5. MODE OF TRANSMISSION

Cutaneous infection is by contact with tissues of animals (cattle, sheep, goats, horses, pigs and others) dying of the disease; possibly by biting flies that had partially fed on such animals; by contact with contaminated hair, wool, hides or products made from them, such as drums, brushes or rugs; or by contact with soil associated with infected animals or contaminated bone meal used in gardening. Inhalation anthrax results from inhalation of spores in risky industrial processes -- such as tanning hides and processing wool or bone -- where aerosols of B. anthracis spores may be produced. Intestinal and oropharyngeal anthrax arise from ingestion of contaminated undercooked meat; there is no evidence that milk from infected animals transmits anthrax. The disease spreads among grazing animals through contaminated soil and feed; among omnivorous and carnivorous animals through contaminated meat, bone meal or other feeds; and among wildlife from feeding on carcasses infected with anthrax. Accidental infections may occur among laboratory workers.

In 1979, an outbreak of largely inhalation anthrax occurred in Yekaterinburg (Sverdlovsk), Russia (see star in center of map), in which 66 individuals were documented to have died of anthrax and 11 infected persons were known to have survived; many other cases are presumed to have occurred. Investigations disclosed that the cases occurred as the result of a plume emanating from a biological research institute and led to the conclusion that the outbreak had resulted from an accidental aerosol generated in work related to biological warfare studies.

ADDENDUM

The following book provides more details of the Sverdlovsk accident. 

Biohazard tells more than you ever wanted to know about the Soviet Union's bioweapons programme, and is written by the person pre-eminently qualified to do so: Colonel Kanatjan Alibekov, First Deputy Chief and technical head of that program from 1988 to 1992, when, fortunately for all of us, he turned down an invitation to head a bioweapons program in his native Kazakhstan and defected to the USA. There he changed his name to Ken Alibek and turned his research interests around; he is currently working on broad-spectrum immunity against microbial pathogens....

...He says that Russia's stockpiles of plague, tularemia, and smallpox have been destroyed, but says nothing about their anthrax stocks. The first three have use-by dates and need to be stored in the cold and periodically restocked. Dried anthrax lasts forever in room temperature storage. And of course, those stocks can all be built up again, since the seed agents are still there. He gives many details, gleaned secondhand, about the accidental release of anthrax from the bioweapons facility in Sverdlovsk in 1979, which killed at least 66 people. He recounts the Soviet cover-up and the successful duping of many US scientists as late as 1988 by a tour of Soviet specialists carrying selected "evidence" that the outbreak was due to eating contaminated meat, despite the fact, obvious to myself and others at the time of the tour, that this explanation could not account for the lack of reported cases in children. But Alibek insists on a March 30 date for the accident that does not jibe with the one deduced from meteorological data reported by the local airport, which showed that only on April 2 could the plume of aerosol have covered the part of the city that was infected. And he does not mention that necropsy specimens were hidden from the KGB by the widow of the pathologist involved, and were given to US scientists in 1993. These specimens reveal that the cases were of pulmonary anthrax, not gastrointestinal disease. Moreover, sequencing of the strains recovered from those specimens showed several different types in the same victim -- something never found in natural infections....

Source: Woodall J. Review of Alibek, K. Biohazard, 1999 in The Lancet 354 (9189), p. 1568, 1999.