Outbreak Watch: August 7, 2026
- Heather McSharry, PhD
- 10 hours ago
- 16 min read
Summary
Three weeks can change an outbreak considerably. In this Outbreak Watch, Ebola cases in the Democratic Republic of the Congo are closing in on 4,000, New World screwworm continues circulating in Texas, and the massive U.S. cyclosporiasis outbreak has expanded into additional states. We’ll separate the evidence from speculation about whether the Ebola virus is mutating, look at what new screwworm detections may tell us about undetected circulation in wildlife, and examine why a false-positive lettuce test doesn’t erase the epidemiologic evidence behind the Cyclospora investigation.
Plus, we’re introducing a new way of looking beyond the active outbreaks: Global Signals and Surveillance Milestones, including Chile’s sweeping response to an alarming rise in hantavirus mortality, H5 avian influenza, Oropouche virus, the highest U.S. measles case count in roughly three decades, and rising Hansen’s disease cases in Florida.
Listen here or scroll down to read full episode.
Full Episode
Welcome back to Outbreak Watch.
Before we dive in, I'm making a small change to how I organize this series. Not every important infectious disease story is an "outbreak". Some are rapidly evolving outbreaks, some are broader global signals that could influence future disease risk, and some are important surveillance milestones that help us recognize longer-term trends. So from now on, we'll cover three sections: Active Outbreaks, Global Signals, and Surveillance Milestones. Let's start with this week's Active Outbreaks, which takes us first to Central Africa.
Active Outbreaks
Ebola in the Democratic Republic of the Congo
When we last talked about this outbreak just three weeks ago, the DRC had reported a little over 2,100 confirmed Ebola cases. The latest figures from the DRC's Ministry of Health, in their SitRep#82 published August 5, indicate 3973 confirmed cases and 1801 deaths. That's almost a thousand deaths since our last update with a 45.3% case fatality rate. Now that number can be affected by reporting accuracy and other confounders but either way it's a horrific regional outbreak afffecting five provinces in northeastern DRC, reaching 51 of their combined 140 health zones. This is now the second-largest Ebola outbreak ever recorded, behind only the devastating West African epidemic of 2014 through 2016.
But the case numbers only tell part of the story. Health officials are becoming increasingly concerned that the outbreak is spreading faster than response efforts can keep up. Between sixty and seventy percent of new cases are now being identified outside of known contact networks, meaning many infected people were never being monitored in the first place. At one Ebola treatment center operated by Doctors Without Borders, roughly ninety percent of admitted patients were not on any official contact-tracing list before they became ill.
Those numbers point to a virus that is staying one step ahead of investigators... one of the biggest problems is that public health teams are struggling to find transmission chains before they disappear into the community.
Now, you've probably also seen the headlines suggesting that the virus may be mutating. Let's talk about that. The Africa CDC announced this week that scientists plan to study virus samples to determine whether genetic changes could be contributing to the unusual severity of this outbreak. That's exactly what scientists should do. Whenever an outbreak behaves differently than expected, one of the questions researchers ask is whether the virus itself has changed.
But asking that question is not the same thing as finding evidence that it has.
At this point, I have not seen evidence that mutations are responsible for the rapid spread or the high mortality being reported and we don't need a mutated virus to explain what we're seeing. There is overwhelming evidence that many patients are never reaching treatment early enough. In fact, more than two-thirds of reported deaths are occurring in the community rather than inside Ebola treatment centers... more on that in a sec. But also, contact tracing remains incomplete and conflict continues to limit access to affected areas. Millions of people have been displaced by violence, and today the United Nations confirmed that Ebola has now reached several internally displaced persons camps, where crowded conditions and limited access to healthcare make outbreaks much harder to control.
The situation became even more complicated today when authorities quarantined nearly two hundred passengers aboard a river boat traveling toward Kinshasa after a former passenger—who had left the vessel weeks earlier—died with symptoms consistent with Ebola. Laboratory testing is still underway, and importantly, there are no confirmed Ebola cases in Kinshasa at this time. But this investigation illustrates exactly how aggressively public health officials respond whenever there is even a possibility that the virus could be carried into one of Africa's largest cities.
Another challenge emerged today as healthcare workers at the center of the outbreak protested unpaid wages, forcing disruptions at several treatment facilities. It's a reminder that outbreaks depend on healthcare workers being able to show up every day with the resources and support they need to do an extraordinarily difficult job.
But let's go back to the idea that a significant number of ebola deaths are occuring outside of care centers. I think this ties directly to the high case fatality rate. Supportive care is crucial for ebola. Careful management of fluids and electrolytes, treatment of shock and secondary infections, and intensive supportive care dramatically improve survival. And if people are dying in their communities, not in care centers, then they are not getting medical care, and their risk of death is significantly higher. We generally talk about how without supportive care, CFR for the most virulent ebola species is around 90%, so this detail is significant.
If patients remain in their communities until they're critically ill—or never reach treatment at all—then mortality will rise, even if the virus itself hasn't changed. That doesn't mean scientists shouldn't investigate the virus. They absolutely should. But it's important not to mistake a hypothesis under investigation for evidence that the hypothesis is correct. If evidence comes to light that mutations are driving CFR up or otherwise impacting transmission or disease, I will absolutely let you know.
Now, there was also one encouraging piece of news this week. Researchers have begun the first Phase 1 clinical trial of an mRNA vaccine designed specifically against the Bundibugyo species of Ebola—the virus responsible for this outbreak. The study is taking place in Canada and represents the first vaccine candidate developed specifically for this Ebola species.
It's also another example of how the mRNA platform continues to expand beyond COVID-19. Just this week, the FDA approved the first mRNA-based seasonal influenza vaccine in the United States. While this new Ebola vaccine won't influence the current outbreak—it still has to go through clinical testing—it represents exactly the kind of scientific progress that could make future outbreaks far easier to control.
For this outbreak....over the coming weeks I'll continue watching for: whether contact tracing begins catching up with transmission, whether more cases appear outside the current outbreak region, what testing reveals about the quarantined riverboat passengers, and whether scientists identify any meaningful biological changes in the virus itself.
Right now, though, the evidence points much more strongly toward a public health response struggling under extraordinary conditions than toward a virus that has suddenly become more dangerous.
For more info on this species of Ebola and it's transmission and pathogenesis, check out my episode, Containing Ebola.
New World Screwworm in the United States
Now let's turn to New World screwworm here in the United States.
Since our last update, additional detections have continued to be reported in Texas. The Latest reports indicate 45 cases in 15 TX counties and 1 NM county. The most recent case was detected in a sheep that prompted officials to reclassify part of the quarantine area as an active infested zone and issue a modified movement order for livestock. The total number of affected premises has grown to 35, and additional counties remain under movement restrictions as surveillance expands.
But the new sheep case caught my attention for a different reason. The previous confirmed detection in that area had been more than a month earlier. If a county appears quiet for weeks and then suddenly produces another infected animal, that doesn't necessarily mean the infestation just arrived. It raises the possibility that screwworm flies have continued reproducing in the surrounding environment without being detected until another susceptible livestock animal happened to develop a noticeable wound. One of the fundamental challenges with this parasite is that we often only detect it in animals after they've become infested. And livestock are only part of the picture.
From the very beginning of this outbreak, I've said my greatest concern is wildlife. Livestock can be inspected. Ranchers can treat wounds. Veterinarians can examine suspicious cases. But white-tailed deer, feral hogs, coyotes, javelina, and other wildlife don't receive routine inspections. If screwworm becomes established in free-ranging wildlife, those animals could quietly sustain local fly populations for weeks before anyone realizes they're there. And we are not doing the kind of surveillance needed to be able to say that's not happening.
Interestingly, a paper published this week in Nature Ecology & Evolution makes much the same point. The authors argue that wildlife surveillance has become a critical gap in our understanding of New World screwworm and that relying primarily on livestock detections likely underestimates where the parasite is actually circulating. To me, that's one of the most important developments of the week because it reinforces something epidemiologists have been worrying about all along.
Another important development is that Texas has now launched its New World Screwworm Certified Inspector Program. Instead of relying exclusively on veterinarians and state officials, trained inspectors can now perform animal examinations and issue movement certificates under the state's response program. Expanding the number of qualified people who can inspect animals should make surveillance faster and reduce delays when animals need to move out of regulated areas.
There was also less encouraging news regarding long-term preparedness. The USDA's new sterile fly production facility in Texas remains under construction, but the expected timeline for reaching full production has slipped again. Every month matters because sterile insect release remains the cornerstone of screwworm eradication. The more sterile males available, the more effectively officials can overwhelm wild populations and drive them toward extinction.
More than 400 million sterile flies have already been released across affected areas, and despite continued detections, officials believe those releases have substantially slowed what could otherwise have become a much larger outbreak.
So what am I watching now? I'm watching for detections well outside the current infested zones. And I'm watching for more evidence that wildlife is serving as an undetected reservoir.
For details on screwworm and how we eradicated it from the US...until we...didn't, check out my episode On the Fly.
The U.S. Cyclosporiasis Outbreak
Now, let's check in on the largest cyclosporiasis outbreak the United States has seen in years. Since our last update, the outbreak has continued to expand geographically.
Michigan remains the epicenter. State health officials have now confirmed 12,485 illnesses, 279 hospitalizations, and, tragically, two deaths. According to the Michigan Department of Health and Human Services, both individuals had significant underlying medical conditions, and dehydration associated with cyclosporiasis may have contributed to their deaths.
Those deaths are an important reminder that severe dehydration can become dangerous, particularly in older adults and people with underlying health conditions.
Also of note this week is that Massachusetts reported additional illnesses linked to recalled lettuce that had already been distributed to local restaurants before it could be removed from circulation, while Ohio reported a second consecutive week of significant increases in cyclosporiasis cases. So keep in mind that contaminated and recalled food may still be present in restaurant inventories or already in transit through the distribution system, which means new illnesses can continue appearing after a recall.
One final thing, because I know many of you have seen the online discussions surrounding the FDA's reversal of that laboratory result. I've seen a lot of speculation about why the agency withdrew the positive finding. Right now, I haven't seen evidence that supports those claims. And if I had, I'd tell you. The FDA maintains that while the laboratory result was determined to be a false positive, the epidemiologic evidence supporting the investigation did not change. And honestly, that's the part I think is most important. In outbreak investigations, a laboratory test is one piece of evidence. Epidemiology is another. If thousands of unrelated people become ill after eating the same food, distributed through the same supply chain, that evidence doesn't suddenly disappear because one laboratory sample turns out not to be what investigators initially believed.
In other words, the false-positive laboratory result doesn't change the epidemiologic picture. The investigation is still pointing investigators toward the same place, and that's why public health officials continue to focus their attention on Taylor Farms.
And most importantly for consumers, the practical advice hasn't really changed. If you've purchased recalled shredded iceberg lettuce or products containing it, don't eat them. And if you develop prolonged watery diarrhea that seems to improve and then returns again—especially during the summer months—ask your healthcare provider whether you should be tested specifically for Cyclospora. Standard stool testing doesn't always include it automatically.
I'll continue watching this outbreak for: whether additional states continue reporting substantial increases, and whether investigators can more definitively narrow the contamination to a specific farm or production source.
Global Signals
Those are the active outbreaks I'm following this week. But I'm also interested in the signals that come before outbreaks or the decisions that shape what happens after them. So here are a few global infectious disease signals that caught my attention this week.
The first signal this week is actually a really encouraging example of proactive public health. For the first time in its history, Chile has declared a nationwide Health Alert for hantavirus. The alert remains in effect through July 2027 and covers thirteen administrative regions stretching from Atacama to Magallanes, including Chilean Antarctica—the geographic range of the long-tailed mouse that carries Andes hantavirus. This wasn't done in response to a hypothetical threat.
As of the week before this declaration, Chile had recorded 46 confirmed hantavirus cases and 18 deaths in 2026, resulting in a 39% case fatality rate—roughly double what the country has typically experienced in recent years. That's an alarming increase, and it's exactly the kind of signal that warrants a stronger public health response. At this point, the increase is an epidemiologic observation, not an explanation. It could reflect delayed presentation to care, reduced access to intensive care in rural regions, or differences in which patients are being diagnosed, and what I mean by that is that it could be that only really sick patients are diagnosed while mild cases go unreported. When that happens CFR can look unusually high... or it could be a combination of all of those factors. CFR alone does not demonstrate that Andes virus has become more virulent.
But what I find especially interesting is that Chile didn't respond only to hantavirus.
The declaration also strengthens preparedness for mosquito-borne diseases like dengue and Zika, expands planning for avian influenza, accelerates procurement of critical supplies, allows health authorities to hire specialized personnel more quickly, strengthens epidemiologic surveillance, and improves coordination across affected regions.
So, instead of creating separate emergency responses every time a different infectious disease becomes a problem, Chile is using one serious outbreak to strengthen the infrastructure needed to detect and respond to several biological threats at once. That's a really smart systems approach.
2. Oropouche virus
The second signal I'm continuing to watch is Oropouche virus. Most people have never heard of it, but over the past two years we've watched this virus expand well beyond the parts of the Amazon Basin where it was historically considered endemic. So, I'm not watching individual case numbers so much as geography. When an insect-borne virus begins establishing itself in new ecological regions, that can be a more important long-term signal than whether one country reports a few dozen additional cases in a given week.
3. H5 avian influenza
I'm also still watching H5 avian influenza. Not because of individual spillover events. We've now seen enough of those to know they happen. The question I'm interested in iswhether the virus shows evidence of sustained mammal-to-mammal transmission or acquires adaptations that fundamentally change how it behaves. That's still the threshold that matters most. And every new spillover provides another opportunity for the virus to adapt, but opportunity isn't the same thing as outcome. So for now, that's the signal I'm watching—evidence that the biology itself has changed.
4. Mpox Clade I
I'm also keeping an eye on mpox Clade I. The outbreak remains a concern internationally, and I'm watching for sustained transmission becoming established outside the regions where it has historically circulated. That isn't happening on a large scale today, but it's one of those developments that deserves quiet attention before it becomes tomorrow's headline.
Surveillance Milestones
Finally, there are also two important infectious disease milestones I'd like to mention. These aren't rapidly evolving outbreaks in the same sense as Ebola or Cyclospora, so I don't plan to cover them every week. But both crossed important thresholds recently, and I think they're worth having on your radar.
Measles
The first is measles. The United States now has recorded 2,371 confirmed measles cases across 45 jurisdictions this year, surpassing the record-breaking 2,289 total cases recorded for all of 2025 and marking a 35-year high. And to top off this gorious antivax win, roughly 93% of the individuals infected were unvaccinated. That's an unfortunate milestone, but not an unexpected one. Once measles becomes established in under-vaccinated communities, outbreaks can continue for months because the virus is so extraordinarily contagious. So I'm expecting this to continue. And as it does, older people will be more at risk so get your measles antibody titer checked and get boosted if needed.
Leprosy
The second is Hansen's disease, more commonly known as leprosy. Florida continues to report increasing numbers, with locally acquired infections becoming more common than they were a decade ago. Health officials believe many of these infections are associated with exposure to nine-banded armadillos, one of the few known non-human reservoirs of Mycobacterium leprae. While the disease remains rare, isn't highly contagious, and is curable with modern antibiotics, it's another reminder that zoonotic diseases don't always arrive dramatically. Sometimes they become established gradually, one case at a time, until we realize the ecology has changed. That's one I'll continue watching.
The common thread running through all of tonight's stories is that infectious diseases rarely surprise us overnight. They leave clues first—in surveillance data, in changing geography, in ecological shifts, in preparedness decisions, and sometimes in a single unexpected case. The challenge for public health isn't simply responding to outbreaks. It's recognizing those signals early enough to change what happens next."
That's all for this week's Outbreak Watch.
I'll continue keeping an eye on these stories—and if the evidence changes, I'll bring you the update.
Until next week, stay healthy, stay informed, and spread knowledge not diseases.
ANNOTATED CITATIONS AND RESOURCES
Democratic Republic of the Congo Ministry of Health. 2026. Ebola Situation Report No. 82.
🌐 Free online resource https://insp.cd/sitrep-n082-mve-b_04-08-2026/
➡ Official outbreak situation report providing the most current case counts, deaths, affected health zones, and operational updates from the DRC Ministry of Health.
USDA Animal and Plant Health Inspection Service (APHIS). 2026. Current Status of Confirmed U.S. Cases of New World Screwworm.
🌐 Free online resource https://www.aphis.usda.gov/animals/animal-health/livestock-and-poultry-disease/current-status/us-confirmed-cases-new-world
➡ Official USDA dashboard tracking confirmed New World screwworm detections in the United States and summarizing the federal response.
Andrews, J.R., Weese, J.S. & Bogoch, I.I. 2026. Renewed investment is needed as the New World screwworm returns to the USA. Nat Ecol Evol
🔒Subscription required at publisher's site but author provided link on X (below)
The authors emphasize the importance of renewed investment in sterile insect production, veterinary and wildlife surveillance, diagnostic capacity, and cross-border coordination. Particularly relevant to this episode is their warning that surveillance focused primarily on livestock may underestimate transmission occurring in wildlife.
Michigan Department of Health and Human Services. 2026. Infectious Disease Outbreaks.
🌐 Free online resource https://www.michigan.gov/mdhhs/keep-mi-healthy/infectious-diseases/infectious-disease-outbreaks
➡ Official Michigan outbreak dashboard providing current cyclosporiasis case counts, hospitalizations, and ongoing investigation updates.
Centers for Disease Control and Prevention (CDC). About FoodNet.
🌐 Free online resource https://www.cdc.gov/foodnet/about/index.html
➡ Describes CDC's Foodborne Diseases Active Surveillance Network (FoodNet), including the 2025 transition that made surveillance for Campylobacter, Cyclospora, Listeria, Shigella, Vibrio, and Yersinia optional while continuing routine surveillance for Salmonella and Shiga toxin-producing E. coli (STEC). Provides important context for the discussion of reduced foodborne disease surveillance and its potential impact on recognizing outbreaks.
Lay, K. 2026. Ebola virus behind massive outbreak in DRC could be mutating, officials say. The Guardian, 6 August 2026.
🌐 Free online resource
https://www.theguardian.com/world/2026/aug/06/ebola-virus-drc-mutating
➡ Describes Africa CDC plans to investigate whether viral changes could be contributing to its unusual severity. Also documents extensive community deaths, inadequate contact tracing, plans for active case finding, and investigation of a suspected case associated with a riverboat traveling toward Kinshasa. Importantly, the article reports mutation as a hypothesis being investigated, not an established explanation for the outbreak’s severity.
United Nations. 2026. Ebola virus reaches displacement camps in DR Congo. UN News, 6 August 2026.
🌐 Free online resource
https://news.un.org/en/story/2026/08/1168092
➡ Reports Ebola infections among internally displaced people in Ituri Province and cases in multiple displacement camps. Describes the additional challenges created by conflict, displacement, limited water and sanitation infrastructure, population movement, and disrupted access to healthcare.
Associated Press. 2026. Congo monitors 200 boat passengers near Kinshasa after a traveler dies with Ebola-like symptoms. The Seattle Times, 6 August 2026.
🌐 Free online resource
➡ Reports the precautionary monitoring and quarantine of nearly 200 riverboat passengers after a former passenger died with Ebola-like symptoms. Also documents continuing problems with untracked transmission and strikes by health workers over unpaid wages. No Ebola cases had been confirmed in Kinshasa at the time of publication.
CNN. 2026. Congo Ebola response challenged by health worker payroll crisis. CNN, 6 August 2026.
🌐 Free online resource
https://www.cnn.com/2026/08/06/africa/congo-ebola-payroll-crisis-health-workers-intl
➡ Describes disruptions to the Ebola response associated with unpaid healthcare workers and illustrates how workforce, financing, and health-system constraints can interfere with treatment and outbreak control during a rapidly expanding epidemic.
Reuters. 2026. Moderna begins first human trial of Bundibugyo Ebola vaccine. Reuters, 4 August 2026.
🌐 Free online resource
➡ Reports the beginning of the first human trial of Moderna’s experimental mRNA-1469 vaccine against Bundibugyo ebolavirus. The Phase 1 study in Canada will evaluate safety and immune responses in approximately 80 healthy adults and represents an important step toward a vaccine specifically targeting an Ebola species for which no approved vaccine currently exists.
NPR. 2026. New kind of flu shot is on the way as the FDA approves Moderna’s mRNA-based vaccine. NPR, 6 August 2026.
🌐 Free online resource
https://www.npr.org/2026/08/06/nx-s1-5923342/moderna-mrna-flu-vaccine
➡ Reports FDA approval of Moderna’s mRNA-based seasonal influenza vaccine for adults aged 50 and older. Provides contemporary context for the expanding use of the mRNA vaccine platform beyond COVID-19 and alongside development of an mRNA vaccine against Bundibugyo ebolavirus.
The Boston Globe. 2026. Mass. Cyclospora cases spike amid national outbreak. The Boston Globe, 5 August 2026.
🌐 Free online resource
https://www.bostonglobe.com/2026/08/05/metro/taco-bell-cyclospora-massachusetts-lettuce/
➡ Reports increasing cyclosporiasis cases in Massachusetts associated with recalled lettuce distributed to local restaurants, including distribution occurring after the recall. Illustrates how contaminated products can remain within food distribution networks even after recall actions begin.
Ohio Capital Journal. 2026. Ohio sees second week of ‘significant’ increases in cyclosporiasis cases. Ohio Capital Journal, 6 August 2026.
🌐 Free online resource
➡ Reports a second consecutive week of substantial increases in Ohio cyclosporiasis cases during the expanding multistate outbreak, providing state-level evidence of continued geographic and epidemiologic expansion.
Ministerio de Salud de Chile. 2026. Ministerio de Salud declara Alerta Sanitaria por hantavirus desde Atacama a Magallanes. Ministry of Health, Chile, 28 July 2026.
🌐 Free online resource
➡ Official Chilean Ministry of Health announcement establishing the country’s first formal health alert for hantavirus, covering regions from Atacama through Magallanes and remaining in effect through July 2027. The alert followed an unusually high observed hantavirus case-fatality rate in 2026 and expands authorities’ ability to strengthen surveillance, staffing, procurement, and preparedness. The measure also supports response capacity for other biological threats, including arboviruses and avian influenza.
Centers for Disease Control and Prevention. 2026. Measles Cases and Outbreaks. CDC.
🌐 Free online resource
https://www.cdc.gov/measles/data-research/index.html
➡ CDC’s current national surveillance page for U.S. measles cases and outbreaks. Provides regularly updated case counts, outbreak information, geographic distribution, and historical comparisons used to place the current resurgence in the context of U.S. measles activity over previous decades.
Florida Today. 2026. Leprosy cases rise in Florida. Florida Today, 6 August 2026.
🌐 Free online resource
➡ Reports unusually high numbers of Hansen’s disease, or leprosy, cases in Florida and discusses locally acquired disease and the potential role of nine-banded armadillos as a reservoir for Mycobacterium leprae. Provides context for the longer-term epidemiologic shift toward sustained local acquisition of this rare infection in Florida.