Disease Name: Ascariasis
Transmission and Reservoirs: Ascarid eggs are found in fecal contaminated soil (8) and are transmitted when a person ingests the eggs by eating uncleaned vegetables. They eggs may also be transmitted if a person touches their mouth with unwashed hands that have been contaminated with eggs from the soil (9). This is a type of foodborne vehicle transmission. Ascariasis is not contagious, as it cannot be directly spread from person to person (1). Reservoirs for Ascariasis include soil, food and water infected by contaminated soil and hu! mans (2)
Etiological Agent: Ascaris lumbricoides
General Characteristics: Ascariasis is a helminthic disease caused by the largest parasitic roundworm (nematode) called Ascaris lumbricoides (3). Once ingested, the ascarid eggs hatch into larvae in the stomach (6). The newly hatched larvae move throughout the bloodstream to the lungs and then to the throat where they are swallowed back into the stomach and intestines (3). The larvae develop into adult worms in the intestines. The worms reach maturity approximately 2 months after initially b! eing ingested from the soil (1). Ascariasis most commonly occurs in tropical and subtropical locations (4) where there is poor personal hygiene (3), mediocre sanitation and where human feces is used as fertilizer (1). Over 1 billion people worldwide are infected with Ascariasis (11). Children are more likely to become infected with Ascariasis than adultís (9), and around 20,000 children die each year from the infection (7).
Tests for Identification: The most common test that doctors use to identify Ascariasis involves examining a patientís feces (12). This is called the Stool ova and parasites exam (3). By viewing a fresh fecal smear under a microscope, a doctor can detect ascarid eggs or ova in the feces. X-ray images of the abdomen called an abdominal film or an abdominal X-ray test can also identify Ascariasis. The electromagnetic radiation of the X-ray penetrates the body and forms and image on film (3). The image produced can show internal complications from an ascarid infection (8). Doctors may chose to perform routine blood counts to test for Ascariasis. Testing positive for anemia may be a sign that the patient is positive for Ascariasis (3). Currently, there is no blood test capable of diagnosing an ascarid infection (6).
Historical Information: The oldest written documentation of Ascaris is from China nearly 4,690 years ago. Roughly 3,500 years ago, Ascaris was referred to in a book called Ebersí Papyrus written in Egypt. Other ancient authors like Hippocrates, Aristotle and Albertus Magnus referred to roundworms in their writings. When microscopes first became available, there was an increased interest in the tiny nematodes and their makeup. A microbiologist named Tyson wrote about his microscopic findings in 1685 and cal! led it Morphology of Ascaris (13).
Signs and Symptoms: Many people infected with Ascariasis have no symptoms (1, 3, 6); however, the more ascarid worms involved in the infection increases the severity of the symptoms (1). A mild case of Ascariasis may include worms in stool, loss of appetite, fever and coughing up worms. A more severe case of the infection may involve vomiting, shortness of breath, swelling of the abdomen, severe stomach pain, intestinal blockage and biliary tract blockage (1). The first symptoms of an ascarid infection usually occur when the larvae reach the lungs (7).
Virulence Mechanisms: Ascarid eggs have a sticky coating, which allows them to easily attach to human hands and be transferred to the mouth to cause infection (11). The size of an ascarid worm and the amount of eggs a female ascarid worm releases daily are two other virulence factors of Ascariasis. An adult ascarid worm can grow to be 12 to 14 inches long, which is large enough to perforate bile or pancreatic ducts. Female ascarid worms release over 200,000 eggs per day (7), which causes high worm burden throughout the human body. This mass of worms can cause abdominal pain and intestinal obstruction (5). Extreme worm burdens can even cause rupture of the intestines (7), hiatal hernia, duodenal ulcer, appendicitis, invasion of other organ systems, malnutrition and stunted growth (12).
Treatment: Patients with an ascarid infection can usually be prescribed antihelminthic medication to kill the intestinal roundworm. These medications include albendazole, mebendazole, pyrantel pamoate (5), amoxicillin and hyoscine butylbromide (8). The medications are normally taken for 1 to 3 days and have very few side effects (5). Approximately 3 weeks after treatment a doctor may re-examine a patientís stool to check for any eggs or worms. The treatment is repeated if the patient is still infected with Ascariasis (4). Surgical extraction is necessary in rare cases where the ascarid worms cause an intestinal or liver obstruction or abdominal infection (1).
Prevention: There is no vaccine available for Ascariasis (6). Prevention of ascarid infection involves avoiding soil contaminated with human feces, disposing of diapers correctly, washing hands with soap and water before handling food, and washing, peeling and cooking all raw fruits and vegetables before consumption (6). To prevent reinfection of Ascariasis, keep fingernails short and clean, sterilize contaminated clothing and bedding and sanitize any other items that have been contaminated. (1). In 1997, a program was initiated in rural areas of Hamadan Province, Islamic Repub! lic of Iran. The test entailed giving the population a single dose of 400mg albendazole at 3-month intervals for 2 years. The program ended in December 1999 and was then evaluated. Before treatment, 53.3% of the population was infected with Ascariasis. After treatment, only 6% tested positive for the disease. This study attested that the systematic mass chemotherapy treatment provided sufficient control of ascarid infection (10).
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3. Parsons, Christopher. "Ascariasis". 07/30/02. URL: http://www.nlm.nih.gov/medlineplus/ency/article/000628.htm accessed on 4/29/03.
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10. University of Florida, College of Medicine. "Ascaris lumbricoides". 04/09/99. URL: http://medinfo.ufl.edu/year2/mmid/bms5300/bugs/asclum.html#AA4 accessed on 5/2/03.
11. US Food and Drug Administration. "Ascaris lumbricoides and Trichuris trichiura". 01/07/03. URL: http://www.cfsan.fda.gov/~mow/chap30.html accessed on 4/24/03.
12. Kemp, Charles and Roberts, Amy. "Ascariasis". 12/02. URL: http://www3.baylor.edu/~Charles_Kemp/ascariasis.htm accessed 5/2/03.<
13. University of California. "HISTORY" URL: http://ucdnema.ucdavis.edu/imagemap/nemmap/Ent156html/intro/history accessed on 4/28/03.