ICEH Resources Information Sheet

HYDATID DISEASE

Pronunciation: High-dat-id

What causes Hydatid Disease?

Hydatid disease is caused by the tapeworm Echinococcus granulosa (eh-shin-o-cock-us gran-u-losa) which produces eggs that form cysts in human organs. The disease is serious and can be fatal.

Dogs, dingoes and foxes are the primary host for this parasite, and herbivores (plant eaters) like sheep, cattle, horses, pigs, goats, kangaroos and wallabies are intermediate hosts. Cats and other carnivores are not suitable hosts for this parasite.

Hydatid disease has been around since ancient times, and is thought to have reached Australia around 40 000 years ago in the dingo ancestors. It is not a nationally notifiable disease.

What does it look like?

Adult worms are 3-6 mm long, and are made up of a scolex (head), neck and segmented body (3-4 bits). Eggs are 0.3-0.4 mm big, and the cysts are round, thick walled, fluid filled sacks that develop slowly. The cysts are usually 1-7cm in size, but can reach 10cm. Cysts often occur in the liver and lungs.

Echinococcus granulosa
tapeworm & larvae

Where does it occur?

Echinococcus granulosa is found worldwide, except for Antarctica. The disease is most common when there is close association between infected dogs and humans. It is generally a problem in sheep farming areas.

Hydatid Disease in Australia

Australian / Indigenous Significance

Hydatid disease is endemic (constantly present) in the east and west of Australia. There are 3 distinct strains: a domestic strain that spreads between sheep and dogs; a sylvatic strain between dingoes, wallabies and kangaroos; and a Tasmanian strain amongst sheep and domestic dogs. It has been noted that hydatid disease is notoriously under reported in Australia.

In Tasmania, a control campaign has eliminated the transfer of hydatid disease from animals to humans.

Symptoms: What to look out for?

Most cases are diagnosed by accident during other medical checks. It is common for people to be asymptomatic (not feel sick) until cysts are quite big. Symptoms will also vary depending on the number of cysts, their location, and their size.

When a cyst breaks open, it can cause severe allergic reactions. It can release protoscoleces (infective larvae) that may start secondary infections. Liver cysts may cause jaundice (yellow skin) if they break open, and lung cysts can cause coughing, tiredness, and chest pain.

How do you diagnose (confirm) a case?

Confirmation of hydatids is based on a person having tumour-like symptoms, living in an area where the disease is endemic, and having contact with dogs or other canines. Diagnosis of asymptomatic cases is done by surgically removing tissue specimens and examining them with a microscope. Diagnosis may also involve x-rays and blood tests, ultrasound, or examination of cyst fluid with a microscope.

How does it spread?

Human infection most often occurs in children, and is caused by the hand to mouth transfer of eggs after handling infected dogs. The disease can also be acquired by a person swallowing food, water or soil contaminated with eggs or by mouth contact with contaminated items like eating utensils or toys. Flies can spread eggs from faeces (shit) onto other surfaces or objects.

How does it reproduce?

The adult worms live in the intestines of canines, and produce eggs that pass out of the dog in its faeces. It takes around 6 weeks for eggs to be produced after infection. Eggs can survive in the environment for several months, and are resistant to freezing and disinfectants. When the eggs are swallowed by a suitable intermediate host like a sheep, they hatch and release oncospheres (infective embryo) in the intestines.

The oncospheres then go through the intestine wall, and move by the blood stream to various organs where they form cysts containing millions of infective larvae. Cysts can remain viable in hosts for years.

Canines become infected when they eat cyst-contaminated organs of dead animals, and the infective larvae are released from the cyst. The larvae develop into adults in the intestine and live for around 6 months.

How infectious is it?

Hydatid disease is acquired from not washing hands after handling infected animals, and does not spread from human to human. Infected people remain infected until treated. Adult worms have been known to live for up to 2-3 years inside canine hosts, but usually die within 6 months. Canine reinfection can occur.

How long does it take for symptoms to appear?

It can take anywhere from 12 months to many years for symptoms to start.

Who is most at risk?

Children are most at risk of getting hydatids, because they are more likely to have close contact with infected dogs and have the least understanding of the importance of good personal hygiene like washing hands after playing with animals.

How do we prevent it from occurring?

Community education on good personal hygiene practices is a main way to reduce the occurrence of hydatid disease. Emphasis should be placed on the importance of:

• Avoiding contact with dog faeces.
• Washing hands after touching dogs, and before handling or eating food.
• Not feeding offal (animal organs) to dogs, and making sure that offal from animal slaughtering is disposed of so dogs cannot get to it. This can be done by incinerating or burying it.
• Worming high-risk dogs every 6 weeks in endemic areas, and culling stray dogs after community consulation.
• Preventing dogs from accessing areas used to grow food and areas where children play.
• Encouraging children not to play with working dogs or dogs they are not familiar with.
• Cleaning of animal living areas regularly, and collecting faeces hygienically and disposing of it so it does not contaminate soil.

How can it be controlled?

Checks should be done to see if household members of an infected person or other close contacts have been infected.

Sources of infection like pets and other farm animals should be checked, and treated where required. It should also be determined what practices led to the infection, and information provided to infected people or owners of infected animals on how to prevent the disease occurring.

Human treatments usually require the surgical removal of the cyst. Dogs can be treated with special worming drugs that are available from veterinarians or environmental health workers.

Case Study

Hydatid Disease: medical problems, veterinary solutions, political obstacles
(McCullagh, 1996) & Echinococcus and Hydatid Disease (Thompson & Lymbery, 1995)

In Tasmania a successful hydatid disease eradication campaign has been run over the last couple of decades, and now there have been no cases of human hydatid disease for many years. Before this, a study in the 1960s indicated that Tasmania then had the highest rate of human hydatid disease in Australia.

The first proposals for hydatid control were developed in 1960 and 1961. However, these plans failed due to a lack of financial and public support. After this, Dr T. Beard started a hydatid disease awareness campaign, and persuaded farmers groups to set up special ‘hydatid committees’ to promote practices for the prevention of hydatid disease. The committee promoted practices like proper disposal of offal from animal slaughtering and not feeding raw offal to dogs.

Three of these committees combined in 1963 to form the Tasmanian Hydatids Eradication Council, which gave advice to Government departments involved with hydatid disease. The Council also continued to educate the public on how to prevent the disease occurring.

The Department of Agriculture oversaw the official hydatids eradication campaign, which was started in 1965. The campaign involved identifying infected dogs using a mobile laboratory, and educating dog owners on prevention methods. In 1967 the program focused on rural dogs because urban dogs rarely had the disease.

Compulsory hydatid control measures were brought in during 1969 to 1975. These included: restricting the movement of infected dogs and livestock, and the quarantining of properties where the infected sheep numbers were greater than the state average. A farm could also be placed under quarantine if an infected cyst was found in a sheep sent for slaughtering.

Treatments given to infected dogs during the campaign varied as new drugs were developed. The number of infected dogs in Tasmania dropped steadily during the campaign, as did the number of infected sheep, cattle and humans. In 1985-1986 no infected dogs were identified, and only 4-8 hydatids cysts were found in approximately 500 000 sheep slaughtered. The last case of an infected cow was on King Island in 1985-1986. This was unusual in that no hydatid cases had occurred on this island since 1971, and it was thought an infected dog must have brought the disease to the island.

There have been no reported cases of human hydatid disease since 1977. Now the concern is that people remain alert for the disease so that it does not re-establish itself in Tasmania.

Glossary

Resources

Community Education Flyer to print out
Available at: iceh.uws.edu.au/fact_sheets/hydatids_flyer.pdf
[1 page sheet for community information, 102KB PDF file]

Carnie, J. et al, 1997, ‘Hydatid Disease’, in The Blue Book: Guidelines for the control of infectious diseases, Department of Human Services, Victoria. Available from: www.dhs.vic.gov.au/phd/hprot/inf_dis/bluebook/infdis.pdf
[Information on control of hydatid disease]

Chin, J., 2000, Control of Communicable Disease Manual, 17th edn, American Public Health Association, Washington DC, pp. 478-481.
[Book on infectious diseases that is often referred to in health departments (technical language)]

Despommier, D.D., Gwadz, R.W., Hotez, P.J. 1995, Parasitic Diseases, 3rd edn, Springer-Verlag, New York, pp.93-100.
[Book on diseases caused by parasites (technical language)]

Division of Parasitic Diseases. 2002, Echinococcus, Centres for Disease Control, Atlanta. Available from: www.dpd.cdc.gov/dpdx/HTML/Echinococcosis.htm
[American fact sheet on Echinococcus, with a very good life cycle drawing]

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.167-172.
[Book focusing on infectious diseases in Australia (technical language)]

Gemmel, M.A. & Roberts, M.G. 1998, ‘Cystic echinococcus’, in Zoonoses, eds S.R. Palmer, Lord Soulsby & D.I.H. Simpson, Oxford University Press, New York. pp. 665-688.
[Book on diseases that move from animals to humans (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’, MJA, Vol 159, pp. 464-466.
[Article on various worm related diseases that occur in Australia (technical language)]

Hydatid Disease Fact Sheet, 2001. Queensland Health, Brisbane.Available from: www.health.qld.gov.au/publications
[Fact sheet on Hydatids Disease, good for general community]

McCullagh, P.J. 1996, ‘Hydatid disease: medical problems, veterinary solutions, political obstacles’, MJA, Vol 164, pp. 7-8. Available at: www.mja.com.au/public/issues/jan1/mccull/mccull.html
[Article on control of hydatids in Australia (technical language)]

Raw, L. 2001, ‘Human health in relation to pets in urban and Indigenous communities’, in Rural and Remote Environmental Health, eds. D.V. Canyon and R.S. Speare. Available from: www.tropmed.org/rreh
[Journal article discussing diseases relating to animals in communities]

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.

Thompson, R.C.A. & Lymberry, A.J. (1995), Echinococcus and Hydatid Disease, CAB International, Oxon.
[In depth book on hydatid disease, with sections addressing the disease in Australia (contains technical language)]

You’ve got what?_specific conditions_hydatid disease, Dept of Human Services, South Australia. Available from:
http://www.dhs.sa.gov.au/pehs/disease-control-stats.htm
[ Fact sheet on hydatid disease, good for general community]

Created November 2003
by Margaret Davidson