Virus Hunters

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Virus Hunters

The people of San Joaquim were dying—they were bleeding to death from a disease nobody had ever seen before. They called it “el tifo negro,” the black typhus, later to become known as Bolivian hemorrhagic fever. In this little one-horse garrison town in the lowlands on the Amazonian side of the Bolivian Andes, close to the Brazil border, soldiers and citizens alike were sickening, and no one knew why.

Under the Alliance for Progress established by President John F. Kennedy (1917–1963) between the United States and Latin America, Bolivia asked for help from the United States, and a team was flown in from the National Institute of Health's Middle America Research Unit in the Panama Canal Zone. Heading it was physician Karl Johnson, one of the great virus hunters of the end of the twentieth century. I was greatly privileged to be working with his team, on a traveling fellowship from the Rockefeller Foundation, at the time he isolated the causative agent from a human case. It was a new virus, which he named Machupo virus, after a local place name.

Everybody knows that viruses are really nasty pieces of work. They are even smaller than bacteria, and untouched by antibiotics, so for many there is no cure, nor even a preventive vaccine. They are responsible for some of the deadliest diseases on the planet: Ebola, yellow fever, smallpox, AIDS, SARS (severe acute respiratory syndrome), polio, and influenza, both human and bird, to name only seven. The scientists who tackled them have gone down in history as the “virus hunters,” and some of them paid for their research with their lives.

At the beginning of the twentieth century, the United States Army played a prominent role in the fight against yellow fever. A number of United States military physicians and volunteers died in early tests that proved that the virus was transmitted by mosquitoes. This discovery paved the way for control programs led by General William C. Gorgas, which resulted in the eradication of yellow fever from Havana, Cuba, and of the urban disease from Brazil. It also permitted the completion of the Panama Canal, work on which had been stalled by the huge toll exacted by yellow fever and malaria.

The Rockefeller Foundation's International Health Division set up laboratories in Africa and South America specifically to study yellow fever at its source. Six of their researchers died of the disease, but their work paid off with the isolation of the virus and the development of the 17D yellow fever vaccine, still one of the best vaccines ever invented.

The stories of these pioneer researchers are told in many books, but I want to tell you about two modern virus hunters with whom I had the good fortune to work myself. In San Joaquim, Karl Johnson had set up a breeding colony of hamsters and a separate infected animal room, well screened against mosquitoes and with the individual cages fitted with virus filters in their steel mesh lids. A separate lab had a glove box, inside which the hamsters could be inoculated safely with specimens. The only problem with this was that there was only one glove box, and it had to be sterilized with a disinfectant spray and left for an hour between each litter of hamsters inoculated, which slowed down the work and meant working very late hours. There was also a thatched hut where the zoologist took the rodents he trapped in the town for processing and where the entomologist combed their fur for ectoparasites, such as ticks and mites, in case these were involved in the transmission of the disease (they weren't). There was an autopsy room for humans, but the dead cow that came in at night with a history of bleeding had to be necropsied on a wooden bullock cart in the open air by the light of hurricane lamps. The cow was negative for the virus.

The colonel in charge of the town's garrison invited us to take our meals with him in his quarters. There is a photo of him at the head of the table dining with the team. A week later he was dead from the black typhus. But shortly after that there was euphoria—hamsters inoculated with autopsy material from another victim came down with signs of infection, and a virus was isolated from their brains. Now reagents could be made to test for antibodies in the blood of survivors and wildlife.

The next step was to find out where the disease was coming from and how to stop its transmission. Karl suspected the wild rodents that seemed to have recently overrun the town. He set up a system to trap out all the rats in one half of the place. Lo and behold, after that, no more cases occurred in that area. So the trapping was extended to the whole town, and the epidemic was stopped cold.

What eventually emerged was an extraordinary story. Apparently anti-malaria teams had deluged the town with DDT on a control visit. Cats are highly susceptible to DDT, and they get a fatal dose of it by preening their fur after being caught in the spraying or rubbing against surfaces that have been sprayed. All the cats in the town had died, so the wild rodents from the fields and forest around the town were able to infiltrate the houses in their quest for easy pickings. Some of them were infected with the virus, which they excreted in their urine and droppings inside houses. These dried out in the tropical heat and turned to dust, which, when stirred up by walking through or sweeping the rooms, was inhaled by the inhabitants, giving them the disease. So an intervention to control one fatal disease ended up causing another.

All this was in 1963. Thirteen years later, Karl was working for the United States Public Health Service as head of the Centers for Disease Control's Special Pathogens lab (the euphemism for the lab that handled the most dangerous disease agents known, needing Biosafety Level 4 containment, either in a chain of glove boxes or in negative pressure labs with the researchers wearing space suits). He found himself called out to investigate another hemorrhagic fever epidemic, this time in Yambuku, Zaire (now known as the Democratic Republic of the Congo). The American researchers found that the virus was transmitted by the inadequately sterilized, reused needles and syringes used for giving injections to the patients. The epidemic was being spread in the hospital. Worse, local burial custom demanded that the relatives remove by hand the viscera of the dead person, and of course this was done with out any concept of sterile precautions, so that the blood of the deceased infected the relatives. When these practices in the hospital and home were stopped, the epidemic ceased.

WORDS TO KNOW

ANTIGEN: Antigens, which are usually proteins or polysaccharides, stimulate the immune system to produce antibodies. The antibodies inactivate the antigen and help to remove it from the body. While antigens can be the source of infections from pathogenic bacteria and viruses, organic molecules detrimental to the body from internal or environmental sources also act as antigens. Genetic engineering and the use of various mutational mechanisms allow the construction of a vast array of anti-bodies (each with a unique genetic sequence).

ANTIGENIC SHIFT: Antigenic shift describes an abrupt and major genetic change (e.g. in genes coding for surface proteins of a virus).

DROPLET TRANSMISSION: Droplet transmission is the spread of microorganisms from one space to another (including from person to person) via droplets that are larger than 5 microns in diameter. Droplets are typically expelled into the air by coughing and sneezing.

NECROPSY: A necropsy is a medical examination of a dead body: also called an autopsy.

PANDEMIC: Pandemic, which means all the people, describes an epidemic that occurs in more than one country or population simultaneously.

STRAIN: A subclass or a specific genetic variation of an organism.

Karl's lab showed that the disease agent was a new member of a new family of viruses, the Filoviridae or “thread viruses” because they looked like partially coiled threads (some say more like shepherd's crooks) under the electron microscope. Karl named it Ebola virus, after a nearby river. He couldn't call it Congo virus because that name had already been taken by another, different virus isolated earlier in the same country, which was eventually named as the causative agent of Crimean-Congo hemorrhagic fever.

The labs run by Karl were dynamic places full of eager young researchers bubbling over with ideas about the viruses that cause disease and their epidemiology— where they hide in nature, how they are transmitted, and why they suddenly emerge to cause outbreaks. I would dearly have liked to have joined his lab, but instead I was hired by the Rockefeller Foundation to run their virus lab at the mouth of the Amazon, and so came to know well another modern virus hunter—Bob Shope.

I first met Bob on that same Rockefeller Foundation travel fellowship that took me to Bolivia. His family was away at the time and I was a guest in his home in Belem, Brazil, so we spent many happy hours both in the lab and in his house discussing the riddles of the viruses of the rain forest. His lab had a small mammal recapture program with a grid of traps in the forest at the edge of town, where wild rodents and marsupials were trapped daily, weighed and measured, and obliged to donate a blood sample so that their medical history could be followed. They were exposed to forest mosquitoes that transmitted all sorts of interesting viruses to them, which were then isolated from their blood samples in lab mice. Many of the viruses were new to science. Other mammals such as bats, sloths, and tree porcupines were also caught and studied, and a series of ingenious mosquito traps baited with monkeys or mice were run daily to provide pools of mosquitoes, sorted by species, which also yielded more such viruses. There were even lab workers who volunteered to go out into the forest at night to catch mosquitoes coming to bite them. Some of the human volunteers didn't manage to catch all the mosquitoes before the insects got their bites in, so they came down with jungle fevers. The viruses isolated from their blood provided proof that some of these new viruses could cause disease in people who went into the forest to hunt, collect timber, or clear plantations.

When Bob left Belem for the Yale Arbovirus Research Center (YARU), where he worked as researcher and then director for 30 years, I took over his lab and kept in close touch with him for many years. “Arbovirus” is short for “arthropod-borne virus,” meaning viruses transmitted by fleas, ticks, and mites, as well as mosquitoes. YARU became a World Health Organization Collaborating Center and the world reference center for these and other viruses, because many viruses isolated from wildlife by field labs established around the world by the Rockefeller Foundation, France's Pasteur Institutes, and others turned out not to be transmitted by arthropods—notably Machupo and Ebola. Bob became a living encyclopedia of information on the origins and interrelationships of hundreds of viruses from around the world, including the many viruses from wildlife related to rabies. Some of these have become what we now call emerging diseases. He mentored students and post-docs from around the world, who worked in his lab on Rift Valley fever, Lassa fever, Argentinean, Brazilian, and Venezuelan hemorrhagic fevers, and other dangerous viruses. But he never forgot the lessons from his field experience in Brazil with exotically named viruses such as Caraparu, Oriboca, and Marituba. After his retirement, the YARU lab closed and he took the world reference collection of arboviruses to the University of Texas Medical Branch at Galveston, where he worked until his death in 2004.

So although it is all the rage now to go into molecular virology and sequencing, I hope that at least some of today's students will be inspired by the examples of Karl and Bob to go out into the field and get their hands dirty trapping wildlife and mosquitoes, finding out what viruses they are carrying and what makes those viruses tick. Because those viruses are the emerging diseases of the future, and we need to know as much as we can about them before they strike.