BACILLUS ANTHRACIS
Table of contents :

  • Epidemiology
  • Proteomics
  • Transmission
  • Symptoms & signs
  • Laboratory examinations
  • Therapy
  • Prevention
  • Web resources

  • Epidemiology :

    Not flagellated (on the contrary of other Bacilli) ; sticky R (caput Medusae) or S colonies (streptobacillus; a.k.a. bamboo cane-shaped). Vegetative forms may be destroyed by wet heat (2' at 75°C or 1'30" at 150°C) or sunlight. Spores normally survive temperatures up to at least 80°C for 10 minutes. One of the methods of killing off contaminants in the lab is to heat shock the sample to 80° for 10 minutes. This kills contaminants and can stimulate heat-resistant Bacillus anthracis spores to germinate. Therefore, is seems that to be sure meat is properly decontaminated, one would need to cook meat at or over 100°C for > 10 minutes. 80°C is getting a little hot for the comfort of anthrax spores and, if you are using that temperature to select them out from other bacteria, you may start to lose some. I don't know the precise decimal reduction figures though (not sure anyone does), but if the population is large enough, some will survive 10 min at that temp too. Probably, in practice, when a lab person says he has applied 80°C for 10 min, the centre of the container never reaches that temperature. Some prefer 60-65°C for 15-20 min myself, making some attempt to ensure that the whole thing does achieve those conditions. Heat sterilisation temperatures are normally in excess of 135°C. We have never been impressed by the germination potential of "heat shocking" but it certainly helps, especially if one is not comfortable in identifying B. anthracis colonies, in removing the competing growth noise on the plate. Eating or not eating anthrax carcasses essentially comes down to the poverty level in rural areas. In areas where meat of any variety is rarely eaten, the risk is accepted. Members of some religions will not eat an animal that died, but moribund animals will have their throats cut so that the carcass can be salvaged and the meat sold and/or consumed by the family. It happens all over, viz that Minnesota farmer's family in Roseau County in 2000, that near-miss in Texas where an anthrax goat was in the farmer's deep freeze waiting for Sunday when his veterinarian came to investigate the caprine deaths, and in Central Russia. "Properly cooked" is a matter of definition.
    Proteomics : Transmission : a zooanthroponosis from vegetative forms or > 2,500÷55,000 spores coming from... While long-term soil contamination is possible, it is associated with burying animal carcasses (=> "damned fields"), not from surface contamination, which persists for only 3 months to 3 years without disinfection : anthrax spores do not survive well in acid soils, but spores in the acid peat soil (mean pH < 4.5) on Gruinard Island [the site of field trials of anthrax weapons in the UK during World War II in 1942 and 1943] survived in many thousands per gram until the island was decontaminated in 1986. There had been multiple trials in the same restricted area with explosive devices, which by their nature are inefficient producers of aerosols, essentially dumping > 98% of the surviving contents of all the small bombs and mortars around the point of explosion. One of the conundrums of this organism is that the disease consistently does not persist in regions with acid soils.  This is true whether we look at North America, where it was very common pre-1955 east of the Mississippi, with significant industrial contamination in New England, and now is totally absent, to acid soil areas in India, etc.  And in the UK, where we had 400-600 cases per year for decades thanks to contaminated livestock feeds, once proper controls were instituted, it soon disappeared from all but a very few areas, and there has not been a livestock case since 1997. There were only some 100 cases since 1980. B. anthracis spores seem to perform like other bacterial spores, in that they have a negative surface charge and thus adhere to organic matter in soil. This will normally prevent their dispersal. The exosporium is a key player in this adhesion. Spores can be produced and stored in a dry form and remain viable for decades in storage or after release : boiling at 100°C for 30' kills endospores. Disinfection of contaminated articles may be accomplished using a 0.05% hypochlorite solution (1 tbsp. bleach per gallon of water).
    => anthrax / splenic fever (a.k.a. carbonchio in Italy).  Clinical manifestations depend on entry way: There is no evidence of person-to-person transmission of anthrax.
    Pathogenesis : germination from spores to bacilli produces a substantial stimulus for the secretion of the cytokines IL-6, TNF-a, IL-10, and IL-12 p40. Pretreatment of mouse macrophages with the TLR9 ligand ISS-1018, or the TLR7 ligands R-848 and IT-37, results in a substantial decrease in the subsequent secretion of IL-6 and TNF-a in response to B. anthracis infection of macrophages. Furthermore, the TLR7 and TLR9 ligands significantly decreased anthrax-induced cytotoxicity in the macrophagesref.
    Laboratory examinations : direct diagnosis : Therapyref : Prevention : heterologous immune antiserum and subunit vaccine. Mass vaccination is not the best way to deal with the threat of anthrax attacks by terrorists. Far better is to ensure that the right treatments will be delivered to those exposed as soon after the attack as possible. Chief among those treatments should be antibiotics. Supplying them to everyone exposed within 6 days of the outbreak's detection would cut disease cases by around 70%. But after 10 days or more (the wait endured by many exposed to the US postal anthrax attacks in late 2001), cases are decreased by < 50%. That would minimize disease by maximizing the chances that anthrax spores in the body are killed off before they can germinate in the lymph nodes and cause sickness. Pre-emptive mass vaccination is unlikely to improve these numbers unless the coverage is very extensive. The existing vaccine, though effective, requires months of injections, and distributing it to the general public is likely to be very costly. But this doesn't mean that there is no role for a new, improved vaccineref. Delivering a vaccine to those already exposed could reduce the length of antibiotic treatment required or help to fend off an antibiotic-resistant strain of the pathogen. In the 2001 attacks, < 50% of people completed their 60-day antibiotic course. There were 19 disease cases and 5 fatalities in total, and although nobody got sick after stopping their antibiotics early, this behaviour could easily have led to more disease. In July 2004, President George W. Bush signed legislation to empower Project BioShield, which will provide funding for research against anthrax. The most effective pre-attack measures should include training and vaccination of all healthcare workers who would have to deal with an outbreak. Pre-emptively supplying antibiotics such as ciproflaxin, to be taken if needed by those exposed. It would be difficult, however, to ensure that those given the drugs could be relied on to use them correctlyref. Vaccine research should still continue because of the benefits in supplying it to those exposed, rather than simply blanketing the population.
    animal model 
    ID50
    LD50
    [bacteria]blood at death
    Mus musculus
    5 cells
    1,000 units/kg
    107 / mL
    Macaca mulatta
    3,000 cells
    2,500 unit/kg
    107 / mL
    Rattus norvegicus 106 cells 15 units/kg
    105 / mL
    Animals surviving naturally-acquired anthrax are immune to reinfection.
    differential characteristic
    B.anthracis
    B.cereus
    B.thuringiensis 
    requirement for thiamin
    +
    -
    hemolysis of sheep RBCs
    -
    +
    glutamyl-polypeptide capsule
    +
    -
    lysis by g phage
    +
    -
    motility
    -
    +
    growth on chloralhydrate agar
    -
    +
    string-of-pearls test
    +
    -
    It is considered by CDC as a category A biological weaponref
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