The Pentagon has confirmed that a probe of US defence laboratories and their handling of infectious materials, including anthrax cultures shipped to Australia, now includes plague and encephalitis.
The revelation follows months of investigation into the mishandling of live anthrax cultures that were shipped to South Korea and Australia.
Pentagon spokesman Peter Cook says the federal civilian Centres for Disease Control and Prevention has issued assurances that there is no suggestion of risk to health workers or the general public.
"That doesn't mean we're not trying to get to the bottom of this," Cook said.
The Pentagon last week closed all nine Pentagon laboratories after the discovery of more mishandled anthrax cultures.
Cook declined to confirm that it was "bubonic plague" at issue, but said a "form of plague" had been found in a freezer outside of a containment area in one of the labs. The CDC found the material in the course of its investigation.
He said it was possible the material had been labelled incorrectly.
Cook said there was concern about the handling of equine encephalitis in the laboratories.
In May, the Pentagon advised all 24 US laboratories and the two foreign labs to stop working with the anthrax samples during the investigation.
In South Korea in May, 22 people were treated with antibiotics after a live anthrax sample arrived at Osan Air Base near Seoul.
The anthrax shipments were part of a US military effort to develop a new diagnostic test to identify biological threats.
The mistake was discovered after a private commercial lab reported it was able to grow live Bacillus anthracis from the samples, the Pentagon said in May.
The Pentagon said at the time that the anthrax bacteria may not have been treated properly - or "killed" - before being sent out.
Anthrax bacteria can be killed in a number of ways, including irradiation - which is used for some government mail in the United States - or with anti-bacterial chemicals.
