A debate is brewing in scientific circles over what’s causing infectious diseases to emerge and spread more quickly than ever before. While some argue that improvements in detection are causing a perceived increase in outbreaks, others point to a number of societal and environmental changes driving viruses to new places.
“The biggest force is us changing how we use land,” said Dr. Jay Varma, chief medical officer and executive vice president at Siga Technologies, which specializes in therapies for health security and medical countermeasures. “We cut down forests and jungles more aggressively, so that brings us into contact with wild species. Then viruses spill over to people, and more people live in cities, which allows infectious diseases to spread faster. And then we have more international travel, which allows you to bring a disease to a major city within 24 hours.”
Climate change is also often cited as a major factor behind the rising number of outbreaks because the warming planet is driving more people and virus-carrying hosts — like mosquitos — to different parts of the planet.
“For the first time in decades, there was a malaria transmission in Florida. We now see that dengue virus and other tropical diseases are becoming endemic in southern Europe and the U.S., and there’s every expectation that as the earth continues to warm … the vectors that carry these infections are going to spread farther north,” Varma said.
“Diseases we thought were off the playing field are now coming back.”
Dr. Jay Varma
Chief medical officer, executive vice president, Siga Technologies
Whatever the reason for the uptick in outbreaks, Varma, who spent much of his career in public health roles including as director of the CDC’s international emerging infections program, said there is consensus that in the last 50 years, viruses have caused increased disruptions on the “city, national and global level.”
“Diseases we thought were off the playing field are now coming back,” Varma said.
Here are three viruses on the move in the U.S. that health officials are watching closely.
An mpox turnaround
The backstory: Mpox jumped into the global spotlight in 2022 after an outbreak triggered more than 30,000 cases in the U.S. within one year. But the viral zoonotic disease’s spread never ended, and cases are once again on the rise around the world.
The Democratic Republic of Congo is currently reporting a record 400 suspected cases every week. And so far this year, the CDC has recorded nearly 580 mpox patients in the U.S. — far more than the total of 298 cases in 2023.
Although some experts believe the dominant strain of mpox could be deadlier than in the past, Varma urged caution in evaluating the available fatality estimates.
“What’s been published is largely data from outbreaks and routine case reporting in DRC and neighboring countries, and that indicates the death rate is between 5% to 10%,” he explained. “But many experts in this disease believe that’s an overestimate … [because these countries] don’t [always track] mild cases. So your fatality rate is more elevated.”
Mpox resembles a milder version of smallpox, but it can be a painful ordeal that causes blisters, rash, fever and respiratory symptoms.
Similar to the 2022 outbreak, Varma said the current spike is primarily driven by sexual contact between men. But he noted that there’s now documented evidence it’s occurring in heterosexual populations in Africa, and that the transmission pattern has become “worrisome.”
How it’s controlled: There are currently two approved vaccines for mpox. The most widely used is made by Bavarian Nordic, and public health officials have ramped up inoculation efforts since 2022. Varma pointed out, however, that stigma around the disease has created roadblocks to wider uptake of the vaccine.
Siga is also testing a treatment called Tpoxx in mpox patients. Already approved for smallpox, the therapy is currently available in the U.S. on a compassionate-use basis, and according to the CDC, 7,563 patients were prescribed the drug for mpox in 2022.
The two most advanced mpox studies using Tpoxx are late-stage trials still enrolling in various countries. Varma said the company hopes it will start to receive efficacy data from those studies next year.
A measles comeback
The backstory: For a few decades, the U.S. had the measles under control. After a highly effective vaccination campaign launched in the 1970s, the U.S. declared measles “eliminated” in 2000, meaning there was no “continuous disease transmission for greater than 12 months,” according to the CDC. That status came under threat in 2019 when the U.S. recorded 1,249 new cases, mostly driven by an outbreak in New York. Now, measles hotspots dot the whole country.
The Yeshiva Kehilath Yakov School in Brooklyn. After a 2019 outbreak of measles in the area’s Orthodox Jewish community, New York City ordered all yeshivas to exclude all students who weren’t vaccinated against measles from classes.
Drew Angerer via Getty Images
As of March 28, 97 cases have been reported this year in 18 states — already far outpacing the 59 cases reported in all of 2023. Outbreaks have bubbled up in a migrant shelter in Chicago, a day care in Philadelphia and an elementary school in Florida.
Two doses of the measles vaccine are considered 97% effective, but inoculation rates have been dropping. Last year, the CDC reported measles coverage was 93% — below a pre-COVID-pandemic rate of 95%. With medical mistrust growing, the vaccine exemption rate for kindergarteners also jumped to 3% in the 2022-2023 school year.
While public health officials have become adept at containing outbreaks, the highly contagious virus that infects around 90% of exposed, unvaccinated people can still be deadly. The CDC estimates that 1 in 5 unvaccinated people with measles end up in the hospital, and the virus kills 3 of every 1,000 sickened children, according to University of Chicago Medicine.
How it’s controlled: In 2018, the FDA approved a drug called GamaSTAN to provide post-exposure protection against the measles and hepatitis A. Developed by Grifols, a plasma-derived drug specialist, GamaSTAN is the only immune globulin treatment on the market as a post-exposure prophylactic for hep A and measles.
There are no other therapies targeting measles specifically, but in 2014, researchers from Georgia State University, the Emory Center for Drug Development and the Paul-Ehrlich-Institut in Germany announced the discovery of a novel antiviral measles candidate called ERDRP-0519. Scientists have since announced positive results for the drug in animal model testing.
The bird flu … in cows?
The backstory: A recent spate of avian influenza cases involving livestock have put experts on alert.
Earlier this week, Texas health officials reported that a man contracted H5N1 from cattle — the first case of this specific influenza strain jumping from a cow to a human, and only the second recorded case in U.S. history.
So far, H5N1 has been reported in 12 cow herds across five states, and the CDC has classified the outbreak as “sporadic” in poultry flocks and mammals.
Although H5 strains can be highly infectious, the handful of cases reported in humans have been mild. Still, cows don’t typically carry the virus.
Scientists are also keeping a close eye on whether the H5N1 strain will jump to pigs, who can carry hybrid forms of viruses that spread to humans. An outbreak of H1N1 in 2009, which was triggered by a human catching the virus from pigs, ultimately killed more than 12,000 people in the U.S., according to the CDC.
How it’s controlled: To prepare for emerging avian flu outbreaks, the CDC identifies viruses for vaccine candidates that could be manufactured in response. In a recent analysis of the genomic sequences in virus specimens collected from the H5N1 patient in Texas, the CDC reported that “the virus is very closely related to two existing HPAI A(H5N1) candidate vaccine viruses that are already available to manufacturers, and which could be used to make vaccine if needed.”
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