A l'iles de Ré à ecouter interessant :
ADVERSE HEALTH CONSEQUENCES FOLLOWING AERIAL SPRAYING WITH
BACILLUS THURINGIENSIS (VAR. KURSTAKI) (BTK), TO CONTROL THE GYPSY
MOTH: FLAWS IN GOVERNMENT RISK ASSESSMENTS AND IN PUBLIC HEALTH
By R.B. Philp, D.V.M., Ph.D.
We summarize the points made in the literature and remarks below:
- Bt is the same cellular organism as B. cereus (causes gastroenteritis) and B. anthracis (causes anthrax). The only difference is in one "organelle" of the cell, called a plasmid, that produces proteins. Each plasmid produces a unique protein that attacks a target life form. In the case of Bt, that life form is a caterpillar or other insect life forms.
- Can Bt become anthrax? Theoretically, yes - it could exchange a plasmid with a wild anthrax germ. Also, it is not easy to tell anthrax, B. cereus, and Bt apart - they look the same and grow in the same environments, and even test the same in some genetic tests. See this Seattle Weekly article for an interesting view.
- When Bt is sprayed, it can and does infect many people in the target zone, setting up colonies in their respiratory tract and maybe in their intestines that live for weeks or months. The effects of this are not known. Obvious symptoms do not appear, but what could happen years from now as a result of these infections is anyone's guess. It is suspected that "symptomless" infections can challenge the immune system and cause disease later (diabetes, multiple sclerosis, and lupus are some under consideration).
- There is growing evidence that exposure to inhaled bacterial antigens that generate immune responses in humans (a potential for allergic reactions) can trigger skin allergic reactons of various types in some individuals. Bt falls into this category. Epidemiological studies have so far almost completely ignored dermatological symptoms. There are a significant number of anecdotal reports of skin symptoms after sprayings of Bt products in New Zealand (see New Zealand CC-PAM Health Incident Report at this link).
- The same Bt pesticides that are sprayed on crops produce detectable residues in foods, even processed foods such as pasta. Gastroenteritis (food poisoning or "stomach flu") can result. It is estimated that a sizeable percentage of such diseases that were previously thought to be caused by B. cereus are actually caused by Bt insecticides.
- People with sensitive immune systems could be affected in ways we do not yet know, but immune responses are seen when Bt infections establish in humans.
- Closing your house up will not prevent Bt from getting in. Staying indoors for even one day after a spraying will still expose you to significant amounts of Bt spores.
- Bt endotoxins may cause unexpected effects; for instance, some insects consuming genetically modified crops that produce Bt endotoxin actually grow faster. This could because the toxin is actually being used as food, but in experiments the insects had all the preferred food they could eat. An even more probable reason could be that Bt endotoxin acts as a hormone mimicing substance (this is not the first bacterial toxin to show this behavior). These types of substances (also called endocrine disrupters) are increasingly suspected of causing serious health problems in humans.
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:
- The culture media used to grow Bt in the lab is the same media used to grow other human pathogenic bacteria.
- The conditions for growth of Bt (pH 7.4, temperature 37oC, moist environment) are found in humans.
- Humans develop antibodies to the Bt organism.
- Even four months after a single exposure, Bt organisms of the same strain as the pesticide used in the exposure can be cultured from nasal swabs. It is unlikely that the original spores would still be present after this period of time.
- There are a few studies that show Bt canand does cause gastroenteritis in humans and that you can recover culturable Bt from nursery workers feces, indicating that Bt can live and grow in the intestinal tract.
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.
Katerine : Liberté (2010)