Tom Geisbert's electron microscope

Tom Geisbert's electron microscope is the instrument through which an ambiguous culture from the Reston monkeys becomes compelling visual evidence of a filovirus. Its role is more than technical: by transforming hidden cellular activity into photographs that could be examined and compared, it changed what the researchers could claim about the outbreak, and how urgently they had to act. The images first raised the possibility of Marburg, then helped demonstrate that the virus was reproducing in the monkeys themselves.

Instrument and operator

Geisbert was an intern at the Institute and had been hired to operate its electron microscope, an essential tool for photographing objects too small to see with ordinary light microscopy, including viruses in tissue. He had grown up near Fort Detrick, where his father worked as chief building engineer, and had once watched people in protective suits through the Institute's heavy windows. Now he worked among the samples he had once only glimpsed from outside. Identifying and classifying virus particles suited his meticulous attention: he practiced with specimens and learned to recognize different agents by their forms in images.

For Geisbert, the instrument was both specialized laboratory equipment and the center of a solitary practice. He liked working in the hot-zone suites and could spend long stretches absorbed in samples. His attention to images was not casual looking. It involved searching through complicated cellular landscapes in which a virus might be present but difficult to find, then judging whether the shapes he saw belonged to a recognizable agent. The microscope did not offer an automatic diagnosis; it gave him a view that had to be interpreted and tested against other evidence.

From culture to specimen

The Reston investigation reached Geisbert through Monkey O53. After samples from the animal arrived, Joan Rhoderick cultured material from its spleen, throat wash, and blood serum in flasks of living monkey-kidney cells. On the morning of November 17, 1989, Geisbert went to examine those cultures before leaving for a Thanksgiving hunting trip. Rhoderick had noticed that one flask was behaving abnormally. Under a light microscope, Geisbert saw that the cell layer had deteriorated; many cells had detached, and the culture fluid had become cloudy. Several flasks showed similar damage.

The appearance alone left room for an ordinary laboratory explanation. Peter Jahrling suspected bacterial contamination, a familiar problem in cell culture, but the flask had no smell of the soil bacterium he suspected. He and Geisbert returned to inspect it, and Jahrling asked that it be examined with the electron microscope. Geisbert separated a small amount of the cloudy culture by centrifuging it. A pinhead-sized pellet collected at the bottom of the tube. He preserved the material in plastic resin, preparing a specimen that could later be cut thin enough for examination.

That preparation linked the microscope to a sequence of practical steps: a sick monkey supplied the sample; cultured cells gave the unknown agent an opportunity to multiply; centrifugation concentrated material; resin preserved it; and thin sections made it possible to search the cells at far greater magnification. The machine's images would matter because they emerged from this chain of handling, not from an isolated glimpse of an unidentified object.

The images and the first identification

On November 27, Geisbert returned to the preserved sample. He used a diamond knife to cut thin slices from the resin-embedded cell material and mounted a slice for examination. Inside the electron microscope, the cell appeared as a dense, intricate landscape. As he moved across it and magnified the view, he found that the cell was not merely damaged: it was filled with threadlike particles. Their form identified them as filoviruses, the family that includes Marburg and Ebola.

Geisbert recognized a resemblance to Marburg, a frightening possibility because he and Jahrling had previously handled material from the monkey culture without knowing what it contained. He also compared the new forms with the distinctive patterns he had studied in Peter Cardinal's samples. The task was not simply to spot a familiar outline: the particles looked like a filovirus, but their shapes did not match Marburg exactly. Geisbert photographed what he saw, developing the negatives so that the images could be inspected and discussed beyond the microscope itself.

He carried the photographs to Jahrling, who examined them and measured the particles. Their discussion kept the identification provisional: the images supported a filovirus, while the question of which one remained unresolved. The photographs nonetheless altered the situation. What had first looked like a ruined culture now appeared to contain an agent that might pose a serious danger to laboratory workers. The microscope made the unknown visible, but it did not, by itself, settle its name.

Independent evidence and confirmation

The next morning, Geisbert used the microscope to examine slices of Monkey O53's liver. This time the images showed particles budding from the cells, along with inclusion bodies within them. The evidence established that the virus was present and reproducing in the monkey's tissue; the finding made laboratory contamination a much less tenable explanation. Geisbert took the photographs to Jahrling, and together they brought them to C. J. Peters. The images persuaded Peters that an agent was growing in the monkeys, though the precise identification still required test results.

That distinction matters to the microscope's contribution. It supplied direct visual evidence of viral particles and their relationship to infected cells, while a separate serum test provided evidence about the agent's identity. When Jahrling tested the monkey culture against reference sera, including Nurse Mayinga N.'s blood serum, the reaction identified Ebola Zaire rather than Marburg. Repeating the test produced the same result. The combination of the microscope images and the independent laboratory test corrected the early suspicion: the Reston monkeys were dying of Ebola, not Marburg.

Significance in the investigation

The electron microscope did not resolve every question raised by the outbreak. It could show the particles and their activity in tissue, but it could not establish how the infection first entered the monkeys, explain why the human caretakers who later tested positive remained without symptoms, or prove every route of transmission. Those questions depended on other observations and tests. Its crucial contribution was narrower and decisive: it helped distinguish an active viral infection from a failed or contaminated culture and supplied images that researchers could share, scrutinize, and compare.

In the investigation, the microscope thus functioned as both an instrument and a means of making evidence portable. Geisbert's initial view became photographs on Jahrling's desk and then proof presented to Peters; subsequent liver images strengthened the conclusion that the agent was replicating in the animals. The result was not a diagnosis produced by a machine alone, but a diagnosis built by joining visual evidence to sample preparation, expert interpretation, and independent testing. The microscope's importance lies in that progression: it changed a cloudy flask from an unexplained laboratory problem into a visible, testable, and urgent biological threat.