- Ascaris lumbricoides is the largest parasitic roundworm that infects humans in the world. It is also the commonest worm infection in humans. Ascaris suum infects pigs, but it infects humans less frequently. A. lumbricoides may also infect pigs.
- Ascariasis frequently occurs in areas of poverty, with poor nutrition and sanitation. However, pig farmers or those who handle raw pig manure may acquire ascariasis in areas where it is otherwise uncommon.
- Mode of transmission is fecal-oral, such as by swallowing eggs in food or water contaminated by feces.
- It occurs in warm, humid parts of the world, such as the tropics, as well as warm, wet periods in temperate areas.
- Up to 1.2 billion people globally have ascariasis.
- Worldwide, severe ascariasis causes 60,000 deaths per year, especially in children.
What Is Ascariasis?
The Ascaris roundworm (roundworms are also known as nematode or helminth worms) causes the disease ascariasis. Ascariasis is mainly an intestinal infection of the small bowel. The adult worms can reach about 12 inches in length and reach such high numbers that in severe cases, they can cause blockage of the biliary ducts or intestine. This most often occurs in children and may be life threatening.
What Causes Ascariasis? How Does Ascariasis Spread?
Infection with the roundworm, Ascaris lumbricoides, causes human ascariasis. This species of Ascaris is the main cause of human ascariasis, but Ascaris suum (from pigs) can occasionally infect humans, as well. People acquire this parasite by swallowing Ascaris eggs in soil, food, or water contaminated with human feces. The eggs remain infectious in soil for years. Waste disposal services, clean water, and basic sanitation are key factors in preventing this disease. Spread of ascariasis occurs wherever there is poverty, malnutrition, and contamination of the environment with human waste. Other sources of spread are pig farms and raw pig manure used as fertilizer.
Adult female (larger) and male (smaller) Ascaris worms. The adult female may grow to over 12 inches long. SOURCE: CDC.
The life cycle of ascariasis is as follows. People swallow eggs in contaminated food or water. The eggs hatch into tiny larvae in the intestine. The larvae burrow into the intestine and travel in the blood to the lungs. After maturing in about 10-14 days, they burrow out into the airways, where people cough up the larvae and then swallow them. Once the larvae reach the small intestine, they grow into adults. Adult Ascaris worms live in the small intestine of humans, where they mate and lay eggs that pass in stool. The eggs pass into the environment, and the cycle continues. Eggs become infective after about three weeks or more in soil, depending on warmth and humidity, and can stay infective for years. One adult female can lay up to 200,000 eggs per day. It takes two to three months from the time people swallow the eggs to the time she starts laying eggs. Adult worms may live up to two years and grow as long as 12 inches.
Life cycle of Ascaris lumbricoides; SOURCE: CDC
What Are Risk Factors for Ascariasis?
Risk factors for ascariasis include severe poverty, malnutrition, and most of all, lack of basic sanitation and clean water (for hygiene, drinking, and food preparation). Pig farmers and people who handle raw pig manure or use it as fertilizer are at risk for the pig species of ascariasis. Pigs often have no symptoms.
What Is the Incubation Period for Ascariasis?
The incubation period (time from infection to symptoms) for ascariasis can vary. The first symptoms may be fever, cough, or shortness of breath as the larvae migrate through the lungs in the first weeks of infection. This may become a continuous occurrence as people continue to ingest eggs over time. Since the adults take up to three months to mature and may live one to two years, it may take several months before symptoms occur. Symptoms may be subtle, such as a cough or mild abdominal discomfort, or dramatic, such as coughing up or passing a live worm in stool. Later infection or higher volume of parasites, especially in children, may cause blockage of the intestine or digestive organs by a bolus (tangled mass) of worms. This may happen after weeks to months.
What Are Ascariasis Symptoms and Signs?
Symptoms and signs of ascariasis range from mild to severe. These include the following:
A CDC laboratory technician holds a mass of Ascaris lumbricoides worms passed by a child in Kenya, Africa. SOURCE: CDC, Henry Bishop.
How Do Medical Professionals Diagnose Ascariasis?
Ascariasis is readily diagnosed by the visual identification of a larval or adult worm that someone has vomited, coughed up, or found in his/her stool. It is most often diagnosed by finding the characteristic eggs in stool. The stool is diluted with saline solution and examined under a microscope. This test is called examination for ova and parasites, or "O & P." Ascaris lumbricoides eggs are quite large and very typical in appearance. Ascaris can also affect the lungs, intestines, and the liver and biliary tract. Medical professionals may use abdominal ultrasound or computed tomography (CT) scanning to diagnose a mass of Ascaris worms in the hepatobiliary tract.
A fertilized Ascaris egg in an unstained stool specimen at 400x magnification; SOURCE: CDC, Dr. Mae Melvin.
What Is the Treatment for Ascariasis?
The treatment for ascariasis is anti-helminthic (roundworm-killing) drugs, taken by mouth. These include albendazole, ivermectin, and mebendazole. Albendazole and ivermectin are available in the U.S. for human treatment as ready-to-prescribe pills, but a compounding pharmacy must specially prepare mebendazole.
All of these drugs may be given in pregnancy if the benefit outweighs the risk, as a pregnancy category C drug (meaning that there is no well-controlled data on human pregnancies, or that there is animal evidence of effects on the unborn fetus but not in humans). There is no data on whether albendazole or mebendazole is found in human milk, but ivermectin is present in low amounts. Use these drugs with caution and when benefit outweighs risk in breastfeeding mothers. Medical professionals will calculate carefully the doses for very young or small children; expert consultation with public health departments or the Centers for Disease Control and Prevention may be helpful.
There is no effective over-the-counter treatment or home remedy for ascariasis.
What Is the Prognosis for Ascariasis?
The prognosis for ascariasis once the parasite is eliminated is very good as long as reinfection can be prevented and transmission risks are removed.
Undiagnosed or untreated infections can result in multiple complications. Complications such as intestinal blockage may require surgery. Severe infection of the lungs may result in respiratory failure. Mild infection of the lungs may result in chronic cough. Chronic infections in growing children may lead to growth retardation and malnutrition.
Is It Possible to Prevent Ascariasis?
Ascariasis is preventable through education about sanitation and hygiene, and ensuring that communities have access to water treatment, personal and environmental hygiene, safe disposal of human waste, adequate nutrition, and health care. Do not use human waste (night soil) to fertilize food crops.
Those who raise pigs, handle raw manure, or use pig manure to fertilize food crops must be aware of the risk of acquiring pig ascariasis. It is almost impossible to remove the Ascaris eggs from an area where pigs have lived, because they are resistant to freezing and heat and may survive for 10 years. Thus, preventing ascariasis exposure from pigs requires awareness and close attention to personal hygiene when working with pigs or their manure.
- Wash hands with soap and clean water before handling food or touching the mouth.
- Wash fruits and vegetables grown with manure with clean water before eating. Peeling or cooking them kills germs and parasite eggs.
- Wash hands with soap and clean water after touching pigs, their environment, or pig manure.
- Supervise children closely around pigs and teach them the above precautions.
- Consult with a veterinarian about managing and preventing ascariasis in your pigs.
Miller, L.A., et al. "Ascariasis in Humans and Pigs on Small-Scale Farms, Maine, USA, 2010-2013." Emerg
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Switzerland. World Health Organization. "Water sanitation hygiene -- Water related diseases." Accessed Dec. 15, 2018. <https://www.who.int/water_sanitation_health/diseases-risks/diseases/ascariasis/en/>.
United States. Centers for Disease Control and Prevention. "Ascariasis." Feb. 15, 2018. <https://www.cdc.gov/parasites/ascariasis/>.
United States. Centers for Disease Control and Prevention. "DPDx -- Laboratory Identification of Parasites of Public Health Concern, Ascariasis." Jan. 3, 2018. <https://www.cdc.gov/dpdx/ascariasis/index.html>.