Humans can become infected with a variety of parasitic worms, known medically as helminths. Some of the most common worms that infect humans include roundworms, tapeworms, pinworms, whipworms, hookworms, and threadworms. These worms live inside the body and can cause a disease called helminthiasis. While not all worm infections cause symptoms, some can lead to abdominal pain, diarrhea, weakness, weight loss, respiratory problems, and impaired growth and nutrition in children. Understanding what allows these worms to infect humans and propagate is important for prevention and treatment.
How do humans get infected with worms?
Humans can get infected with parasitic worms through several routes:
Fecal-Oral Transmission
Many intestinal worms are transmitted when a person ingests microscopic eggs or larvae that have been passed in the feces of an infected person or animal. Sources include:
– Contaminated food or water
– Dirt on unwashed hands
– Soil containing feces used as fertilizer
Once ingested, the eggs or larvae hatch in the digestive tract, where they mature into adult worms that produce more eggs to continue the life cycle. This fecal-oral transmission occurs with roundworms, whipworms, hookworms and pinworms. Proper hygiene, including handwashing, sanitation, and clean drinking water can help prevent these infections.
Undercooked Meat
Eating undercooked or raw meat can transmit worm larvae to humans. This is most common with tapeworms found in beef, pork, and fish. Cooking meat to safe internal temperatures kills any parasites present. Freezing meat can also kill worms if maintained at specific temperatures and durations.
Bug Bites
Worm larvae can be transmitted through the bite of an infected insect. Mosquitos can transmit lymphatic filariasis and dog heartworm, while black flies spread river blindness. Avoiding bug bites in endemic regions can reduce risk of transmission.
Skin Contact
Some worm larvae can penetrate the skin directly when walking barefoot in soil contaminated with human or animal feces containing eggs. Hookworm most commonly infects humans this way. Wearing shoes and not using contaminated soil to make mudbricks or for flooring can prevent infection.
Mother-to-Child
A few worm infections can be transmitted directly from an infected mother to her baby during pregnancy. The larvae travel through the placenta before birth or in breastmilk after birth. This occurs mainly with roundworm and hookworm infections. De-worming pregnant women can help prevent infections in newborns.
Why are some groups at higher risk of worm infections?
While parasitic worms can infect people of all ages and backgrounds, certain populations are at higher risk. Understanding the factors that increase susceptibility can help target prevention efforts.
Children
Children are particularly vulnerable to worm infections due to their developing immune systems and greater exposure risks from play and hygiene behaviors. In some tropical areas, children can get reinfected multiple times per year. Chronic worm infections contribute to malnutrition, anemia, and impaired growth and development.
Impoverished Communities
Poverty is a major risk factor for worm infections globally. Contributing factors include:
– Lack of clean drinking water and sanitation
– Insufficient hygiene due to limited access to soap
– Close contact with soil due to lack of paved roads and floors
– Consumption of undercooked meat and fish
– Overcrowded conditions
Impoverished urban communities can have higher worm prevalence than rural areas due to dense populations and unsanitary living conditions.
Tropical & Sub-tropical Climates
Worm eggs and larvae thrive in warm, moist environments with temperatures over 60°F. As a result, global worm infections are concentrated in tropical and subtropical regions of Asia, Africa, Latin America, and the Southern US. Well-drained, arid areas have lower transmission.
Displacement & Disasters
Breakdowns in sanitation and hygiene due to emergencies such as natural disasters, conflict, famine, and displacement can facilitate outbreaks of worm infections. Refugee camps are often hotspots for parasites due to cramped conditions and inadequate facilities.
Immunocompromised Individuals
People with weakened immune systems due to HIV/AIDS, cancer treatment, organ transplant, or medical immunosuppressants may experience more severe symptoms from worm infections. The immune system plays an important role in controlling parasites, so compromise provides less defense.
How do worms affect human health?
The effects of a worm infection depend on the type of worm, number of worms, and location in the body. While mild cases may be asymptomatic, moderate and heavy infections can cause escalating impacts.
Intestinal Worms
Worms living in the human intestinal tract can cause symptoms including:
– Abdominal pain
– Diarrhea, gas, bloating
– Nausea, vomiting
– Weight loss
– Fatigue
– Itching around the anus (pinworms)
They deprive the body of nutrients and can cause anemia, malnutrition, intestinal blockages, and impaired growth and cognitive development in children.
Tissue & Organ Worms
Some worms migrate through tissue and organs. Symptoms may include:
– Fever, rash, swelling
– Cough, chest pain (lung worms)
– Abdominal lump (liver worms)
– Eye redness, itching, vision loss (eye worms)
– Lower leg swelling (lymphatic worms)
Severe cases with heavy worm loads can cause organ damage or abscesses. Eye worms can cause blindness if not treated.
Allergic Reactions
Allergies can develop as the immune system reacts to proteins secreted by worms. Reactions like itching, rash, and edema occur most frequently with tissue worms but can happen with any infection. In extreme cases, anaphylaxis may occur.
Diagnosing worm infections
There are several approaches physicians use to diagnose parasitic worm infections:
Medical History
Doctors ask about symptoms, travel history, potential exposure sources, and risks like barefoot walking or eating raw meat. Recent immigration from endemic areas warrants screening.
Physical Exam
The physical exam looks for signs like abdominal tenderness, distension, swelling, rashes, or eye lesions. Growth and nutritional status are evaluated.
Blood Tests
A complete blood count can reveal anemia and eosinophilia (increased eosinophils, a type of white blood cell). Eosinophilia suggests a parasitic infection. Specific antibody blood tests help diagnose some worm infections.
Stool Ova & Parasite Test
Microscopic examination of stool samples detects worm eggs or larvae. Repeated sampling may be needed, as egg shedding can be intermittent.
Tissue Biopsy
For worms residing in organs, ultrasound or endoscopy can guide biopsy sampling to identify larvae. This is important for eye, liver and lung worms.
Molecular Diagnostics
Polymerase chain reaction (PCR) can detect worm DNA in stool, blood or tissue to diagnose an active infection. This method is more sensitive than microscopy.
Imaging Studies
Methods like X-ray, CT scan, MRI, and ultrasound visualize worms in tissues and the damage they cause. Ultrasound detects swollen lymph nodes with filariasis and cysts of cysticercosis in muscles and brain.
Treatment and Prevention
The foundation of treating worm infections is prescription anti-parasitic medication. Preventive measures are key for reducing risk and reinfection.
Medication
Several types of safe, effective oral and topical drugs kill worms. The choice depends on the specific worm. Common anti-parasitic drugs include:
– Albendazole
– Mebendazole
– Ivermectin
– Thiabendazole
– Praziquantel
Light infections may require a single dose. More severe cases need several weeks of treatment.
Sanitation and Hygiene
Improving sanitation infrastructure and access to clean water prevents fecal-oral worm transmission. Handwashing with soap and keeping fingernails short reduces infections.
Cook Meat Thoroughly
Cooking beef, pork, fish and game meats to safe internal temperatures (at least 145°F) kills any worm larvae and eggs. Freezing can also inactivate worms at specific time-temperature combinations.
Wear Protective Clothing and Shoes
Boots, gloves, and protective clothing provide a barrier against worm larvae when working with contaminated soil. This prevents penetration through the skin.
Mass Drug Administration
Periodic preventive deworming of children in endemic areas reduces worm burden in communities. Some countries provide routine anti-parasitic treatment through schools.
Improve Living Conditions
Reducing overcrowding, improving flooring and drainage, and eliminating contact with contaminated soil limits exposure opportunities. Housing improvements and resettlement programs aid prevention.
Health Education
Teaching people in endemic areas how worms spread and prevention methods empowers them to take protective actions. Children benefit from school-based education.
Global Impact and Control Efforts
Worm infections remain a major global health problem, especially in tropical developing regions. But increased preventive efforts are having an impact.
Scale of Worm Infections
According to the WHO, over 1.5 billion people are infected with soil-transmitted helminths worldwide, while over 186 million people have schistosomiasis. Over 868 million children require preventive chemotherapy for worms. Endemic areas include sub-Saharan Africa, Asia, Latin America, and the Caribbean.
| Continent | Number infected with soil-transmitted helminths | Number infected with schistosomiasis |
|---|---|---|
| Africa | 612 million | 192 million |
| Americas | 122 million | 1.3 million |
| Eastern Mediterranean | 151 million | 6.3 million |
| Europe | 2.7 million | No data |
| South-East Asia | 638 million | 49 million |
| Western Pacific | 778 million | 77 million |
Progress and Challenges
Increased global efforts to control intestinal worms and schistosomiasis have achieved progress:
– Over 5 billion treatments administered from 2006-2018
– 60%+ reductions in several countries
– Elimination as public health problem in 9 countries
However, much work remains. Only about a third of at-risk populations receive preventive chemotherapy. Improvements in water, sanitation and hygiene are essential long-term solutions but lag in rural and poor communities. Ongoing medication access, snail control, case identification, and public education must continue in endemic zones to reach control and elimination goals.
Conclusion
Parasitic worm infections impose a substantial health burden worldwide, predominately in tropical developing regions. Poverty, inadequate sanitation and hygiene, and certain behaviours that bring people in contact with contamination enable transmission of worm larvae and eggs. Children are especially vulnerable. While anti-parasitic medicines effectively treat active infections, broad preventive measures including health education, infrastructure improvements, hygiene promotion, and periodic deworming are required to provide lasting protection and reduce worm prevalence. Ongoing global efforts have made progress but require expanded commitment and investment to eliminate worms as a public health problem.