Soilborne illness and disease

• ANATOMY OR SYSTEM AFFECTED: All
• ALSO KNOWN AS: Soil-transmitted diseases

Definition

Soilborne illnesses and diseases are caused by numerous microorganisms and parasites that live in soils. Soil serves as an ecosystem for diverse microbes that perform various roles and that range from useful organisms in biological and geological processes to dangerous transmitters of diseases. According to the World Health Organization (WHO) in 2023, soil-transmitted helminth (STH) infections are among the most common infections throughout the world, affected about 1.5 billion people, or 24 percent of the population. They affect the poorest communities, which have little or no access to clean water and sanitiation, in Sub-Saharan Africa, China, South America, and Asia. In 2021, WHO treated more than 500 million children in these countries with medications. This was about 62 percent of the children at risk.

Causes

Soilborne, or soil-transmitted, diseases are common, especially in tropical regions, and affect more than two billion people globally in the early twenty-first century, according to the World Health Organization (WHO). This included 654 school-age children, 108 million adolescent girls, and 138.8 million pregnant and lactating women. Scientists estimate that the lifespans of people infected with the most prevalent soilborne diseases and parasites are reduced by 43.5 million life years, more than the lifespan reductions of measles and malaria and exceeded only by tuberculosis.

Most soilborne illnesses are transmitted from soil to humans through the pathogens (such as bacteria, fungi, protozoa, and worms) that are shed in fecal material, which contaminate soil. These pathogens infect people who eat the plants grown in the contaminated soil or who drink water polluted by that soil. Human and nonhuman animals infected with soil-transmitted illnesses perpetuate the cycle when their feces contact soil. Bacteria and viruses associated with enteric diseases, specifically infections in the gastrointestinal tract, often are transmitted to humans in soils that have been used to bury sewage. Landfills that do not have procedures to control leaching enable bacteria and viruses to contaminate soil.

Helminthiasis is a frequently diagnosed disease reported worldwide that is transmitted by contact with soil. Eggs from worms, or helminths, are dormant in soil until they enter human or animal bodies, move through those bodies as larvae, and mature within three months into worms that infest the intestines. Worm infestation is often chronic, as parasites can live several years in their hosts. Soils host numerous types of worms (also referred to as nematodes), including roundworms, hookworms, and whipworms, which transmit diseases to humans.

The roundworm Ascaris lumbricoides infects humans with ascariasis. According to WHO, more than one billion humans are infected with this worm. Soils host these parasites’ eggs. Roundworms are prolific, producing approximately 200,000 eggs daily. Humans are exposed to these immature worms by touching contaminated soil or by swallowing dirt or food that has not been adequately cleaned. Inside human bodies, roundworm eggs hatch into larvae that then invade essential body parts, including nerves and organs.

Other worms transmitted through soil include the hookworms Necator americanus and Ancylostoma duodenale. Those larvae enter skin from soil, infecting people with ancylostomiasis. WHO states approximately 740 million people have hookworms. The disease trichuriasis results from eggs from the whipworm, Trichuris trichiura, contaminating soil. About 795 million people have this infection, according to WHO.

Humans also are infested with the threadworm Strongyloides stercorali, which causes the disease strongyloidiasis as it moves from soil into the feet. Through worm eggs shed in fecal material, infested domestic pets expose humans to parasites and diseases associated with them, including visceral larva migrans and toxoplasmosis infections caused by Toxoplasma gondii.

As a cause of anthrax infections, dormant Bacillus anthracis bacteria spores often exist in soil for long durations, ranging from several years to decades. Growing grass blades transport anthrax spores from soil when grass-grazing animals ingest them. Associated with listeriosis, the bacterium Listeria monocytogenes is frequently found in soils and manure, contaminating livestock and plants used as food sources. The Brucellosis bacterium, often associated with livestock, can enter bodies through exposure to touching or breathing dust. The Leptospira interrogans bacterium, which causes leptospirosis, is present in soil and muddy areas where rodent urine containing that pathogen soaks into the ground. The Acinetobacter baumannii bacterium, which lives in soil, causes acinetobacter.

Most soil-transmitted disease deaths involve the pathogen Clostridium tetani, responsible for the deaths of approximately 450,000 infants and 50,000 adults each year. Scientists state that this bacterium’s spores can be dormant in soil for almost one-half century and can still infect humans. C. botulinum bacteria spores also remain dormant in soils for extended times, causing botulism infections that are spread through foods. Soils in tropical areas often host the bacteria Burkholderia pseudomallei and B. mallei, which infect people with melioidosis and glanders when they touch or inhale soil or eat foods cultivated in contaminated fields. Nocardiosis infections occur when people breathe Nocardia bacteria found in dust or when contaminated soil contacts a person’s skin injury.

Rarer, and often more deadly, soil-transmitted diseases occur when Chromobacterium violaceum bacteria infect humans by spreading from skin openings through the circulatory system and attacking organs simultaneously, preventing their function. Although Legionnaires’ disease is usually transmitted through air or water, the Centers for Disease Control and Prevention (CDC) in 2000 reported cases in which the bacterium Legionella longbeachae infected people who had touched potting soil. Scientists have linked poliovirus 1 to soil, noting that the virus can survive more than three months underground and contaminate crops.

Fungi in soils, including the fungi Mucorales, Aspergillus, Fusarium, and Blastomyces dermatitidis, also transmit diseases. Cryptococcus neoformans can infect people who inhale dust containing it, leading to cryptococcal meningitis. Histoplasmosis is another soilborne illness, this time caused by Histoplasma fungus, which exists in soils as mold and affects the lung. Fungal Coccidioides immitis spores in soil cause coccidioidomycosis infections.

Risk Factors

Socioeconomic factors increase the risk of a person being infected with soilborne diseases. Poor sanitation exposes humans to soils contaminated with microorganisms and parasites. Areas without hygienic toilets or other devices to contain human wastes contribute to soil-transmitted infestations. Inadequate sewage systems result in fecal material being present near houses, schools, and other buildings. Rain washes these soils into water supplies, often rivers and ponds, which people use as a source for drinking water and use for bathing, swimming, fishing, and cleaning of cooking and eating implements.

Impoverished populations often lack access to sufficient preventive medical care. Illiteracy and restricted educational opportunities result in people not having information on preventing soilborne diseases or on treating those conditions if infected. Many people who suffer soil-transmitted diseases do not consume diets with nutritional foods that provide vitamins and minerals. They often eat foods that have not been thoroughly cooked or cleaned, and they do not have access to pasteurized products and boiled water. Pregnant women and people with weak immune systems or other health problems are extra-susceptible to soilborne illnesses and suffer miscarriages and mortality caused by infections.

Populations living in areas where crops are fertilized with feces or irrigated with polluted water risk being infected by diseases transmitted by soil, either by consuming foods, especially vegetables and fruits, grown in those soils or by working in contaminated fields. Runoff from pastures can contaminate communities with pathogens associated with livestock manure. Risks associated with contacting contaminated soils increase with people’s proximity to landfills or other sites where sewage is stored in soil and where pathogens seep into the ground.

Dangers associated with exposure to soil depend on how accessible a person’s skin is to contacting soils directly. People who work outdoors , performing landscaping, agricultural, forestry, sewage, or other jobs that involve contact with soil are at high risk of acquiring soil-transmitted illnesses. Hikers and others participating in outdoor recreation come into contact with soils and the pathogens they host. Children’s risk is increased because they often play in dirt that can be contaminated. People with the disorder called pica (in which they consume, among other non-nutritive substances, soil) are especially vulnerable to soilborne illnesses.

Weather can intensify the occurrence of soilborne diseases. Floods, for example, can force to the surface underground soil layers and the pathogens they host. Violent storms such as hurricanes and typhoons can move soil and pathogens great distances. Soilborne diseases identified as potential biological weapons also present public safety concerns. Terrorists have threatened to use anthrax spores secured from soil sources. The CDC designated B. pseudomallei and B. mallei to be bioterrorism agents because of their universal availability in soils.

Symptoms

Various symptoms are exhibited by people infected with soil-transmitted diseases. Probably the most obvious symptom associated with soilborne illness is the shedding of parasites while vomiting or during a bowel movement. People infected with soil-transmitted helminths often suffer gastrointestinal pain and swollen stomachs. Other organs occasionally swell. Infected people frequently experience diarrhea, nausea, bloody bowels, and vomiting, and they can become anemic.

Soil-transmitted infections usually cause people to become weak and listless. Fevers, rashes, headaches, and stiffness are common symptoms too. Infected persons often are not strong enough to attend school or perform labor. Some people with soilborne illnesses exhibit impaired cognition, experiencing problems with memory and language functions. Long-term symptoms include decreased mental and physical development in children. Lung damage from soilborne illness is often exhibited through pneumonia, coughing, or asthma. Although most adults do not exhibit the symptoms of toxoplasmosis infection, children who were infected in utero develop symptoms as they mature. Health problems associated with toxoplasmosis include blindness, deafness, and retardation.

Illnesses associated with soil often weaken immune systems, causing people to develop infections and conditions unrelated to soil. Soil-transmitted diseases are sometimes described as food-borne illnesses, even though pathogens such as Escherichia coli O157:H7 and Salmonella, which are associated with food poisoning, are present in soil that contaminates foods. Poor agricultural yields, damaged plants, and ill livestock may indicate the presence of pathogens and parasites in soil.

Screening and Diagnosis

Medical professionals evaluate those with soil-transmitted illnesses according to conditions and physical ailments unique to each person. Examinations usually begin with recording an infected person’s medical history and asking where the person lives and if they have traveled to other areas. This geographical information helps clinicians determine the most likely soil-transmitted disease infected the patient.

Health care workers assess various tissue samples to diagnose soilborne diseases associated with microorganisms. Specimens acquired for analysis frequently include blood, sputum, urine, feces, skin, bone marrow, and cerebrospinal fluids. Blood tests reveal the presence of antibodies to bacteria. X rays and biopsies are often used to detect fungal soil-transmitted diseases such as cryptococcosis. Some physicians utilize magnetic resonance imaging or computed tomography scans to assess damage by mucormycosis and other microbe infections.

For diagnosis of helminth infections, patients provide fecal samples for laboratory analysis to detect evidence of parasites and to examine worms. Technicians utilize several methods to evaluate specimens, including formalinethyl acetate sedimentation and Kato-Katz fecal-thick smear to count worm eggs. Medical personnel use imaging procedures and tools, such as endoscopy and ultrasonography, to determine any internal damage to organs and intestines.

Treatment and Therapy

Persons diagnosed with soil-transmitted diseases undergo various methods to treat their infection. Many treatments focus on removing worms and include tablets composed of benzimidazole anthelmintics. The drugs most frequently dispensed include albendazole and mebendazole in doses of 400 to 500 milligrams (mg) for children two years of age and older and for adults, including women who have reached their second trimester of pregnancy. Toddlers younger than two years of age receive 200 mg. Amounts of the drug praziquantel are determined by measurements of the patients’ height with a dose pole. Helminth-infected persons often receive iron and vitamin A supplements. People at risk of being reinfected receive additional drug doses at later times.

Researchers are developing new pharmaceuticals and methods to control soil-transmitted parasites that have become resistant to standard treatments. Other drugs sometimes used include levamisole, pyrantel pamoate, nitazoxanide, and tribendimidine. Many soilborne infections caused by microbes are treated with antibiotics. These drugs, however, often cannot defeat pathogens that become resistant to antibiotics. Medical researchers have tested the use of recombinant larval antigen ASP2 to create a hookworm vaccination. Scientists have investigated incorporating outer membrane proteins in a leptospirosis vaccine, reporting successes in 2010 in strengthening immunities in test animals. In 2024, James Cook University reported that researchers were targeting proteins secreted by hookwork larvae to develop a vaccine. Clinical trials in Australia and Europe showed that the vaccine offered partial protection against hookworms.

Prevention and Outcomes

Most people contact soil daily. Interaction with soil varies depending on a person’s activities, exposure to the outdoors, and dietary habits. People can minimize the possibility of being infected by avoiding areas most likely to host parasites and pathogens. One should wash his or her hands, feet, or any bare skin that has been in contact with soil. Wearing gloves while gardening lessens hazards associated with handling soils. Wounds, cuts, abrasions, cracks, and other skin damage should be covered with bandages. Shoes prevent soilborne illnesses from being transmitted through the soles of the feet. People should avoid inhaling dust. Masks help block spores in areas where fungi thrive in soil.

Soil contaminant hazards can be minimized through purifying water supplies, cleaning unsanitary sites, and providing sanitary toilet facilities. Other preventive measures include washing soil from raw foods harvested from gardens or bought at markets. Cooking meats thoroughly to destroy parasites helps reduce risks associated with consuming livestock products that might have been infected while animals grazed on forage that grew on contaminated soil.

The transmission of diseases associated with soil can be prevented by not eating soil. Crops fertilized with raw waste or irrigated with wastewater should not be consumed. Agricultural laborers should avoid handling those contaminated soils. People should regularly deworm domesticated pets and not touch any fecal material.

Some schools, particularly in tropical regions or developing countries, sponsor programs to deworm students. Health care personnel provide children with medical treatments to purge and prevent further helminth infections. Educational presentations teach children and adults hygienic behavior and discourage contact with hazardous soils. Several charities and shoe manufacturers distribute free shoes in impoverished communities where residents are at risk of contracting soilborne diseases.

Bibliography

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