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Bacillus anthracis

Also known as: Anthrax

Industry of interest: Defence

Classification: Bacteria

Microbiology: Bacillus anthracis is a Gram-positive endospore-forming rod more commonly called “anthrax”. In 2001 the organism was used as part of a terrorist attack on the USA, where a highly virulent strain of anthrax was mailed to senators killing 5 people. This has heightened the concern around anthrax as a biological weapon (Schwartz, 2009).

Biology

Habitat and transmission: B. anthracis is commonly found in soil where it can lie dormant, potentially for hundreds of years. Herbivores often disturb soil when grazing and can ingest or inhale the B. anthracis spores. B. anthracis can be transmitted readily from close contact with animals, soil or through ingestion of contaminated meat (from an infected animal) (Schwartz, 2009). Occupations at high risk of infection include veterinary surgeons, livestock farmers, butchers and persons who handle hides or wool. In addition, in 2009, several heroin users in Glasgow contracted anthrax from contaminated heroin supplies.

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Treatment and antibiotic resistance: Contrary to popular belief, antibiotics are very effective in controlling B. anthracis infections if used early enough. Antibiotics such as ciprofloxacin, doxycycline, erythromycin, vancomycin and penicillin are all useful for treatment of B. anthracis infections (Moayeri and Leppla, 2004). There is also a monoclonal antibody (Raxibacumab) that is currently showing promise in clinical trials , which can be used in the prophylaxic treatment of B. anthracis infection. B. anthracis has shown some resistance to antibiotics in laboratory testing and possesses antimicrobial enzymes such as b-lactamases (Bryskier, 2002).

Prevention and control: Preventative measures include immunisation of humans and animals and post exposure antibiotic prophylaxis (Bryskier, 2002). The currently available vaccines include AVA (anthrax vaccine adsorbed), which is licensed in the USA and AVP (anthrax vaccine precipitated), which is licensed in the UK; these are used to create immunity to B. anthracis pre-exposure (Bryskier, 2002). Where people or animals have died from B. anthracis, great care must be taken to handle and dispose of the body and clothes because spores will remain viable for many years. The inactivation of spores is difficult, but oxidate chemicals, such as hydrogen peroxide vapour, are sporicidal and have been used to decontaminate buildings contaminated with B. anthracis spores (Canter).

Disease and symptoms: B. anthracis can cause three types of disease in humans and animals known as cutaneous, gastrointestinal and pulmonary infection (Schwartz, 2009).  Toxins play a vital role in all types of infection, from germination stage to the initiation of vascular collapse (in the case of respiratory anthrax). In early infection, the toxin acts to suppress immune system cells and cytokine responses, promoting bacterial growth (Moayeri and Leppla, 2004). Later in disease the toxin (at lethal levels) induces cytokine responses that cause shock and subsequently lead to death of the host. B. anthracis has 3 polypeptides that make up the anthrax toxin; protective antigen (PA), lethal factor (LF) and odema/edema factor (EF) (Moayeri and Leppla, 2004).

References:

Bryskier A. (2002) Bacillus anthracis and antibacterial agents. 8(8): 467-478.

Canter D.A., Gunning D., Rodgers P., O'Connor L., Traunero C., Kempter C.J. (2005) Remediation of Bacillus anthracis contamination in the U.S. Department of Justice mail facility. Biosecur.Bioterror. 3: 119-127.

Moayeri M. and Leppla S.H. (2004) The roles of anthrax toxin in pathogenesis. Curr Opin Microbiol. 7(1): 19-24.

Schwartz M. (2009) Dr Jekyll and Mr Hyde: a short history of anthrax. Mol Aspects Med. 30(6): 347-355.

 

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