November 13, 2009

Amebiasis, Ascariasis

Amebiasis is an intestinal illness caused by a microscopic parasite called Entamoeba histolytica. Approximately 1,000 cases are reported each year in New York State.

Who gets amebiasis?

Anyone can get amebiasis, but it is recognized more often in people arriving from tropical or subtropical areas, individuals living in institutions, and men who have sex with men.

How is amebiasis spread?

Amebiasis is contracted by consuming contaminated food or water containing the cyst stage of the parasite. It can also be spread by person-to-person contact.

What are the symptoms of amebiasis?

People exposed to this parasite may experience mild or severe symptoms or no symptoms at all. Fortunately, most exposed people do not become seriously ill. The mild form of amebiasis includes nausea, loose stools, weight loss, abdominal tenderness and occasional fever. Rarely, the parasite will invade the body beyond the intestines and cause a more serious infection, such as a liver abscess.

How soon after exposure do symptoms appear?

The symptoms may appear from a few days to a few months after exposure but usually within two to four weeks.

For how long can an infected person carry this parasite?

Some people with amebiasis may carry the parasite for weeks to years, often without symptoms.

Where are the parasites that cause amebiasis found?

The parasite lives only in humans. Fecal material from infected people may contaminate water or food, which may spread the parasites to anyone who consumes them.

How is it diagnosed?

Examination of stools under a microscope is the most common way for a doctor to diagnose amebiasis. Sometimes, several stool samples must be obtained because the number of amoeba being passed in the stool, which varies from day to day, may be too low to detect from any single sample.

What is the treatment for amebiasis?

Specific antibiotics such as metronidazole can be prescribed by a doctor to treat amebiasis.

Should an infected person be excluded from work or school?

Although people with diarrhea due to amebiasis should not attend school or go to work, it is not necessary to exclude infected persons when they feel better and stools are normal. Casual contact at work or school is unlikely to transmit the disease. Special precautions may be needed by foodhandlers or children enrolled in daycare settings. Consult your local health department for advice in such instances.

What precautions should the infected person follow?

The most important precautions are careful handwashing after each toilet visit and proper disposal of sewage. Homosexual males should refrain from intimate contact until effectively treated.

Adapted from: New York State Department of Health


The disease and how it affects people

Ascariasis is an infection of the small intestine caused by Ascaris lumbricoides, a large roundworm. The eggs of the worm are found in soil contaminated by human faeces or in uncooked food contaminated by soil containing eggs of the worm. A person becomes infected after accidentally swallowing the eggs. The eggs hatch into larvae within the person's intestine. The larvae penetrate the intestine wall and reach the lungs through the blood stream. They eventually get back to the throat and are swallowed. In the intestines, the larvae develop into adult worms. The female adult worm which can grow to over 30cm in length, lays eggs that are then passed into the faeces. If soil is polluted with human or animal faeces containing eggs the cycle begins again. Eggs develop in the soil and become infective after 2-3 weeks, but can remain infective for several months or years.

Children are infected more often than adults, the most common age group being 3-8 years. The infection is likely to be more serious if nutrition is poor. They often become infected after putting their hands to their mouths after playing in contaminated soil. Eating uncooked food grown in contaminated soil or irrigated with inadequately treated wastewater is another frequent avenue of infection.

The first sign may be the passage of a live worm, usually in the faeces. In a severe infection, intestinal blockage may cause abdominal pain, particularly in children. People may also experience cough, wheezing and difficulty in breathing, or fever.


Ascariasis is found worldwide. Infection occurs with greatest frequency in tropical and subtropical regions, and in any areas with inadequate sanitation.

Scope of the Problem

Ascariasis is one of the most common human parasitic infections. Up to 10% of the population of the developing world is infected with intestinal worms – a large percentage of which is caused by Ascaris. Worldwide, severe Ascaris infections cause approximately 60,000 deaths per year, mainly in children.


Health education providing the following messages reduces the number of infected people:

  • avoid contact with soil that may be contaminated with human faeces;
  • wash hands with soap and water before handling food;
  • wash, peel or cook all raw vegetables and fruits;
  • protect food from soil and wash or reheat any food that falls on the floor.

The availability of water for use in personal hygiene as well as proper disposal of human faeces will also reduce the number of cases. Where wastewater is used for irrigation waste stabilization ponds and some other technologies are effective in decreasing transmission due to food grown in contaminated soil.

Infected individuals (and domestic animals) should be treated with medicine to reduce disease transmission. Ascariasis can be effectively treated with mebendazole or pyrantel pamoate.

Adapted from: WHO