Toxicity and Infectivity of Bacillus thuringiensis to Mammals Based on Studies Submitted to the US Environmental Protection Agencya

Bacterial Species Animal/Test Dose per Animal Effect

B. thuringiensis Rat/Acute Oral > 1011 spores/kg No toxicity or infectivity susbp. kurstaki' Rat/Acute Dermal > 1011 spores/kg No toxicity or infectivity

Effect ra

Rat/Inhalation > 107 spore/L No toxicity or infectivity

Rat/2-year Oral 8.4 g/kg per day Weight loss, but no toxicity or infectivity Human/Acute Oral 1 g/day for 3 days No toxicity or infectivity

B. thuringiensis Rabbit/Acute Oral > 109 spores subsp. israelensisc Rabbit/Acute Dermal > 6.3 g/kg

Rat/Acute Oral > 1011 spores/kg

No infectivity No toxicity or infectivity No pathogenicity or infectivity No toxicity or infectivity No infectivity

Rat/Acute Dermal Rat/Inhalation

> 1011 spores/kg 8 x 107 spores a Data from McClintock, J.T., Schaffer, C.R., and Sjoblad, R.D., A Comparative review of the mammalian toxicity of Bacillus thuringiensis-based pesticides, Pestic. Sci. 45, 95, 1995. b Principal insecticidal proteins: Cry1Aa, Cry1Ab, Cry1Ac, and Cry2Aa. c Principal insecticidal proteins: Cry4Aa, Cry4Ab, Cry11Aa, and Cyt1Aa.

are based on a lack of reported effects, i.e., the overall lack of reported infections or other documented cases of disease, especially in areas where human populations numbering in the tens of thousands have been exposed to Bt applications during aerial spray programs to eliminate lepidopteran forest pests (see Section 3.3.2.3).

As noted above, bacterial insecticides based on Bt have been used commercially for almost 50 years, and current commercial production of these insecticides is estimated to be several tons annually.37 Given this level of human exposure resulting from the use of Bt insecticides in agriculture, forestry, and vector control, numerous studies have been published on the direct or putative effects of Bt on human health.5 An overall assessment of these studies demonstrates that Bt poses little if any risk to human health.5636 Just as compelling, as noted above, is the extreme rarity of reports of putative clinical infections in humans caused by Bt, or reports that Bt — especially the Bt strains in commercial products as opposed to isolates from natural environments — are the cause of gastrointestinal illness resulting from food poisoning. To substantiate the view that Bt insecticides are safe for humans, below we provide an overview and assessment of the literature regarding Bt as a source of putative infections and gastrointestinal illness, paying particular attention to whether any of these cases were caused by strains that originated from commercial bacterial insecticides.

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