Predator or Prey? The Sneaky Life Cycle That Makes Hydatids Such a Deadly Parasite

A parasite that affects the behaviour of the host for its own benefit?? Unbelievable! Find out why Meat & Livestock Australia (MLA) now consider hydatids to be one of our most important disease risks.

Almost all animals can be infected by hydatids. However, the type of infection an animal gets depends on whether they are a ‘predator’ (carnivores including dogs, foxes, dingoes, wolves) or ‘prey’ (herbivores including sheep, cattle, goats, kangaroos, pigs, and horses).

In Australia, hydatids is both a meat quality and public health issue due to risk of infection in people. However, processor feedback has also confirmed that they also have a big impact on growth rates and carcase quality of cattle and pose a risk to sheep and goats.

The parasite cripples the prey animal by creating large, cancer-like larval cysts in their internal organs, making them easier to be chased down and eaten by the predator! This allows the cunning parasite to complete their life cycle as an adult tapeworm in the predator and release a new generation of sneaky killers into the environment.

Introduction and life cycle

Hydatids is caused by a range of tiny tapeworms that live inside the intestines of predator (carnivorous) animals. They only grow to a size of 3-6mm, making them the smallest tapeworms on the planet. Having these tapeworms inside their guts doesn’t seem to affect the host (mainly dogs and dingoes) much at all.

The head (scolex) holds fast to the lining of the intestine using suckers and hooks. The segments (proglottids) arise from the neck region of the worm and mature as they move towards the tail. Because they are hermaphroditic, each segment grows a complete set of male and female sexual organs, which produce eggs and sperm. The hindmost segment detaches and is expelled with the dog’s faeces, allowing an average 823 eggs per segment to be voided onto the ground.

If the eggs contaminate pasture, they are easily picked up by herbivores such as our cattle, sheep and goats, but also by wallabies, kangaroos or wild pigs. The danger however is that because they are spread by our household dogs, often these eggs end up in vegetable gardens, drinking water or on the dog’s coat, from where they can infect people.

Each year, many cases of hydatids are diagnosed in people across the world. In Australia, cases are mainly seen in rural areas. Because the larval cysts in humans do not respond well to medicines, surgical excision is usually required.

Types of hydatids

Various species of hydatids tapeworms exist in different parts of the world. These are adapted to the type of host species available. For example, in the northern hemisphere E. multilocularis primarily infects wolves and foxes (predator) and a range of field mice, voles and lemmings (prey). South American hydatids species infect dogs (E. vogeli) or cats, including jaguars and pumas (E. oligarthus).

In Australia, dogs (predator) and livestock (cattle, sheep and goats- prey) are the most common hosts around farms, while foxes and dingoes maintain the life cycle in the wild, along with their herbivore prey (kangaroos, wallabies, feral pigs). Note that related species of tapeworms cause diseases such as sheep measles and bladder worm (common in Australian sheep) and beef measles (seen rarely in Australia). 

Distribution and frequency of hydatids infection

Hydatid tapeworms and their larval cysts are seen in animals across Australia, but the incidence in Tasmania is very low thanks to a very successful control campaign. A survey of cattle slaughtered in Australian abattoirs in 2011-2013 showed that only 9 head of cattle (out of approximately 21m head inspected) had complete condemnations due to hydatids, while 31 head of sheep (out of 17.9m head inspected) were condemned. Liver condemnations are more frequent however, with an estimated 2% positive lines in sheep inspected at Wagga Wagga abattoir in 2006 (Ian Links, NSW DPI).

In cattle, a study by University of Queensland researchers sponsored by MLA (B.FLT.3006) found hydatid lesions in the liver of 2.3% of feedlot cattle, out of 400,000 head inspected between 2014-2020 in southeast Queensland. 

Impact on cattle and sheep

Hydatid disease was added to the MLA’s list of priority diseases in cattle in 2022, due to increasing awareness of the economic impact, currently estimated at $10m/year in cattle alone. Hydatid cysts usually grow in the liver, but can also infect lungs and other internal organs including bones and brain. Infection is associated with decreased carcase value, particularly in Wagyu cattle.

Control

Reducing infection rates in livestock depends on restricting the number of eggs deposited on pasture by dogs. This can be done by:

1. Regular treatment of farm dogs (every 6 weeks) with a hydatids-specific wormer containing praziquantel
2. Restricting dogs from eating roadkill or dead stock in paddocks
3. Disposing of dead stock as well as all viscera (guts) from home kills
4. Only feeding dogs safe meat (i.e. frozen meat, -18C for 5 days) or commercial dog food

Control of feral dogs, dingoes and foxes is more difficult but in some areas, baiting with praziquantel has led to lower infection rates.

For more information about hydatids and control methods, see WormBoss.