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United States Department of Agriculture

Agricultural Research Service

Title: The Mammalian Safety of Bacillis Thurengiensis-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 1, 2001
Citation: Siegel, J.P. 2001. The mammalian safety of bacillis thurengiensis-based insecticides. Journal of Invertebrate Pathology. 77: 13-21.

Interpretive Summary: One hundred seventy seven (177) products containing the insect pathogen Bacillus thuringiensis (Bt) have been registered in the United States as of 1995. Numerous laboratory studies have been conducted on its safety and these studies have demonstrated that Bt is noninfectious and nontoxic to mammals at doses used in the field. Mortality has occurred in these laboratory studies only when exceedingly high doses were used (>=one hundred million spores per mouse). In contrast, as little as one spore of Bacillus anthracis can kill a mouse. The have only been two literature reports of human infection in the last four years. The infected individuals had received extensive burns or blast injuries that compromised their immune system. Several studies have followed aerial spray campaigns of Bt and these studies reported no increase in illness after spraying. Several recent papers have reported that in the laboratory, isolates of Bt produce Bacillus cereus enterotoxins, which can cause vomiting and diarrhea However, there is no evidence that commercial products contain these toxins, and based on the laboratory and field studies 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 Bacillus thuringiensis (Bt). Numerous laboratory studies have demonstrated that Bt and Bt products are noninfectious and are toxic to mammals only at a dose >/= one hundred million colony forming units (cfu) per mouse (a human equivalent based on weight of > 100 billion cfu). There are only two literature reports of Bt infection in man between the year 1997 and the present, and 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 reported no increased incidence of illness. Some recent papers have expressed concern about the production of Bacillus 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 inhuman antibody levels following exposure to Bt products have been reported but there was no increased incidence of asthma or other illness. Based on laboratory studies and field experience, Bt insecticides have an excellent safety record.

Last Modified: 12/21/2014
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