1990 Reston outbreak policy of isolating the monkeys and letting the outbreak subside

The 1990 Reston outbreak policy of isolating the monkeys and letting the outbreak subside replaced an immediate eradication response with a decision to leave infected animals in their rooms and observe the outbreak’s course. Agreed jointly by the United States Army, the Centers for Disease Control and Prevention, and Hazleton Research Products, it reflected competing aims: limiting intervention, preserving monkeys where possible, and learning how Ebola Reston virus behaved in a confined population.

Background and Change in Approach

In December, the Army had cleared the monkey house and returned it to Hazleton Research Products. The company then restocked the building with crab-eating monkeys from the same facility near Manila, animals trapped in the rain forests of Mindanao. Less than a month later, in mid-January 1990, monkeys in Room C began dying with bloody noses, and Dan Dalgard alerted Peter Jahrling that the building appeared to be affected again. The virus had returned with the new monkeys from the Philippines.

The circumstances differed from those of the first outbreak. Because there had been no human casualties during that earlier episode, the agencies and company chose not to send the Army back in protective suits to eliminate the monkey population. Dalgard hoped that at least some animals could be saved, while Hazleton wanted to avoid another Army intervention. The policy therefore changed both the immediate response and the conditions under which the outbreak would unfold: instead of ending it through a building-wide operation, the parties would allow transmission to continue among the monkeys.

The Decision and Its Rationale

The decision was explicitly framed as an experiment. The confined building, with its interconnected rooms and shared air space, would make it possible to observe what the virus did in a monkey population without immediately removing infected animals. This was not a controlled laboratory study, but the agencies treated the outbreak as an opportunity to watch its natural course in an enclosed setting.

That rationale carried a tension. Leaving the monkeys alone might spare some of them and reveal the scale and character of the disease, but it also meant accepting further deaths and continued exposure within the facility. The policy did not establish that the virus was safe for people; the absence of human casualties during the first outbreak was the specific precedent cited for the decision. The evidence describes a choice under uncertainty, not proof that the uncertainty had been resolved.

The Outbreak Under Observation

Ebola Reston virus moved rapidly from room to room. The affected monkeys developed symptoms that resembled a severe respiratory illness: clear and green mucus, sometimes mixed with blood, and extensive lung damage. When a single monkey with a nosebleed appeared in a room, about 80 percent of the animals there generally died soon afterward. The account describes the infection as extraordinarily infectious among monkeys.

By January 24, the infection had reached Room B; over the following weeks it spread into Rooms I, F, E, and D, where virtually all the animals died. The pattern suggested that the virus might be passing through the building’s air-handling ducts, though the account presents this as an apparent route rather than a confirmed mechanism. Scientists also suspected that the virus might have changed in character since the December outbreak. Its cold-like symptoms and rapid spread raised the possibility of adaptation in a new host population, but the policy itself did not prove that a new strain had emerged.

Consequences and Significance

Allowing the outbreak to run its course exposed how severe Ebola Reston virus could be in macaques while making the monkey house a setting for ongoing observation rather than immediate clearance. The policy’s central contrast was stark: the previous response had removed the affected population, while the 1990 decision kept the animals in place so that the infection’s progress could be watched. The hoped-for benefit of preserving some monkeys and gaining knowledge was set against the scale of mortality that followed.

The decision also left a human-risk question unsettled. In mid-February, a Hazleton caretaker identified as John Coleus cut his thumb while performing a necropsy on an infected monkey; the blade had been in contact with liver tissue and blood. The Centers for Disease Control and Prevention did not place him in isolation, while scientists at the Institute feared the consequences of the exposure and emphasized how little was known about the virus. This episode does not establish that the monkey-isolation policy caused the injury, but it shows that observing an outbreak in place did not remove the hazards of handling infected animals. The policy’s significance lies partly in that distinction: letting the virus proceed among monkeys could generate evidence, but it could not make the surrounding work risk-free.