Gulls carry a range of bacteria, viruses, and parasites that can infect people, and research increasingly shows that the strains living in gull guts overlap genetically with those circulating in human populations. A GPS-tracking study of yellow-legged gulls found that more than a third tested positive for Salmonella, about a third for Campylobacter, and a quarter for Chlamydia. The bigger concern, though, is not just what gulls carry but where they carry it and how hard the resulting infections are to treat.
The Bacteria That Turn Up Most Often
Three bacterial groups dominate gull-disease research: Salmonella, Campylobacter, and pathogenic strains of E. coli. In a study that combined GPS tracking with lab sampling of 19 gulls nesting along the Mediterranean coast, roughly 37 percent carried Salmonella, 31 percent carried Campylobacter, and 25 percent carried Chlamydia, with no individual bird carrying more than one of these at a time.1PubMed Central. Pathogen transmission risk by opportunistic gulls moving across human landscapes Those are not obscure lab curiosities. Salmonella and Campylobacter are among the most common causes of food poisoning worldwide, responsible for diarrhea, fever, and abdominal cramps that can sometimes require hospitalization.
What the birds eat matters enormously. Research along the northeastern Iberian coast found that Campylobacter rates in gull chicks were directly tied to how much garbage the colony consumed.2PubMed Central. Influence of refuse sites on the prevalence of Campylobacter spp. and Salmonella serovars in seagulls Gulls foraging at landfills and sewage outflows pick up human pathogens, carry them in their intestines, and deposit them in droppings wherever they go next. A broad review of disease events in gulls and terns catalogued 569 recorded microbial outbreaks in these birds, with salmonellosis accounting for about 10 percent of all events.3Journal of Vertebrate Biology. Pathogenic microorganisms associated with gulls and terns (Laridae)
Gull Strains and Human Strains Are Sometimes Nearly Identical
Knowing that gulls carry Salmonella is one thing. Knowing that the Salmonella in a gull is essentially the same organism making people sick in a nearby city is quite another. A study in Barcelona sampled over 500 birds, including yellow-legged gulls, Audouin’s gulls, and pigeons, for Salmonella. About 9 percent of yellow-legged gulls tested positive, compared with about 3 percent of Audouin’s gulls and less than 1 percent of pigeons. All of the bird isolates were the same serovar, Typhimurium, that routinely shows up in human foodborne illness.4PubMed. Prevalence of Salmonella spp. isolated from seagulls and pigeons in Barcelona, Spain and its genetic relatedness with Salmonella human clinical isolates
When researchers paired gull and human isolates and sequenced their whole genomes, they found that one Audouin’s gull strain and one human clinical strain differed by only four single-letter changes across their entire genomes. That degree of genetic closeness strongly suggests the strains share a recent common source, whether the gull picked it up from a human waste stream and spread it, or both gull and patient acquired it from overlapping environments. Either way, the practical takeaway is that these are not distant relatives. The bacteria in a gull’s gut can be functionally identical to the ones landing people in hospitals.
Drug-Resistant Bacteria in Gull Droppings
Perhaps the most worrying dimension of gull-borne disease is not the pathogens themselves but how resistant those pathogens are to treatment. Standard antibiotics work by targeting bacterial machinery, but bacteria can acquire genes that neutralize those drugs. Gulls, because they feed at landfills and sewage facilities where antibiotic residues concentrate, have become efficient collectors and distributors of these resistance genes.
Researchers in Porto, Portugal, found that gull droppings on public beaches contained E. coli strains producing extended-spectrum beta-lactamases, enzymes that break down a broad class of antibiotics often used as front-line treatments in hospitals.5PubMed Central. Seagulls and beaches as reservoirs for multidrug-resistant Escherichia coli The same pattern has appeared thousands of miles away. In Patagonia, at the southern tip of South America, E. coli strains recovered from both migratory and resident gulls belonged to international clonal lineages associated with human and animal infections, carrying the same resistance genes found in clinical settings on other continents.6PubMed. Genomic evidences of gulls as reservoirs of critical priority CTX-M-producing Escherichia coli in Corcovado Gulf, Patagonia
A scoping review synthesizing findings from multiple studies confirmed the broader pattern: gulls living near human settings or agricultural fields pick up antibiotic-resistant bacteria from anthropogenic sources, particularly when feeding at landfills and near wastewater.7Frontiers in Microbiology. The Role of Gulls as Reservoirs of Antibiotic Resistance in Aquatic Environments: A Scoping Review And it is not just about which bacteria they carry. A comparison of gull feces, soil, and water found that gull droppings were enriched in resistance genes classified as “high risk” compared with the surrounding environment.8PubMed. Variability of faecal microbiota and antibiotic resistance genes in flocks of migratory gulls and comparison with the surrounding environment In other words, the birds are not just passive carriers. Their gut environment appears to concentrate resistance in ways that amplify the problem.
A study comparing gulls feeding at landfills versus rice paddies drove the point home. Gulls using landfills carried significantly more resistance genes and a greater abundance of potential pathogens, including Staphylococcus. The researchers found strong links between specific resistance genes and pathogenic bacteria in these birds, suggesting that resistance and disease-causing ability travel together.9PubMed. Winged resistance: Storks and gulls increase carriage of antibiotic resistance by shifting from paddy fields to landfills When a gull picks up a resistant pathogen at the landfill and drops it on a beach towel or in a reservoir, the infection it seeds could be much harder to treat than one acquired through a more conventional route.
Viruses Found in Gulls
Bacterial diseases get the most attention in gull research, but these birds host viruses as well. Highly pathogenic avian influenza (H5N1) has been detected in seagulls in multiple regions. A molecular study of dead gulls at a lake in Iraq identified H5N1 clade 2.3.4.4b, the lineage responsible for recent devastating outbreaks in wild birds and poultry worldwide. Analysis of the virus’s receptor-binding region, though, showed it still preferred binding to avian-type cell receptors rather than the mammalian type.10PubMed. Molecular characterization and genetic analysis of highly pathogenic H5N1 clade 2.3.4.4b in seagulls from Dukan Lake, Iraq That preference means the current strains in gulls are not well adapted to infecting human airways, but it does not eliminate the risk entirely. H5N1 has sporadically infected people who handled infected birds, and every new host gives the virus another chance to acquire mutations that improve human transmission.
Avian paramyxovirus type 1 (the agent behind Newcastle disease in poultry) has also been detected in gull feces. A survey along the coast of southern Brazil found the virus in kelp gull droppings, the first confirmed detection in that species.11PubMed Central. Molecular detection of paramyxovirus and coronavirus in fecal samples of shorebirds from Southern Brazil Newcastle disease virus can cause conjunctivitis and mild flu-like symptoms in people who handle infected birds, though serious illness is rare. More exotic agents have been documented too: researchers working in gull colonies have occasionally contracted Soldado virus, a tick-borne pathogen associated with a brief feverish illness that resolves on its own.3Journal of Vertebrate Biology. Pathogenic microorganisms associated with gulls and terns (Laridae) For most beachgoers, these viral risks are quite small compared with the bacterial ones, but for wildlife biologists, poultry farmers, and anyone handling sick or dead gulls, the exposure profile is different.
Parasites Worth Knowing About
Cryptosporidium, a microscopic parasite that causes watery diarrhea and is notoriously hard to kill with standard water chlorination, has been found in gull droppings. A study in Thailand identified Cryptosporidium species in seagull samples, including C. meleagridis, a species known to infect humans.12PubMed Central. Molecular identification of Cryptosporidium spp. in seagulls, pigeons, dogs, and cats in Thailand Cryptosporidium infection in healthy adults is usually a miserable but self-limiting bout of diarrhea lasting a week or two. In young children, elderly people, or anyone with a weakened immune system, it can become serious. Because gulls regularly defecate in or near recreational water, they add another route by which Cryptosporidium can reach swimmers and water supplies beyond the well-known pathways of agricultural runoff and sewage overflow.
From Landfill to Beach
Gull biology creates a particularly efficient pipeline for moving pathogens from concentrated waste sites into the places where people swim, eat, and drink. Gulls feed at landfills and treated-wastewater lagoons during the day, then roost on beaches, reservoirs, or urban rooftops at night. A radio-telemetry study documented individual gulls traveling between human waste sites and public beaches within the same day. Testing of those birds’ droppings revealed markers for both gull-associated and human-associated bacteria, including a fecal marker (HF183) that is normally used specifically to detect human sewage contamination in water.13PubMed Central. Potential for gulls to transport bacteria from human waste sites to beaches When a water quality test at a beach detects human fecal markers, the assumption is a sewer leak or stormwater overflow. But it could be a gull that swallowed bacteria at a sewage lagoon that morning and defecated on the sand that afternoon.
Beach sand itself acts as a reservoir. A study at a freshwater beach in Indiana found that bird feces, shoreline sand, and sediment were much more important drivers of E. coli contamination than riverine inputs.14PubMed. Evaluating the impacts of foreshore sand and birds on microbiological contamination at a freshwater beach Bacteria deposited in sand by gulls can survive for days and get resuspended into the water when waves wash over the beach or when children dig in the sand. This complicates beach management because monitoring programs typically sample the water, not the sand, and may miss a contamination source sitting just above the waterline.
Drinking water is not immune either. An older but widely cited investigation of a major water supply found that the number of E. coli in the water correlated with the number of gulls roosting on the reservoir. Identical Salmonella serotypes were recovered from the gulls, from the untreated water, and on three occasions from the treated water that had already passed through the purification plant.15Water Research. The contamination of a major water supply by gulls (Larus sp.): A study of the problem and remedial action taken Modern treatment systems are far more robust, but in any community where a reservoir or open water storage sits under a gull flight path, the birds remain a recognized contamination input that water managers have to account for.
Why the Problem Is Hard to Fix at a City Level
The difficulty with gull-related disease risk is that you cannot solve it by targeting one beach, one rooftop colony, or one landfill. Gulls are mobile, opportunistic, and legally protected in many countries. Hazing birds off one site often pushes them to the next one, and a gull that loses access to a landfill will shift to restaurant dumpsters, fishing harbors, or outdoor dining areas. Research on urban gull management has repeatedly found that uncoordinated, site-specific control efforts relocate the problem to surrounding areas rather than reducing it overall. An integrated, landscape-level approach is needed to make a meaningful dent in the conflict between gulls and urban populations.16Landscape and Urban Planning. Gulls in urban environments: landscape-level management to reduce conflict
In practice, that means the most effective interventions happen upstream. Covering landfills or capping waste ponds reduces the food source that supports large gull populations near cities. Enclosed waste transfer stations deprive gulls of the garbage-feeding that loads their guts with resistant bacteria in the first place. Some coastal cities have experimented with egg-oiling or nest removal on rooftops to control breeding, though these methods are labor-intensive and raise welfare concerns. No single strategy eliminates the risk, but cutting off the link between open waste and gull foraging addresses the root of the pathogen-transfer chain.
Practical Steps for Everyday Exposure
For most people, the realistic risk from gulls is not catching a rare virus. It is picking up a gastrointestinal bug after handling something contaminated with gull droppings, or swallowing water at a beach where gulls have been loafing. A few straightforward habits reduce the odds considerably:
- Avoid feeding gulls: Food handouts draw birds into close contact with people and concentrate droppings in high-traffic areas like boardwalks and picnic spots.
- Wash hands after beach visits: Sand in gull-heavy areas can harbor elevated levels of E. coli and other fecal bacteria, especially near the waterline where birds congregate.
- Cover food outdoors: Gulls are bold food thieves, and a bird that has just come from a landfill may leave bacteria on anything it touches.
- Rinse off after swimming: Recreational water at beaches with large gull populations may carry higher bacterial loads than monitoring data suggest, since tests sample water and may miss sand-derived contamination.
- Do not handle sick or dead birds: Avian influenza and other viral agents pose their highest risk through direct contact with infected carcasses or respiratory secretions. If you find a dead gull, report it to local wildlife authorities rather than picking it up.
Children, older adults, and immunocompromised individuals face greater consequences from infections like Cryptosporidium or Salmonella, so extra caution around gull-heavy areas makes sense for those groups. But for a typical healthy adult, a day at a beach with gulls overhead is not a medical emergency in waiting. The risk is low on any given day. It is the cumulative, population-level exposure across millions of beachgoers and the silent spread of antibiotic-resistant bacteria through the environment that makes gull-disease research a serious public health concern rather than just a curiosity of wildlife biology.
Migratory Gulls and Long-Distance Pathogen Dispersal
Many gull species migrate hundreds or thousands of kilometers between breeding and wintering grounds. That mobility gives them an outsized role in moving pathogens across borders. A drug-resistant E. coli strain picked up at a European landfill can end up in the coastal waters of West Africa months later when the bird migrates south. The Patagonia study mentioned earlier is a vivid example: E. coli clones belonging to international sequence types associated with human infections were found in gulls at the remote tip of South America, far from any dense urban center.6PubMed. Genomic evidences of gulls as reservoirs of critical priority CTX-M-producing Escherichia coli in Corcovado Gulf, Patagonia Those bacteria did not originate in Patagonian wilderness. They were carried there, likely over many stopovers and perhaps through bird-to-bird transmission at shared roosting sites along the way.
This migratory dimension means gull-borne disease is not strictly a local issue solvable by local beach management. Resistance genes and pathogens circulate through gull populations that span entire hemispheres. Surveillance programs tracking avian influenza already monitor migratory waterbirds for this reason, but bacterial surveillance in wild birds remains patchier. The GPS-tracking study from the Mediterranean showed that the greatest bacterial spread risk concentrated within about five kilometers of a breeding colony, with pathogen-positive birds visiting fishing ports, tourist beaches, and water ponds at comparable rates regardless of which bacterium they carried.1PubMed Central. Pathogen transmission risk by opportunistic gulls moving across human landscapes That local clustering is reassuring in one sense, since it suggests the highest-risk zone is relatively contained. But combine that local hotspot with a bird that will relocate hundreds of kilometers in a few weeks, and you get a system capable of seeding new hotspots along an entire coastline.