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Anthrax backgrounder (JUST so we're all on the same page)

Original post date by yours truly: 10/9/01

http://www.anthrax.osd.mil/Site_Files/articles/INDEXjournals_editorials/NEJMATXReview%5Creview.htm Inhalational Anthrax
Inhalational anthrax is rare, usually occurring after the inhalation of pathogenic endospores from contaminated animal hides or products.
Before the introduction of hygienic measures in the 1960s, including vaccination, workers in goathair mills, for example, were regularly exposed to high concentrations of viable anthrax spores.
Nevertheless, for reasons that are not understood, few cases of inhalational anthrax occurred among them. ^49-51 When dispersed in the atmosphere as an aerosol, anthrax spores can present a respiratory hazard even far downwind from the point of release, as demonstrated by animal tests on Gruin-ard Island in the United Kingdom, ^52-55 and by an accidental release from a military biologic facility in the city of Sverdlovsk in the former Soviet Union. ^2,56-58
Inhalational anthrax is usually fatal, even with aggressive antimicrobial therapy. It appears that only about one fifth of those who contracted inhalational anthrax in Sverdlovsk recovered. ² Anthrax spores are about 1 to 2 µm in diameter, a size that is optimal for inhalation and deposition in the alveolar spaces. ^51,59-61
Although the lung is the initial site of contact, inhalational anthrax is not considered a true pneumonia.
In most but not all cases, there is no infection in the lungs. ^58,62 Rather, the endospores are engulfed by alveolar macrophages and transported by them to the mediastinal and peribronchial lymph nodes, with the spores germinating en route.
Anthrax bacilli multiply in the lymph nodes, causing hemorrhagic mediastinitis, and spread throughout the body in the blood. ^43,62
Data from the Sverdlovsk outbreak indicate a modal incubation time of approximately 10 days for inhalational anthrax. However, the onset of symptoms occurred up to six weeks after the reported date of exposure. ^2,57
Such long incubation times presumably reflect the ability of viable anthrax spores to remain in the lungs for many days. ^51,63,64 Longer incubation periods may be associated with smaller inocula.
The initial symptoms most often reported are fever, nonproductive cough, myalgia, and malaise, resembling those of a viral upper respiratory tract infection. Early in the course of the disease, chest radiographs show a widened mediastinum, which is evidence of hemorrhagic mediastinitis, and marked pleural effusions.
After one to three days, the disease takes a fulminant course with dyspnea, strident cough, and chills, culminating in death. ^34,59
In Sverdlovsk, the mean time between the onset of symptoms and death was 3 days (range, 1 to 10). Although accompanying evidence of clinical signs of pneumonia in these cases is lacking, some of the autopsies from the Sverdlovsk outbreak showed a focus of necrotizing hemorrhagic pneumonitis, possibly at the portal of infection. ⁵⁸
Submucosal hemorrhages occurred in the trachea and bronchi, with hemorrhage and necrosis of peribronchial lymph nodes. Hemorrhagic mediastinal lymph nodes represent the primary lesion; however, gastrointestinal and leptomeningeal lesions are the result of hematogenous spread. There may be wide individual variation in susceptibility to inhalational anthrax, as suggested by experimental studies in nonhuman primates and by the absence of persons younger than 24 years among the 66 deaths reported in the Sverdlovsk outbreak. ^2,51,57