Four studies in monkeys have shown that anthrax spores can persist in the lung for a long time. If anthrax spores were released again in the United States, this could be a problem for people exposed to large amounts of spores. These people would normally be treated with antibiotics, but there is a risk that some spores could remain after these people stopped taking antibiotics. Antibiotics work as long as you take them, but do not protect after you stop taking them. There is a possibility that anthrax spores could still be inside that person when the antibiotics are stopped. To protect exposed people after they stop taking antibiotics, they may be offered three doses of anthrax vaccine. This would not be a regular licensed use of anthrax vaccine (it would be an "off-label" use of the vaccine). Three doses of anthrax vaccine may provide immunity from anthrax infection that lasts for several months or longer.

The four monkey studies include:

Friedlander and colleagues, 1993: Out of a group of 29 Rhesus monkeys (macaques) exposed to anthrax spores and then given antibiotics for 30 days, five monkeys died 36 to 58 days after inhaling about 440,000 anthrax spores. This was 6 to 28 days after the monkeys stopped taking antibiotics.

Glassman, 1966: In a study of cynomolgus monkeys, "several of the animals ... died of culturally proven anthrax after prolonged incubation periods -- one animal died 98 days after inhaling anthrax spores." The author did not define 'several.'

Gochenour and colleagues, 1963: In a study of 38 Rhesus monkeys treated with penicillin for 5 days, one monkey died of anthrax meningitis "25 days after completion of an apparently successful course of [penicillin] therapy." Anthrax spores were found in the lungs of all surviving monkeys tested (30 monkeys, apparently) 55 to 84 days after inhaling 7,000 to 1,016,000 anthrax spores.

Henderson and colleagues, 1957: Among Rhesus monkeys, "up to 42 days after exposure, large numbers of spores were recoverable [from the lung]." The monkeys still had 2% of these spores in their lungs 50 days later. Between 1/2% and 1% of the spores persisted to day 75 and "traces" persisted to day 100.

Bibliography

     Friedlander AM, Welkos SL, Pitt MLM, Ezzell JW, Worsham PL, Rose KJ, Ivins BE, Lowe JR, Howe GB, Mikesell P, Lawrence WB. Postexposure prophylaxis against experimental inhalation anthrax. Journal of Infectious Diseases 1993;167:1239-42.

     Glassman HN. DIscussion of industrial inhalation anthrax. Bacteriological Reviews 1966;30:657-659 (commenting on pages 646-657).

     Gochenour WS Jr., Sawyer WD, Henderson JE, Gleiser CA, Kuehne RW, Tigertt WD. On the recognition and therapy of Simian woolsorter's disease. Journal of Hygiene (Cambridge) 1963;61:317-325.

     Henderson DW, Peacock S, Belton FC. Observations on the prophylaxis of experimental pulmonary anthrax in the monkey. Journal of Hygiene 1956;54:28-36.