Do Crows Carry Diseases Affecting Humans?

Crows harbor several pathogens capable of infecting people, including bacteria like Campylobacter jejuni and Salmonella, the fungus Cryptococcus neoformans, and viruses such as West Nile virus and H5N1 avian influenza. That said, the actual risk of catching something from a crow is low for most people. The connection between crows and human disease is less about crows attacking or directly infecting us and more about what accumulates in their droppings, where they forage, and how they fit into broader disease cycles involving mosquitoes and contaminated environments.

The West Nile Virus Connection

The disease most famously linked to crows is West Nile virus. When the virus arrived in the northeastern United States in 1999, one of the earliest and most visible signs was a wave of dead crows. Of 295 birds laboratory-confirmed with West Nile virus infection during that initial outbreak, 89% were American Crows.¹ The die-off was so striking that public health officials built a national surveillance system around it, using crow deaths as an early warning that the virus was circulating in an area before humans started getting sick.

Here is the important nuance: crows do not transmit West Nile virus to people. The virus passes through mosquito bites. A mosquito feeds on an infected bird, picks up the virus, and later bites a human. Crows are amplifying hosts, meaning their blood carries enough virus for mosquitoes to acquire it efficiently, but you cannot catch West Nile from touching a crow, being near one, or even handling a dead one (though gloves are still wise for other reasons). American Crows are actually among the most vulnerable birds to the virus. Experimental infection studies found that American Crows succumbed to West Nile virus infection after widespread viral replication and depressed immune responses, while the closely related Fish Crow remained clinically normal throughout the same experiment.²

So while crows are deeply entangled in the West Nile story, they are more victims and sentinels than they are villains. Crow mortality data from early in the season turned out to be a useful predictor of whether a county would see human West Nile cases. One analysis found that high densities of reported dead crows and the proportion of crows testing positive for the virus were each associated with roughly seven times the odds of at least one human case appearing in that area.³ If you see a lot of dead crows in your neighborhood, it is not the dead crows themselves that threaten you. It is the mosquitoes that infected them.

Bacteria in Crow Droppings

The more direct health concern from crows involves their feces. Like many wild birds, crows shed bacteria in their droppings, and some of those bacteria cause illness in humans. The one that has received the most research attention is Campylobacter jejuni, a leading cause of bacterial gastroenteritis worldwide. A study of free-ranging American Crows in California’s Sacramento Valley found Campylobacter species in about two-thirds of the birds sampled. Of those isolates, 93% were C. jejuni, and a meaningful fraction carried virulence genes known to be associated with human disease.⁴ A separate study that looked at seasonal and age-related variation confirmed the picture, finding over half of crow samples positive for the bacterium.⁵

The practical concern is that crows roost in enormous communal groups, sometimes numbering in the thousands, and they do this in urban and suburban areas. A large winter roost concentrated in a park, a parking lot, or near a water source deposits a significant amount of fecal matter in a small area. Anyone walking through, letting children play in, or drawing water near a heavily used roost site could encounter these bacteria. Campylobacter infection in humans typically causes diarrhea, cramping, and fever, and while most people recover without treatment, it can be serious for young children, the elderly, and those with weakened immune systems.

Campylobacter is far from the only bacterium involved. Investigations of birds foraging at an open landfill in Iran found E. coli in all five bird species sampled, including rooks (a close relative of crows), along with Salmonella, Yersinia, and Klebsiella.⁶ These are all organisms that cause gastrointestinal illness or, in more severe cases, bloodstream infections in people. The finding highlights how landfills serve as hotspots where birds pick up and then redistribute pathogens across the landscape.

Avian Influenza and H5N1

Highly pathogenic avian influenza, particularly the H5N1 strain, has drawn global attention in recent years. Crows are susceptible to H5N1, and a 2023 study demonstrated that crows can acquire the virus through cannibalism, meaning by eating the carcasses of infected crows. In that experiment, virus shedding was detected from the third through the eleventh day after exposure, and all four crows in the study developed antibodies to H5N1 by two weeks.⁷ This matters because crows are scavengers and regularly feed on dead animals, including other crows. Once H5N1 enters a crow colony, this behavior could sustain transmission within the group.

For humans, the risk from H5N1 has historically come from close contact with infected poultry rather than wild birds. But the scenario researchers worry about is a bridge: wild crows pick up the virus from poultry operations or contaminated environments, spread it among themselves, and then carry it into urban settings where people, pets, and backyard chickens might be exposed. This is still more of a theoretical concern than a proven route of human infection, but it underscores why wildlife disease researchers keep a close eye on corvids during avian influenza outbreaks.

Psittacosis and Other Respiratory Risks

Chlamydia psittaci, the bacterium that causes psittacosis (sometimes called parrot fever), is another pathogen found in wild birds including corvids. Psittacosis in humans causes a flu-like illness that can progress to pneumonia, and it spreads through inhaling dust contaminated with dried bird droppings or secretions. A study at a wild bird refuge center found C. psittaci in over a quarter of birds sampled, with multiple genotypes circulating. More telling, 30% of the human workers at the center tested positive for the bacterium in their throat swabs, confirming that the pathogen had jumped from birds to people in that setting.⁸

That study involved a rehabilitation facility where people were handling birds daily in enclosed spaces, which is a higher-risk scenario than most people will ever encounter with wild crows. But it illustrates the principle: when bird droppings accumulate in confined or poorly ventilated areas and dry into dust, inhaling that dust becomes a real route of infection. This is relevant for anyone cleaning up a crow roost site, working in a barn or warehouse where crows nest, or doing construction work that disturbs old bird droppings. A dust mask, or better yet an N95 respirator, is not overkill in those situations.

A Fungal Pathogen in Crow Droppings

Cryptococcus neoformans is a fungus that thrives in bird droppings and can cause serious infections in humans, particularly cryptococcal meningitis in people with compromised immune systems, such as those living with HIV/AIDS. Pigeon droppings have long been recognized as a major environmental reservoir. Research from India found C. neoformans in crow pellets for what appears to be the first time, a finding the authors considered significant given how widespread crows are across the Indian subcontinent.⁹ Like psittacosis, the infection route involves inhaling fungal spores from dried droppings rather than any direct contact with the bird.

For healthy people, breathing in a small number of Cryptococcus spores rarely causes illness. The body’s immune system handles it. The risk is concentrated among immunocompromised individuals, for whom even low-level environmental exposure can lead to life-threatening disease. This is worth knowing if you or someone in your household has a weakened immune system and you live near a large crow roost.

Antibiotic-Resistant Bacteria

Beyond the question of which specific pathogens crows carry, there is a growing concern about what kind of bacteria they carry. Urban birds, including corvids, have been found harboring bacteria resistant to multiple antibiotics. A study of urban birds in central Spain found that nearly half of E. coli isolates from the birds tested were resistant to at least one antibiotic, and about 39% of those resistant strains qualified as multidrug-resistant.¹⁰ That particular study focused on storks and gulls, but the broader literature consistently finds the same pattern in corvids that share the same urban environments and food sources.

Crows pick up resistant bacteria from the same places they pick up everything else: landfills, sewage outflows, agricultural runoff, and dumpsters behind hospitals and restaurants. They then spread these bacteria across the landscape through their droppings. This does not mean a crow is going to give you an untreatable infection, but it does mean that crow droppings in urban environments may contain bacteria that are harder to treat if they do cause illness. It is one of the quieter ways that antibiotic resistance circulates in the environment.

Why Crows in Particular

You might wonder whether crows are especially dangerous compared to other birds. The honest answer is that most of these pathogens are found in many wild bird species. Pigeons, gulls, starlings, and geese all carry overlapping sets of bacteria and fungi. What makes crows stand out is their ecology. They are highly synanthropic, meaning they thrive alongside people. They feed on human garbage, forage in agricultural fields, and roost in urban centers. They are also remarkably social and congregate in massive winter roosts, concentrating fecal contamination in small areas. And they are intelligent generalists that exploit nearly every food source available, from roadkill to fast-food leftovers to other dead birds.

This lifestyle maximizes their exposure to pathogens from human and animal waste streams and maximizes the chance that those pathogens end up deposited where people live, work, and play. A solitary songbird living deep in a forest carries its own suite of parasites, but those rarely overlap with human spaces. A crow that commutes between a landfill, a dairy farm, a park, and a downtown parking garage is picking up pathogens from every stop along the way.

Are Waterborne Parasites a Real Concern?

Some researchers have investigated whether wild birds, including crows, contribute to contamination of drinking water sources with parasites like Cryptosporidium and Giardia, both of which cause gastrointestinal illness. These parasites have been detected in wild bird droppings, which initially raised alarms about bird-to-human transmission through water supplies. However, a closer look at the evidence suggests the risk is probably overstated. A review concluded that the zoonotic species of Cryptosporidium and Giardia found in wild migratory birds are likely due to mechanical carriage or spillback from birds grazing on pastures already contaminated by livestock.¹¹ In other words, the birds are picking up parasites from cattle droppings and passing them through, not serving as true hosts that amplify the infection. Livestock remain the primary concern for waterborne parasites, not birds.

Practical Steps for Reducing Risk

For most people going about their daily lives, the risk from crows is minimal. You are not going to catch a disease from watching crows in your yard or having them visit your bird feeder. The risk concentrates in specific scenarios:

Large roost sites: If thousands of crows roost near your home, the accumulated droppings can harbor Campylobacter, Salmonella, Cryptococcus, and other organisms. Avoid letting children play in areas heavily coated with droppings, and wash hands thoroughly after any contact.
Cleaning up droppings: Dried bird feces become airborne dust, which is the main route for C. psittaci and Cryptococcus. Wet the area down before sweeping or scraping to keep dust from becoming airborne. Wear a respirator mask and gloves.
Dead birds: Do not handle dead crows with bare hands. During West Nile virus season or avian influenza outbreaks, many local health departments want you to report dead crows rather than dispose of them yourself. Use a plastic bag turned inside out to pick up the bird if you must move it.
Water sources: If you collect rainwater or maintain an open water feature, keep it covered or away from areas where large numbers of birds congregate.
Immunocompromised individuals: People with HIV/AIDS, organ transplant recipients on immunosuppressive drugs, and others with weakened immune systems face higher risk from fungal pathogens like Cryptococcus. These individuals should avoid areas with heavy bird droppings accumulation.

Climate Change and an Expanding Picture

The geography of crow-associated disease risk is not static. West Nile virus transmission depends on mosquito populations, and warmer temperatures extend the range and activity season of the Culex mosquitoes that carry the virus. Research has found that warmer winter temperatures are associated with greater declines in crow abundance after West Nile virus emergence, likely because milder winters support larger mosquito populations the following summer.¹² Urban heat islands compound the effect, since cities are both warmer and more densely populated by crows.

As global temperatures rise, the range of mosquito-borne diseases like West Nile is expected to push into areas that were previously too cold to sustain transmission, potentially bringing the crow-mosquito-human disease cycle to communities that have not dealt with it before.¹³ For people living in northern latitudes who have regarded West Nile as a southern problem, that assumption may need updating in the coming decades. The crows in your neighborhood may once again serve as the earliest visible warning, just as they did in New York in 1999.