Various techniques are used for the direct identification of B. anthracis in clinical material. Firstly, specimens may be Gram stained.Bacillus spp. are quite large in size (3 to 4 μm long), they grow in long chains, and they stain Gram-positive. To confirm the organism is B. anthracis, rapid diagnostic techniques such as polymerase chain reaction-based assays and immunofluorescence microscopy may be used.[30]
All Bacillus species grow well on 5% sheep blood agar and other routine culture media. Polymyxin-lysozyme-EDTA-thallous acetate can be used to isolate B. anthracis from contaminated specimens, and bicarbonate agar is used as an identification method to induce capsule formation. Bacillus spp. usually grow within 24 hours of incubation at 35 °C, in ambient air (room temperature) or in 5% CO2. If bicarbonate agar is used for identification, then the medium must be incubated in 5% CO2. B. anthracis colonies are medium-large, gray, flat, and irregular with swirling projections, often referred to as having a "medusa head" appearance, and are not hemolytic on 5% sheep blood agar. The bacteria are not motile, susceptible to penicillin, and produce a wide zone of lecithinase on egg yolk agar. Confirmatory testing to identify B. anthracis includes gamma bacteriophage testing, indirect hemagglutination, and enzyme linked immunosorbent assay to detect antibodies.[31] The best confirmatory precipitation test for anthrax is the Ascoli test.
Prevention[edit]
Vaccines[edit]
Main article: Anthrax vaccines
Vaccines against anthrax for use in livestock and humans have had a prominent place in the history of medicine, from Pasteur's pioneering 19th-century work with cattle (the second effective vaccine ever) to the controversial 20th century use of a modern product (BioThrax) to protect American troops against the use of anthrax in biological warfare. Human anthrax vaccines were developed by the Soviet Union in the late 1930s and in the US and UK in the 1950s. The current FDA-approved US vaccine was formulated in the 1960s.
Currently administered human anthrax vaccines include acellular (United States) and live spore (Russia) varieties. All currently used anthrax vaccines show considerable local and general reactogenicity (erythema, induration, soreness, fever) and serious adverse reactions occur in about 1% of recipients.[32] The American product, BioThrax, is licensed by the FDA and was formerly administered in a six-dose primary series at 0, 2, 4 weeks and 6, 12, 18 months, with annual boosters to maintain immunity. In 2008, the FDA approved omitting the week-2 dose, resulting in the currently recommended five-dose series.[33] New second-generation vaccines currently being researched includerecombinant live vaccines and recombinant subunit vaccines.
Prophylaxis[edit]
If a person is suspected as having died from anthrax, every precaution should be taken to avoid skin contact with the potentially contaminated body and fluids exuded through natural body openings. The body should be put in strict quarantine. A blood sample should then be collected and sealed in a container and analyzed in an approved laboratory to ascertain if anthrax is the cause of death. Then, the body should be incinerated. Microscopic visualization of the encapsulated bacilli, usually in very large numbers, in a blood smear stained with polychrome methylene blue (McFadyean stain) is fully diagnostic, though culture of the organism is still the gold standard for diagnosis. Full isolation of the body is important to prevent possible contamination of others. Protective, impermeable clothing and equipment such as rubber gloves, rubber apron, and rubber boots with no perforations should be used when handling the body. No skin, especially if it has any wounds or scratches, should be exposed. Disposable personal protective equipment is preferable, but if not available, decontamination can be achieved by autoclaving. Disposable personal protective equipment and filters should be autoclaved, and/or burned and buried. B. anthracis bacillii range from 0.5–5.0 μm in size. Anyone working with anthrax in a suspected or confirmed victim should wear respiratory equipment capable of filtering this size of particle or smaller. The US National Institute for Occupational Safety and Health – and Mine Safety and Health Administration-approved high-efficiency respirator, such as a half-face disposable respirator with a high-efficiency particulate air filter, is recommended.[34] All possibly contaminated bedding or clothing should be isolated in double plastic bags and treated as possible biohazard waste. The victim should be sealed in an airtight body bag. Dead victims who are opened and not burned provide an ideal source of anthrax spores. Cremating victims is the preferred way of handling body disposal. No embalming or autopsy should be attempted without a fully equipped biohazard laboratory and trained, knowledgeable personnel.
Delays of only a few days may make the disease untreatable, so treatment should be started even without symptoms if possible contamination or exposure is suspected. Animals with anthrax often just die without any apparent symptoms. Initial symptoms may resemble a common cold—sore throat, mild fever, muscle aches, and malaise. After a few days, the symptoms may progress to severe breathing problems and shock, and ultimately death. Death can occur from about two days to a month after exposure, with deaths apparently peaking at about eight days after exposure.[35] Antibiotic-resistant strains of anthrax are known.
Early detection of sources of anthrax infection can allow preventive measures to be taken. In response to the anthrax attacks of October 2001, the United States Postal Service(USPS) installed biodetection systems (BDSs) in their large-scale mail cancellation facilities. BDS response plans were formulated by the USPS in conjunction with local responders including fire, police, hospitals and public health. Employees of these facilities have been educated about anthrax, response actions, and prophylactic medication. Because of the time delay inherent in getting final verification that anthrax has been used, prophylactic antibiotic treatment of possibly exposed personnel must be started as soon as possible.
Treatment[edit]
Anthrax cannot be spread directly from person to person, but a person's clothing and body may be contaminated with anthrax spores. Effective decontamination of people can be accomplished by a thorough wash-down with antimicrobial soap and water. Waste water should be treated with bleach or other antimicrobial agent. Effective decontamination of articles can be accomplished by boiling them in water for 30 minutes or longer. Chlorine bleach is ineffective in destroying spores and vegetative cells on surfaces, though formaldehyde is effective. Burning clothing is very effective in destroying spores. After decontamination, there is no need to immunize, treat, or isolate contacts of persons ill with anthrax unless they were also exposed to the same source of infection.
Antibiotics[edit]
Early antibiotic treatment of anthrax is essential; delay significantly lessens chances for survival.
Treatment for anthrax infection and other bacterial infections includes large doses of intravenous and oral antibiotics, such as fluoroquinolones (ciprofloxacin), doxycycline,erythromycin, vancomycin, or penicillin. FDA-approved agents include ciprofloxacin, doxycycline, and penicillin.[36]
In possible cases of pulmonary anthrax, early antibiotic prophylaxis treatment is crucial to prevent possible death.
In May 2009, Human Genome Sciences submitted a Biologic License Application (BLA, permission to market) for its new drug, raxibacumab (brand name ABthrax) intended for emergency treatment of inhaled anthrax.[37] If death occurs from anthrax, the body should be isolated to prevent possible spread of anthrax germs. Burial does not kill anthrax spores.
In recent years, many attempts have been made to develop new drugs against anthrax, but existing drugs are effective if treatment is started soon enough.
Monoclonal antibodies[edit]
On 14 December 2012, the US Food and Drug Administration approved raxibacumab injection to treat inhalational anthrax. Raxibacumab is a monoclonal antibody that neutralizes toxins produced by B. anthracis that can cause massive and irreversible tissue injury and death. A monoclonal antibody is a protein that closely resembles a human antibody, and identifies and neutralizes foreign material such as bacteria and viruses.[38]
History[edit]
Etymology[edit]
The English name comes from anthrax (ἄνθραξ), the Greek word for coal,[39][40] possibly having Egyptian etymology,[41] because of the characteristic black skin lesions developed by victims with a cutaneous anthrax infection. The central, black eschar, surrounded by vivid red skin has long been recognised as typical of the disease. The first recorded use of the word "anthrax" in English is in a 1398 translation of Bartholomaeus Anglicus' work De proprietatibus rerum (On the Properties of Things, 1240).[42]
Anthrax has been known by a wide variety of names, indicating its symptoms, location and groups considered most vulnerable to infection. These include Siberian plague,Cumberland disease, charbon, splenic fever, malignant edema, woolsorter's disease, and even la maladie de Bradford.[43]
Discovery[edit]
Robert Koch, a German physician and scientist, first identified the bacterium that caused the anthrax disease in 1875 in Wolsztyn.[21][44] His pioneering work in the late 19th century was one of the first demonstrations that diseases could be caused by microbes. In a groundbreaking series of experiments, he uncovered the lifecycle and means of transmission of anthrax. His experiments not only helped create an understanding of anthrax, but also helped elucidate the role of microbes in causing illness at a time when debates still took place over spontaneous generation versus cell theory. Koch went on to study the mechanisms of other diseases and won the 1905 Nobel Prize in Physiology or Medicine for his discovery of the bacterium causing tuberculosis.
Although Koch arguably made the greatest theoretical contribution to our understanding of anthrax, other researchers were more concerned with the practical questions of how to prevent the disease. In Britain, where anthrax affected workers in the wool, worsted, hides and tanning industries, it was viewed with fear. John Henry Bell, a doctor based inBradford, first made the link between the mysterious and deadly "woolsorter's disease" and anthrax, showing in 1878 that they were one and the same.[45] In the early twentieth century, Friederich Wilhelm Eurich, the German bacteriologist who settled in Bradford with his family as a child, carried out important research for the local Anthrax Investigation Board. Eurich also made valuable contributions to a Home Office Departmental Committee of Inquiry, established in 1913 to address the continuing problem of industrial anthrax.[46] His work in this capacity, much of it collaboration with the factory inspector G. Elmhirst Duckering, led directly to the Anthrax Prevention Act (1919).
First vaccination[edit]
Further information: Anthrax vaccines
Anthrax posed a major economic challenge in France and elsewhere during the nineteenth century. Horses, cattle and sheep were particularly vulnerable, and national funds were set aside to investigate the production of a vaccine. The noted French scientist Louis Pasteurwas charged with the production of a vaccine, following his successful work in developing methods which helped to protect the important wine and silk industries.[47]
In May 1881, Pasteur - in collaboration with his assistants Jean-Joseph Henri Toussaint, Émile Roux and others - performed a public experiment at Pouilly-le-Fort to demonstrate his concept of vaccination. He prepared two groups of 25 sheep, one goat, and several cows. The animals of one group were injected with an anthrax vaccine prepared by Pasteur twice, at an interval of 15 days; the control group was left unvaccinated. Thirty days after the first injection, both groups were injected with a culture of live anthrax bacteria. All the animals in the unvaccinated group died, while all of the animals in the vaccinated group survived.[48]
After this apparent triumph, which was widely reported in the local, national and international press, Pasteur made strenuous efforts to export the vaccine beyond France. He used his celebrity status to establish Pasteur Institutes across Europe and Asia, and his nephew, Adrien Loir, travelled to Australia in 1888 to try and introduce the vaccine to combat anthrax in New South Wales.[49] Ultimately the vaccine was unsuccessful in the challenging climate of rural Australia, and it was soon superseded by a more robust version developed by local researchers John Gunn and John McGarvie Smith.[50]
The human vaccine for anthrax became available in 1954. This was a cell-free vaccine instead of the live-cell Pasteur-style vaccine used for veterinary purposes. An improved cell-free vaccine became available in 1970.[51]
Society and culture[edit]
The virulent Ames strain, which was used in the 2001 anthrax attacks in the United States, has received the most news coverage of any anthrax outbreak. The Ames strain contains two virulence plasmids, which separately encode for a three-protein toxin, called anthrax toxin, and a polyglutamic acid capsule. Nonetheless, the Vollum strain, developed but never used as a biological weapon during the Second World War, is much more dangerous. The Vollum (also incorrectly referred to as Vellum) strain was isolated in 1935 from a cow in Oxfordshire. This same strain was used during the Gruinard bioweapons trials. A variation of Vollum known as "Vollum 1B" was used during the 1960s in the US and UK bioweapon programs. Vollum 1B is widely believed[52] to have been isolated from William A. Boyles, a 46-year-old scientist at the U.S. Army Biological Warfare Laboratories at Camp (later Fort) Detrick, Maryland, (precursor to USAMRIID), who died in 1951 after being accidentally infected with the Vollum strain. The Sterne strain, named after the Trieste-born immunologist Max Sterne, is an attenuated strain used as a vaccine, which contains only the anthrax toxin virulence plasmid and not the polyglutamic acid capsule expressing plasmid.
Site cleanup and decontamination[edit]
Anthrax spores can survive for very long periods of time in the environment after release. Chemical methods for cleaning anthrax-contaminated sites or materials may useoxidizing agents such as peroxides, ethylene oxide, Sandia Foam,[53] chlorine dioxide (used in the Hart Senate Office Building), peracetic acid, ozone gas, hypochlorous acid, sodium persulfate, and liquid bleach products containing sodium hypochlorite. Nonoxidizing agents shown to be effective for anthrax decontamination include methyl bromide, formaldehyde, and metam sodium. These agents destroy bacterial spores. All of the aforementioned anthrax decontamination technologies have been demonstrated to be effective in laboratory tests conducted by the US EPA or others.[54] A bleach solution for treating hard surfaces has been approved by the EPA.[55]
Chlorine dioxide has emerged as the preferred biocide against anthrax-contaminated sites, having been employed in the treatment of numerous government buildings over the past decade. Its chief drawback is the need for in situ processes to have the reactant on demand.
To speed the process, trace amounts of a nontoxic catalyst composed of iron and tetroamido macrocyclic ligands are combined with sodium carbonate and bicarbonate and converted into a spray. The spray formula is applied to an infested area and is followed by another spray containing tert-butyl hydroperoxide.[56]
Using the catalyst method, a complete destruction of all anthrax spores can be achieved in under 30 minutes.[56] A standard catalyst-free spray destroys fewer than half the spores in the same amount of time. They can be heated and exposed to the harshest chemicals, but they do not easily die.[vague]
Cleanups at a Senate office building, several contaminated postal facilities, and other US government and private office buildings showed decontamination to be possible, but it is time-consuming and costly. Clearing the Senate office building of anthrax spores cost $27 million, according to the Government Accountability Office. Cleaning the Brentwood postal facility outside Washington cost $130 million and took 26 months. Since then, newer and less costly methods have been developed.[57]
Cleanup of anthrax-contaminated areas on ranches and in the wild is much more problematic. Carcasses may be burned, though it often takes up to three days to burn a large carcass and this is not feasible in areas with little wood. Carcasses may also be buried, though the burying of large animals deeply enough to prevent resurfacing of spores requires much manpower and expensive tools. Carcasses have been soaked in formaldehyde to kill spores, though this has environmental contamination issues. Block burning of vegetation in large areas enclosing an anthrax outbreak has been tried; this, while environmentally destructive, causes healthy animals to move away from an area with carcasses in search of fresh grass. Some wildlife workers have experimented with covering fresh anthrax carcasses with shadecloth and heavy objects. This prevents some scavengers from opening the carcasses, thus allowing the putrefactive bacteria within the carcass to kill the vegetative B. anthracis cells and preventing sporulation. This method also has drawbacks, as scavengers such as hyenas are capable of infiltrating almost any exclosure.
The experimental site at Gruinard Island is said to have been decontaminated with a mixture of formaldehyde and seawater by the Ministry of Defence. It is not clear whether similar treatments had been applied to US test sites.
No comments:
Post a Comment