Scientists grasping for clues
Silent, rapid spread complicates effort to contain covid-19 threat
One of the great mysteries of the coronavirus is how quickly it rocketed around the world.
It first flared in central China and, within three months, was on every continent but Antarctica, shutting down daily life for millions. Behind the rapid spread was something that initially caught scientists off guard, baffled health authorities and undermined early containment efforts — the virus could be spread by seemingly healthy people.
As workers return to offices, children prepare to return to schools and those desperate for normalcy again visit malls and restaurants, the emerging science points to a menacing reality: If people who appear healthy can transmit the illness, it may be impossible to contain.
“It can be a killer and then 40% of people don’t even know they have it,” said Dr. Eric Topol, head of Scripps Research Translational Institute. “We have to get out of the denial mode, because it’s real.”
Researchers have exposed the frightening likelihood of silent spread of the virus by asymptomatic and presymptomatic carriers. But how major a role seemingly healthy people play in swelling the ranks of those infected remains unanswered — and at the top of the scientific agenda.
The small but mighty coronavirus can unlock a human cell, set up shop and mass produce tens of thousands of copies of itself in a single day. Virus levels skyrocket before the first cough, if one ever arrives. And astonishing to scientists, an estimated 4 in 10 infected people don’t ever have symptoms.
“For control, to actually keep the virus from coming back, we’re going to have to deal with this issue,” said Rein Houben, a disease tracker at the London School of Hygiene and Tropical Medicine.
The dire toll of more than 580,000 worldwide deaths from the coronavirus has faded to the background as cities lift restrictions. But the slyness of the virus remains on the minds of many scientists, who are watching societies reopen, wondering what happens if silent spreaders aren’t detected until it’s too late.
Travelers with no coughs can slip past airport screens. Workers without fevers won’t be caught by temperature checks. People who don’t feel tired and achy will attend business meetings.
And outbreaks could begin anew.
THE FIRST HINTS
As early as January, there were signs people could harbor the virus without showing symptoms. A 10-year-old boy in China who traveled to Wuhan had no symptoms but tested positive along with six others in his family who had coughs and fevers. More troubling was a report out of Germany: A business traveler from China spread the virus to colleagues in Munich, even though she appeared healthy.
Still, many scientists remained unconvinced. Some questioned whether the Chinese businesswoman truly didn’t have symptoms. They suggested she might have had mild ones she attributed to jet lag.
The concept of people unwittingly spreading disease has never been an easy one to grasp, from the polio epidemic of mid-century America to the spread of HIV decades later.
At the turn of the 20th century, a seemingly healthy New York cook named Mary Mallon left a deadly trail of typhoid infections that captivated the public and led to her being forced into quarantine on an East River island. “Typhoid Mary” remains a haunting symbol of silent spread.
As covid-19 emerged, health officials believed it would be like other coronaviruses and that people were most infectious when showing symptoms like cough and fever, with transmission rare otherwise.
“We were thinking this thing is going to look like SARS: a long incubation period and no transmission during the incubation period,” said Lauren Ancel Meyers, a disease modeler at the University of Texas at Austin.
At U.S. airports around the country, travelers returning from hot spots including China who didn’t have symptoms were allowed to go on their way.
“We were reassuring ourselves and the public that contact with an asymptomatic person was not a risk,” said Dr. Jeff Duchin of King County, Washington, where the first major U.S. cluster of coronavirus cases broke out at the Life Care nursing home.
Behind the scenes, scientists like Meyers were sharing their alarming finding with health officials.
Meyers had assembled a team of students who scoured websites of Chinese health departments looking for dates of symptom onset in situations where there was enough information to figure out who infected whom.
Between Jan. 21 and Feb. 8, they found several cases where the person
“It can be a killer and then 40% of people don’t even know they have it. We have to get out of the denial mode, because it’s real.” — Dr. Eric Topol, head of Scripps Research Translational Institute
Sophia Garabedian had been dealing with a persistent fever and painful headache when her parents found her unresponsive in her bed one morning last fall.
Doctors ultimately diagnosed the then-5-year-old Sudbury, Mass., resident with eastern equine encephalitis, a rare but severe mosquito-borne virus causing brain swelling.
Garabedian survived the potentially fatal virus after about a month in Boston hospitals, but her parents say her ordeal and ongoing recovery should be a warning as people take advantage of the outdoors this summer.
“It’s been a rough year,” said David Garabedian, her father. “With any brain injury, it’s hard to tell. The damage is there. How she works through it is anyone’s guess.”
As the coronavirus pandemic subsides for now in the hard-hit Northeast, public health officials in the region are warning about another potentially bad summer for eastern equine encephalitis and other insect-borne illnesses.
Eastern equine encephalitis saw an unexpected resurgence last summer across 10 states: Alabama, Connecticut, Georgia, Indiana, Massachusetts, Michigan, New Jersey, North Carolina, Rhode Island and Tennessee.
There were 38 human cases and 15 deaths from the virus, with many of the cases in Massachusetts and Michigan, according to the Centers for Disease Control and Prevention. Most years, the country sees just half a dozen cases of the virus in humans, the agency said.
In Massachusetts and New Jersey, officials have already detected eastern equine encephalitis in mosquitoes this year, the earliest on record in those states. There have been no human or animal cases yet.
“It’s unnerving,” said Scott Crans, who heads up mosquito control efforts for the New Jersey Department of Environmental Protection. “It could signal a busy year.”
Crans and other state health officials say eastern equine encephalitis, which has no cure in humans, tends to come in two- to three-year cycles, but they also stress mosquito borne-diseases are notoriously tricky to predict.
A relatively mild winter may have benefited mosquito populations, but below-average rainfall could have also provided a welcome counterweight, he said.
Local health officials are also warning about the risk of contracting other insect-borne illnesses as more people are spending a longer time outdoors amid the coronavirus pandemic.
In Michigan, an invasive mosquito known to transmit dengue, Zika and other tropical viruses has already been detected for the first time this season, said Mary Grace Stobierski, the state’s public health veterinarian.
The state also had its first case of West Nile virus this season. A more common but less severe mosquito-borne disease than eastern equine encephalitis, it can cause fevers, headaches, body pain and other symptoms. The infection was found in a captive hawk in early June.
Ticks are also expected to be out earlier and in larger numbers this season because of the relatively mild winter, warned Aaron Bernstein, a pediatrician at Boston Children’s Hospital and a director at Harvard’s School of Public Health.
That could mean more cases of debilitating Lyme disease and other tick-related illnesses for local health care systems already feeling the pressure of responding to the coronavirus, he said.
“Some of the people going into the woods more now might not be experienced with how to protect themselves in the forest, and that’s a concern,” he said.
Officials say people should avoid the evening and early morning hours when mosquitoes are most active, use bug spray and wear long clothing where possible when outdoors.
The CDC has offered states additional help with mosquito testing this season as the coronavirus pandemic has overwhelmed state public health offices, said Candice Hoffmann, an agency spokeswoman.
Officials in eight states and the District of Columbia have so far taken up the offer: Maryland, Ohio, North Carolina, South Carolina, Vermont, Maine, Florida and Arizona.
During last year’s eastern equine encephalitis outbreak, the CDC provided about $700,000 in emergency funding and technical assistance to Rhode Island, Indiana, Michigan, and Massachusetts on top of roughly $18 million it provided to states for annual vector-borne disease surveillance, Hoffmann said.
In Michigan, where six of that state’s 10 cases of EEE last year proved fatal, officials this summer have launched a pilot program to improve the state’s response to mosquito-borne illnesses.
Ned Walker, a medical entomologist at Michigan State University heading up the effort, said the goal is to create the kind of regular mosquito surveillance system already in place in Massachusetts and elsewhere to better predict and prepare for disease outbreaks.
In Connecticut, officials have boosted the number of testing sites for mosquitoes in its high risk eastern portion, according to Philip Armstrong, a virologist with the state Department of Environmental Sciences.
In Massachusetts, which was the hardest hit by eastern equine encephalitis last year, with 12 cases and 6 fatalities, officials have been testing earlier, more often and in a wider range of locations this year in order to quickly identify infection clusters, said State Epidemiologist Catherine Brown. A pilot effort is also testing the efficacy of different larvicides to help cull the mosquito population at its earliest stages, she said.
One troubling development: the two earliest cases of eastern equine encephalitis in mosquitoes this year were found in a northern part of the state close to New Hampshire, rather than the virus’ typical hotspots near Cape Cod, where officials also detected the virus in a mosquito sample last week.
That, along with last year’s widespread cases, strongly suggests the territory of eastern equine encephalitis-carrying mosquitoes is expanding, according to Brown. Climate changes that are causing warmer summers and altering bird migration patterns and local mosquito populations could be among the drivers, she said.
Meanwhile an environmental group is calling on Massachusetts to avoid resorting to widespread aerial spraying of insecticide, which took place six times last year as cases surged.
Maryland-based Public Employees for Environmental Responsibility filed a complaint with the Massachusetts Inspector General’s office this month, arguing that 2019’s aerial spraying cost more than $2 million but wasn’t effective in reducing eastern equine encephalitis-carrying mosquitoes.
Brown disputes the group’s assertion, but acknowledges the insecticides can be toxic to bees and other species, another concern raised by the group. “Last year was unprecedented,” she said. “No one wants to do that again.”
Back in Sudbury, David and Kirstin Garabedian say they’re optimistic their daughter can continue to heal from eastern equine encephalitis.
Now 6, she was able to return to kindergarten in January before the coronavirus pandemic shuttered schools weeks later. But her parents say she still regularly goes to speech and occupational therapy to deal with lingering speech and memory problems.
Kirstin Garabedian says she understands people want to take advantage of the outdoors this summer.
“Go outside and enjoy yourself, but take the proper precautions,” she said. “Just be vigilant. Use common sense.”