Hydatid Tapeworm
The Hydatid Tapeworm (scientific name Echinococcus granulosis) is one
of a number of tapeworms that infect dogs. The reason this tapeworm
is considered the most significant is that, unlike the other tapeworms
found in dogs, it can cause an extremely serious and lifethreatening disease in humans.
Hydatid tapeworm disease in humans used to be a much bigger
problem in Australia than it is now, largely due to the increase in
feeding of commercial diets, better worming practices, and the move
towards life in the cities rather than rural areas. Despite this there are
still a number of people, particularly children, who are diagnosed each
year with this disease, and one or two people who die from it. Certain
groups of people are at higher risk of contracting the disease, and most
do not know they are affected until the disease is well advanced.
Understanding the Lifecycle of the Hydatid Tapeworm
Like many worms, the hydatid tapeworm has a complex lifecycle that
involves a number of species. The mature worm lives and reproduces
inside the dog’s intestines so it is considered a dog tapeworm (called
the ‘definitive host’). It may also live in the intestines of dingoes and
occasionally foxes too. The dog usually shows no signs of infection at
all, and some dogs have been found with thousands of tapeworms in
their intestines with no apparent illness.
The hydatid tapeworm is so tiny that it cannot be seen in the dog’s
droppings – unlike other types of tapeworms that infect dogs which can
be seen with the naked eye. The adult tapeworm can live inside the
dog for a number of years, and during this time it will periodically
produce and shed eggs which pass out in the dog’s droppings. These
eggs can survive for months in the environment if the conditions are
right – cool, moist, and overcast conditions are perfect.
The lifecycle of the hydatid tapeworm continues via an ‘intermediate
host’ – meaning that the dog cannot be directly reinfected by eating the
eggs of the tapeworm it passes in its own droppings. Instead, there
has to be another lifecycle phase inside a different species of animal.
In the case of the hydatid tapeworm, the intermediate host is sheep,
cattle, or kangaroos that graze on the egg-infested pasture.
Once inside the intermediate host, the eggs hatch into larvae. These
larvae then migrate through the stomach wall and into the bloodstream
before lodging somewhere in the animal’s body - most often the liver
and lungs. The larvae then mature to form a ‘hydatid cyst’ which is a
watery, fluid filled cyst in these organs. These cysts contain smaller
capsules, with each capsule containing up to 40 hydatid heads – each
of which are capable of turning into an adult tapeworm in the dog’s
intestines once they are ‘digested’.
Luckily, in cattle, many of the cysts end up ‘dying’ and only about 10%
can go on to infect a dog. But in sheep and kangaroos, the cysts are
far more likely to remain infective, and the cysts can continue to grow
over the life of the animal. When a dog (or dingo) eats the offal from
an infected sheep or kangaroo, it also eats the cysts - the life cycle is
then completed. Once inside the dog, the cyst releases the hydatid
heads and they mature into adult tapeworms ready to start laying eggs
within about seven weeks.
So why is this tapeworm such a concern?
The hydatid tapeworm does not cause any serious disease in the dog,
so you would not think it would be a problem in our greyhounds. The
worst effects are on the intermediate host – the sheep or kangaroo that
ends up with huge cysts in their liver, lungs or other organs. The size
of these cysts can lead to damage and eventually severe failure of
these organs.
The reason this tapeworm is so significant is because sometimes a
HUMAN inadvertently becomes the intermediate host – ingesting the
eggs of the tapeworm. Similar to the effect in sheep and cattle, the
infected human can develop these large hydatid cysts in their liver,
lungs or even kidneys or brain.
So how do humans contract Hydatid disease?
Humans can become infected with the tapeworm by accidentally eating
the eggs that have been shed by dogs. Obviously most humans avoid
eating dog droppings (although toddlers can sometimes put things in
their mouth that they shouldn’t!), but it is possible to eat contaminated
food, or to come into contact with the eggs from handling an infected
dog.
The hydatid eggs are quite sticky, and can remain stuck on the dog’s
coat especially around the anus area. Dogs then lick to groom
themselves, and the eggs can be moved through the coat, or can
transfer to the face and mouth area of the dog. When a human pats or
handles the dog, it is then possible to transfer the eggs onto their
hands. People who eat, drink or smoke without washing their hands
can then transfer these eggs into their mouth.
Alternatively, humans can become infected from eating raw vegetables
(often home-grown ones) that have been contaminated by dog’s
droppings. Making sure that dogs do not contaminate the vegie
garden, and that all vegies are thoroughly washed can help avoid this.
Note: It is NOT POSSIBLE for humans to become infected
by eating the contaminated offal of sheep or cattle!
Once inside the human, the damage done depends on where the
hydatid cyst forms, and also the size the cyst reaches. If the cyst gets
large, the organ it is in will have reduced or altered function – a big cyst
in the lungs can make a human very short of breath, a large cyst in the
brain can act like a brain tumour. Often the human does not even
know they are infected – until the organ fails, and then it is a case of
being very sick and needing major surgery to remove the cyst.
Unfortunately, there is no drug to treat the hydatid cysts in humans –
surgery is the only option to remove them! Sometimes during surgery
the cyst leaks or bursts, and each of the leaked hydatid heads may go
on to form another cysts, so multiple surgeries are often required.
Am I at risk?
The people with the greatest risk of becoming infected are those in
rural areas where dogs and sheep or kangaroos live in close proximity.
Anyone who feeds raw offal from sheep, cattle or kangaroos to their
dogs is also at an increased risk.
What can I do to avoid infection?
The Department of Primary Industries (Ag Note May 2008) recommends
that the following measures to break the Hydatid tapeworm lifecycle:
 Avoid feeding offal from possible intermediate hosts – especially
sheep and kangaroos
 Do not allow dogs to roam or scavenge from sheep or kangaroo
carcasses
 Treat dogs regularly with a worming product that contains
praziquantel to remove hydatid tapeworm – it is recommended
that dogs that are highly at risk are treated every 6-8 weeks to
keep them free from hydatids
 Feeding offal to dogs, even if boiled, carries a significant risk of
transmitting hydatids so feed commercially prepared foods

 Wash your hands after handling dogs and before eating and
smoking and make sure any children are taught to do the same.
Supervise if necessary.
 Don’t allow dogs to lick you own or your children’s faces
 Don’t allow dogs to defaecate near vegie gardens or children’s
play areas
At present Tasmania and New Zealand are both free of Hydatid disease,
so if you are planning on travelling with your greyhound to Tasmania
you will find it is a requirement of entry into the state that all dogs are
treated with a worm tablet to kill hydatids before they are allowed off
the plane or ferry. The disease continues to be a problem in the rest of
Australia so be careful, worm regularly, and avoid high-risk feeding
practices.
If you have any questions about suitable worming products, worming
programs, or hydatid disease, please ask your veterinarian for advice.