Many people in high income countries talk about measles, polio or cholera as problems of the past, wiped out by vaccines and clean water. Yet in 2024, the United States logged 128 confirmed measles cases, and global health agencies counted hundreds of thousands of cholera infections. I want to look at five diseases that still lurk behind those assumptions, drawing on primary surveillance data to show where they persist, why they keep resurfacing and what we still do not see in the numbers.
Measles Resurges in the U.S. Amid Vaccine Hesitancy
Measles was declared eliminated as a continuous threat in the United States more than two decades ago, but current surveillance shows that it has not disappeared. According to the primary national measles tally maintained by the Centers for Disease Control and Prevention, there were 128 confirmed measles cases in 2024, including 89 outbreak associated cases spread across 20 jurisdictions, a pattern that undercuts the idea that it is only a distant memory. The Primary measles data page notes that these figures come from ongoing case investigations and that they are updated as new reports arrive, which means even this total may not capture every mild or unreported infection.
CDC leaders have tied these flare ups to gaps in vaccination coverage, warning that clusters of unvaccinated children and adults give the virus room to spread once it is imported. Those warnings are backed by weekly National Notifiable Diseases Surveillance System tables, which aggregate measles along with other infections from state health departments and feed into the same Supports the national data stream. Because NNDSS data are provisional and depend on local reporting, the agency cautions that some cases may be reclassified or added later, and that mild infections might never be tested at all, which leaves some uncertainty around how much silent measles transmission is occurring between recognized outbreaks.
Dengue’s Expanding Threat in the Americas and U.S.
While measles rides on immunity gaps, dengue is taking advantage of ecological and travel patterns across the Americas and the United States. An Official CDC Health Alert Network advisory described record dengue activity in the Americas and reported more than 8 million suspected cases in the region in 2024, along with over 2,000 travel associated infections identified in U.S. residents returning from affected countries. The same advisory highlighted that Puerto Rico had issued an emergency declaration in response to its own surge, a reminder that U.S. territories are part of this regional wave.
Dengue is not only arriving on airplanes. The CDC maintains a dedicated CDC outbreak hub for 2024 that tracks where the virus has been transmitted locally in U.S. states and territories and links directly to the Health Alert Network notices for each development. Those updates describe a January to December 2024 timeline of activity and confirm that dengue is no longer purely an imported infection, even if the exact number of locally acquired cases outside well documented areas such as Florida remains uncertain. Clinical guidance in the same materials stresses that clinicians should consider dengue in patients with compatible symptoms and recent travel or residence in outbreak zones, since missing those cases can distort surveillance and delay mosquito control.
Polio’s Hidden Circulation Detected in Wastewater
Polio is often taught as a triumph of vaccination campaigns, yet recent detections show that the virus can still surface in places that consider it long gone. A Peer reviewed CDC investigation into a paralytic polio case in New York documented how vaccine derived poliovirus type 2 was found in wastewater samples and genetically linked to that single patient. The report described environmental sampling methods that tested sewage from multiple sites and used sequencing to connect the wastewater virus to a circulating strain, a level of laboratory detail that leaves little doubt that the virus was moving through at least some part of the community.
What remained far less clear, even with that strong laboratory evidence, was how many people had actually been infected and whether transmission continued after the initial response. The same outbreak investigation noted that most poliovirus infections are asymptomatic and that detection in wastewater can precede or outnumber recognized clinical cases, which is why environmental surveillance has become a central tool for high income settings that might otherwise miss the pathogen. Globally, the Regulatory announcement from WHO about prequalification of an additional novel oral polio vaccine type 2, or nOPV2, framed this detection in New York as part of a wider need to respond to ongoing poliovirus type 2 outbreaks, reinforcing that the disease remains a current, deadly capable threat rather than a closed chapter.
Rabies Remains Nearly Always Fatal from Wildlife Bites
Rabies rarely dominates headlines in the United States, but that is partly because prevention works, not because the virus has vanished. A CDC explainer on protecting public health from rabies, which is grounded in U.S. surveillance operations, describes how national testing identifies a steady stream of infected wildlife and records between 1 and 3 human deaths each year. The same page emphasizes that rabies is effectively 100%-fatal once symptoms appear, and that an estimated 4,000 people required post exposure prophylaxis, or PEP, in 2023 after possible exposures, illustrating how much effort goes into preventing those few deaths.
Those PEP numbers represent a hidden burden of care that sits behind the reassuringly low death counts. The rabies explainer explicitly Supports the idea that persistent circulation in bats and other wildlife continues to generate thousands of potential exposures that must be evaluated and often treated with a multi dose vaccine series and immune globulin. Because many encounters with wild animals occur in rural or remote areas, the CDC also notes that some exposures may never be reported, which suggests that the recorded 4,000 PEP courses in 2023 might underestimate the true number of people who needed or received urgent preventive treatment.
Ebola and Cholera Flare in Fragile Regions
Far from U.S. suburbs, two older scourges, Ebola and cholera, keep reappearing in places where health systems are fragile and populations are on the move. A qualitative assessment by CDC of the Sudan ebolavirus event in Uganda described how responders used outbreak status indicators to track the epidemic and deployed ring vaccination and contact tracing to contain it. That work was echoed in a WHO AFRO announcement that documented Uganda’s outbreak timeline and reported 42 cases and 5 deaths, along with the last patient discharge and the 42-day countdown used to declare the end of transmission, which the regional office described as Good for illustrating how Ebola control still depends on rapid, resource intensive operations.
Cholera has been even more widespread. A Formal WHO Weekly Epidemiological Record summarized the 2024 cholera burden and reported that multi country outbreaks accounted for 347,000 cases and 5,000 deaths that year, with trends compared against previous years to show that transmission remained higher than global control targets. A WHO Disease Outbreak News update on acute watery diarrhea, or AWD, and cholera Provides more detailed case fatality ratios of 1 to 3 percent in some affected regions, while a separate WHO situation report was described as Useful for explaining how limited oral cholera vaccine supply, conflict and climate related displacement have kept outbreaks smoldering. Together, these official tallies show that cholera remains a mass killer where clean water, sanitation and vaccination coverage are weakest, and that underreporting in conflict zones likely hides a portion of the true toll.
Why These Diseases Still Matter and What to Watch
Across measles, dengue, polio, rabies, Ebola and cholera, a common thread is that confirmed case counts represent only the visible part of a larger problem. The CDC describes its National Notifiable Diseases Surveillance System as an Authoritative framework that is Useful for tracking infectious diseases using weekly and annual tables, while a Technical CDC notice on NNDSS publication criteria Helps explain the difference between provisional and finalized data and Points to the underlying Evidence. Those methods lend credibility to the measles, dengue and rabies figures cited earlier, but they also highlight that diseases with mild or asymptomatic infections, such as dengue and polio, are likely undercounted even in well resourced settings, while Ebola and cholera numbers from conflict zones are constrained by access and security.
These gaps matter because they shape how governments and communities perceive risk and allocate resources. Hospitalizations from measles, the strain of thousands of rabies PEP courses, the displacement linked to cholera and the intensive Ebola ring vaccination campaigns described in the Supports the CDC assessment of Uganda’s outbreak all point to ongoing health and economic impacts that go beyond headline case counts. At the same time, the High authority of the cholera Evidence base and the Provides lab detail from New York’s polio investigation show how much effort is going into refining surveillance. What remains missing in many places are long term, comparable data on how climate shifts, vaccine hesitancy and population movements will interact with these pathogens over the coming decades, an uncertainty that argues for sustained attention even when the diseases seem, at first glance, to belong to another era.
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*This article was researched with the help of AI, with human editors creating the final content.
