10 locally acquired malaria cases were reported in the US in 2023—a surprise

Florida reports 71 imported malaria cases annually—4% of all the US cases.

A malaria case in Maryland stumped doctors in 2023—leading to the wrong treatment and underscoring the challenge of physicians being mindful of tropical diseases in our interconnected world.

West Nile virus was detected in UK mosquitoes for the first time in 2023

Fragments of the virus were detected in mosquitoes that were being collected in Britain for the first time in 2023, but the UK government considers the overall risk to people to be low. As of spring 2026, there have never been detected locally-acquired cases of the disease.

81% of Florida's leprosy cases occur in central Florida, raising concerns

Researchers noted in 2023 that about one-fifth of new US leprosy cases were reported in the central part of the Sunshine State. What's more, about a third of the new US cases overall appear to have been acquired locally, raising questions about whether the disease is now naturally occurring in parts of the southeastern US.

Discover the latest information on US measles cases from official outbreak tracking figures.

US West Nile case numbers were up 40% in 2025 across the United States though theories vary to explain this surge.

West Nile was reported in 47 states in 2025, with more than 1,400 people severely affected

Tracking numbers from the CDC indicate that the virus spread widely that year, with more than 2,000 reported human cases and many states seeing more than 25 sickened people. More than 1,400 people had neuroinvasive cases of the disease—meaning the virus had entered the nervous system, which can cause severe, potentially life-threatening illness.

Explore this database to discover Lyme disease incidence in your county.

Measles cases in the US reached a 35-year high in 2026 as vaccination rates dropped.

CDC does not require docs to report hand, foot, and mouth cases which makes tracking difficult

Mid-Atlantic states saw a surge of hand, foot, and mouth disease in 2025 for as-yet unknown reasons. Virginia, Maryland, and New Jersey, reported elevated outbreak numbers in 2025 as compared to other recent years, but since the US Centers for Disease Control and Prevention does not require mandatory reporting of positive HFMD cases—unlike strictly notifiable diseases like measles—it's hard to truly know the extent of the outbreaks and how significant the caseload is as compared to prior years across the region or country.

See the total number of Lyme cases per state in 2023

New York, Pennsylvania, and Massachusetts had the highest total number of Lyme disease cases in 2023. New York had more than 22,000 cases that year. Maine had one of the highest Lyme incidence rates of disease that year—213 per 100,000 people—but only 2,942 cases overall.

See the incidence of Lyme disease across all 50 states in 2023

The US states with the highest rate of Lyme disease—meaning cases per 100,000 people—were Rhode Island, Vermont, and Maine, in 2023. Rhode Island had 260 cases per 100,000 people, based on cases reported to the US Centers for Disease Control and Prevention. (Some users may encounter a paywall.)

Lyme disease is the most common vector-borne illness in the US

In the US, ticks account for 90% of all disease transmission from bites, including mosquitoes. And Lyme disease is the most common vector-borne disease in the US overall, with estimates suggesting there are about 475,000 Lyme cases annually across the nation.

See the geographic spread and incidence of malaria

This graphic shows the estimated global burden of malaria in 2025 as new cases per 1000 people at risk.

Hear what it's like to have malaria from a patient who suffered from the mosquito-borne disease.

More than 20 mosquito-borne and tick-borne diseases are found in the US

Children, older adults, and people with compromised immune systems are at particular risk of poorer health outcomes from these diseases. But dog owners and outdoor enthusiasts are among those at particular risk of contracting these illnesses, which include Lyme disease, Zika, and the condition Alpha-gal Syndrome.

Up to 225 cases of leprosy in the US are diagnosed each year

Most cases in the US are imported, meaning someone was infected in a country where it was more common. Since symptoms can sometimes take decades to appear, tracing the origin of the disease can be hard.

There may be 500,000 additional malaria deaths by 2050 according to peer-reviewed research published in 2026.

Anopheles mosquitoes are developing resistance to insecticides.

See Virginia's spike in HFMD cases in 2025

The state's own tracking showed a significant jump in HFMD cases in July 2025 as compared to the prior few years, and that more people were visiting the emergency room and urgent care centers for the disease, but epidemiologists could not explain why the numbers were so high.

Researchers are breeding genetically modified mosquitoes to be malaria-resistant.

Measles was declared eliminated in the US in 2000, meaning the country had been free of continuous disease transmission for 12 months or more.

Iceland, the last mosquito-free country, detected them in 2025.

West Nile Virus has been detected in American alligators, and outbreaks have led to substantial economic losses on alligator farms.

Environmental conditions, shifting immunity, and viral strain could help explain 2025 spike

The surge in HFMD in the summer and early fall of 2025 in the mid-Atlantic could be the result of a confluence of factors, including a more virulent strain of disease-causing virus, good environmental conditions for the virus to spread—hot, humd—and a potential immunity gap among kids due to milder HFMD outbreaks the previous year.

See MS prevalence by region in the United States

This map underscores that people in the northeastern United States have more cases of the disease as compared to the south, west, and midwest. On an individual level, these numbers may still differ based on genetic makeup and other factors irrespective of where people live.

Zika virus shocked scientists because the mosquito-borne disease causes birth defects

This revelation, confirmed in 2016, marked the first time that a mosquito-borne disease was known to cause birth defects. Fetuses exposed to the Zika virus during pregnancy sometimes suffer from neurological complications and microcephaly, a small-headed condition associated with neurological development issues and impairment.

A look at the 2025 measles outbreak in West Texas and surrounding areas

A measles outbreak in the summer of 2025 ultimately led to more than 900 cases and the deaths of two young children. The highly contagious virus requires vaccination rates near 95% to achieve herd immunity—the Texas outbreak spread through areas of significant mistrust of vaccines, including the area’s Mennonite community.

The mosquito's role in the transmission of malaria was confirmed in 1897.

West Nile virus found in the UK for the first time

The West Nile virus, which mainly spreads between birds and mosquitoes, was detected in the UK for the first time. While no evidence exists for any human infections, climate change may be expanding mosquitoes—and the diseases they carry—farther north.

Children under 5 account for 76% of all malaria deaths in Africa

The main hypothesis for why the disease hits this age group the hardest is that children this young have still-developing immune systems. Pregnant women and people with HIV/AIDS are also at higher risk of severe infection.

Explore inside a mosquito factory where millions of mosquitoes are bred weekly

In Medellin, Colombia, scientists are infecting Aedes aegypti mosquitoes with Wolbachia, a bacterium that wouldn't otherwise infect the species, but does block its ability to transmit dengue, Zika, yellow fever, and chikungunya. In the wild, infected mosquitoes would breed with wild mosquitoes, pass down Wolbachia, and thus reduce disease transmission.

Read a study about racial differences in Lyme disease diagnosis

The research published in September 2025 examined differences in Lyme disease diagnosis among Medicaid and Medicare beneficiaries using data from 2016 to 2021. It notes that though US Lyme disease surveillance data indicates more than 90% of diagnosed Lyme cases are among white people, people of color—particularly those who identify as Black or African American—have higher rates of more severe disease of Lyme, with symptoms including arthritis and neurologic impacts.

Antimalarials must be taken before traveling to a malaria-endemic area

Malaria prevention involves avoiding getting bitten by mosquitoes (with bug spray and clothing choices) and taking malaria preventative drugs before, during, and after spending time in an area with malaria risk. The drug must be in the blood before the traveler is exposed to malaria parasites.

At least 7 eastern college campuses experienced surprisingly large HFMD outbreaks in 2018

The outbreaks at the college level caused a particularly nasty set of symptoms, including the usual blisters in the mouth and on the hands and feet—but also affected the genitals. They surprised health officials who weren't sure why so many young adults were being sickened, including more than 120 kids at Johns Hopkins University. The disease also caused outbreaks at campuses including Princeton, Dartmouth, West Virginia University, Lehigh University, Wesleyan University in Connecticut, and Mars Hill University in North Carolina.

Malaria mosquitoes in a lab were wiped out using CRISPR

Scientists at Imperial College London disabled a gene in female Anopheles gambiae mosquitoes to make them infertile and propagated the infertility mutation at unnaturally high rates using a gene drive. The entire population collapsed within a dozen generations, showing promise for subsequent with mosquitoes in mimicked tropical environments.

Wolbachia is also being used to slash mosquito numbers

The naturally occurring bacterium does not naturally infect Aedes aegypti mosquitoes, but communities in locations including California and Texas have released male mosquitoes infected with Wolbachia and reported a significant drop in subsequent mosquitoes: When infected males mate with uninfected wild females, the eggs don't hatch.

Adults usually have some immunity to HFM Disease—but can still spread it

In 2025, certain eastern states including Virginia and West Virginia reported a sizable uptick in their HFMD cases, particularly in their schools and daycare centers, though the reason for the larger outbreaks remains unknown. When adults or teens get the disease, their symptoms are usually mild or even asymptomatic. Still, they may pass the disease between people, too. (Some users may encounter a paywall.)

How we helped make Aedes aegypti mosquitoes such a problem

Mosquito genome sequencing data suggests that Aedes aegypti mosquitoes first started specializing on human blood around 5,000 years ago—when climates shifted and humans started domesticating plants in Africa and stored large amounts of water that may have attracted the bugs.

Pregnancy makes someone more attractive to the mosquito species that transmits malaria.

More than 1 in 7 people worldwide have had Lyme disease

Research published in 2022 suggests that 14.5% of the world's population has contracted Lyme disease. Researchers arrived at that estimate by analyzing the presence of Lyme disease antibodies (indicating prior infection) across 89 studies conducted between January 1984 and December 2021. The works collectively included blood samples from more than 150,000 people. (Some user may encounter a paywall.)

The Burmese pythons in the Florida Everglades and the spotted lanternfly—native to Asia and now found throughout the US—are among the invasive species accidentally introduced and spread by humans.

Mosquito-borne illnesses have killed two captive orcas at SeaWorld since they became water park attractions.

See this graphic of the complex malaria transmission lifecycle.

From 1970 to 2017, invasive species have caused $1.28T in damage globally

The costliest species were the Asian tiger and yellow fever mosquitoes ($149B), which arrived in the US from Asia and sub-Saharan Africa, respectively. The bulk of their damage came from their transmission of diseases such as Zika, chikungunya, and dengue. (Some readers may experience a paywall.)

'Sloth fever' is an emerging health threat, especially to pregnant women

This disease, caused by the Oropouche virus, is found in animals including sloths, primates, and birds. It primarily spreads through the bite of midges—insects commonly called "no-see-ums." It's endemic to the Amazon region, but US travelers are increasingly contracting it internationally.

See this diverse list of vector-borne diseases

Human illnesses caused by parasites, viruses, and bacteria, and transmitted by a living organism—often small, bloodsucking ones like mosquitoes, ticks, and sandflies—are known as vector-borne diseases. That carrier is called a vector. These diseases disproportionately affect the poorest populations in tropical and subtropical areas.

Wolbachia: the bacteria that could eliminate dengue fever

Dengue fever, transmitted by mosquitoes, kills more people annually than all types of natural disasters combined. However, mosquitoes that host Wolbachia bacterium have their ability to transmit the virus naturally suppressed, offering a route to eliminating nearly 25,000 deaths annually.

Powassan virus, a rare tick-borne disease named after the Canadian town where it was discovered in 1958, is on the rise in the northeastern United States, and it kills roughly 10% to 15% of patients with symptomatic disease.

Molecular evidence suggests the deadliest malaria parasite may be 100,000 years old.