Workers scouring government laboratories in the wake of the July discovery of smallpox and the mishandling of other infectious agents in federal facilities in recent months have found half a dozen more improperly stored substances — including the deadly toxin ricin and the bacteria that cause plague.

Officials at the National Institutes of Health said Friday a search on their sprawling Bethesda campus had turned up five different misplaced biological materials in recent weeks. All of them are considered so dangerous — they are known as “select agents” — that the government requires them to be stored in specially secured facilities. But in these cases, the 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 staphylococcal enterotoxin, a frequent cause of food-borne illness, at a lab within the agency’s Center for Food Safety and Applied Nutrition that was not registered to handle it.

The latest discoveries came during an unprecedented sweep of government labs after the discovery in July of long-forgotten vials of the smallpox virus inside an FDA lab on the NIH campus in Bethesda. Investigators have been investigating how the vials, dating from 1954, wound up in a storage space inside an FDA biologics lab.

Officials at both agencies said Friday that they promptly reported the additional discoveries to the Centers for Disease Control and Prevention, and that no employees were endangered.

The smallpox virus in a 1975 electronmicrograph. (CDC via AP)

“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 a “clean sweep” of the agency’s labs.

At the same time, he said, NIH is a facility that routinely conducts research “on the most dangerous materials out there. All of these were found in containers that were intact, and there have been no exposures. It reminds us, just like my garage at home, that from time to time, we need to check.”

Three of the hazardous samples were found at the NIH Clinical Center’s Department of Medicine, which stores thousands of microbial samples from a collection that dates to the 1950s, Johnson said. In that collection, employees found two vials of the bacteria that cause plague, which has killed millions in pandemics historically but now appears only in limited areas, usually in sub-Saharan Africa, according to the CDC.

Employees also found two vials of a rare bacterium called Burkholderia pseudomallei, which causes Melioidosis — common in tropical climates. It can cause chest and joint pain, skin infections and fever. Workers also discovered three vials of the bacterium that causes tularemia, also known as rabbit fever, a rare but contagious and potentially fatal disease.

The NIH search also turned up a vial of ricin in a chemical lab where it was not supposed to be in use. The sample was in a historical collection dating from 1914. Ricin, a toxin produced by the castor bean plant, is extremely poisonous if inhaled, injected or ingested. While it has legitimate research uses, it also has been a tool of bioterrorism.

Finally, researchers found two vials of the nerve toxin that causes botulism, a muscle-paralyzing disease, in a lab of the National Institute of Child Health and Human Development, Johnson said. Researchers are allowed to have individual quantities below half a milligram. But the total contained in the two vials was over the allowable limit.

The NIH said the improperly stored materials were discovered between July 29 and Aug. 27.

“The finding of these agents and toxins highlights the need for constant vigilance in monitoring laboratory materials in compliance with federal regulations on biosafety,” NIH Director Francis Collins wrote in an e-mail to employees Friday.

The FDA’s discovery, meanwhile, came on July 15, though the agency did not disclose the findings to employees or the public until Friday.

Agency officials said that while the FDA’s food safety research center in College Park has labs registered to work with staphylococcal enterotoxin, samples of the pathogen were discovered in the freezer of a lab that had not been registered with the CDC to handle the bacteria.

Stephen Ostroff, the FDA’s acting chief scientist and the official overseeing the agency-wide inventory, said in an e-mail to employees Friday that while the vials were safely stored, they collectively contained eight milligrams of staphylococcal enterotoxin — three milligrams more than the quantity needed to be considered a dangerous “select agent.” Given that, officials decided to report the finding to the CDC and relocated the substance to a lab registered to handle it.

In an interview with a Washington Post reporter on July 31, FDA Director Margaret A. Hamburg was asked whether the agency had found any additional misplaced pathogens during the ongoing sweep of its labs.

“I’m happy to report that in the cold room inventories across the agency, we have not found any other stocks of unexpected hazardous biological materials,” she said at the time.

Ostroff added, “There’s always a chance that something will be where it’s not supposed to be, and we want to make sure that’s not the case.”

FDA officials said Hamburg and Ostroff did not learn of the staphylococcus until Aug. 4. “Importantly . . . there have been no other improperly stored hazardous materials identified in the FDA-wide inventory,” Ostroff wrote to employees.