Hydatid Tapeworm

The hydatid tapeworm (Echinococcus granulosus) is a very important parasite as humans can become infected, with serious illness possible. However, humans do not become infected from contact with sheep or goats, or by eating sheep or goat meat or offal. Humans generally pick up infection from domestic dogs.

Neither the sheep or goats, nor the dog suffer major ill effects from hydatids.

The dog carries the adult hydatid tapeworm, which is about 4-6 mm long, with tapeworm eggs and segments being passed in its dung. The sheep, goat or human swallows the eggs released from the tapeworm segments, which further develop in the small intestine leading to cyst formation in tissues such as the liver or lungs.

Sheep or goats tend to suffer no obvious effects and after initial exposure their resistance generally prevents new cysts from forming. In humans, the cysts also generally form in the liver and lungs, but occasionally in other organs, even bones; if they become large or burst they can cause serious illness or even death. Surgery is generally required to remove cysts.

This disease can largely be prevented by:

• preventing dogs from eating fresh sheep or goat offal (liver, heart, lungs, kidneys)
• regular treatment of working dogs and pets in hydatid endemic districts with praziquantel
• washing hands after patting dogs whose coats may be soiled with tapeworm eggs

If you feed raw food to dogs, see the information in the box down the page.

Note: The large tapeworm segments often visible in the dung of sheep or goats, and described as looking like cooked grains of white rice, are not from the hydatid tapeworm, but are segments of the intestinal tapeworm Moniezia expansa and are not a cause for concern.

Treatment of sheep or goats for the M. expansa tapeworm will have no effect on the hydatid cysts in the liver or lungs.

Life cycle

Hydatids are primarily parasites of dogs, dingoes and foxes. Dogs become infected by eating offal containing hydatid cysts. These cysts have thick walls and may enclose many smaller cysts containing small tapeworm heads, giving them a sandy looking appearance (‘hydatid sand’). The cysts develop into adult worms once inside the gut of the dog. The adults then produce microscopic eggs with thick shells to protect them from environmental extremes. The eggs are passed into the environment when the dog defaecates and can be spread by insects, wind and water. The eggs are also very sticky and can adhere easily to the dog’s coat and transfer to human hands when patting the dog.

Tapeworm eggs eaten by sheep or goats (intermediate hosts) can lead to cysts developing in organs such as the liver and lungs. Sheep and goats both acquire strong resistance (immunity) to new cysts developing, but this has little effect on existing cysts. In order to complete the life cycle, raw infected sheep or goat offal must be eaten by dogs, dingoes or foxes. Other intermediate hosts include cattle, horses, pigs, kangaroos and wallabies. Rabbits can also be infected with hydatids but it is considered rare.

Threat to humans

Hydatid cysts can cause life-threatening disease in humans, caused by ingestion of eggs passed by dogs and then development of a cyst or cysts within the human body. This can be a particular risk in children with close contact with pet or working dogs where there has been less attention to hygiene (hand washing) and where dogs have eaten raw offal infected with hydatid cysts (note, not all offal contains hydatids cysts).

Hydatid disease in humans is generally treated by surgical removal of cysts. Life-threatening complications can occur when cysts develop in critical parts of the body such as the brain, liver or lungs.

Hydatids, and sheep measles (cysts of Taenia ovis in muscle meat) have similar life cycles: in flocks and herds where one occurs, the other may also occur.

The chance of infection is increased by the proximity of wild dogs, access by intermediate hosts to infected dogs’ faeces, and cool climates, which favour survival of eggs and cysts in the environment. Outbreaks can occur whenever appropriate hosts and the parasite come together, but are more common in some parts of Australia than others.

Control is based on breaking the life cycle; there are a number of methods. The most effective is to completely prevent dogs from eating carcasses, meat or organs from sheep, goats, pigs (except pigs raised in intensive piggeries), kangaroos or wallabies.

Washing hands with soap and water when around dogs will also reduce the risk of human infection.

Feeding raw meat to dogs

For those who wish to feed raw meat and offal to their dogs, the cysts present in offal can be inactivated by carefully using one of the following methods (as per Chapter 8.5. WOAH Terrestrial Animal Health Code):

1. heat treatment to a core temperature of at least 80°C for ten minutes or an equivalent time and temperature;
2. freezing to minus 20°C or below for at least two days.
   • Domestic freezers are normally about minus 18°C, but as some may not be maintained at this low temperature, freezing for 5 days is advised to account for the higher temperatures of domestic freezers; this also ensures larger pieces of offal are frozen to the core for long enough. Inexpensive thermometers can be purchased at kitchen shops to check your freezer temperature.

All farm dogs and any other dogs allowed into areas where there is livestock or kangaroos, wallabies or feral deer or pigs, should be regularly treated with praziquantel (5 mg/kg), which is found in “allwormer” products for dogs.

Raw feeders or those with dogs known to scavenge carcasses should also consider treating with praziquantel at 6 weekly intervals.

Other tapeworms in dogs: Taenia pisiformis, T. serialis and Dipylidium caninum are common tapeworms of dogs, foxes and dingoes and should be differentiated from T. ovis (sheep measles), T. hydatigena (bladder worm) and the hydatid tapeworm E. granulosus. The intermediate hosts of T. pisiformis and T. serialis are the rabbit and hare. The flea and possibly the biting louse are the intermediate hosts for D. caninum.

Further information:

NSW DPI Primefact – Hydatids – the basics (87 KB)

NSW DPI Primefact – Hydatids, you too can be affected (190 KB)