Understanding the Lifecycle of the Hydatid Tapeworm

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Edgar Clarke
5 years ago
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1 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.

2 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.

3 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!

4 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

5 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.

Hydatid Disease. Overview

Hydatid Disease. Overview Hydatid Disease Overview Hydatid disease in man is caused principally by infection with the larval stage of the dog tapeworm Echinococcus granulosus. It is an important pathogenic zoonotic parasitic infection