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. In May, 2001, a resolution of the World Health Assembly of the United Nations emphasized the need for increased medical intervention to minimize the occurrence of soil-transmitted diseases. The next year, the United Nations reiterated the goal of preventing soilborne worm infestations.
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). In
2010, more than one-half million children internationally suffered sicknesses,
particularly helminthiasis infections, contracted from soil. Although most people
survive these illnesses, sources indicate approximately 12,000 to 135,000 people
die yearly from soilborne helminth infections. Scientists estimate that the life
spans 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.
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 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
Albonico, Marco, Dirk Engels, and Lorenzo Savioli. “Monitoring Drug Efficacy and Early Detection of Drug Resistance in Human Soil-Transmitted Nematodes: A Pressing Public Health Agenda for Helminth Control.” International Journal of Parasitology 34, no. 11 (2004): 1205-1210. Reviews pharmaceuticals and techniques to assess which helminths resist chemotherapy, emphasizing the necessity for continued research and development.
Albonico, Marco, et al. Preventative Chemotherapy in Human Helminthiasis. Geneva: World Health Organization, 2006. Outlines treatment procedures and drug doses for people representing various age and risk factors. Glossary, charts, appendices.
Ambrosioni, Juan, Daniel Lew, and Jorge Garbino. “Nocardiosis: Updated Clinical Review and Experience at a Tertiary Center.” Infection 38, no. 2 (2010): 89-97. Presents authors’ experiences with this soilborne disease during a twenty-year period, noting how patients were infected and noting their symptoms, diagnoses, and treatments.
Bethony, Jeffrey, et al. “Soil-Transmitted Helminth Infections: Ascariasis, Trichuriasis, and Hookworm.” The Lancet 367 (May 6, 2006): 1521-1532. Summarizes information regarding the most prevalent soil-transmitted worm infections, including statistics and prevention and treatment methods.
Brooker, Simon, et al. “Global Epidemiology, Ecology, and Control of Soil-Transmitted Helminth Infections.” In Global Mapping of Infectious Diseases, edited by Simon I. Hay, Alastair Graham, and David J. Rogers. Amsterdam: Elsevier, 2006. Considers environmental factors that affect the geographical distribution of nematodes and the occurrence of soilborne diseases.
De Siqueira, Isadora Cristina, et al. “ Chromobacterium violaceum in Siblings, Brazil.” Emerging Infectious Diseases 11, no. 9 (2005): 1443-1445. Case study of an incident in which three brothers were exposed to soil contaminated with bacteria. Images show microscopic view of bacteria and a scan of organ damage.
“Legionnaires’ Disease Associated with Potting Soil—California, Oregon, and Washington, May-June, 2000.” Journal of the American Medical Association 284, no. 12 (September 27, 2000): 1510. Reports rare incidences in which persons acquired this usually waterborne disease by handling gardening materials.
Santamaría, Johanna, and Gary A. Toranzos. “Enteric Pathogens and Soil: A Short Review.” International Microbiology 6, no. 1 (2003): 5-9. Examines how disposing solid wastes contaminates soil with microorganisms, noting several soilborne disease outbreaks.
World Health Organization. “Soil-Transmitted Helminthiasis: Number of Children Treated 2007-2008: Update on the 2010 Global Target.” Weekly Epidemiological Record 85 (April 16, 2010): 141-148. Discusses efforts to prevent worm infections, providing statistics and a map showing locations of the most urgent cases.
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