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AMOEBIASIS

Pronunciation: Am-ee-be-as-is

Other words: Amoebic Dysentery, Entamoeba histolytica

What causes Amoebiasis?

Amoebiasis is caused by the protozoan parasite Entamoeba histolytica (ent-am-ee-ba hist-o-lit-e-ca). This parasite can live in humans commensally (without causing harm), or it can invade tissues causing intestinal or extra-intestinal disease.

Entamoeba histolytica is the 3rd highest cause of death and illness due to a parasitic disease, causing 50 000 to 100 000 deaths a year worldwide.

People with chronic (long term) or asymptomatic (don’t feel sick) infections are the main reservoir of the E. histolytica. This parasite lives only in humans, and the illness was first identified in 1903.

Amoebiasis is not a Nationally Notifiable Disease.

Diagram of Trophozoite and cyst

Entamoeba histolytica

What does it look like?

Entamoeba histolytica can only be seen with a microscope, and exists in 2 forms. An infective cyst measuring 0.1-0.2 mm, and a trophozoite (parasite) 0.1-0.6 mm in size (invasive stage).

Australia map

Amoebiasis in Australia

Where does it occur?

Cases of amoebiasis are most common in tropical and subtropical regions, especially in areas with poor sanitation. It is indigenous to Australia.

Australian / Indigenous Significance

Amoebiasis is of concern due to its presence in Indigenous communities. Over 15 months, 6 cases of amoebic appendicitis were sighted at the Royal Darwin Hospital. This is significant because amoebic appendicitis is very rare, and all the cases were in Indigenous Australians, four of whom were from remote communities.

Symptoms: What to look out for?

Amoebiasis rarely occurs in children under 5 years, and symptoms are similar to those of other diseases, so early diagnosis is important to ensure correct treatment. There are two forms of amoebiasis infections:

1. Intestinal (invasive) amoebiasis
This occurs when the parasite enters intestinal tissues, and is most common in young adults. Infected people may not feel sick, or they may have chronic, mild or rapid severe illness (elderly or sick people).

Diarrhoea (runny tummy) is the main symptom and may be mild or severe. Amoebic Dysentry may also occur, which is when diarrhoea contains blood or mucous. People with amoebic dysentery may also have abdominal pain, fever, weight loss, or flatulence. Appendicitis may occur, but this is rare. People with repeated or long-term infections may also get tumour-like growths in the large intestine.

2. Extra-intestinal amoebiasis
This is caused by the trophozoites penetrating the intestinal wall and spreading by the bloodstream to other organs. In the liver the trophozoites can cause amoebic hepatitis (liver enlargement), as well as the formation of ulcers. Trophozoites can also create abscesses in the brain, lungs or heart. Fever may occur with amoebic hepatitis, and people with liver abscesses may have shoulder pain.

How do you diagnose (confirm) a case?

Amoebiasis is diagnosed by finding trophozoites or cysts in stool samples (faeces), or in ulcer smears using a microscope. Invasive amoebiasis may be confirmed by finding red blood cells in trophozoites.

How does it spread?

Amoebiasis is a communicable disease that can spread from human to human. The disease can be obtained by people swallowing food or water that contains cysts. Many outbreaks occur through the contamination of drinking water with cysts. Flies have also been linked with the spread of this disease.

The disease can also be spread by a person not washing their hands after going to the toilet or changing a nappy, and then handling food or non-food materials that come into contact with other people.

People may also get amoebiasis through sexual contact that involves contact with faeces.

How does it reproduce?

First method:
People swallow the cysts, which hatch and release amoebas into the small intestine. The amoebas then divide into eight trophozoites, which may invade the tissues of the large intestine, and develop into cysts that are passed in the faeces (intestinal amoebiasis).

Second method:
Alternatively, the trophozoites can penetrate into the blood stream and spread to other parts of the body (extra-intestinal amoebiasis). Cysts are not produced in extra-intestinal amoebiasis, and the trophozoites reproduce by division.

Strains that do not cause illness may live in the middle of the large intestine.

Lifecycle of Entamoeba histolytica

Lifecycle for Entamoeba histolytica

How infectious is it?

People remain infectious as long as cysts are present in their faeces. This can continue for years.

How long does it take for symptoms to appear?

It usually takes 2-4 weeks for symptoms to start. However, it can take a few days, a couple of months, or even a year before a person feels sick.

Who is most at risk?

Anyone can get amoebiasis, but it is most common in young to middle aged adults. Homosexual males with more than one partner are at greater risk of getting this disease, and it is a common cause of diarrhoea in travellers returning from developed countries.

handwash

no faeces in water

kettle for boiling water

 

How do we prevent it from occurring?

Community education on good personal hygiene practices is the main method for preventing amoebiasis. Emphasis should be placed on the importance of:

  • Washing hands after going to the toilet, and before handling or eating food.
  • Using clean and safe water for drinking and preparing food.
  • Washing raw fruits and vegetables in safe water prior to eating or preparing.
  • Disposing of human faeces in a sanitary manner.
  • Preventing the contamination of water supplies with faeces.
  • Avoiding sexual practices that involve contact with faeces.
  • Using safe food handling practices.
  • Avoiding drinking unsafe water, especially during recreational activities.
  • Treating water that has been obtained from untreated sources.

Sand filtration will remove most cysts, and diatomaceous earth filters will remove all cysts present in water. Portable water filters (pore sizes <1.0 µm) will remove cysts, and boiling water vigorously for 1 minute can also make it safe to use.

Chlorine is not very effective in killing cysts. Iodine can be used to treat small quantities of water (drink bottles etc). 8 drops of 2% iodine solution (Betadine) can be added to around 1 litre water. Water purification tablets like Globaline® are available from camping stores and chemists, and can be used to treat small amounts of drinking water. Before drinking the water, it should be left to stand for 10 minutes after adding the treatment, and 30 minutes if the water is cold.

How can it be controlled?

People with symptoms of amoebiasis should visit their doctor immediately so they can get proper treatment, and know how to prevent disease from spreading to other people.

Faeces samples of household members and close contacts should be collected and tested to find out who has been infected (Check with State or Territory health department for procedures).

When a cluster of possible amoebiasis cases occur, immediate laboratory testing is necessary to confirm E. histolytica, and rule out other diseases. People need to identify what they ate and drank before becoming ill to try and find the source of the outbreak, and any potential sources of infection should be investigated (food and water etc) .

People must be careful when handling faeces, vomit, dirty bedding or clothing of infected individuals, and wash hands thoroughly after contact.

Items like dishes or sheets can be disinfected by:

  1. Heat treatments such as using hot water washing machines to wash sheets, or by soaking dishes in very hot water.
  2. Chemical disinfection with solutions that contain 10% formaldehyde (formalin) or 5% ammonia.

Faeces can be disposed of into modern sewage systems without preliminary disinfection. Plastic nappies should not be placed in sewage systems. These can be sealed in a plastic bag and disposed of with household waste.

People with amoebiasis must not share their towel, face washer or sheets with other people, or prepare or handle food for them. Workers with amoebiasis should not work with food, or in childcare or health care settings until they have finished their medication or treatment. Children with amoebiasis should not attend childcare or school until diarrhoea has stopped.

Case Study

A School Waterborne Outbreak of Shigella sonnei & Entamoeba histolytic
(Chen et al, 2001)

A rare waterborne outbreak of Entamoeba histolytic and Shigella sonnei occurred at a primary school in Taiwan during 1993. The school was identified as the possible source of infection, because the people with S. sonnei and E. histolytica infections had not visited countries where the diseases were endemic, and the only link between cases was that they attended the same school. The school also had a high absenteeism rate from similar illnesses before the students were hospitalised.

An investigation was done to find the source of the outbreak. This involved interviewing local doctors, laboratories, and hospitals that treated the students, and surveying family members and students for symptoms. A positive case was defined as a person with diarrhoea during August-September, or any 2 of the following: belly cramps, nausea, vomiting, blood or mucous in stools. Laboratory testing was done to check for S. sonnei or E. histolytica, and samples from every student were collected and tested for certain bacteria and parasites. All students were given a questionnaire that asked about school water, restaurants visited, travel, parties, home water supply, swimming, and their illness history. Illness history included when it started, how long it lasted, symptoms and medical treatment.

The investigation to identify the outbreak source included inspecting the school kitchen, and interviewing and examining all staff that handled food. School water supplies (well and town water) were tested for faecal pollution and bacteria. The well was checked for sewage contamination by adding red dye to the nearest toilet, and then checking for the dye in the well water. Food handling and waste disposal systems were also reviewed. Statistical calculations were done to see what was most likely to cause the outbreak.

Water testing identified that the well water was contaminated with sewage, and the following control measures were put in place:

  1. Students and teachers were informed to boil water before use.
  2. Students were requested to wash hands after going to the toilet and before eating.
  3. The water supply systems was shut off and disinfected.
  4. Preventative medications were given to all students and staff.

Cases stopped once the well water was shut off. The water supply was suspected because the risk of becoming ill increased the more a student used school water. Staff did not drink the school water and none became ill. This suspicion was further supported by the high coliform bacteria counts in the water supply, and the presence of red dye in the well water.

Glossary

Abdominal To do with Barrang, beli, buurrbiyn, dhulmu, kem, kunto, muhh, munto, tidli, yeek, belly area, tummy, gut, middle, or midriff.
Abscesses A skin sore that contains pus, which often has swollen tissue around it. Also known as a boil or festering sore.
Amoebic Dysentery When a person has diarrhoea that contains blood or mucus.
Appendicitis Inflammation of the appendix, which is a small outgrowth at the beginning of the large intestine.
Asymptomatic When a person has a disease, but doesn’t feel sick.
Chronic Illness When a person remains ill or infected for a long period of time.
Commensal An animal or plant that lives on or in another organism without causing harm.
Communicable Disease Diseases caused by the transfer of a germ or its toxin (poison) from an infected person, animal or object to a new host.
Contamination Presence of germs or parasites on the body, or in clothes, bedding, toys, medical tools, water or food. Other words are to pollute, sully or taint.
Cyst Protective infectious reproductive structure ingested by hosts, causing illness.
Diarrhoea Watery or liquid faeces, runny tummy, dysentery, runs or trots.
Faeces Guna, guni, gunan, gurla, guunang, kuma, kun, kuna, kuuenyuk, ngukin, roo, thaka, excretement, shit or stools.
Flatulence Buurag, nyirrij, rdirryun, thumbirraarri, farting or wind.
Hepatitis Disease that causes inflammation or enlargement of the liver.
Host A person or animal that can become infected with a germ or parasite.
Infection When germs or parasites enter the body of a host and start multiplying.
Intestine Gut, organ located in tummy, part of digestive system.
Mucous Karra, ngaltya, artengkwelknga, nyili, nyuugam, snot, bogie, phlegm or sputum
Notifiable Disease A disease where cases must be reported to the appropriate health authority.
Parasite Plants or animals that may be extremely small (single cell) or very large (1m long worms), which need another plant or animal host to live. Animal parasites include protozoa, worms, mites and lice.
Protozoan (plural: protozoa) A living organism that is made up of many cells.
Reservoir The main source of a germ in the natural environment where it lives and multiplies. May be soil, water, plants, animals or combination of these.
Trophozoite The free-living stage for a protozoan parasite when it can move and feed.
Stool Sample A sample of human faeces, used to check for organisms that cause disease.
Ulcer Muula. An open sore on the skin, or inside the body (stomach etc) that contains pus.

 

Resources

 

For more information
click on these websites

Community Education Flyer to print out
Available at: iceh.uws.edu.au/fact_sheets/amoebiasis_flyer.pdf
[1 page sheet for community information, 121KB PDF file]

Amoebiasis Fact Sheet, Department of Human Services, Victoria. Available from: www.dhs.vic.gov.au/phd/hprot/idci/am.html.
[Fact sheet on amoebiasis, good for general community]

Chen, K., Chen, C. & Chiu, J. 2001, ‘A School Waterborne Outbreak Involving Both Shigella sonnei and Entamoeba histolytic’, Journal of Environmental Health, Vol 64, No 4, pp. 9-26.
[Journal article on outbreak of Shigellosis and Amoebiasis]

Chin, J., 2000, Control of Communicable Disease Manual, 17th edn, American Public Health Association, Washington DC, pp. 11-13.
[Book on infectious diseases that is often referred to in health departments (technical language)]

Clark, C.G. 2003, The Entamoeba Homepage, London School of Hygiene and Tropical Medicine. Available from: homepages.lshtm.ac.uk/entamoeba/
[Website on the parasite that causes amoebiasis (technical language)]

Despommier, D.D., Gwadz, R.W., Hotez, P.J. 1995, Parasitic Diseases, 3rd edn, Springer-Verlag, New York, pp. 151-159.
[Book on disease caused by parasites (technical language)]

Fernando, R.L., Fernando, S.E. & Leong, A.S.Y. 2001, Tropical Infectious Diseases: Epidemiology, Investigation, Diagnosis and Management, Greenwich Medical Media Ltd, London, pp. 5-16
[Book that focuses on infectious diseases in Australia (technical language)]

Griffiths, O. & Henderson, H. 1997, Environmental Health for Aboriginal Communities: A Training Manual for Environmental Health Workers, Office of Aboriginal Health, East Perth, pp. 16-28.
[Training manual for Environmental Health Workers in Western Australia]

Grove, D.I. 1993, ‘Worms in Australia’, Medical Journal of Australia, Vol 159, pp. 464-467.
[Article on various worm diseases that occur in Australia (technical language)]

Lloyd, S. 1998, ‘Occasional and miscellaneous zoonoses’, in Zoonoses, eds S.R. Palmer, Lord Soulsby & D.I.H. Simpson, Oxford University Press, New York.
[Book on diseases that spread from animals to humans (technical language)]

McCarthy, J.S. et al. 2002. ‘Endemic invasive amoebiasis in northern Australia’, Medical Journal of Australia, Vol 177, p. 570.
Available: www.mja.com.au/public/issues/177_10_181102/mcc10129_fm.html
[Journal article on specific cases of amoebiasis (technical language)]

Stanley, S.L. 2003, ‘Amoebiasis’, The Lancet, Vol 361, Issue 9362, pp. 1025-1034.
[Journal article reviewing amoebiasis (technical language)]

Thielberger, N. & McGregor, W. 1994, Macquarie Aboriginal Words: a dictionary of words from Australian Aboriginal and Torres Strait Islander languages, Macquarie Library Pty Ltd, NSW.

Zardawi, I.M., Kattampallil, J.S. & Rode, J.W. 2003, ‘Amoebic Appendicitis’, Medical Journal of Australia, Vol 178, pp. 523-524. Available: www.mja.com.au/public/issues/178_10_190503/letters_190503_fm-2.html
[Journal article on specific cases of amoebiasis (technical language)]


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Created October 2003
by Margaret Davidson

copyright UWS 2003
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