SummaryThe human health effects of Btk are only one aspect of its effect on the environment. This page attempts to survey current literature, mostly peer reviewed, to present a balanced picture of problems that could eventually arise when Bt is introduced on a large scale into a populated setting. There are no long-term studies of health effects to date, so the information presented here allows you to make up your own mind as to whether it is a good idea to spray Bt on humans or not.
We summarize the points made in the literature and remarks below:
Can Bt live in Humans?This is an interesting question. There are no absolutely definitive studies addressing this issue, but there is a good deal of circumstantial evidence that Bt can and does survive and grow in humans:
No Spray Zone has prepared survey paper, available
here, that reviews the current literature (through 2005) on Bt and
its human health effects. The paper assumes some knowledge of medical
and biological terminology. In addition, a 2006 article published in
the Journal of Pesticide Reform
presents the information in the NSZ survey paper in a less technical
form. You can find it here.
of these articles have good bibliographies that are more
exhaustive than the list below.
This study shows that Bt can and does infect humans via inhalation. The infections are asymptomatic in healthy individuals and last at least for a few months. The immune responses noted are a little disturbing because not only will some people develop allergies to Bt, but there is some evidence that chronic diseases such as Gulf War syndrome, fibromyalgia, MCS, rheumatoid arthritis, and other autoimmune diseases may be partly caused by these "subclinical" infections by organisms heretofore considered to be harmless.
Immune responses in farm workers after exposure to Bacillus thuringiensis pesticides
Bernstein IL, Bernstein JA, Miller M, Tierzieva S, Bernstein DI, Lummus Z, Selgrade MK, Doerfler DL, Seligy VL Division of Immunology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA. firstname.lastname@example.org
Environ Health Perspect 1999 Jul;107(7):575-82
Although health risks to pesticides containing Bacillus thuringiensis (Bt) have been minimal, the potential allergenicity of these organisms has not been evaluated. Therefore, a health survey was conducted in farm workers before and after exposure to Bt pesticides. Farm workers who picked vegetables that required Bt pesticide spraying were evaluated before the initial spraying operation (n = 48) and 1 and 4 months after (n = 32 and 20, respectively). Two groups of low- (n = 44) and medium- (n = 34) exposure workers not directly exposed to Bt spraying were also assessed. The investigation included questionnaires, nasal/mouth lavages, ventilatory function assessment, and skin tests to indigenous aeroallergens and to a variety of Bt spore and vegetative preparations. To authenticate exposure to the organism present in the commercial preparation, isolates from lavage specimens were tested for Bt genes by DNA-DNA hybridization. Humoral immunoglobulin G (IgG) and immunoglobulin E (IgE) antibody responses to spore and vegetative Bt extracts were assayed. There was no evidence of occupationally related respiratory symptoms. Positive skin-prick tests to several spore extracts were seen chiefly in exposed workers. In particular, there was a significant (p < 0.05) increase in the number of positive skin tests to spore extracts 1 and 4 months after exposure to Bt spray. The number of positive skin test responses was also significantly higher in high (p < 0.05) than in low- or medium-exposure workers. The majority of nasal lavage cultures from exposed workers was positive for the commercial Bt organism, as demonstrated by specific molecular genetic probes. Specific IgE antibodies were present in more high-exposure workers (p < 0.05) than in the low and medium groups. Specific IgG antibodies occurred more in the high (p < 0.05) than in the low-exposure group. Specific IgG and IgE antibodies to vegetative organisms were present in all groups of workers. Exposure to Bt sprays may lead to allergic skin sensitization and induction of IgE and IgG antibodies, or both.
This recent study shows that anthrax and Bt are virtually the same organism. In fact, it is clear that Bt could become anthrax, if the right plasmids were available.
Review of paper in AAAS Journal (Science), June 16, 2000,
Remarkably, it appears that the ubiquitous soil-living
occasional food-poisoning culprit Bacillus cereus, the widely used
biocontrol pathogen Bacillus thuringiensis, and the life-threatening
warfare agent Bacillus anthracis are the same species, despite the
differences in phenotype. The secret appears to lie in the plasmids
by B. anthracis and B. thuringiensis. When ten B. cereus-like strains
isolated for biochemical and genetic analysis from soil taken from
outbreak sites, they were found by Helgason et al. to have the same
marker as the implicated B. anthracis strains, but no plasmids. In
natural environments these species have a relatively low rate of clone
formation, and it is known that all three Bacillus species are
able to take up plasmids. Indeed, plasmid exchange between B. cereus
B. anthracis has been verified experimentally. However, before sounding
a general alarm, it cannot be ruled out that there is some other
but as yet undetected, feature of the B. anthracis genome that makes it
alone of the three species particularly adept at retrieving and
This paper states that the difference between Bt and B. cereus is virtually nil. B. cereus causes acute gastroenteritis and meningitis.
A complete physical map of a Bacillus thuringiensis chromosome
Carlson-CR; Kolsto-AB J-Bacteriol. 1993 Feb; 175(4): 1053-60
Bacillus thuringiensis is the source of the most widely used
pesticide, through its production of insecticidal toxins. The toxin
are often localized on plasmids. We have constructed a physical map of
a Bacillus thuringiensis chromosome by aligning 16 fragments obtained
digestion with the restriction enzyme NotI. The fragments ranged from
to 1,350 kb. The size of the chromosome was 5.4 Mb. The NotI DNA
patterns of 12 different B. thuringiensis strains showed marked
The cryIA-type toxin gene was present on the chromosome in four
was extrachromosomal in four strains, and was both chromosomal and
in two strains. A Tn4430 transposon probe hybridized to 5 of the 10
chromosomal fragments, while cryIA and the transposon often hybridized
to different extrachromosomal bands. Ten of the strains were hemolytic
when grown on agar plates containing human erythrocytes. Nine of the
were positive when assayed for the presence of Bacillus cereus
We conclude that B. thuringiensis is very closely related to B. cereus
and that the distinction between B. cereus and B. thuringiensis should
Here is an example how acute toxic shock effects and longer lasting infections can result from Bt exposure. Of course, 100,000,000 spores in your nose is a lot of product. However, it does establish that infection can occur, and you can postulate in cases of weak immune response that an infection with a lower initial dose could be troublesome.
Bacillus thuringiensis serotype H34 isolated from human and insecticidal strains serotypes 3a3b and H14 can lead to death of immunocompetent mice after pulmonary infection
Hernandez,E; Ramisse,F; Cruel,T; le Vagueresse,R; Cavallo,JD
FEMS-Immunol-Med-Microbiol. 1999 May; 24(1): 43-7
In 1995, we isolated a strain of Bacillus thuringiensis
from severe human tissue necrosis. This bacterium was able to induce
in immunosuppressed mice after cutaneous infection. Its potential
for immunocompetent hosts was investigated in a mouse model of
infection. Mice infected intranasally by a suspension containing 10(8)
spores died within 8 h in a clinical toxic-shock syndrome. In the same
conditions, infection with a mutant without crystalline toxin, with the
supernatant from a culture containing 108bacteria/ml and by
the insecticidal strain serotypes 3a3b or H14 led to identical results.
Lower inocula simply induced a local inflammatory reaction with
persistence observed during the course of 10 days.
The study published by Green et al, is touted by agriculture departments and others as proof of no health effects. In fact the only conclusion was that the level of risk for Btk and other existing or future microbial pesticides in immunocompromised hosts deserves further study. This study was not, as we have been trying to point out, looking for long-term effects. To date there has never been one on Btk.
Public health implications of the microbial pesticide Bacillus thuringiensis: an epidemiological study, Oregon, 1985-86
Green-M; Heumann-M; Sokolow-R; Foster-LR; Bryant-R; Skeels-M Am-J-Public-Health. 1990 Jul; 80(7): 848-52
Bacillus thuringiensis var. kurstaki (B.t.-k) is a microbial
which has been widely used for over 30 years. Its safety for a human
living in sprayed areas has never been tested. Surveillance for human
caused by B.t.-k among Lane County, Oregon residents was conducted
two seasons of aerial B.t.-k spraying for gypsy moth control. Bacillus
isolates from cultures obtained for routine clinical purposes were
for presence of Bacillus thuringiensis (B.t.). Detailed clinical
was obtained for all B.t.-positive patients. About 80,000 people lived
in the first year's spray area, and 40,000 in the second year's area. A
total of 55 B.t.-positive cultures were identified. The cultures had
taken from 18 different body sites or fluids. Fifty-two (95 percent) of
the B.t. isolates were assessed to be probable contaminants and not the
cause of clinical illness. For three patients, B.t. could neither be
in nor out as a pathogen. Each of these three B.t.-positive patients
preexisting medical problems. The level of risk for B.t.-k and other
or future microbial pesticides in immunocompromised hosts deserves
Apparently our own cells are not sufficiently different from those of insects so that we suffer no harm from Bt pesticide exposure. Two Canadian scientists have done a simple, elegant experiment and reported their important and disturbing findings at the American Society for Microbiology conference in Chicago, spring of 1999. In this study commercial Bt products containing Bacillus thuringiensis kurstaki spores and their parasporal inclusion bodies (Btk toxin) were tested for toxic effects on insect and human cells.
Q-218 Comparative Cytotoxic Effects of Commercial Insecticidal Bacillus thuringiensis Products Using insect and Human Cell Bioassay.
A.F Tayabali, V.L. Seligy, H Health Canada, Ottowa, Ontario Canada.
Presented at General Meeting, American Society of Microbiologists, May 1999, Chicago.
Quoting the study, "The patterns of damage to insect and human
were the same". Their conclusion, "This study establishes for the first
time the cytotoxic effects of commercial Bt products, which are largely
target cell independent, resulting from an infection-like process."
This study shows that even remaining indoors during an aerial spray does not save you from being exposed to Btk organisms. In fact, your long-term exposure may be greater in your home or office than if you camped outside for a few days after the spraying. Also, wind speed and direction are major factors in bacterial dispersal.
Spatial and Temporal Distribution of Airborne Bacillus thuringiensis var. kurstaki during an Aerial Spray Program for Gypsy Moth Eradication
Kay Teschke,1,2 Yat Chow,2 Karen Bartlett,2 Andrew Ross,2 and
From Environmental Health Perspectives Volume 109, Number 1, January 2001 Environ Health Perspect 109:47-54 (2001). [Online 12 December 2000] http://ehpnet1.niehs.nih.gov/docs/2001/109p47-54teschke/abstract.html
We measured airborne exposures to the biological insecticide
thuringiensis var. kurstaki (Btk) during an aerial spray program to
gypsy moths on the west coast of Canada. We aimed to determine whether
staying indoors during spraying reduced exposures, to determine the
of temporal decay of airborne concentrations, and to determine whether
drift occurred outside the spray zone. During spraying, the average
airborne Btk concentration measured outdoors within the spray zone was
739 colony-forming units (CFU)/m3 of air. Outdoor air concentrations
over time, quickly in an initial phase with a half time of 3.3 hr, and
then more slowly over the following 9 days, with an overall half-time
about 2.4 days. Inside residences during spraying, average
were initially 2-5 times lower than outdoors, but at 5-6 hr after
began, indoor concentrations exceeded those outdoors, with an average
244 CFU/m3 vs. 77 CFU/m3 outdoors, suggesting that the initial benefits
of remaining indoors during spraying may not persist as outside air
indoors with normal daily activities. There was drift of culturable Btk
throughout a 125- to 1,000-meter band outside the spray zone where
were made, a consequence of the fine aerosol sizes that remained
(count median diameters of 4.3 to 7.2 µm). Btk concentrations
the spray zone were related to wind speed and direction, but not to
from the spray zone.
Here is a quote from the USDA's Final EIS on Gypsy Moth Control, Appendix F Vol. III of V (Nov. '95) showing that there could be at least some difference in infectivity depending on the composition of the bacterial suspension:
"...several studies indicate that B.t.k. can be recovered from exposed mammals but that recovery decreases relatively fast after exposure is terminated. In this respect, the study by Oshodi and Macnaughtan (1990, Btk preparation manual by the manufacturer of Foray48B Novo Nordisk) is somewhat unusual. After inhalation exposure to Foray 48B, the numbers of viable B.t.k. spores recovered from the lungs [of mammals] did not decrease substantially during a 28-day observation period." (p. 4-6).
It looks like Bt can actually survive in the gut of a human and set up residence there also.
Isolation and characterization of Bacillus cereus-like bacteria from faecal samples from greenhouse workers who are using Bacillus thuringiensis-based insecticides
International Archives of Occupational and Environmental Health, 2001
Gert B. Jensen1, , Preben Larsen2, Bodil L. Jacobsen3, Bodil Madsen3, Andrea Wilcks1, Lasse Smidt1 and Lars Andrup1
(1) Department of Chemical Working Environment, National
of Occupational Health, Lerso Parkalle 105, 2100 Copenhagen, Denmark
Abstract: Since the discovery of the insecticidal
Bacillus thuringiensis at the beginning of the twentieth century, this
bacterium has been used increasingly against various insect pests. In
of the extensive use of B. thuringiensis, only sporadic clinical
case reports have been published. In recent years, the close
between B. thuringiensis and the human pathogen Bacillus cereus has
confirmed. In practice, only the insecticidal activity of B.
distinguishes the two species. However, both species are composed of
of isolates with varying potential for causing adverse effects in
The aim of this study was to employ molecular biology methods for
of occupational exposure to B. thuringiensis-based biopesticides by
of specific genetic information including plasmid profiles and random
polymorphic DNA (RAPD). Methods: Faecal samples from 12 persons,
in Danish greenhouses, were collected for microbial analysis. Seven
were using B. thuringiensis-based insecticides, whereas five persons
employed at greenhouses that did not use B. thuringiensis. The bacteria
were isolated on B. cereus-specific solid substrate, and colonies were
further identified using the polymerase chain reaction (PCR). The PCR
was used for the identification of the enterotoxin genes HblA and BceT.
The expression of enterotoxins was detected with two commercial
kits. Primers specific for 16S-23S spacer region were used to identify
the bacteria as members of the B. cereus group. Several primers towards
insecticidal genes have been used in order to further characterize the
isolates as subspecies of B. thuringiensis.
IDEAS AND PERSPECTIVES Could Bt transgenic crops have nutritionally favourable effects on resistant insects?
Ali H. Sayyed , Hugo Cerda and Denis J. Wright
Ecology Letters, (2003) 6: 167-169 2003.Blackwell Publishing Ltd/CNRS
R. Spiewak, C. Skorska, A. Góra1, A. Horoch, J.
Ann Agric Environ Med 2001, 8, 255–259.
Abstract: 75 farming
students (49 males and 26 females aged 16–23 years) underwent
dermatological, laryngological and pulmonary examination, skin prick
tests with common and farm allergens, Phadiatop and total IgE
measurement. After that, the migration inhibition tests with antigens
of airborne microbes typical for farm environment (Saccharopolyspora rectivirgula, Pantoea
agglomerans, and Aspergillus fumigatus) were carried out.
Possible differences between students with positive results and those
non-reactive were sought.
(12) Maternal and fetal exposure to pesticides associated to genetically modified foods in Eastern Townships of Quebec, Canada
Aziz Aris, Aziz and Leblanc, Samuel
J. Reproductive Toxicology, 2, 2004
Pesticides associated to genetically modified foods (PAGMF), are engineered to tolerate herbicides such as glyphosate (GLYP) and gluphosinate (GLUF) or insecticides such as the bacterial toxin bacillus thuringiensis (Bt). The aim of this study was to evaluate the correlation between maternal and fetal exposure, and to determine exposure levels of GLYP and its metabolite amino methylphosphoricacid (AMPA), GLUF and its metabolite 3-methylphosphinicopropionicacid (3-MPPA) and Cry1Abprotein (a Bt toxin) in Eastern Townships of Quebec, Canada. Blood of thirty pregnant women (PW) and thirty-nine non pregnant women (NPW) were studied. Serum GLYP and GLUF were detected in NPW and not detected in PW. Serum 3-MPPA and CryAb1 toxin were detected in PW, their fetuses and NPW. This is the first study to reveal the presence of circulating PAGMF in women with and without pregnancy, paving the way for a new field in reproductive toxicology including nutrition and utero-placental toxicities.
To our knowledge, this is the first study to highlight the presence of pesticides-associated genetically modified foods in maternal, fetal and non pregnant women’s blood. 3-MPPA and Cry1Ab toxin are clearly detectable and appear to cross the placenta to the fetus. Given the potential toxicity of these environmental pollutants and the fragility of the fetus, more studies are needed, particularly those using the placental transfer approach.
Thus, our present results will provide baseline data for future studies exploring a new area of research relating to nutrition, toxicology and reproduction in women. Today, obstetric-gynecological disorders that are associated with environmental chemicals are not known.
This may involve perinatal complications (i.e. abortion, prematurity, intra uterine growth restriction and preeclampsia) and reproductive disorders (i.e. infertility, endometriosis and gynecological cancer). [emphasis NSZ]
Thus, knowing the actual PAGMF concentrations in humans constitutes a cornerstone in the advancement of research in this area.