Crab-eating macaque

The Crab-eating macaque is both a wild primate of Southeast Asian forests and a routinely traded laboratory animal in The Hot Zone. In the Reston outbreak, monkeys shipped from the forests of Mindanao died in unusual numbers, and the virus that spread among them ultimately infected human caretakers without making them visibly ill. Their story links the macaque’s natural history to the risks of capturing, transporting, and confining wild animals—and to questions the book leaves unresolved about how viruses move between species.

Identity and Natural History

Also called the long-tailed macaque, the Crab-eating macaque lives in coastal rain forests and along rivers and mangrove swamps. Its long, arched tail, doglike snout, and sharp canine teeth distinguish it physically; its adaptable diet includes fruit, vegetables, insects, grass, roots, small pieces of clay, and crabs. The book describes monkeys raiding farmers’ crops and retreating quickly into the forest when people approach. Their familiar call gives rise to the name kra in some places, while people living near them may regard them as troublesome crop-raiders.

The macaques’ daily routines are shaped by both predators and their own social organization. At night, a troop settles in a leafless tree, often over a river, where the monkeys can watch in several directions. At sunrise, the adults gather their young and move through the branches in search of food. In mangroves, a macaque waits beside a crab’s hole, seizes the animal as it emerges, removes its claws, and eats it. The tactic can fail: a crab may catch a monkey’s fingers, provoking an abrupt struggle and alarm calls.

A troop is led by a dominant male, who maintains his position through staring. When a human stares directly at a dominant male in a cage, the animal may rush the bars and try to attack. The book presents this response as a contest in which the monkey cannot afford to appear fearful when its authority is challenged. Two dominant males confined together may fight until only one remains alive. These behaviors matter in the quarantine facility: the macaques were intelligent, socially responsive animals, not interchangeable cargo, yet they were kept separately in cages under artificial light and fed biscuits and fruit.

Capture and the Laboratory Trade

The macaques at the center of the Reston outbreak originated in the coastal forests of Mindanao. They were transported by boat to Ferlite Farms, a monkey-wholesale facility near Manila, where they were grouped in large cages. From there, they were crated and flown first to Amsterdam, then to New York City; a truck carried them down the East Coast to the Reston Primate Quarantine Unit. On October 4, 1989, Hazleton Research Products accepted a shipment of one hundred monkeys. Two had died in their crates, a loss the book notes was not unusual during transport.

The facility formed part of a larger import system: about sixteen thousand wild monkeys entered the United States each year, and imported animals had to spend a month in quarantine before onward shipment. The requirement was intended to prevent infectious diseases from spreading to other primates, including humans. Yet the journey itself brought animals from different circumstances into crowded transport and holding environments. The book places this trade in a wider context, noting that the export of primates for research exposed trappers and handlers to wild animals carrying unfamiliar viruses and brought different monkey species into proximity. It presents those conditions as a possible setting for cross-species transmission, not proof that the trade caused a particular virus to emerge.

The Reston Outbreak

By November 1, colony manager Bill Volt had counted twenty-nine deaths among the hundred monkeys in the October shipment. Most deaths had occurred in Room F. At the same time, the building’s thermostat had failed, leaving the heating system running and the air-conditioning inactive. The heat offered a possible explanation for the monkeys’ condition, but inspection raised doubts: two sick animals had fevers, and after they died, their enlarged spleens and small amounts of blood in the intestines did not fit neatly with heat stress. Dan Dalgard, the facility’s consulting veterinarian, considered whether an infectious agent was spreading. Another shipment arrived that day and was placed in Room H, two doors from Room F.

A later outbreak followed the facility’s decontamination and restocking. After the Army certified the building as safe, Hazleton again acquired monkeys from the same facility near Manila. In mid-January, monkeys in Room C began dying with bloody noses, and the virus spread rapidly through the building. It appeared to move through the air-handling ducts: after illness became apparent in one room, about eighty percent of its monkeys died soon afterward, and further rooms were affected in the weeks that followed. The animals developed respiratory symptoms as well as bleeding, and the infection devastated the confined population. The book describes the episode as an experiment in what the virus would do in a dense monkey population, though the decision to leave the animals undisturbed was also intended to avoid another military intervention and, if possible, save some of them.

Infection, Uncertainty, and Significance

Four men who had worked as caretakers at the monkey house eventually tested positive for Ebola Reston virus. One, John Coleus, had cut his thumb while examining a dead monkey; the other infections could not be explained by such a cut. The book reports that the men did not become ill and that the virus later cleared from their blood. Researchers therefore considered whether it had entered the other caretakers through contact with the lungs, possibly by air. The evidence prompted concern about transmission, but it did not establish every route by which the men had become infected, nor did the episode answer why the virus multiplied in them without causing apparent disease.

The Crab-eating macaque thus occupies two connected but distinct places in the account: as a wild animal with its own social and feeding patterns, and as a traded primate confined within a system designed to manage infectious risk. The book links the movement of monkeys and the degradation of tropical habitats to a broader discussion of emerging viruses, while recognizing that the origins and pathways of particular infections remain uncertain. In Reston, the macaques’ deaths exposed a failure of containment’s reassuring boundary: the animals were kept apart from the outside world, but they were not isolated from one another, from the building’s shared air, or from the people who cared for them.