Ascariasis

 

by Mera Plummer

 

 

Disease

            Ascariasis, a large round worm named   Ascaris lumbricoides. (1)

 

Transmission

           

Eggs of Ascaris are found in the feces of humans.  They can be found in contaminated soil. The eggs can remain viable for months to years within the soil.  The eggs can also be transmitted through undercooked produce previously contaminated with soil containing the eggs.  Ascaris infection is generally found in places with poor sanitation.  Once humans pass the eggs the eggs contaminate the soil and can become infectious in a few weeks. Humans obtain the infection with accidental ingestion of the infectious eggs. The larvae are carried through the lungs and then to the throat.  The eggs will hatch once they reach the small intestine.  The eggs then develop into adult worms that continue to lay eggs that are then passed through the feces.  The cycle takes about two to three months.  (1,3,5)

Reservoir

Ascaris eggs are found in the soil.  The optimum soil is warm, moist, and shaded. Humans also act as reservoirs. The eggs are passed through the feces. Eggs can also be found on chopping boards, coins, door handles, fingernail dirt, fruit, vegetables, furniture, insects, nasal discharge, money, and public bathrooms. (1, 2, 3, 4, 5, )

General Characteristics of Ascariasis

            The fertile eggs can range from 45 to 75 µm in length.  Fertile eggs are round with a thick shell.  They have an external mammillated layer that is generally brown.  Sometimes this outer layer is absent.  Unfertilized eggs are larger and can be measured up to 90 µm in length. 

            Roundworms are essentially a tube within a tube. Adult roundworms range from 15 to 35 cm.  Female roundworms tend to be larger than the males. The digestive system is not very developed and the reproductive system is very large and developed compared to the rest of the body.  They have a one-way digestive tract that goes from the mouth to the anus. They also have a cavity between the digestive tract and the body wall that is called psuedocoel.  This develops from the blastocoel.  (5)

Key tests for Identification

A microscopic examination stool sample from a possible infected patient is the most common technique for diagnosing. A physician will collect a stool sample.  The sample will be examined for eggs or live worms.  The sample is taken and fixed in 10% Formalin and a wet mount of the sediment is examined.  Where Formalin is not available the sample is just examined on the wet mount slide.  If the lungs have been infected the physician will look for evidence of larvae in the lungs or stomach fluid.  Blood tests can also be done.  If a person is infected the eggs will not appear in a stool sample for at least 40 days.  This will be done in case a person is infected with only male worms, eggs will not be present in a stool.  With the blood test the white blood cells, eosinophils, will indicate the infestation of Ascaris lumbricoides. If a person has a severe infestation an X-ray may be taken.  An ultrasound, CT, or MRI scan may also be taken in order to determine if there are worms in the pancreas, liver or bile ducts. (3,4)

Signs and Symptoms

Signs of infection include worms in stool, coughing up worms, loss of appetite, fever, and wheezing.  In severe cases you will see vomiting, shortness of breath, abdominal distention, severe stomach or abdominal pain, intestinal blockage, and liver and gallbladder blockage. (1, 3, 4, 5)

Historical Information   

            Ascariasis is an ancient infection, the eggs have been found in Peru dating back from 2277 BC, Brazil 1669 to 1420 BC.  In the old world scientists have recorded the presence of Ascaris in a Middle Kingdom Egyptian mummy dating back from 1938 to 1600 BC. In Tennessee, in Big Bone Cave, a sample was taken from an 1800 paleofecal specimen.  The scientists concluded from their research in this cave that the Ascaris species was present 2177 +/- 145 years ago. The Chinese, Egyptian medical papyri, Hippocrates in the fifth century, and texts from Roman and Arabic writing all have recorded the infection of A. lumbricoides.  It was not until the 17th century that doctor Edward Tyson created a detailed description of how the worm was described. Shortly after another description of the worms anatomy can be found in Osservazioni Intorno Agli Animali Viventi che si Trovano Negli Animali Viventi written by Francisco Redi.  Together these two publications mark the beginning of the sub discipline of helmithology. It wasn’t until 1862 that French medical scientist Camir Joeseph Davine and Italian scientist Giovanni Battista Grassi infected himself, through ingestion, to begin to determine the eggs in fecal matter.  In 1922 a Japanese pediatrician, Shimesu Koino, also infected himself and a volunteer in order to research and discover the life stages of the roundworms.  Today we still continue to research Ascaris in order to fully understand this disease. (5)

Virulence Factors

There are not any known virulence factors of Ascariasis however, scientists are continuing to research this subject in order to get a better understanding.  What we do know is that with a large infestation worms are known to clog intestines.  Round worms infect a human so that a person may so little to no signs for a while. They also have a life cycle where there may be several worms inside a person’s body and also eggs that are removed by the withdrawal of the feces.  The eggs can then live in the soil and continue to contaminate more people.    

Treatment

There is no vaccine. However, once infected an anti-parasitic medication will be administered by a physician.  Typical anti-helminthic drugs are such as mebendazole, albendazole, and pyrantel pamoate.  One dose is administered at first but in more sever cases numerous doses may be taken.  If a person is heavily infected surgery may need to be done in order to remove the worms and repair damage that the worms may have caused.  Surgery is preformed if a person has an intestinal obstruction, bile duct obstruction, or appendicitis. (3, 4)

Prevention

The best way to prevent infestation is to have good hygiene.  Always wash your hands with soap and water.  Also, it is important to wash fruits and vegetables thoroughly.  When visiting developing countries drink bottled water or boiled water, avoid eating raw fruits or vegetables, and eat foods that you have prepared yourself or have been completely cooked and are hot.  (1, 2, 3, 4, 5)

Local cases

Roughly four million people are infected with Ascariasis. Infections tend to be in persons that have migrated from developing countries.  They are endemic low-income families in the southeastern part of the country. There are very few cases in the United States. (5)

Global Cases

Over 1.4 billion people are infected with Ascariasis in the world. Ascariasis has been found in 150 of the 218 countries around the world.  Cases are distributed as follows South America, Central America and the Caribbean 8.3%, Africa and the Middle East 16.7%, and Asia and the Oceania region 75%. (5)

Sources:

1."Ascariasis." Medpedia. 2007. 04 May 2009  http://wiki.medpedia.com/Ascariasis.

 

2."Ascariasis- Blue Book: IDEAS - Victorian Government."  Victorian Government Health Information, Australia. 15 Jan. 2008. Victorian Government Health Organization. 05 May 2009 http://www.health.vic.gov.au/ideas/bluebook/ascariasis#id

 

3."Ascariasis Infection." CDC. 8 Sept. 2008. Divsion of Paracistic Diseases. 4 May 2009 http://www.cdc.gov/ncidod/dpd/parasites/ascaris/factsht_ascaris.htm

 

4."Ascariasis: Tests and diagnosis." Mayo Clinic medical information and tools for healthy living . Ed. Mayo Clinic Staff. 20 Feb. 2008. Mayo Foundation for Medical Education and Research. 07 May 2009 http://www.mayoclinic.com/health/ascariasis/DS00688/DSECTION=tests%2Dand%2Ddiagnosis.

 

5.Shoff, William H., and Micheal E. Greenberg. "Ascariasis." EMedicine. 11 June 2008. Web MD. 4 May 2009 http://emedicine.medscape.com/article/996482-overview