Do Earthworms Carry Diseases? The Real Risks Explained

Earthworms are not significant carriers of disease to humans through ordinary contact, but they can serve as intermediate hosts or mechanical carriers for certain parasites and bacteria that affect livestock, poultry, pets, and occasionally people. The real risks depend heavily on context: whether you are gardening in clean soil, handling worms used in composting sewage-laden waste, or watching your dog gulp one down. For most people picking up a worm in the garden, the danger is negligible, but the biology behind how earthworms interact with pathogens and pollutants is more complicated than a simple “safe” or “unsafe” answer suggests.

Bacteria That Hitch a Ride

Earthworms spend their lives eating soil, decaying plant matter, and animal manure, so they inevitably encounter bacteria along the way. Research has shown that some dangerous bacteria can survive passage through an earthworm’s gut and even multiply in the process. In one study, E. coli O157:H7, the strain responsible for serious foodborne illness in humans, was detected on the earthworm’s skin, in its intestine, and in its excreted casts after the worms fed on contaminated manure. The concentration of the bacterium in casts actually exceeded the original inoculation level, meaning the worms amplified the pathogen rather than destroying it.¹ That finding matters primarily for agricultural and composting settings where manure from infected animals is present. A worm in your lawn that has not been eating contaminated material is not going to be coated in E. coli O157:H7.

A related concern arises in sewage treatment. Earthworms are sometimes used to process sewage sludge, and research on this application found that while the worms generally reduced or eliminated harmful bacterial pathogens in the sludge, gut transit actually increased the abundance of some pathogenic species.² So the picture is mixed: earthworms are broadly good at cleaning up waste, but they are not a perfect sterilization system. Certain bacteria can slip through or even thrive.

How Earthworms Move Bacteria Through Soil

Beyond hosting bacteria internally, earthworms physically transport microbes from one part of the soil to another. A study tracking marked bacteria found that transport through soil columns occurred only when earthworms were present. The primary mechanism was not water flowing through worm burrows but rather the worms burying surface litter deeper into the ground, carrying bacteria with it.³ Less than a tenth of a percent of the applied bacteria were leached through by water alone, even with worm channels available. This means earthworms are less like plumbing that lets contaminated water rush downward and more like tiny bulldozers slowly mixing soil layers together. For anyone worried about well contamination or groundwater, the earthworm’s role is real but modest compared to factors like heavy rainfall or poor drainage.

Parasites That Use Earthworms as Stepping Stones

The oldest and best-documented disease risk from earthworms involves parasites that use worms as intermediate hosts, meaning the parasite must pass through an earthworm before it can infect its final host. This matters far more for animals than for people.

Gapeworm (Syngamus trachea) is a classic example. This parasite infects the trachea of chickens, turkeys, and wild birds, causing them to gasp for air. The connection to earthworms was established in the 1880s, when researchers found gapeworm larvae encysted in earthworm guts. Birds become infected by eating earthworms carrying the larvae.⁴ If you keep backyard poultry, this is a genuine concern. Free-ranging chickens eat earthworms constantly, and in areas where gapeworm is endemic, the worms in your yard can be a persistent source of reinfection.

Pig lungworm (Metastrongylus species) follows the same pattern. Earthworms are the obligatory intermediate host, meaning the parasite cannot complete its life cycle without them.⁵ Pigs root through soil and eat earthworms as part of their natural foraging behavior, picking up lungworm larvae in the process. One study explored whether earthworms infected with lungworm larvae could also transmit mycoplasmal pneumonia to pigs, but found that while the worms successfully delivered the lungworm infection, they did not pass along the bacterial lung disease.⁶ That is a small reassurance: earthworms are not generalized vehicles for every pathogen in the soil, just specific ones that have evolved to exploit them.

Earthworms also play a role in moving geohelminth eggs, the eggs of soil-dwelling parasitic worms like Toxocara (roundworm) and others that can infect humans. Under natural conditions, living geohelminth eggs were carried in earthworm castings from deeper soil layers to the surface for at least a year after the soil was initially contaminated.⁷ This is relevant anywhere dogs, cats, or raccoons defecate in soil. Even after the feces are gone, earthworms can keep cycling parasite eggs back to the surface where children or gardeners might contact them.

What About Pets Eating Earthworms

Dogs and cats frequently eat earthworms, and pet owners understandably wonder whether this is dangerous. The primary risk is the same intermediate-host issue described above: earthworms can carry encysted larvae of parasites that infect pets. Dogs that eat earthworms may pick up certain parasites, and cats can face similar exposures through predation on invertebrates. A review of zoonotic parasites associated with predation by dogs and cats noted the role of invertebrate prey, including earthworms, as a source of parasitic infections.⁸

Lungworm in dogs is a growing concern in parts of Europe and elsewhere. While dogs more commonly acquire lungworm from slugs and snails, earthworms can also serve as carriers. If your dog regularly eats earthworms and you live in an area where lungworm is present, keeping up with regular deworming treatment through your vet is worthwhile. An occasional earthworm eaten in a clean garden is unlikely to cause problems, but a dog that obsessively roots for worms in manure-contaminated soil is at higher risk.

Can Humans Get Sick From Handling Earthworms

For humans, the direct disease risk from touching earthworms is extremely low. You are not an intermediate or final host for the parasites that use earthworms in their life cycle, with very rare exceptions. A mid-twentieth-century review of animal parasites and human disease noted that some parasites can reach maturity in humans but are “rarely involved in medical problems because infection is acquired only by eating uncooked earthworms and insects.”⁹ In other words, you would need to eat a raw earthworm to face any meaningful parasite risk, and even then serious illness is rare.

The more realistic human health concern is indirect. Earthworms cycling geohelminth eggs to the soil surface, as described earlier, can increase the chance that a child playing in contaminated soil ingests Toxocara eggs, which cause visceral larva migrans. But the earthworm is just one factor in a chain that starts with infected animal feces in the soil. Good hand hygiene after gardening, deworming pets, and keeping sandboxes covered do far more to prevent these infections than worrying about earthworms specifically.

Earthworms’ Built-In Antimicrobial Defenses

One reason earthworms are not crawling disease factories, despite living surrounded by bacteria, fungi, and parasites, is that they have surprisingly robust immune defenses. Earthworms produce coelomic fluid, the liquid filling their body cavity, which has documented antibacterial and antibiofilm properties. Research on the species Pheretima posthuma found that both the coelomic fluid and body paste inhibited biofilm formation by various pathogenic bacterial strains.¹⁰ This is not just academic curiosity: these antimicrobial secretions are part of why earthworms help reduce pathogen loads in composting systems rather than simply spreading everything they swallow.

Earthworms also appear to have immune-receptor-like molecules on their immune cells. A study looking for Toll-like receptors on earthworm coelomocytes (their immune cells) found that while most mammalian-type receptors were not detectable, about 10% of coelomocytes did bind bacterial flagellin, a component of bacterial flagella that triggers immune responses in many animals. The earthworm immune system is simple compared to ours, but it is not absent. These defenses help explain why many pathogens are actually destroyed during gut transit rather than amplified.

Vermicomposting and Pathogen Reduction

Vermicomposting, using earthworms to break down organic waste, is widely promoted as a sanitation technique, and the evidence broadly supports the idea that it reduces pathogens. A review comparing composting and vermicomposting found that earthworms can be regarded as a way of eliminating pathogenic bacteria from organic solid waste, thanks to gut transit mechanisms that kill many microbes.¹¹ A more detailed review outlined several mechanisms at work: enzymes in the gut directly inhibit bacteria, coelomic fluids have antibacterial properties, and the worms stimulate beneficial microbes in the surrounding material that outcompete pathogens.¹²

The caveat, as the sewage sludge research showed, is that this process is not total sterilization. Some pathogens can survive or even increase. If you run a vermicomposting bin at home, the finished product is generally much safer than the raw inputs, but treat it like any compost: wash your hands after handling, and if you composted pet waste or material from unknown sources, let the finished vermicompost cure before using it on food crops.

Heavy Metals and Chemical Contamination

A less obvious risk from earthworms has nothing to do with disease organisms and everything to do with chemistry. Earthworms are excellent bioaccumulators of certain metals and organic pollutants, which means they concentrate these substances in their tissues at levels that can exceed what is in the surrounding soil.

A study of earthworms in Punjab, Pakistan, found significant bioaccumulation of calcium, manganese, copper, and strontium, with tissue concentrations exceeding soil levels. Interestingly, group-1 carcinogenic metals like lead, cadmium, and chromium did not show consistent bioaccumulation, suggesting limited biological uptake despite their presence in the soil.¹³ However, other research has documented clear accumulation of cadmium and mercury in earthworm tissues, with body concentrations exceeding substrate levels.¹⁴ The discrepancy likely reflects differences in soil chemistry and earthworm species, but the general principle holds: earthworms soak up metals from their environment.

This matters primarily through the food chain. Earthworms are a major dietary component for birds, moles, shrews, and other wildlife. Pollutants taken up by earthworms accelerate the transfer of chemicals into food webs through bioaccumulation and biomagnification, and the harm can be most severe at higher trophic levels even when the earthworms themselves seem unaffected.¹⁵ If you keep chickens that eat earthworms from contaminated soil near old industrial sites, lead paint areas, or heavily treated agricultural land, the metals could accumulate in the birds and their eggs. For home gardeners, this is mainly a concern if your soil has known contamination history.

Microplastics and Organic Pollutants

A newer area of research involves earthworms interacting with microplastics in soil. Tiny plastic fragments are now widespread in agricultural and urban soils, and earthworms inevitably ingest them. The concern is not the plastic itself but rather the toxic organic chemicals that cling to it, such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs).

Research found that when earthworms were incubated in soil containing microplastics that had been pre-contaminated with these chemicals, ingestion of the plastics acted as a significant pathway for pollutant uptake into worm tissues. The effect varied by plastic type and chemical, with some plastics releasing their contaminant load more readily than others.¹⁶ Whether microplastics increase or decrease pollutant uptake actually depends on the contamination sequence: if clean plastics are mixed into already-polluted soil, they can absorb pollutants and reduce what the worm takes up, acting like a sponge. But if the plastics arrive pre-loaded with chemicals, they become delivery vehicles.¹⁷ Smaller microplastic particles contributed the most to bioaccumulation, suggesting that as plastics in the environment continue to fragment into ever-smaller pieces, this problem could grow.

For most people, this is not an immediate personal health risk. You are not eating earthworms. But the finding has implications for food safety in agriculture: crops grown in soils with heavy microplastic contamination could indirectly be affected by the way earthworms redistribute pollutants through the root zone.

Earthworms as Fungal Carriers in Forests and Farms

Earthworms also spread fungi through soil, which has consequences for agriculture and forestry rather than human health. When the common earthworm Lumbricus terrestris was fed various fungal species, it maintained full viability of several plant pathogens through its gut, excreting them in viable form in its casts. This included Fusarium and Verticillium, both economically damaging crop pathogens.¹⁸ A broader review confirmed that earthworm casts contain higher amounts of fungal spores and infective propagules than surrounding soil, and that spores can survive in dried casts. In at least one documented case, plant pathogens found in seedlings along forest edges were traced to passive vectoring by earthworms.¹⁹

The earthworms were selective, though. While oomycete and ascomycete plant pathogens passed through intact, most basidiomycete fungi (which include many mushroom-forming species) did not survive gut transit. The one exception was the root parasite Armillaria ostoyae, a serious forest pathogen, which survived at lower concentrations. For farmers and foresters, this means earthworms are not neutral bystanders in soil disease dynamics. They can spread certain soilborne crop diseases across a field, even as they improve soil structure and fertility in other ways.

Earthworms as Invasive Species Vectors

An often-overlooked angle on earthworms and risk has nothing to do with disease at all, but with ecological disruption. Live earthworms sold as fishing bait are a documented vector for invasive species introductions. A survey of the bait industry found that earthworms sold in one state frequently originated from entirely different regions, and anglers releasing unused bait introduced non-native earthworm species along with any pathogens or organisms they carried.²⁰ In parts of North America where native forests evolved without earthworms after the last ice age, the introduction of European earthworm species has dramatically altered forest floor ecosystems by consuming the thick leaf litter that many native plant species depend on. The worms themselves are the problem in this scenario, reshaping soil chemistry and destroying habitat for native ground-nesting birds and salamanders. Any pathogens or parasites they carry along for the ride only add to the damage.