WASHINGTON — Workers searching government laboratories in the wake of the July discovery of smallpox have found six more improperly stored, dangerous pathogens – including ricin, the neurotoxin botulism and the bacteria that causes plague.

On Friday, officials at the National Institutes of Health said the search on its sprawling Bethesda campus had turned up five different misplaced pathogens in recent weeks. All of the microbes are considered so dangerous that the federal government requires them to be stored in special high-security facilities. Instead, these vials were in regular labs, often part of collections of samples that date back decades.

Simultaneously, the Food and Drug Administration said it had found vials of staphylococcus enterotoxin, a frequent cause of foodborne illness, at a lab within the agency’s Center for Food Safety and Applied Nutrition that was not registered to handle it.

The latest unearthing of improperly stored toxins came during an unprecedented sweep of government labs prompted by the discovery in early July of long-forgotten vials of the smallpox virus inside an FDA lab on the NIH campus in Bethesda. Investigators have been trying to piece together how the vials, dated from 1954, wound up in a shared storage space inside an FDA biologics lab.

Officials at both agencies said Friday that they promptly reported the additional pathogens that have been unearthed to the Centers for Disease Control and Prevention, and that no employees were ever in danger of infection.

“These things were stored in locations where they should not have been stored,” said Alfred Johnson, director of the NIH’s office of research services, which is coordinating the a “clean sweep” of the agency’s labs.