The world lost the preeminent virus “hunter,” Dr. Karl M. Johnson on October 10, 2023. Karl played a critical role in the discoveries of some of the most horrific diseases on the planet: the viral hemorrhagic fevers, including the Machupo and Ebola viruses. He also led in the development of laboratory safety innovations, which reduced the risk to laboratory workers while studying such deadly viruses.
What Is A Virus Hunter?
Virus hunters are the men and women who run boldly into harm’s way, frequently in the middle of epidemics, where others fear to tread. They pursue their prey in austere, hazardous settings to root out the origins of some of the deadliest diseases on the planet, with names like Ebola, Marburg and Lassa. Their mission: to determine what causes the diseases, where they exist in nature, how they are transmitted and how to stop them. It is a relatively small “club,” and their work frequently extends back to the high containment laboratories that have specialized air handling and filtration, decontamination protocols, equipment and procedures to support their work.
What Is A Viral Hemorrhagic Fever?
There are four families of viruses that cause the diseases known as viral hemorrhagic fevers (VHFs), a term that originates from two characteristics of the illnesses: fever and hemorrhage (bleeding), with the latter occurring in some of the most severe cases. Unlike what you might see in the movies, though, people don’t actually bleed from their eyeballs (although they can have bleeding in the eyes). Instead, they develop problems clotting their blood, typically leading to blood oozing from sites where the skin has been punctured by a needle or other sharp instruments to obtain a blood sample, insert an intravenous catheter or conduct other medical procedures. Other sites of bleeding can include the gums around the teeth, and in the most severe forms, from the gastrointestinal tract resulting in bloody vomit or diarrhea. In addition to causing bleeding, the VHFs also happen to kill efficiently, with death rates approaching 80-90% in some outbreaks.
How Do Viral Hemorrhagic Fevers Spread?
The VHFs spread to humans in different ways depending on the virus: from contact with or inhaling the excretions of rodents or through mosquito or tick bites. To complicate things, the blood and body fluids of victims are jam packed with viral particles, making the diseases highly contagious to household members and caregivers who may have direct contact with a patient’s blood or body fluids. The VHFs can also cause copious diarrhea, which provides ample opportunities for spread to others from splashes or small fluid droplets. In some Ebola outbreaks, simultaneous exposures of large numbers of individuals who had direct contact with the deceased during funeral rites have led to super spreader events. Characteristics of the viruses that facilitate spread make hunting for the origins of such diseases and caring for the victims extremely risky.
Karl’s Scientific Achievements
After completing his medical training, Karl initially worked on respiratory viruses at the National Institute of Allergy and Infectious Diseases of the NIH. A turning point came in 1962 when an opportunity opened up at the NIH’s Middle America Research Unit (MARU) in Panama. Some colleagues advised him at the time that such a move could be a career killer. Instead, the opposite occurred – the opportunity proved fortuitous.
While at MARU, Karl led a response team into the heart of a deadly epidemic of a mysterious new hemorrhagic fever illness in a remote part of Bolivia, accessible only by puddle-jumper aircraft. His team toiled under extremely challenging conditions, but they ultimately discovered a brand-new virus, which Karl named Machupo after a nearby river. He and his team members also determined the disease’s rodent host and how it spread, but not early enough to prevent Karl and a team member from becoming infected. Fortunately, they recovered.
Karl later moved to the CDC, where he founded the Special Pathogens Branch, which focused on discoveries of similar hazardous diseases. While there, he set up the CDC’s first laboratory where the lab workers don “space” suits. Like something out of a science fiction novel, the workers remain fully encapsulated inside a giant body condom while working with the deadly viruses. In 1976, Karl was called upon again to lead a team into the heart of the jungle during a deadly epidemic – this time in Zaire (now the Democratic Republic of the Congo) and in Sudan, where they discovered two species of the “king” of the deadly hemorrhagic fever viruses: Ebola. Using the same model as he did with Machupo, Karl named the disease after a local river close to the site of the outbreak.
Karl’s Legacy
I first met Karl when I was the Chief of the Medical Division at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), which has laboratories with specialized features for handling VHFs safely. Karl had previously led VHF work at USAMRIID, so before meeting him, I was already inspired by his work. He was compiling a summary of the capabilities of similar containment laboratories across the U.S. He had a wry sense of humor and a mischievous twinkle in his eye. It wasn’t hard to imagine him leading a team into the unknown to hunt down a killer virus.
Karl left a legacy behind from his discoveries of VHFs in the field and in the lab. One might say that the foundation for the eventual licensure of a vaccine against Ebola virus, which was tested in recent outbreaks in Africa, started over four decades ago in the remote jungles of central Africa due to Karl’s and his team’s valiant work. But beyond the field work, Karl’s ultimate legacy may well be his inspiration of a whole cadre of virus hunters, who have the same sense of adventure and spirit of scientific discovery. No doubt they will continue to make significant breakthroughs for decades to come around the globe. Karl Johnson, a heartfelt thank you, and may you rest in peace.
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