An overview of anthrax infection including the recently identified form of disease in injection drug users

Abstract

Purpose Bacillus anthracis infection (anthrax) can be highly lethal. Two recent outbreaks related to contaminated mail in the USA and heroin in the UK and Europe and its potential as a bioterrorist weapon have greatly increased concerns over anthrax in the developed world. Methods This review summarizes the microbiology, pathogenesis, diagnosis, and management of anthrax. Results and conclusions Anthrax, a gram-positive bacterium, has typically been associated with three forms of infection: cutaneous, gastrointestinal, and inhalational. However, the anthrax outbreak among injection drug users has emphasized the importance of what is now considered a fourth disease form (i.e., injectional anthrax) that is characterized by severe soft tissue infection. While cutaneous anthrax is most common, its early stages are distinct and prompt appropriate treatment commonly produces a good outcome. However, early symptoms with the other three disease forms can be nonspecific and mistaken for less lethal conditions. As a result, patients with gastrointestinal, inhalational, or injectional anthrax may have advanced infection at presentation that can be highly lethal. Once anthrax is suspected, the diagnosis can usually be made with gram stain and culture from blood or tissue followed by confirmatory testing (e.g., PCR). While antibiotics are the mainstay of anthrax treatment, use of adjunctive therapies such as anthrax toxin antagonists are a consideration. Prompt surgical therapy appears to be important for successful management of injectional anthrax.

Protective-antigen (PA) based anthrax vaccines confer protection against inhalation anthrax by precluding the establishment of a systemic infection

“…Protective antigen (PA) is the receptor binding component of the tripartite exotoxin which forms binary complexes either with the lethal factor (LF) or the edema factor (EF), in generating lethal toxin (LT) or edema toxin (ET) respectively. 1 These toxins are released in copious amounts during the vegetative growth of B. anthracis and are readily detectable in the serum of an infected host. 2 Both purified LT and ET when administered intravenously or intraperitoneally in microgram quantities have proven to be deadly in in vivo animal studies attesting to their pivotal role in the overwhelming systemic pathophysiology associated with B. anthracis infection in non-immune susceptible hosts.…”

“…2 Both purified LT and ET when administered intravenously or intraperitoneally in microgram quantities have proven to be deadly in in vivo animal studies attesting to their pivotal role in the overwhelming systemic pathophysiology associated with B. anthracis infection in non-immune susceptible hosts. 1 A large body of evidence has amassed to indicate that an immune response to PA is an intense effort has been launched to develop improved anthrax vaccines that confer rapid, long lasting protection preferably with an extended stability profile amenable for stockpiling. Protective antigen (Pa)-based vaccines are most favored as immune responses directed against Pa are singularly protective, although the actual protective mechanism remains to be unraveled.…”

Anthrax infection in an intravenous drug user

“…Dear Editor, We read with great interest the recent review by Hicks and colleagues on anthrax infection and the recently described variant affecting intravenous drug users [1]. At our institute, we have had firsthand experience of this particular group of patients and offer a case as an example of an unusual presentation and its particular relevance to critical care.…”

Opening moves: early events in anthrax pathogenesis and their consequences for dissemination

“…More recently a new form of anthrax deemed "injectional" anthrax has been reported in heroin users in Northern Europe [14,20,21]. These infections have typically involved patients who injected heroin in to the skin and not directly into the bloodstream.…”

“…These infections have typically involved patients who injected heroin in to the skin and not directly into the bloodstream. Unlike cutaneous anthrax, with its characteristic eschar and low mortality, injectional anthrax had only slight changes to the skin that resembled pathologies common to intravenous injection drug users and had higher mortality [20]. Given the relatively few cases of injectional anthrax it is unclear why injection into the skin leads to higher rates of mortality.…”