Ebola Reston disease in macaques

Ebola Reston disease in macaques was a severe infection that could spread rapidly through a captive colony and kill most animals in an affected room. Its recurrence at a Reston monkey facility in January 1990 showed that an earlier cleanup had not ended the threat: the virus returned with newly imported macaques and moved through the building, producing prominent respiratory symptoms.

Recurrence and Spread

After the United States Army certified that the monkey house had been cleared, Hazleton Research Products resumed operations and brought in crab-eating macaques from the same facility near Manila, animals trapped in the rain forests of Mindanao. Less than a month later, in mid-January, monkeys in Room C began dying with bloody noses. Dan Dalgard alerted Peter Jahrling that the facility appeared to be affected again. Testing identified Ebola Reston virus. In contrast to the previous response, the United States Army, the Centers for Disease Control and Prevention, and Hazleton Research Products chose to isolate the monkeys and let the infection run its course. Dalgard hoped to save some animals, while the company wanted to avoid another military intervention.

Respiratory Signs and Spread Through the Building

The January outbreak presented a pattern different from the one seen in December. In affected rooms, the monkeys developed respiratory illness, including runny noses, red eyes, and pneumonia; after an animal showed a nosebleed, roughly 80 percent of the other monkeys in that room died soon afterward. The infection then advanced from room to room, apparently traveling through the building’s air-handling ducts. By January 24 it had reached Room B, and over the following weeks it entered Rooms I, F, E, and D, where nearly all the animals died.

The combination of rapid transmission and changed symptoms led researchers to suspect that they were seeing a mutant strain. They could not establish that the virus had changed in a month, but the episode suggested how quickly Ebola Reston might behave differently in a new host population. Its respiratory presentation also recalled viruses associated with childhood colds, while the severity of the monkey outbreak made clear that this resemblance did not make the infection benign.

Disease Course and Pathology

The macaques’ illness could advance with extraordinary speed. During the December outbreak, examinations of animals that had been dead for only a few hours revealed intestinal damage so extensive that the gut lining had sloughed away. In some cases the tissue was too badly affected for a full examination, and investigators instead collected liver and spleen samples. These findings gave the Institute’s researchers a concrete measure of the disease’s severity beyond the visible signs in living animals.

The outbreak also showed how rapidly the virus could overwhelm an individual animal. The apparent state of the carcasses suggested a far longer period of decline than had actually elapsed, while extensive viral material in the sampled organs underscored the scale of infection. Read alongside the January recurrence, these observations made the macaque colony a stark setting in which to watch Ebola Reston’s course: the illness could present with shifting clinical signs, yet remain highly lethal to the animals.

Human Infection and the Animal–Human Contrast

The outbreak also revealed a striking difference between infection in macaques and infection in people. Four men who had worked as caretakers in the monkey house eventually tested positive for Ebola Reston virus, showing that the virus had entered their bloodstreams and multiplied. None recalled becoming ill, and the infection later cleared from their blood without known lasting effects. Their experience contrasted sharply with the extensive disease and mortality among the monkeys.

The route of those human infections remained uncertain. One caretaker had a clear exposure while handling an infected animal, but three of the four men had not cut themselves. Researchers therefore concluded that the virus had likely reached them through contact with the animals’ lungs, and that it could spread through the air among monkeys. The episode established neither that macaque disease and human infection followed the same course nor that airborne transmission posed the same risk to people; instead, it left two facts side by side: severe disease in the colony and symptomless infection in the exposed workers.