrhea during BT aerial spray campaigns. Increases in human antibody levels following exposure to BT products have been reported but there was no increased incidence in asthma or other illness. Based on laboratory studies and field experience BT insecticides have an excellent safety record.

Technical Abstract: The United States Environmental Protection Agency between the years 1961 and 1995 registered 177 products containing viable Bacillis thuringiensis (BT). Numerous laboratory studies have demonstrated that BT and BT products are toxic to mammals only at a dose equal to or less than 100 million colony forming units (cfu) per mouse (a human equivalent based on weight of f>100 billion cfu). In contrast, as few as three vegetative cells of the mammalian pathogen B. anthracis can kill mice (a human equivalent of >one thousand cfu). There are only two literature reports of BT infection in man between the years 1997 and the present, but all infected individuals had experienced either extensive burns or a blast injury which predisposed them to infection. Two epidemiology studies conducted during large-scale aerial BT serovar kurstaki spray campaigns found no increased incidence of illness. Some recent papers have expressed concern about the production of B.cereus enterotoxins by BT isolates. Laboratory studies found no evidence of illness in rats and sheep fed BT products, nor have epidemiology studies found increased incidence of diarrhea during BT aerial spray campaigns. Increases in human antibody levels following exposure to BT products have been reported but there was no increased incidence in asthma or other illness. Based on laboratory studies and field experience BT insecticides have an excellent safety record.

Last Modified: 9/21/2014
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