Ascariasis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2]

Ascariasis is a globally occurring helminthic infection of humans.^[1] It is the most common human helminth infection.^[2] The transmission of infection is usually from hand to mouth, and humans are the only known host.^[2] Ascariasis is more common in tropical areas of the world and predominantly affects the pediatric age group.^[3]

Ascariasis has been around for several years and the scientific study of Ascaris lumbricoides was promoted by Edward Tyson.^[4]

The transmission of infection is usually from hand to mouth, and humans are the only known host. Following ingestion of infective eggs, larvae hatch and invade the intestinal mucosa. The larvae are carried via the portal, then systemic circulation to the lungs. The larvae mature further in the lungs, penetrate the alveolar walls, and ascend the bronchial tree to the throat. The larvae are then swallowed. Upon reaching the small intestine, they develop into adult worms. The adult worms can live for 1 to 2 years.

Ascariasis is a soil helminth infection caused by the nematode Ascaris lumbricoides.^[2]

Ascariasis can mimic other worm infections, and also gastrointestinal pathologies like peptic ulcer disease, intussusception in children, bile duct stone, etc.^[5][6]

Ascariasis affects at least 1 billion people worldwide and about 4 million people in the United States.^[3] It is more common in the pediatric age group (ages 2-10 years).^[3] Ascariasis is three times more common in African-Americans compared to Caucasians.^[3]

The risk factors for ascariasis are often associated with poor sanitary conditions and environmental fecal contamination.^[1]

Ascariasis is often asymptomatic and more than 80% of infected individuals experience minimal or no symptoms of the disease.^[7] Complications may arise when adult worms move to certain organs such as the bile duct, pancreas, or appendix.^[7] A high worm burden can also result in complications such as intestinal obstruction.^[1] The prognosis is good as most cases of ascariasis are asymptomatic, but mortality can sometimes be as high as 60,000 per year.^[7] Mortality from ascariasis is usually as a result of complications from the infection, approximately 4.6% of patients hospitalized with complications of ascariasis die from the infection.^[8]

Ascariasis is often asymptomatic. It can sometimes present with mild pulmonary and abdominal symptoms such as cough, dyspepsia, and nausea. However, severe cases of ascariasis occasionally occur especially following mechanical obstruction of a viscus.^[7]

The physical examination findings in ascariasis vary and it is usually dependent on the worm burden and the involved organ.^[1] Abdominal tenderness can occur secondary to intestinal obstruction, appendicitis, biliary colic, acute cholangitis, acute cholecystitis, hepatic abscess, etc.^[9]

Ascariasis is frequently diagnosed in the laboratory via microscopic identification of eggs in the feces.^[7]

A chest x-ray can reveal varying sizes of oval or round infiltrates (Loffler’s syndrome). These infiltrates usually resolve spontaneously.^[3] Plain abdominal radiographs and contrast studies can reveal worm masses in bowel loops.^[3][7]

CT scan with contrast can reveal foreign bodies such as worms in the gastrointestinal tract.^[3][7]

Ultrasonography can reveal worms in the biliary tree, pancreatic duct and bowel loops.^[3][7]

Imaging studies such as endoscopic retrograde cholangiopancreatography (ERCP) can identify worms in the pancreaticobiliary tract.^[3]

All ascariasis infection (symptomatic and asymptomatic) should be treated with antimicrobial therapy.^[7] Due to the high rate of reinfection, it is sometimes necessary to repeat antimicrobial therapy.^[1] Antimicrobial therapy with albendazole is usually the treatment of choice for ascariasis, although other antihelminthic medications can effectively eradicate the parasite.^[2]

Ascariasis is usually managed conservatively with medical therapy but surgery may be indicated when medical management fails or complications arise.^[7] Some of the indications for the surgical management of ascariasis include complete intestinal obstruction with inadequate decompression, complications such as volvulus, intussusception or intestinal perforation, acute appendicitis, worms trapped in ducts, etc.^[7]

The prevention of ascariasis is best achieved through improvements in personal hygiene and environmental sanitation.^[10]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2]

Ascariasis has been around for several years and the scientific study of Ascaris lumbricoides was promoted by Edward Tyson.^[1]

Ascariasis is an helminthic infection of man that has been around for so many years. Edward Tyson promoted the scientific study of Ascaris lumbricoides about three centuries ago.^[1]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2]

Ascariasis is the most common human helminth infection.^[1] The transmission of infection is usually from hand to mouth, and humans are the only known host.^[1]

Ascariasis is a soil-transmitted helminth infection with the round worm(nematode) called Ascaris lumbricoides, and humans are the only known host.^[1] The pathogenesis of ascariasis involves the following processes:^[1][2][3]

• The eggs are primarily transmitted from hand to mouth, but they may also be ingested in raw fruits and vegetables grown in soil contaminated with the eggs of ascaris.
• The eggs may also be ingested in water contaminated with the ova of ascaris or via inhalation of ova in regions with high worm burden. Ascaris infection occurs about 9-12 days after egg ingestion.

• Following ingestion of the eggs, the fertilized ova hatch in the small intestine and the larvae penetrates the intestinal mucosa.
• The larvae then proceeds to the lungs via the venous circulation and migrates through the alveoli and the bronchial tree, resulting in pulmonary ascariasis.
• The larvae ascend the bronchial tree to the throat, and are subsequently swallowed and returned to the intestines where maturation into adult worms occur.

• The adult worms have a life span of 10-24 months within the human host. The adult male worms are 10-30cm long, while the adult female worms are larger and they measure up to 40cm long.
• Intestinal obstruction associated with intestinal perforation, volvulus and intussusception can occur in patients with large worm burdens. Worms can also migrate into the biliary tree resulting in biliary colic and pancreatitis.
• Migration of worms to the appendix can result in acute appendicitis.
• The fecund female worm produces a very high output of eggs (about 200,000 eggs/day), and eggs are passed out of the intestine with the feces where they can survive for years in warm, moist, shaded soil.
• At temperatures of 5-10⁰C, the eggs of ascaris can remain viable for as long as two years.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]}}; Associate Editor-In-Chief: Imtiaz Ahmed Wani

Ascaris lumbricoides is the giant roundworm of humans, growing to a length of up to 35 cm (13.779527545 in).^[1] It is one of several species of Ascaris. An ascarid nematode of the phylum Nematoda, it is the largest and most common parasitic worm in humans. This organism is responsible for the disease ascariasis, a type of helminthiasis and one of the group of neglected tropical diseases. An estimated one-sixth of the human population is infected by A. lumbricoides or another roundworm.^[2] Ascariasis is prevalent worldwide, especially in tropical and subtropical countries.

A. lumbricoides, a roundworm, infects humans when an ingested fertilised egg becomes a larval worm that penetrates the wall of the duodenum and enters the blood stream. From there, it is carried to the liver and heart, and enters pulmonary circulation to break free in the alveoli, where it grows and molts. In three weeks, the larva passes from the respiratory system to be coughed up, swallowed, and thus returned to the small intestine, where it matures to an adult male or female worm. Fertilization can now occur and the female produces as many as 200,000 eggs per day for a year. These fertilized eggs become infectious after two weeks in soil; they can persist in soil for 10 years or more.^[3]

The eggs have a lipid layer which makes them resistant to the effects of acids and alkalis, as well as other chemicals. This resilience helps to explain why this nematode is such a ubiquitous parasite.^[4]

A. lumbricoides is characterized by its great size. The male’s posterior end is curved ventrally and has a bluntly pointed tail. Females are wide and long. The vulva is located in the anterior end and accounts for about one-third of its body length. Uteri may contain up to 27 million eggs at a time, with 200,000 being laid per day. Fertilized eggs are oval to round in shape and are long and wide with a thick outer shell. Unfertilized eggs measure long and wide.^[5]

• 
  Magnified 128X, this photomicrograph revealed some of the ultrastructural features displayed by a fertile Ascaris lumbricoides egg. A. lumbricoides is the largest nematode (roundworm) parasitizing the human intestine. From Public Health Image Library (PHIL). ^[6]
• 
  Magnified 125X, this photomicrograph revealed the presence of a fertile Ascaris sp. egg that was found in an unstained formalin-preserved stool sample. See PHIL 411 for an example of an unfertilized Ascaris lumbricoides egg. From Public Health Image Library (PHIL). ^[6]
• 
  Depicted in this 1960 photograph were two Ascaris lumbricoides nematods, i.e., roundworms. The larger of the two was the female of the species, while the normally smaller male was on the right. Adult female worms can grow over 12 inches in length. From Public Health Image Library (PHIL). ^[6]
• 
  This micrograph reveals both fertilized (A) and unfertilized (B) Ascaris eggs, and a Trichuris egg (C); Mag. 125X. From Public Health Image Library (PHIL). ^[6]
• 
  This diagram depicts the various stages in the life cycle of the intestinal roundworm nematode Ascaris lumbricoides. From Public Health Image Library (PHIL). ^[6]
• 
  These are 3 fertilized A. lumbricoides eggs with the one on the right being decorticated, for its outer layer is absent. From Public Health Image Library (PHIL). ^[6]
• 
  This micrograph depicts an embryonated Ascaris lumbricoides egg with no outer mammillated layer, i.e., “decorticated”. From Public Health Image Library (PHIL). ^[6]
• 
  This photomicrograph depicts a fertilized egg of the parasite Ascaris lumbricoides. From Public Health Image Library (PHIL). ^[6]
• 
  Magnified 128X, this photomicrograph revealed some of the ultrastructural features displayed by an infertile, decorticated Ascaris lumbricoides egg. From Public Health Image Library (PHIL). ^[6]
• 
  Magnified 128X, this photomicrograph revealed some of the ultrastructural features displayed by an infertile, Ascaris lumbricoides egg. From Public Health Image Library (PHIL). ^[6]
• 
  Magnified 128X, this photomicrograph revealed some of the ultrastructural features displayed by a fertilized, decorticated Ascaris lumbricoides egg. A. lumbricoides is the largest nematode (roundworm) parasitizing the human intestine. From Public Health Image Library (PHIL). ^[6]
• 
  Magnified 128X, this photomicrograph revealed some of the ultrastructural features displayed by a fertilized, decorticated Ascaris lumbricoides egg. A. lumbricoides is the largest nematode (roundworm) parasitizing the human intestine. From Public Health Image Library (PHIL). ^[6]
• 
  Under a magnification of 125x, this photomicrograph of an unstained mounted formalin-preserved fecal sample revealed the presence of a number of parasitic worm eggs, which included the eggs of a trematode, Fasciolopsis buski, an Ascaris sp. nematode. From Public Health Image Library (PHIL). ^[6]
• 
  Infertile egg of Ascaris lumbricoides. From Public Health Image Library (PHIL). ^[6]
• 
  This photomicrograph revealed some of the ultrastructural features displayed by an infertile Ascaris lumbricoides egg. A. lumbricoides is the largest nematode (roundworm) parasitizing the human intestine. From Public Health Image Library (PHIL). ^[6]
• 
  This micrograph reveals a fertilized egg of the round worm Ascaris lumbricoides; Mag. 400X. From Public Health Image Library (PHIL). ^[6]

More than 2 billion people are affected by this infection.^[3] The United States has a reported prevalence of 0.8% of the total population as of 1987. A. lumbricoides eggs are extremely resistant to strong chemicals, desiccation, and low temperatures. The eggs can remain viable in the soil for several months or even years.^[5]

Eggs of A. lumbricoides have been identified in archeological coprolites in the Americas, Europe, Africa, the Middle East, and New Zealand, the oldest ones being more than 24,000 years old.^[7]

Infections with these parasites are more common where sanitation is poor,^[8] and raw human feces are used as fertilizer.

Often, no symptoms are seen with an A. lumbricoides infection. However, in the case of a particularly bad infection, symptoms may include bloody sputum, cough, fever, abdominal discomfort, intestinal ulcer, passing worms, etc.^[9][10] Ascariasis is also the most common cause of Löffler’s syndrome worldwide. Accompanying symptoms include pulmonary infiltration, eosinophilia, and radiographic opacities ^[11]

Preventing any fecal-borne disease requires educated hygienic habits/culture and effective fecal treatment systems. This is particularly important with A. lumbricoides because its eggs are one of the most difficult pathogens to kill (second only to prions), and the eggs commonly survive 1–3 years. A. lumbricoides lives in the intestine where it lays eggs. Infection occurs when the eggs, too small to be seen by the unaided eye, are eaten. The eggs may get onto vegetables when improperly processed human feces of infected people are used as fertilizer for food crops. Infection may occur when food is handled without removing or killing the eggs on the hands, clothes, hair, raw vegetables/fruit, or cooked food that is (re)infected by handlers, containers, etc. Bleach does not readily kill A. lumbricoides eggs, but it will remove their sticky film, to allow the eggs to be rinsed away. A. lumbricoides eggs can be reduced by hot composting methods, but to completely kill them may require rubbing alcohol, iodine, specialized chemicals, cooking heat, or “unusually” hot composting (for example, over 50 °C (122 °F) for 24 hours^[12])

Infections happen when a human swallows water or food contaminated with unhatched eggs, which hatch into juveniles in the duodenum. They then penetrate the mucosa and submucosa and enter venules or lymphatics. Next, they pass through the right heart and into pulmonary circulation. They then break out of the capillaries and enter the air spaces. Acute tissue reaction occurs when several worms get lost during this migration and accumulate in other organs of the body. The juveniles migrate from the lung up the respiratory tract to the pharynx where they are swallowed. They begin producing eggs within 60–65 days of being swallowed. These are produced within the small intestine, where the juveniles mature. It might seem odd that the worms end up in the same place where they began. One hypothesis to account for this behavior is that the migration mimics an intermediate host, which would be required for juveniles of an ancestral form to develop to the third stage. Another possibility is that tissue migration enables faster growth and larger size, which increases reproductive capacity.^[13]

Most diagnoses are made by identifying the appearance of the worm or eggs in feces. Due to the large quantity of eggs laid, physicians can diagnose using only one or two fecal smears.

Infections can be treated with drugs called ascaricides. The treatment of choice is mebendazole. The drug functions by binding to tubulin in the worms’ intestinal cells and body-wall muscles. Nitazoxanide and ivermectin can also be used.^[5]

• Ascaris lumbricoides Video – DAVE Project
• Ascaris lumbricoides Poll – Research
• Ascaris lumbricoides image library

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2] Furqan M M. M.B.B.S[3]

Ascariasis can mimic other worm infections, and also gastrointestinal pathologies like peptic ulcer disease, intussusception in children, bile duct stone, etc.^[1][2]

• Differential diagnosis of intestinal ascariasis

1. Peptic ulcer disease^[1]
2. Intestinal obstruction from Ascaris lumbricoides can mimic intussusception^[3]

• Differential diagnosis of biliary ascariasis

1. Gallbladder cancer^[4]
2. Retained bile duct stone^[2]

• Other worm infections can sometimes have clinical presentations similar to that of Ascaris lumbricoides

The table below summarizes the findings that differentiate from other nematode infections:

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2]

Ascariasis is a globally occurring helminthic infection of humans.^[1] It is more common in tropical areas of the world and predominantly affects the pediatric age group.^[2]

Ascariasis occur globally and it is the most common helminthic infection of humans.^[1] Ascariasis affects at least 1 billion people worldwide and about 4 million people in the United States.^[2]

Ascariasis occur in all age groups but it is more common in the pediatric age group (ages 2-10 years).^[2]

Males and females are equally affected.

Ascariasis is three times more common in African-Americans compared to Caucasians.^[2]

Ascariasis occurs worldwide although it is more common in tropical regions of the world compared to the temperate regions (the environmental conditions are optimal for the development of the ova in the soil).^[1][3] The majority of people at risk for infection (71% of persons) live in Asia and the Western pacific region.^[2][3] 22% of persons at risk for infection live in Africa and the Middle East, and 11% of persons at risk for infection live in Latin America.^[3] In the US, the majority of the infection occur in the rural southeastern part of the country and it is often associated with poor sanitation.^[2]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2]

The risk factors for ascariasis are often associated with poor sanitary conditions and environmental fecal contamination.^[1]

Risk factors for ascariasis include:^[1][2][3]

• Poor socioeconomic conditions
• Use of human feces as fertilizer
• Lack of hand washing
• Eating unwashed fruits and vegetables
• Environmental contamination with feces

Risk factors for Biliary ascariasis include:^[4]

• Prior cholecystectomy
• Residence in endemic countries

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2]

Ascariasis is often asymptomatic.^[1] Complications may arise when adult worms move to certain organs such as the bile duct, pancreas, or appendix.^[1] A high worm burden can also result in complications such as intestinal obstruction.^[2]

The majority of people infected with Ascaris are asymptomatic although greater than 15% can experience some type of morbidity.^[1]

Complications of ascariasis include the following:^[3][2][4]

• Biliary duct disease
• Hepatic abscess
• Intestinal obstruction associated with perforation, volvulus, and intussusception
• Peritonitis
• Pancreatitis
• Acute appendicitis
• Malabsorption and growth impairment from chronic infection with Ascaris lumbricoides
• Interstitial nephritis and acute renal failure (rare)
• Acute eosinophilic pneumonia resulting in respiratory distress (rare)

The prognosis is good and most cases of ascariasis are asymptomatic, but mortality can sometimes be as high as 60,000 per year in symptomatic patients.^[1] Mortality from ascariasis is usually as a result of complications from the infection, and approximately 4.6% of patients hospitalized with complications of ascariasis die from the infection.^[5]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2]

The prevention of ascariasis is best achieved through improvements in personal hygiene and environmental sanitation.

The prevention of ascariasis is best achieved by:^[1]

• Avoiding ingesting soil that may be contaminated with human feces, including where human fecal matter (“night soil”) or wastewater is used to fertilize crops.
• Washing hands with soap and warm water before handling food.
• Teaching children the importance of washing hands to prevent infection.
• Washing, peeling, or cooking all raw vegetables and fruits before eating, particularly those that have been grown in soil that has been fertilized with manure.
• Avoiding defecating outdoors.
• The use of effective sewage disposal systems.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Fatimo Biobaku M.B.B.S [2]

History and Symptoms | Physical Examination | Laboratory Findings | X Ray | CT | MRI | Echocardiography or Ultrasound | Other Imaging Findings | Other Diagnostic Studies

Medical therapy | Surgery | Prevention | Future or Investigational Therapies

Case #1

• Tapeworm infection
• Toxocariasis

• Video of removal of Ascari lumbricoides with an endoscope
• Images (warning, very graphic): [3], [4]
• CDC DPDx Parasitology Diagnostic Web Site

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