Published Date: 2013-10-14 19:56:38
Subject: PRO/EDR> Infant botulism - USA (07): 8th botulinum toxin
Archive Number: 20131014.2001671
INFANT BOTULISM - USA (07): EIGHTH BOTULINUM TOXIN
**************************************************
A ProMED-mail post
http://www.promedmail.org
ProMED-mail is a program of the
International Society for Infectious Diseases
http://www.isid.org
Date: Thu 10 Oct 2013
Source: Center for Infectious Disease Research and Policy (CIDRAP) [edited]
http://www.cidrap.umn.edu/news-pers...-new-botulinum-toxin-withhold-genetic-details
Scientists have discovered the 1st new type of botulinum toxin in 40 years, and in a highly unusual move, they are keeping the toxin's genetic sequence data secret for now so that no one can make it in a lab before an effective antitoxin can be developed. Until now, _Clostridium botulinum_ was known to produce 7 types of toxins, all of which cause paralysis by blocking neurotransmitters in humans and animals. The last one was discovered in 1970.
The researchers discovered the new toxin, called botulinum neurotoxin type H, or BoNT/H, as a result of a case of infant botulism. They reported the discovery in 2 articles published this week in the Journal of Infectious Diseases (JID). Antitoxins are available for the 7 other botulinum toxin types, but not for the new one.
The authors, most of whom are with the California Department of Public Health (CDPH), themselves proposed to omit the genetic data and consulted with a number of federal government agencies about the handling of their findings, said David C. Hooper, MD, deputy editor of JID and an infectious diseases physician at Massachusetts General Hospital and Harvard Medical School.
"We as editors had a lot of internal discussion as well and decided the information was important enough to proceed with publication, after scientific review, with withholding of the sequence data," he told CIDRAP News. "And it wouldn't be withheld forever," because the plan is to publish the data after an antitoxin is developed.
The authors believed that the genetic sequence information "poses an immediate and unusually serious risk to society," wrote David A. Relman, MD, of Stanford University and the Veterans Affairs Palo Alto Health Care System in California, in an accompanying editorial. He said the authors "decided to exercise voluntary prepublication control and to withhold this specific information."
The handling of the toxin discovery recalls the heated controversy that erupted in late 2011 and early 2012 when 2 teams of authors announced plans to publish details about lab-modified H5N1 avian influenza strains that showed airborne transmissibility in ferrets. The studies were supported by the US National Institutes of Health.
In those cases, the NSABB [National Science Advisory Board for Biosecurity] initially recommended against publication of the full methodological details out of concern that full disclosure could lead to an intentional or unintentional release of dangerous viruses. The recommendation triggered prolonged and intense debate in scientific and public health circles. The board eventually endorsed publication after the authors briefed the group and made some clarifications in their manuscripts. The papers were published in May and June of 2012.
JID's general policy is to require authors to submit gene nucleotide sequences to the International Nucleotide Sequence Databases and include the accession numbers in their manuscript, notes an editorial by Hooper and Editor Martin S. Hirsch, MD. But in this case, they made an exception. The authors had "detailed consultations" with numerous government agencies, including the National Institute of Allergy and Infectious Diseases, CDC, the Department of Homeland Security, and the FBI, the editorial says. The upshot was that they "received approval to publish both manuscripts, while withholding the key gene sequences until appropriate countermeasures were developed."
Stephen S. Arnon, MD, of the CDPH, a coauthor of the 2 reports, commented briefly today [10 Oct 2013] on the background of the decision to withhold the genetic data. "CDPH recognized the potential bio-threat implications of a new botulinum toxin and engaged with appropriate federal agencies in discussions about how to publish information about the new type," he said.
When asked whether the issue triggered much debate, Arnon said: "There was agreement that it would be possible to publish this information to achieve the scientific and public health benefits of making this information known. The information published is important for the diagnosis, treatment, and control of botulism."
The researchers published 2 reports in JID. One, by Jason R. Barash and Arnon, describes how they discovered the new toxin; the other, by Barash, Arnon, and 3 others, describes the genome sequencing of the toxin. Two of the authors are with Los Alamos National Laboratory.
The researchers, according to the 1st report, identified the new toxin after determining that a toxin from a patient sample of _C. botulinum_ could not be neutralized by any of the 7 antitoxins available from the CDC, which cover types A through G. They learned this by dosing mice with combinations of the _C. botulinum_ strain, called IBCA10-7060, and each of the antitoxins.
They also determined that the IBCA10-7060 produces toxin type B as well as type H and that type B was present in larger quantities. In further work, the team used rabbits to develop an antitoxin against IBCA10-7060. They found that it protected mice from the strain, but its potency was fairly low, compared with that of the existing CDC antitoxins.
"The recognition of novel BoNT/H after an interval of almost half a century serves as a reminder that additional novel botulinum toxin types likely await discovery and that for this purpose, the mouse bioassay remains indispensable," the report concludes.
Hooper and Relman said they're not aware of previous cases in which life sciences researchers voluntarily withheld findings because of security concerns, although there were similar cases in the cryptography realm in the 1980s. "I don't know of particular other instances, and this is clearly an exception to our usual practice," said Hooper. "I think these are instances we're striving to think very carefully about and to proceed on a case-by-case basis, to balance the free flow of scientific information with security needs."
Relman told CIDRAP News, "In the world of the life sciences, I am not aware of a definite [previous] example; however, I imagine that it has happened not infrequently, as researchers stumble upon information that poses an unusual risk, e.g., a mutant strain created in the laboratory that has unexpected properties of heightened virulence, transmissibility, or drug resistance."
As for whether the current case sets an important example for future research publication dilemmas, Hooper said, "I think each instance really needs to be decided very carefully on a case-by-case basis, so I don't see this as necessarily setting some strong precedent. It's important that there be careful discussions on how to balance science and security issues." Hooper said he doesn't see any negative effects of the secrecy, aside from the delayed release of the genetic information itself. An effort to develop a suitable antitoxin is underway, "but exactly when it'll be available, once can't say with date certain," he added.
Relman expressed hope that the botulinum toxin discovery "will become a valuable test case where unusually risky information prompts serious discussion about the benefits and risks of limited communication, and the mechanisms by which this can be undertaken, in order to buy time for risk mitigation, e.g., development of new countermeasures."
In his editorial and in comments to CIDRAP News, Relman spoke of scientific information that falls in a "gray area," in that immediate full dissemination may pose security risks, but formal classification as secret might be inappropriate because it could hinder research on needed countermeasures.
In the case of the H5N1 transmissibility studies, he wrote, "the absence of a mechanism, other than classification, for limited distribution of the information confounded policy makers. The need for such a mechanism now deserves renewed serious deliberation and wider discussion, because we are inadequately served by just 2 options, that is, unrestricted dissemination and classification."
He said the toxin discovery is a good example of the kind of data that fall in the gray area. The strategy the authors used "has merit and deserves careful consideration, but some major caveats should be noted," he wrote in the editorial.
One problem is that the strategy offers only temporary benefits, since data will inevitably be disseminated, Relman wrote. Another is that the strategy endangers research in general if decisions to withhold data "are made casually, arbitrarily, or frequently."
"I hope that this discovery forces policy-makers, scientists, and other members of the general society to confront the reality of increasingly frequent and consequential risks that arise from work in the life sciences, and develop more robust strategies for risk mitigation," Relman added in comments to CIDRAP News. "I am quite worried that the challenges and complexities of developing such strategies have caused many scientists, science policy-makers and others in government to turn away, and either proclaim that the risks are not real, or that we have no such mechanisms for limited communication and, therefore, that we should stop working on this," he said.
[Byline: Robert Roos]
--
Communicated by:
ProMED-mail
<promed@promedmail.org>
[Since in infant botulism, the toxin is elaborated in vivo, isolation of the organism from the gastrointestinal tract is more readily done.
The authors of the work and the editors of JID are on firm ground, the moderator believes, in the initial withholding of the specific gene sequences for this newly recognized botulinum toxin. The citations, published online one week ago, are shown below:
Barash JR, Arnon SH: A novel strain of _Clostridium botulinum_ that produces type B and type H botulinum toxins. J Infect Dis 2013; online publication Oct 7. PMID: 24106296
Abstract
--------
Background:
_Clostridium botulinum_ strain IBCA10-7060, isolated from a patient with infant botulism, produced botulinum neurotoxin type B (BoNT/B) and another BoNT that, by use of the standard mouse bioassay, could not be neutralized by any of the CDC-provided monovalent polyclonal botulinum antitoxins raised against BoNT types A-G.
Methods and Results:
The combining of antitoxins to neutralize the toxicity of known bivalent _C. botulinum__ strains Ab, Ba, Af, and Bf also failed to neutralize the 2nd BoNT. Analysis of culture filtrate by double immunodiffusion yielded a single line of immunoprecipitate with anti-A, anti-B, and anti-F botulinum antitoxins but not with anti-E antitoxin. A heptavalent F(ab')2 botulinum antitoxin A-G obtained from the US Army also did not neutralize the 2nd BoNT. An antitoxin raised against IBCA10-7060 toxoid protected mice against BoNT/B (Okra) and against the 2nd BoNT but did not protect mice against BoNT/A (Hall) or BoNT/F (Langeland).
Conclusions:
The 2nd BoNT thus fulfilled classic criteria for being designated BoNT/H. IBCA10-7060 is the 1st _C. botulinum_ type Bh strain to be identified. BoNT/H is the 1st new botulinum toxin type to be recognized in greater than 40 years, and its recognition could not have been accomplished without the availability of the mouse bioassay.
Dover N, Barash JR, Hill KK, Xie G, Arnon SS: Molecular characterization of a novel botulinum neurotoxin type H gene. J Infect Dis 2013; online publication Oct 7. PMID: 24106295
Abstract
--------
We sequenced the 2 botulinum toxin gene clusters of _Clostridium botulinum_ strain IBCA10-7060 type Bh. The sequence of bont/H differed substantially from the sequences of the 7 known bont genes for toxin types A-G. The 5' 1/3rd terminus of bont/H that codes for the botulinum toxin light chain differed markedly from the light chain coding sequences of toxin types A-G. The 3' 2/3rds terminus of bont/H that codes for the botulinum toxin heavy chain contained a novel Hn translocation domain coding sequence and a nonneutralizing type A-like Hc binding domain coding sequence. Bont/H was part of an orfX toxin gene cluster that was located at a unique chromosomal site distant from those used by other botulinum toxin gene clusters. The bont/B sequence was similar to that of subtype bont/B2 and was located within its ha toxin gene cluster at the oppA/brnQ site. Our findings further establish that _C. botulinum_ IBCA10-7060 produces novel BoNT/H.
The mechanism of action of the botulinum toxins varies depending on the toxin type but all do block neuromuscular transmission at synapses causing problems with SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins. Presumably, the novel H toxin works similarly.
Toxin types A, C1, and E cleave synaptosomal-associated proteins of 25 kDa (SNAP-25). Types B, D, F, and G cleave vesicle-associated membrane protein (VAMP), also known as synaptobrevin. Proteolytic cleavage of the SNAREs disables the exocytotic machinery, and thus exocytosis of acetylcholine is inhibited. When the target tissue is a muscle, this chemical denervation results in paresis.
Type A toxin causes an amazingly extended neuroparalysis that lasts for months in humans. Such a prolonged therapeutic effect has been attributed to 1) a long lifetime of the toxin's protease activity, 2) anchoring of the light chain to the presynaptic membrane, 3) persistence of the toxin-truncated SNAP-25, and 4) endplate remodeling. In vivo imaging of individual nerve terminals in mouse muscle revealed that blockade of acetylcholine release results in nerve sprouting, with the creation of functional synapses extra-junctionally. On the eventual recovery of endocytotic/exocytotic activity at the parent terminals, retraction of the sprouts occurs with a return to the exact compact shape of the original endplate. (Source: http://www.neurotoxininstitute.org/chapter_moa_print.htm.)
Related to botulinum toxin as a biowarfare agent, it can be spread by inhalation as well as by ingestion or, with wound and infant botulism, by _in situ_ production of toxin in the cutaneous or gastrointestinal areas. In the Working Group on Civilian Biodefense's review on botulinum toxin as a biological weapon (1), the following is stated (with the citations removed):
"A 4th, man-made form that results from aerosolized botulinum toxin is inhalational botulism. This mode of transmission has been demonstrated experimentally in primates, has been attempted by bioterrorists, and has been the intended outcome of at least one country's specially designed missiles and artillery shells. Inhalational botulism has occurred accidentally in humans. A brief report from West Germany in 1962 described 3 veterinary personnel who were exposed to reaerosolized botulinum toxin while disposing of rabbits and guinea pigs whose fur was coated with aerosolized type A botulinum toxin. Type A botulinum toxin was detected in serum samples from all 3 affected individuals."
The laboratory incident citation (2) is in German. All 3 individuals developed weakness, were treated with antitoxin, and survived. As I recall, none required respiratory support. Unlike many other biological warfare agents, the symptoms of intentional spread of botulism are no different than those of natural disease. Suspicions should arise when a large number of cases occur.
1. Arnon SS, Schechter R, Inglesby TV, et al: Botulinum toxin as a biological weapon. Medical and public health management. JAMA 2001; 285:1059-70.
2. Holzer VE: Botulism from inhalation [in German]. Med Klin 1962; 57:1735-38. - Mod.LL
Subject: PRO/EDR> Infant botulism - USA (07): 8th botulinum toxin
Archive Number: 20131014.2001671
INFANT BOTULISM - USA (07): EIGHTH BOTULINUM TOXIN
**************************************************
A ProMED-mail post
http://www.promedmail.org
ProMED-mail is a program of the
International Society for Infectious Diseases
http://www.isid.org
Date: Thu 10 Oct 2013
Source: Center for Infectious Disease Research and Policy (CIDRAP) [edited]
http://www.cidrap.umn.edu/news-pers...-new-botulinum-toxin-withhold-genetic-details
Scientists have discovered the 1st new type of botulinum toxin in 40 years, and in a highly unusual move, they are keeping the toxin's genetic sequence data secret for now so that no one can make it in a lab before an effective antitoxin can be developed. Until now, _Clostridium botulinum_ was known to produce 7 types of toxins, all of which cause paralysis by blocking neurotransmitters in humans and animals. The last one was discovered in 1970.
The researchers discovered the new toxin, called botulinum neurotoxin type H, or BoNT/H, as a result of a case of infant botulism. They reported the discovery in 2 articles published this week in the Journal of Infectious Diseases (JID). Antitoxins are available for the 7 other botulinum toxin types, but not for the new one.
The authors, most of whom are with the California Department of Public Health (CDPH), themselves proposed to omit the genetic data and consulted with a number of federal government agencies about the handling of their findings, said David C. Hooper, MD, deputy editor of JID and an infectious diseases physician at Massachusetts General Hospital and Harvard Medical School.
"We as editors had a lot of internal discussion as well and decided the information was important enough to proceed with publication, after scientific review, with withholding of the sequence data," he told CIDRAP News. "And it wouldn't be withheld forever," because the plan is to publish the data after an antitoxin is developed.
The authors believed that the genetic sequence information "poses an immediate and unusually serious risk to society," wrote David A. Relman, MD, of Stanford University and the Veterans Affairs Palo Alto Health Care System in California, in an accompanying editorial. He said the authors "decided to exercise voluntary prepublication control and to withhold this specific information."
The handling of the toxin discovery recalls the heated controversy that erupted in late 2011 and early 2012 when 2 teams of authors announced plans to publish details about lab-modified H5N1 avian influenza strains that showed airborne transmissibility in ferrets. The studies were supported by the US National Institutes of Health.
In those cases, the NSABB [National Science Advisory Board for Biosecurity] initially recommended against publication of the full methodological details out of concern that full disclosure could lead to an intentional or unintentional release of dangerous viruses. The recommendation triggered prolonged and intense debate in scientific and public health circles. The board eventually endorsed publication after the authors briefed the group and made some clarifications in their manuscripts. The papers were published in May and June of 2012.
JID's general policy is to require authors to submit gene nucleotide sequences to the International Nucleotide Sequence Databases and include the accession numbers in their manuscript, notes an editorial by Hooper and Editor Martin S. Hirsch, MD. But in this case, they made an exception. The authors had "detailed consultations" with numerous government agencies, including the National Institute of Allergy and Infectious Diseases, CDC, the Department of Homeland Security, and the FBI, the editorial says. The upshot was that they "received approval to publish both manuscripts, while withholding the key gene sequences until appropriate countermeasures were developed."
Stephen S. Arnon, MD, of the CDPH, a coauthor of the 2 reports, commented briefly today [10 Oct 2013] on the background of the decision to withhold the genetic data. "CDPH recognized the potential bio-threat implications of a new botulinum toxin and engaged with appropriate federal agencies in discussions about how to publish information about the new type," he said.
When asked whether the issue triggered much debate, Arnon said: "There was agreement that it would be possible to publish this information to achieve the scientific and public health benefits of making this information known. The information published is important for the diagnosis, treatment, and control of botulism."
The researchers published 2 reports in JID. One, by Jason R. Barash and Arnon, describes how they discovered the new toxin; the other, by Barash, Arnon, and 3 others, describes the genome sequencing of the toxin. Two of the authors are with Los Alamos National Laboratory.
The researchers, according to the 1st report, identified the new toxin after determining that a toxin from a patient sample of _C. botulinum_ could not be neutralized by any of the 7 antitoxins available from the CDC, which cover types A through G. They learned this by dosing mice with combinations of the _C. botulinum_ strain, called IBCA10-7060, and each of the antitoxins.
They also determined that the IBCA10-7060 produces toxin type B as well as type H and that type B was present in larger quantities. In further work, the team used rabbits to develop an antitoxin against IBCA10-7060. They found that it protected mice from the strain, but its potency was fairly low, compared with that of the existing CDC antitoxins.
"The recognition of novel BoNT/H after an interval of almost half a century serves as a reminder that additional novel botulinum toxin types likely await discovery and that for this purpose, the mouse bioassay remains indispensable," the report concludes.
Hooper and Relman said they're not aware of previous cases in which life sciences researchers voluntarily withheld findings because of security concerns, although there were similar cases in the cryptography realm in the 1980s. "I don't know of particular other instances, and this is clearly an exception to our usual practice," said Hooper. "I think these are instances we're striving to think very carefully about and to proceed on a case-by-case basis, to balance the free flow of scientific information with security needs."
Relman told CIDRAP News, "In the world of the life sciences, I am not aware of a definite [previous] example; however, I imagine that it has happened not infrequently, as researchers stumble upon information that poses an unusual risk, e.g., a mutant strain created in the laboratory that has unexpected properties of heightened virulence, transmissibility, or drug resistance."
As for whether the current case sets an important example for future research publication dilemmas, Hooper said, "I think each instance really needs to be decided very carefully on a case-by-case basis, so I don't see this as necessarily setting some strong precedent. It's important that there be careful discussions on how to balance science and security issues." Hooper said he doesn't see any negative effects of the secrecy, aside from the delayed release of the genetic information itself. An effort to develop a suitable antitoxin is underway, "but exactly when it'll be available, once can't say with date certain," he added.
Relman expressed hope that the botulinum toxin discovery "will become a valuable test case where unusually risky information prompts serious discussion about the benefits and risks of limited communication, and the mechanisms by which this can be undertaken, in order to buy time for risk mitigation, e.g., development of new countermeasures."
In his editorial and in comments to CIDRAP News, Relman spoke of scientific information that falls in a "gray area," in that immediate full dissemination may pose security risks, but formal classification as secret might be inappropriate because it could hinder research on needed countermeasures.
In the case of the H5N1 transmissibility studies, he wrote, "the absence of a mechanism, other than classification, for limited distribution of the information confounded policy makers. The need for such a mechanism now deserves renewed serious deliberation and wider discussion, because we are inadequately served by just 2 options, that is, unrestricted dissemination and classification."
He said the toxin discovery is a good example of the kind of data that fall in the gray area. The strategy the authors used "has merit and deserves careful consideration, but some major caveats should be noted," he wrote in the editorial.
One problem is that the strategy offers only temporary benefits, since data will inevitably be disseminated, Relman wrote. Another is that the strategy endangers research in general if decisions to withhold data "are made casually, arbitrarily, or frequently."
"I hope that this discovery forces policy-makers, scientists, and other members of the general society to confront the reality of increasingly frequent and consequential risks that arise from work in the life sciences, and develop more robust strategies for risk mitigation," Relman added in comments to CIDRAP News. "I am quite worried that the challenges and complexities of developing such strategies have caused many scientists, science policy-makers and others in government to turn away, and either proclaim that the risks are not real, or that we have no such mechanisms for limited communication and, therefore, that we should stop working on this," he said.
[Byline: Robert Roos]
--
Communicated by:
ProMED-mail
<promed@promedmail.org>
[Since in infant botulism, the toxin is elaborated in vivo, isolation of the organism from the gastrointestinal tract is more readily done.
The authors of the work and the editors of JID are on firm ground, the moderator believes, in the initial withholding of the specific gene sequences for this newly recognized botulinum toxin. The citations, published online one week ago, are shown below:
Barash JR, Arnon SH: A novel strain of _Clostridium botulinum_ that produces type B and type H botulinum toxins. J Infect Dis 2013; online publication Oct 7. PMID: 24106296
Abstract
--------
Background:
_Clostridium botulinum_ strain IBCA10-7060, isolated from a patient with infant botulism, produced botulinum neurotoxin type B (BoNT/B) and another BoNT that, by use of the standard mouse bioassay, could not be neutralized by any of the CDC-provided monovalent polyclonal botulinum antitoxins raised against BoNT types A-G.
Methods and Results:
The combining of antitoxins to neutralize the toxicity of known bivalent _C. botulinum__ strains Ab, Ba, Af, and Bf also failed to neutralize the 2nd BoNT. Analysis of culture filtrate by double immunodiffusion yielded a single line of immunoprecipitate with anti-A, anti-B, and anti-F botulinum antitoxins but not with anti-E antitoxin. A heptavalent F(ab')2 botulinum antitoxin A-G obtained from the US Army also did not neutralize the 2nd BoNT. An antitoxin raised against IBCA10-7060 toxoid protected mice against BoNT/B (Okra) and against the 2nd BoNT but did not protect mice against BoNT/A (Hall) or BoNT/F (Langeland).
Conclusions:
The 2nd BoNT thus fulfilled classic criteria for being designated BoNT/H. IBCA10-7060 is the 1st _C. botulinum_ type Bh strain to be identified. BoNT/H is the 1st new botulinum toxin type to be recognized in greater than 40 years, and its recognition could not have been accomplished without the availability of the mouse bioassay.
Dover N, Barash JR, Hill KK, Xie G, Arnon SS: Molecular characterization of a novel botulinum neurotoxin type H gene. J Infect Dis 2013; online publication Oct 7. PMID: 24106295
Abstract
--------
We sequenced the 2 botulinum toxin gene clusters of _Clostridium botulinum_ strain IBCA10-7060 type Bh. The sequence of bont/H differed substantially from the sequences of the 7 known bont genes for toxin types A-G. The 5' 1/3rd terminus of bont/H that codes for the botulinum toxin light chain differed markedly from the light chain coding sequences of toxin types A-G. The 3' 2/3rds terminus of bont/H that codes for the botulinum toxin heavy chain contained a novel Hn translocation domain coding sequence and a nonneutralizing type A-like Hc binding domain coding sequence. Bont/H was part of an orfX toxin gene cluster that was located at a unique chromosomal site distant from those used by other botulinum toxin gene clusters. The bont/B sequence was similar to that of subtype bont/B2 and was located within its ha toxin gene cluster at the oppA/brnQ site. Our findings further establish that _C. botulinum_ IBCA10-7060 produces novel BoNT/H.
The mechanism of action of the botulinum toxins varies depending on the toxin type but all do block neuromuscular transmission at synapses causing problems with SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins. Presumably, the novel H toxin works similarly.
Toxin types A, C1, and E cleave synaptosomal-associated proteins of 25 kDa (SNAP-25). Types B, D, F, and G cleave vesicle-associated membrane protein (VAMP), also known as synaptobrevin. Proteolytic cleavage of the SNAREs disables the exocytotic machinery, and thus exocytosis of acetylcholine is inhibited. When the target tissue is a muscle, this chemical denervation results in paresis.
Type A toxin causes an amazingly extended neuroparalysis that lasts for months in humans. Such a prolonged therapeutic effect has been attributed to 1) a long lifetime of the toxin's protease activity, 2) anchoring of the light chain to the presynaptic membrane, 3) persistence of the toxin-truncated SNAP-25, and 4) endplate remodeling. In vivo imaging of individual nerve terminals in mouse muscle revealed that blockade of acetylcholine release results in nerve sprouting, with the creation of functional synapses extra-junctionally. On the eventual recovery of endocytotic/exocytotic activity at the parent terminals, retraction of the sprouts occurs with a return to the exact compact shape of the original endplate. (Source: http://www.neurotoxininstitute.org/chapter_moa_print.htm.)
Related to botulinum toxin as a biowarfare agent, it can be spread by inhalation as well as by ingestion or, with wound and infant botulism, by _in situ_ production of toxin in the cutaneous or gastrointestinal areas. In the Working Group on Civilian Biodefense's review on botulinum toxin as a biological weapon (1), the following is stated (with the citations removed):
"A 4th, man-made form that results from aerosolized botulinum toxin is inhalational botulism. This mode of transmission has been demonstrated experimentally in primates, has been attempted by bioterrorists, and has been the intended outcome of at least one country's specially designed missiles and artillery shells. Inhalational botulism has occurred accidentally in humans. A brief report from West Germany in 1962 described 3 veterinary personnel who were exposed to reaerosolized botulinum toxin while disposing of rabbits and guinea pigs whose fur was coated with aerosolized type A botulinum toxin. Type A botulinum toxin was detected in serum samples from all 3 affected individuals."
The laboratory incident citation (2) is in German. All 3 individuals developed weakness, were treated with antitoxin, and survived. As I recall, none required respiratory support. Unlike many other biological warfare agents, the symptoms of intentional spread of botulism are no different than those of natural disease. Suspicions should arise when a large number of cases occur.
1. Arnon SS, Schechter R, Inglesby TV, et al: Botulinum toxin as a biological weapon. Medical and public health management. JAMA 2001; 285:1059-70.
2. Holzer VE: Botulism from inhalation [in German]. Med Klin 1962; 57:1735-38. - Mod.LL