Hookworm infection is a parasitic disease caused when tiny worm larvae in contaminated soil enter the body, usually through the skin. This most often happens when people walk barefoot in areas with poor sanitation. After entering the skin, the larvae travel through the bloodstream and lungs before reaching the small intestine. Infection can also occur by accidentally swallowing soil or food contaminated with the larvae. Inside the intestine, adult hookworms attach to the intestinal lining and feed on blood, which leads to many of the symptoms of the disease.
Hookworm infection is one of the most common neglected tropical diseases, affecting an estimated 500–700 million people worldwide. It is most widespread in sub-Saharan Africa, Southeast Asia, Latin America, and other warm regions where sanitation is limited. Children, farm workers, and people living in low-income rural areas are most affected. In some communities, more than half of the population may be infected. Because the worms feed on blood, long-term infection can cause iron-deficiency anemia, and in some populations, hookworms are responsible for up to one-third of all anemia cases.
Early symptoms often include an itchy red rash where the larvae enter the skin, sometimes called ground itch. As the larvae move through the body, they may cause coughing and wheezing. Once they reach the intestines, symptoms can include abdominal pain, diarrhea, fever, loss of appetite, and general tiredness. Chronic or heavy infections can lead to ongoing anemia and protein loss, causing pale skin, fatigue, reduced physical strength, and a fast heartbeat. In children, repeated infections may slow growth, affect learning, and hinder school performance. Very severe, untreated cases can lead to complications such as heart failure.
Treatment typically involves taking antiparasitic medications such as albendazole or mebendazole, along with iron supplements to treat anemia. During pregnancy, pyrantel pamoate may be recommended instead, because some other medications may pose risks to the developing fetus. Prevention focuses on wearing shoes, practicing good hygiene, preparing food safely, and improving community sanitation and access to clean water.
Historical Context
Hookworm infection has a long history, with some of the earliest evidence traced to ancient civilizations. Studies of Egyptian mummies have revealed intestinal parasites consistent with hookworms, indicating that the disease affected humans thousands of years ago. Ancient medical texts from regions including Greece, China, and the Middle East also describe symptoms resembling hookworm-related anemia, such as chronic fatigue, pallor, and weakness.
The infection became more widely recognized and scientifically studied in the late 19th and early 20th centuries, particularly following outbreaks in the southeastern United States. During this period, hookworm disease was strongly associated with poor sanitation, poverty, and agricultural labor in warm, humid environments.
The Rockefeller Sanitary Commission (1909–1914) played a major role in identifying and reducing hookworm prevalence in the American South through public health campaigns focused on hygiene, latrine construction, and community education. Similar efforts took place across parts of Africa, Asia, and Latin America under colonial health administrations, where hookworm disease posed significant public health challenges in tropical and subtropical regions. Despite these interventions, hookworm infection remains widespread today, especially in low-income areas with inadequate sanitation infrastructure.
Species of Hookworm
Human hookworm infections are primarily caused by two species: Ancylostoma duodenale and Necator americanus. Although both species have similar life cycles and cause comparable symptoms, they differ in geographic distribution, modes of transmission, and certain biological characteristics.
Ancylostoma duodenale, historically common in the Mediterranean region, northern Africa, India, and parts of East Asia, can infect humans through two main routes: skin penetration and oral ingestion. This species is known to cause more blood loss per worm than N. americanus, making infections potentially more severe when worm burdens are high. A. duodenale larvae can also enter a dormant stage in the muscles and reactivate later, which may prolong infection or contribute to recurrent disease.
Necator americanus is now the most widespread species globally, particularly prevalent in sub-Saharan Africa, Southeast Asia, the Pacific Islands, and the tropical regions of the Americas. Transmission occurs almost exclusively through skin penetration by larvae in contaminated soil. This species generally causes a slightly lower level of blood loss per worm, but because it infects large populations and is more environmentally resilient, it remains a major contributor to the global burden of hookworm-related anemia.
In addition to human-specific hookworms, several animal hookworms, including Ancylostoma caninum, common in dogs, and Ancylostoma braziliense, found in cats and dogs, can infect humans under certain conditions. These infections typically occur when larvae penetrate the skin but fail to complete their life cycle. Instead of reaching the intestine, the larvae migrate within the upper layers of the skin, causing an intensely itchy, winding rash known as cutaneous larva migrans. Although uncomfortable, these infections are usually self-limiting and far less severe than those caused by human hookworms, as the larvae do not develop into adult worms in the human intestine.
Life Cycle of Hookworm
The hookworm life cycle involves distinct stages including the development of eggs and larvae, followed by transmission and infection in the host.
Eggs and Larvae
Hookworm eggs are released into the environment through the feces of an infected person. For the eggs to survive and develop, they require warm, moist, shaded soil, conditions commonly found in tropical and subtropical climates. Within 24 to 48 hours, the eggs hatch into rhabditiform larvae, an early, noninfectious stage that feeds on organic material, such as bacteria and decaying matter, present in the soil.
Over the next 5 to 10 days, the rhabditiform larvae undergo two molts and transform into filariform larvae, the stage capable of infecting humans. Filariform larvae are slender, highly motile, and well-adapted for survival in the environment. Under ideal conditions, temperatures between 20°C and 30°C and adequate moisture, they can remain infectious for two to three weeks. During this time, the larvae typically move vertically within the soil, staying near the surface where human skin contact is most likely. Their ability to survive for extended periods enables ongoing transmission in areas lacking sanitation and consistent footwear use.
Environmental factors strongly influence the success of this stage. Heavy rainfall, poor drainage, and open defecation all increase the likelihood of soil contamination and larval survival. Conversely, extreme heat, dryness, or exposure to direct sunlight reduces larval viability, helping to limit transmission in arid climates.
Transmission and Infection Process
Human infection begins when a person comes into contact with soil containing filariform larvae. The most common route is through the skin, especially when individuals walk barefoot or work with bare hands in contaminated soil. The larvae penetrate the outer layers of the skin using specialized enzymes and mechanical movement. This often produces the characteristic itchy rash known as ground itch.
Once inside the skin, the larvae enter nearby blood vessels and are carried through the bloodstream to the lungs. In the lungs, they break through the capillaries and enter the air spaces, where they may cause transient respiratory symptoms such as coughing or wheezing. The larvae then migrate upward through the bronchial tree to the throat. When they are swallowed, they pass down the esophagus and into the small intestine.
Upon reaching the small intestine, the larvae mature into adult worms over several weeks. Adult hookworms attach to the intestinal wall using sharp mouthparts or cutting plates, depending on the species. Their feeding behavior causes continuous blood loss, which can accumulate over time and lead to iron-deficiency anemia and protein loss. Adult hookworms typically live for 1 to 3 years, though some may survive even longer under favorable conditions.
Female hookworms are highly prolific, producing thousands of eggs per day, a key factor in the persistence of the infection within affected communities. These eggs are passed out in feces, contaminating the environment and restarting the cycle. In areas without proper sanitation systems, open defecation or poorly managed waste disposal significantly increases the likelihood of soil contamination, allowing transmission to continue across generations.
Causes and Risk Factors
Hookworm infection occurs primarily through contact with contaminated environments and specific behaviors.
Modes of Transmission
The primary mode of hookworm transmission is direct skin penetration by infectious larvae found in contaminated soil. This typically occurs when individuals walk barefoot, sit, or work on soil where hookworm eggs have been deposited through human feces. After being excreted, the eggs hatch within 24 to 48 hours, and the larvae mature into the infectious filariform stage within several days under suitable conditions. These larvae are capable of actively penetrating intact skin, using a combination of enzymatic secretion and movement to enter the body.
Although less common, hookworm infection can also occur through oral ingestion, usually when contaminated soil is inadvertently swallowed with unwashed produce, dirty hands, or untreated drinking water. This route is more often associated with Ancylostoma duodenale, which can infect through both ingestion and skin penetration. However, ingestion accounts for a small minority of cases globally; direct contact with infected soil remains the dominant source of transmission.
Once inside the body, the larvae follow a characteristic migration pathway: entering the bloodstream, traveling to the lungs, ascending the respiratory tract, and ultimately being swallowed into the small intestine. It is in the intestine that they mature into adult worms, attach to the intestinal wall, and begin consuming blood, leading to many of the clinical symptoms associated with infection.
Environmental Factors
Environmental conditions play a crucial role in determining where hookworm transmission is possible. Because hookworm eggs and larvae require specific conditions to survive, the infection is largely confined to tropical and subtropical regions, where climates are consistently warm and humid.
Optimal survival and development occur in moist, shaded, and aerated soil, particularly in areas with regular rainfall and temperatures between 20°C and 30°C. These conditions allow larvae to hatch, feed, and mature into infectious forms. Soil type also matters: sandy or loamy soils that drain well tend to support higher larval survival than compact clay soils.
In contrast, dry, cold, or extremely hot environments naturally limit hookworm survival, reducing transmission risk. In many temperate countries, hookworm infection historically occurred during warmer seasons but declined significantly with improved sanitation and climate changes.
Poor sanitation infrastructure, particularly the absence of proper sewage disposal systems, greatly increases the likelihood of soil contamination. Open defecation, faulty latrines, and inadequate waste management create ideal conditions for eggs to enter the environment and complete their life cycle. Seasonal rainfall further supports larval development by maintaining soil moisture and enabling longer survival of the infectious stages.
At-Risk Populations
Hookworm disproportionately affects populations that live or work in environments where exposure to contaminated soil is common. Individuals who routinely walk barefoot remain the most vulnerable, particularly in rural farming communities where fields, footpaths, and household surroundings may be contaminated.
Agricultural workers, especially those engaged in barefoot farming practices, frequently encounter contaminated soil and are at increased risk of infection. Children are another high-risk group because they often play outdoors, have close contact with dirt, and may not consistently wear footwear. Repeated childhood infections contribute significantly to chronic anemia and growth delays in endemic regions.
Communities living in poverty face the highest burden, as limited access to sanitation facilities, footwear, and health education creates conditions that sustain transmission. Migrant laborers, refugees, and individuals living in overcrowded camps are also particularly vulnerable due to shared sanitation facilities, high population density, and frequent exposure to contaminated ground.
People whose occupations involve frequent contact with soil, such as construction workers, miners, gardeners, waste handlers, and sanitation workers, may also face elevated risk if protective measures such as gloves and footwear are not consistently used.
Symptoms and Health Effects
Hookworm infection presents a range of symptoms that vary by stage and severity. Initial signs are often mild, but prolonged infection can lead to significant health problems, including anemia and developmental issues.
Early Signs of Infection
The earliest symptoms appear at the site of larval skin penetration. As hookworm larvae enter the skin—most often on the feet, lower legs, or hands, they trigger localized irritation and inflammation. This results in itching, redness, and a raised rash commonly referred to as ground itch. The rash may persist for several days and can become intensely itchy, especially if multiple larvae penetrate the skin simultaneously.
Within 4 to 10 days after exposure, symptoms may shift as the larvae travel through the bloodstream to the lungs. During this pulmonary migration phase, individuals may develop coughing, wheezing, mild chest discomfort, and shortness of breath, symptoms resembling mild bronchitis or allergic airway reactions. Some people also experience a low-grade fever. These respiratory symptoms are generally transient but may be more pronounced in individuals with asthma, allergic conditions, or repeated exposures.
Once the larvae reach the small intestine, usually one to two weeks after infection, gastrointestinal symptoms begin to appear. These include abdominal pain, particularly in the upper abdomen, nausea, intermittent diarrhea, loss of appetite, and occasionally vomiting. During this stage, the worms begin feeding on blood, but early blood loss is typically small and may go unnoticed.
Chronic and Severe Manifestations
Long-term or repeated hookworm infections have more serious health effects, primarily due to continuous intestinal blood loss, which can reach several milliliters per day in moderate to heavy infections. Over weeks or months, this leads to iron-deficiency anemia, a condition in which the body lacks enough iron to produce healthy red blood cells. Symptoms of anemia include fatigue, weakness, pale skin, dizziness, headaches, cold intolerance, and reduced physical stamina. If anemia becomes severe, individuals may experience tachycardia (rapid heartbeat) and shortness of breath during routine activities.
In children, chronic hookworm infection can significantly impair growth, cognitive development, and academic performance. Persistent anemia and protein loss contribute to growth stunting, lowered concentration, delayed motor development, and poorer school outcomes. In communities where hookworm is endemic, chronic infections are major contributors to childhood malnutrition and cycles of poverty.
Protein loss, resulting from both blood loss and impaired nutrient absorption, can lead to protein-energy malnutrition, a condition marked by swelling (edema), muscle wasting, and compromised immune function. Adults with heavy infections may experience reduced work capacity, impacting agricultural productivity and economic stability.
Complications
Although most complications arise gradually, certain severe outcomes can occur under specific circumstances. Poor hygiene at the site of larval penetration can lead to secondary bacterial infections, causing additional skin inflammation or cellulitis.
In rare cases of extremely heavy worm load, often involving Ancylostoma duodenale, which causes greater blood loss per worm, individuals may develop profound anemia, severe fatigue, or signs of heart strain. Very high worm burdens can occasionally cause intestinal obstruction, though this remains uncommon.
During the pulmonary phase, heavily infected individuals may experience more pronounced respiratory distress, especially if pre-existing respiratory conditions are present.
Pregnant women represent a particularly vulnerable group. Untreated hookworm infection during pregnancy increases the risk of maternal anemia, which in turn raises the likelihood of preterm delivery, low birth weight, postpartum complications, and reduced milk production. Chronic maternal anemia also has long-term developmental consequences for infants, including impaired physical growth and reduced cognitive potential.
Diagnosis of Hookworm Infection
Healthcare providers evaluate symptoms such as abdominal pain, diarrhea, and iron-deficiency anemia. History of walking barefoot in endemic areas or exposure to contaminated soil is relevant.
Physical examination may reveal pallor, indicating anemia, and occasionally rash or itching at larval penetration sites. Severity of symptoms depends on worm load and nutritional status.
Laboratory Testing Methods
The primary diagnostic method for hookworm infection is the microscopic examination of stool samples. A fresh stool specimen is analyzed for the presence of characteristic hookworm eggs, which are oval-shaped with thin shells. Because egg output can vary day-to-day, multiple stool samples collected on separate days may be required for accurate detection. In many laboratories, concentration techniques, such as formalin-ethyl acetate sedimentation or floatation methods, are used to increase diagnostic sensitivity, particularly in cases of light infection where egg counts may be low.
A complete blood count (CBC) serves as an important supportive test. Hookworm infections frequently produce eosinophilia, an elevated level of eosinophils, a type of white blood cell associated with parasitic infections and allergic responses. The CBC also helps identify iron-deficiency anemia, characterized by low hemoglobin levels, reduced mean corpuscular volume (MCV), and other indicators of depleted iron stores. Measuring serum ferritin may further clarify the severity of iron deficiency.
While less commonly used in routine clinical practice, serological tests can detect antibodies against hookworm antigens. These tests may be useful in situations where stool examination is inconclusive or when infections are very light. However, antibody tests cannot easily distinguish between past and current infections, limiting their diagnostic usefulness.
In research settings and some specialized laboratories, molecular diagnostic methods such as polymerase chain reaction (PCR) provide highly specific and sensitive detection by identifying hookworm DNA directly in stool samples. PCR-based testing can differentiate between Necator americanus and Ancylostoma duodenale.
Treatment Options
Treatment focuses on eliminating the parasite and addressing any complications caused by the infection.
Anthelmintic Medications
Anthelmintic therapy is the cornerstone of hookworm management, targeting the adult worms residing in the small intestine. The most widely used medications are albendazole and mebendazole, both belonging to the benzimidazole class. These drugs work by inhibiting microtubule polymerization within the parasite’s intestinal cells, disrupting glucose uptake and essential cellular processes. As a result, the worms become immobilized and eventually die due to energy depletion.
Albendazole is frequently considered the first-line treatment because of its high cure rate and practical single-dose regimen. A standard 400 mg oral dose is often sufficient for mild to moderate infections, making it ideal for community-based deworming programs. Mebendazole, typically administered as 100 mg twice daily for three days or 500 mg as a single dose, is equally effective but sometimes requires longer treatment to achieve optimal results. Both medications are safe for most populations, though mild gastrointestinal discomfort, transient headaches, or nausea may occur as side effects.
In cases where the infection is heavy or longstanding, the destruction of adult worms may not immediately resolve all symptoms, as the body gradually recovers from chronic blood loss and nutrient depletion. Because hookworms feed directly on the host’s intestinal blood supply, many patients, especially children and pregnant women, develop iron-deficiency anemia. For this reason, healthcare providers often pair anthelmintic drugs with iron supplementation to restore hemoglobin levels and replenish iron stores. Ferrous sulfate tablets are commonly used, though liquid formulations may be preferred for children.
Supportive Therapies
Iron supplementation remains central to supportive care, as continuous intestinal blood loss leads to reduced oxygen-carrying capacity and systemic fatigue. Depending on the severity of anemia, treatment may range from oral supplements over several weeks to, in extreme cases, blood transfusions, particularly when hemoglobin levels are dangerously low. Supplementation should be paired with vitamin C when possible to enhance iron absorption.
Chronic hookworm infection not only causes iron deficiency but may compromise protein absorption, leading to weight loss, muscle wasting, or growth faltering in children. A diet rich in protein, such as fish, beans, eggs, and fortified foods, alongside multivitamin supplementation supports recovery and helps rebuild the nutritional reserves depleted during infection. For children in areas with widespread malnutrition, nutritional programs or fortified food distributions may be necessary to ensure full recovery.
Because larvae initially penetrate the skin, secondary bacterial infections can occur at entry sites, especially when hygiene is poor. Clinicians may prescribe topical or systemic antibiotics if signs of infection such as redness, swelling, or pus are present. Persistent gastrointestinal symptoms after treatment may indicate a high worm burden before therapy or reinfection due to ongoing exposure to contaminated soil. In such cases, a follow-up evaluation is essential, and repeat deworming may be considered.
Finally, post-treatment assessment is recommended to confirm parasite clearance. A follow-up stool examination performed two to four weeks after therapy helps determine whether the medication successfully eradicated the adult worms.
Prevention and Control
Effective prevention and control of hookworm focus on reducing exposure to contaminated soil and improving health practices.
Personal Hygiene Measures
Preventing hookworm infection begins with consistent personal hygiene habits that limit exposure to contaminated soil and interrupt the parasite’s transmission cycle. Regular handwashing with soap and clean water, especially after gardening, farming, or any activity involving soil contact, is critical. This practice helps remove possible infective larvae and prevents accidental ingestion of contaminated particles. Handwashing before eating or preparing food is equally important to reduce the risk of oral transmission, even though hookworm primarily enters through the skin.
One of the most effective protective behaviors is wearing shoes outdoors, particularly in communities where open defecation or inadequate sanitation increases the likelihood of soil contamination. Hookworm larvae easily penetrate the skin of the feet, making barefoot walking a major risk factor in endemic regions. Encouraging the use of sturdy, closed footwear helps create a physical barrier that larvae cannot cross. Likewise, keeping fingernails trimmed minimizes accumulation of dirt under the nails and reduces the chance of ingesting contaminated soil during eating or hand-to-mouth activities.
Proper and safe disposal of human feces is essential because individuals with active hookworm infection shed thousands of eggs daily in their stool. When feces are left exposed in the environment, eggs hatch and release larvae that migrate into soil. Encouraging people who suspect infection to seek early medical diagnosis and treatment helps reduce community-level egg contamination.
Sanitation Improvements
At the heart of hookworm prevention lies robust sanitation infrastructure, as the parasite’s lifecycle depends on soil contact with human feces. Clean, functioning latrines prevent eggs from entering the environment, breaking the crucial stage in which larvae develop into their infective form. Constructing accessible latrines, whether simple pit latrines, ventilated improved pit (VIP) latrines, or flush toilets, provides communities with safe alternatives to open defecation. Ensuring that these facilities are well maintained, private, and culturally acceptable increases their use and long-term sustainability.
Effective waste management systems further reduce risks. Proper containment, treatment, or disposal of human waste (such as through septic tanks, composting toilets, or community-managed sanitation systems) prevents eggs from reaching the soil. In rural agricultural communities, educating residents on the dangers of using untreated human waste as fertilizer is equally important, as this practice directly contaminates crops and soil.
Access to clean water and improved drainage systems also contributes indirectly but significantly to hookworm control. Reliable water supply encourages regular hygiene practices, while proper drainage prevents the creation of damp, shaded soil, ideal conditions for larval survival. By reducing moist areas where larvae thrive, well-designed drainage limits the opportunity for infective larvae to persist in the environment.
Zoonotic Transmission
Hookworm species primarily infect animals such as dogs and cats, but some species can also infect humans. These infections occur when larvae in contaminated soil penetrate the skin.
The most common zoonotic hookworms include Ancylostoma braziliense and Ancylostoma caninum. These larvae do not develop fully in humans but can cause cutaneous larva migrans, a skin condition marked by itchy, winding lesions.
Transmission routes include walking barefoot on contaminated soil, direct contact with animal feces, and handling infected animals. Poor sanitation and warm, humid environments increase the risk of exposure.
| Risk Factor | Description |
| Contact with pets | Handling or close contact with infected animals |
| Environmental exposure | Walking barefoot on contaminated soil |
| Poor hygiene practices | Inadequate handwashing after soil contact |
Prevention relies on controlling hookworm infections in animals. Regular deworming of pets, proper disposal of animal feces, and wearing shoes in endemic areas reduce human exposure.
Zoonotic hookworm infections rarely lead to systemic disease in humans but can cause significant discomfort and secondary infections if left untreated. Medical consultation is recommended for suspicious skin lesions.
Hookworm in Animals
Hookworms are parasitic nematodes commonly found in the intestines of various animals, including dogs, cats, and livestock. These parasites attach to the intestinal walls and feed on the host’s blood, which can lead to anemia.
In dogs and cats, Ancylostoma caninum and Ancylostoma tubaeforme are common species causing infection. Symptoms in pets often include weight loss, diarrhea, and lethargy. Puppies and kittens are especially vulnerable to severe infections.
Livestock such as cattle, sheep, and goats may also harbor hookworms, primarily species like Bunostomum phlebotomum. These infections can reduce growth rates and overall productivity in affected animals.
Transmission occurs mainly through skin penetration by infective larvae or ingestion of contaminated soil or feces. Prevention includes maintaining clean living environments and regular deworming protocols.
| Animal | Common Hookworm Species | Primary Symptoms | Transmission |
| Dogs | Ancylostoma caninum | Anemia, diarrhea, weight loss | Skin penetration, ingestion |
| Cats | Ancylostoma tubaeforme | Weakness, poor growth | Skin penetration, ingestion |
| Livestock | Bunostomum phlebotomum | Reduced growth, anemia | Ingestion, soil contact |
Effective veterinary treatment typically involves anthelmintic drugs to eliminate the worms. Monitoring animal health is crucial to prevent severe infections and economic losses in farming.