Bird flu. Mpox, formerly monkeypox. Eastern equine encephalitis. West Nile. Listeria. Dengue. Oropouche. And, of course, Covid.
Have the past few months felt like an unending parade of infectious disease?
A plethora of pathogens dominated headlines all summer, and some of that attention may have been warranted: Oropouche, a tropical infection, and dengue devastated South America; mpox is ravaging parts of Africa; and bird flu holds the potential to flare into a dangerous pandemic.
But in the United States, the threat to public health was much less alarming than it may have seemed.
Mosquitoes sickened some Americans with infections like dengue, malaria, West Nile virus and Eastern equine encephalitis. But with the exception of dengue, the viruses were less of a problem, or at least no worse, this year than last year.
The major public health troublemakers were familiar foes: Covid, measles and whooping cough, along with a litany of noninfectious threats, including drug overdoses, heart disease and cancer, said Dr. Mandy Cohen, director of the Centers for Disease Control and Prevention.
What has changed is how attuned to new pathogens many Americans are after the coronavirus pandemic, she added.
“The fact we just went through a historic pandemic did increase awareness of both public health and disease outbreaks,” Dr. Cohen said. The C.D.C. now tracks diseases more closely and communicates more often than in the past, she noted.
Local public health departments, too, are now quicker to alert residents to new threats and to take precautions — for example, moving sporting events to the daytime to avoid mosquitoes. The proposed measures, and the inevitable pushback, draw attention.
In St. Louis, the politicization of Covid has had a marked effect on how residents react to infectious diseases, said Dr. Matifadza Hlatshwayo Davis, the city’s health director.
Missouri recently reported an individual infected with H5N1 bird flu and may have identified the first instance of human transmission of that virus in the United States.
“But locally, if I’m being honest about what’s actually impacting children and people at a local level,” Dr. Davis said, “what me and my communicable disease bureau are talking about and tracking are things like whooping cough and this Covid surge.”
“The decrease in vaccination during the pandemic has not bounced back,” she added.
Still, her team publicized detailed information about bird flu, aiming to reassure the residents of their low risk. “I have been doing that throughout the summer, because it can feel like, ‘Oh, the sky is falling again,” she said.
Americans are likely to keep seeing increasing reports of disease outbreaks: As the planet warms, mosquitoes and other vectors, and the diseases they carry, are expected to move to higher latitudes.
“We know that in the Northeast, it’s projected to get warmer and wetter, and the rainfall and temperature will all have impacts on mosquito populations,” said Philip Armstrong, a medical entomologist who runs Connecticut’s mosquito surveillance program.
But that narrative offers an incomplete picture: It neglects the intensity and scale of the problem poorer nations are likely to face compared with the United States, said Colin Carlson, an epidemiologist at Yale University who studies the intersection of climate change and infectious diseases.
“Sporadic cases of dengue in Miami or France are interesting, but that’s not going to be the big climate change impact,” Dr. Carlson said.
“Even within the next 25 years, I would say most of the burden of these diseases is going to continue to be in low- and middle-income countries.”
Dengue transmission may have already increased by 18 percent in countries where it is endemic. Most of the toll in the United States is likely to come from the “force of infection from travelers” returning from those nations, Dr. Carlson added.
Parts of the country, such as Southern California and Texas, have been hospitable for mosquitoes for quite some time. But most Americans are shielded from these diseases because of better health care, sanitation and other lifestyle factors.
Public health experts like to cite the example of Laredo, Texas, across the Rio Grande from Nuevo Laredo in Mexico. Nuevo Laredo routinely battles dengue, even though the Texas town has just as many mosquitoes, if not more.
“The mosquitoes don’t really respect the border,” said Dr. Amesh Adalja, an infectious disease physician and senior scholar at the Johns Hopkins Center for Health Security.
But people in Mexican towns are poorer, he said. They do not have air-conditioning, so their windows remain open in the summer, without screens to keep out mosquitoes, while Texans remain protected in their cooled homes.
The threats that garner attention in the United States can sometimes seem arbitrary.
Eastern equine encephalitis, which made waves in August, has a mortality rate of about 30 percent among hospitalized patients and can cause long-term neurological damage.
“It’s a particularly nasty virus, and that’s why I think it generates a lot of concern,” Dr. Armstrong said.
Still, the disease is rare: So far this year, there have been 11 cases. The largest American epidemic, in 2019, totaled 38 cases.
Many diseases naturally fluctuate year to year. There have been no cases of St. Louis encephalitis this year, but 20 people were diagnosed with it last year; 16 were hospitalized and two died.
Powassan virus, which is spread by ticks, has caused severe illness in 38 people this year and killed one; last year, it sickened 49 people and killed eight.
There are no effective treatments for most of these diseases, “so really, the emphasis is on prevention and on mosquito and tick control,” Dr. Armstrong said.
The mosquito that transmits Eastern equine encephalitis is found in forested swampy habitats. Wetland regeneration has expanded its breeding grounds, and extending suburban development into these areas puts people at greater risk.
Zika, dengue, chikungunya and yellow fever viruses all share the same mosquito vector, Aedes aegypti. That mosquito thrives in trash.
“Think about how much junk is in people’s backyards, on the side of the street,” Dr. Adalja said. Cleaning up those areas will make it harder for the mosquitoes to spread, he said.
People tend to associate infectious diseases with the winter respiratory season, when people with the flu, respiratory syncytial virus or, in the past few years, Covid, inundate emergency rooms.
But the summer can also bring infections like enteroviral meningitis and Legionella, said Dr. Robin Patel, an infectious diseases physician at the Mayo Clinic and past president of the American Society for Microbiology.
Doctors may not be familiar with some of these illnesses, and labs do not always have tests for newer pathogens. For these reasons, better awareness of infectious diseases is overall a good thing, Dr. Patel said.
“The more people know about what they might be at risk for,” she said, “the better they can prevent some of these infections — if that’s possible.”
