Horses account for about 96% of the known mammalian cases of West Nile beyond humans

Horses can—rarely—get West Nile, too

The animals can contract the virus via infected mosquito bites, but for horses there are four vaccines available. Though West Nile's often asymptomatic or mild in horses, the disease can sometimes be deadly, killing via severe neurological inflammation. There are no reported instances of people becoming sickened by infected horses or vice-versa.

Horses have four licensed West Nile vaccines—but humans have none

A major hurdle for West Nile vaccine development is the lack of a market for it since so many people are symptomatic for the infections. Still, a growing number of infections, including a 40% spike in 2025, may change that calculation.

How a scientist discovered West Nile is spread by birds

Listen to Tracey McNamara, former chief pathologist at the Bronx Zoo, detailing her surprising late 1990s discovery that established West Nile virus is spread by birds. Financing animal disease surveillance studies, she says, saves human lives and surveillance gaps may fuel missed opportunities to identify dangerous diseases before they jump between species.

West Nile has been detected in at least 2 species of reptiles

Birds remain the main reservoir for the disease, but scientists have detected the virus across a wide range of species, including at least 48 mosquito species, over 320 bird species, more than 25 mammals, and two species of reptiles.

Scientists found that if cats in the lab ate infected rodents they could get West Nile

But beyond the lab setting there have been no known cases of cats or dogs contracting the virus this way. Instead, those animals have been sickened when an infected mosquito bit them—just as with human infection.

US West Nile case numbers were up 40% in 2025, nationally

This surprising surge may be due to warmer temperatures and elevated rainfall—leading to the ideal conditions for mosquitoes to thrive and breed in standing water. Symptoms can be hard to recognize when the disease is mild—similar to a flu. But neurological complications can lead to hospitalization and be deadly.

Animal-to-human pathogens constitute 75% of emerging infectious diseases

Zoonotic diseases encompass more than 200 diseases transmitted from animals to humans, wherein humans are usually accidental hosts. Ranging from rabies to HIV to monkeypox, this overview lists some of the most common viral threats.

Nearly 5,500 crows died during four months in 1999 from West Nile in NYC

Subsequent testing made clear the disease at that point was 100% fatal to crows. From 1999 to 2004, millions of birds died as West Nile spread across North America, but the virus fortunately became less virulent as it moved westward.

Hear from a NYC public health official who led the first US investigation into West Nile

This podcast walks through the investigation into the first US outbreak of West Nile, and how the virus had never been seen in the Western Hemisphere. The official discusses how she thinks the origin of West Nile in the US may have been birds or other animals that were brought here illegally.

Watch how viruses like Ebola can spill over from animals to humans—and vice-versa.

Yes, many animals get malaria—not just humans

Birds, rodents, monkeys, lizards, bats, apes, and livestock are among the species that can become infected with malaria. Infected animals' symptoms often resemble those of humans, including fever, lethargy, loss of appetite and difficulty breathing. Birds will also have ruffled feathers and drooped heads.

Humans are the only known reservoir of poliovirus

The virus has not been found in any other species, which makes humans the only known reservoir for polio. In laboratory settings, nonhuman primates have also been infected with the virus, but there's no evidence that they contract the virus in nature.

Rabies is nearly 100% fatal once symptoms appear

Rabies, a viral disease attacking the central nervous system, is nearly always fatal once symptoms appear. It spreads through the infected animal saliva (typically through bites) and causes encephalitis, leading to severe neurological symptoms and death. See how the lyssavirus—the bugs behind rabies—work once inside the body.

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.

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

The similarly named foot-and-mouth disease doesn't affect humans, unlike HFMD

Though the names are similar, foot-and-mouth disease—also known as hoof-and-mouth disease—exclusively affects animals, primarily those with hooves, such as cattle, sheep, pigs, goats, and even giraffes. It doesn't sicken humans, though both this disease and hand, foot, and mouth disease do come from the same family of viruses—Picornaviridae.

Read the 2012 study about captive orcas and the threat of mosquito-borne illness

Written by orca trainers who went on to become scientists, it states mosquitoes bite orcas at night when the animals hang out close to the surface. What's more, antibiotics used to keep captive orcas healthy also may depress their immune response, boosting the risks of them being unable to fight off diseases like West Nile Virus and encephalitis, which have killed orcas at US water parks.

Watch an expert's take on the rare disease hantavirus—and why it's not of great concern to the general population

This rare zoonotic disease, transmitted to humans primarily through infected rodent droppings, urine, or saliva, is rarely spread between people. The disease was of particular concern in spring 2026, when an outbreak occurred on a 150-person cruise ship, prompting a flurry of action, including contact tracing for passengers in their home countries. The disease can be fatal. But early care—primarily oxygen support—can help patients survive.

Mosquitoes stop flying at wind speeds equivalent to the swishing of a horse's tail

This low-threshold for wind—halting flight at 2 to 3 miles per hour—underscores that the bugs are actually not particularly strong flyers. But they don't need to be particularly robust fliers since their tiny, dark bodies and erratic movements can make them challenging to spot.

Vampire bats are the only mammal to feed exclusively on blood

Scientists believe their ancestors may have eaten parasites and insects off larger animals until vampire bats started feeding directly from those animals. Colonies work together to stay fed, as a vampire bat can die without just two days of eating.

Humans aren't the only mammals who go through menopause, but it's rare in the animal world

While scientists are unsure how many mammals actually experience menopause, they do know for sure that humans aren't the only ones. Orcas and some toothed whales (like belugas and narwhals) go through menopause. And a recent study found chimpanzees also experience the condition, though it's late in life.

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.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

Measles evolved from an ancient cattle disease as early as 3,000 years ago

Genetic analysis suggests that the closest modern relative of measles is a livestock virus known as rinderpest, with the viral strains diverging between 2,000 and 3,000 years ago. The timing coincided with the rise of major cities above 250,000 people, offering a novel transmission route for the newly mutated measles virus.

Nearly 99% of the Smithsonian's specimens are hidden in high-security

At the National Museum of Natural History, nearly 99% of its 147 million specimens are stored in secure research collections rather than on display, where they are actively used for scientific work ranging from tracking invasive species to improving aviation safety.

An Ebola vaccine was developed during the 2018 west African Ebola outbreak, but the 2026 Ebola outbreak is with a different species of the virus, not the one that the vaccine is approved to treat.

The HPV vaccine reduces cervical cancer rates by 90% or more

Cervical cancer is the fourth most common cancer in women globally. Almost all cases (99%) are linked to infection with high-risk human papillomaviruses. However, cervical cancer is both treatable and preventable—and we may be able to prevent most cases through vaccination.

The economics of horseshoe crab blood

Horseshoe crabs are older than dinosaurs and have survived five mass extinctions that wiped most life from the planet. But it's only now that their future as a species is in danger. This blood, worth about $60,000 per gallon, is hyper-sensitized to certain bacteria that are fatal to humans. This 17-minute podcast dives into humanity's pursuit of horseshoe crab blood, a "somewhat magical" mixture heavily relied on by the pharmaceutical industry.

Teen rides stranded scared horse to safety—14 miles out of burning canyon

When wildfires tore through the Los Angeles area in 2025, resulting in one of the worst natural disasters on record, one 16-year-old equestrian named Kalyna Fedorowycz bravely rescued an animal. She saw a horse named Sovereignty in the evacuation zone of the still-raging Palisades Fire, and led and rode him for 14 miles to safety. Sovereignty was eventually reunited with his owner.

See how Budweiser's famous Clydesdales spend their days at Warm Springs Ranch, where roughly 70 to 80 of the beer brand's giant horses can be found at any given time.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

Animal phobias are likely the most common type of phobias, followed by an extreme fear of heights.

Clever Hans was a 1900s horse that was believed to be able to solve math equations, tell time, and read and comprehend German, until a psychology student discovered how he got his answers.

Before humans, the Soviet Union and the United States sent animals—including apes, dogs, and cats—to space during the Space Race.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of life.

Poison ivy's rash-causing compound is found in the plant's roots, stem, and leaves—so coming into contact with any part of the plant can lead to rashes for the 85% of people who are allergic to it.

The Nasdaq's 'Magnificent 7' companies are responsible for roughly 40% of the Nasdaq 100 index's gains, while the remaining 93 companies account for the other 60%.

Fireworks-related ER visits are on the rise—in 2024, they increased by 52% as compared to the prior year.

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

In 2019, a laptop loaded with six of the worst malware in history and described as 'an exhibit of historical weaponry' sold for $1.3M.

Listen to an in-depth conversation on the links between Parkinson's disease and herbicide exposure and the challenging pace of scientific investigation.

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

A 2019 Facebook event called on attendees to "Storm Area 51, They Can't Stop All of Us," resulting in countless memes, the creation of a music festival, and eventually the arrests of those who did try to approach the area.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

Hotels in Cannes, the glamorous city on the French Riviera, hire hawks to ward off seagulls during the city's famous film festival.

For centuries, Niagara Falls has been a magnet for daredevils seeking to conquer one of nature's most powerful wonders, with its 200-foot drop and water rushing at 32 feet per second with 280 tons of force.

44% of Americans say they pray at least once a day—discover how your state's religiosity stacks up against the rest of the country.

Despite being favored by 87% of Americans, Congress does not have term limits.

In 1939, baseball star Lou Gehrig delivered his inspirational 'Luckiest Man' speech after retiring due to the health condition that now bears his name.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.