Scarsdale Vets explain the causes of hydatid cysts and how they are spread, plus advises on control methods.
Some of you may have had part of a carcass condemned due to hydatid cysts (approximately 0.2% of sheep livers are thought to contain these cysts).
Causes & Spread of Hydatid Cysts
They are caused by the larval stage of the tapeworm Echinococcus granulosus. The cysts are zoonotic, meaning they pose a risk to people, and are thus a food safety issue.
The life cycle of the tapeworm is shown below. The most common cycle is between dogs and sheep. Dogs can acquire the infection if they are fed fresh offal or if they scavenge infected sheep carcasses.
Carnivores (dogs and foxes) are definitive hosts.
The tapeworm grows and reproduces within their intestine, spreading the disease via eggs in their faeces. The sheep and cow are an intermediate host and cannot advance the lifecycle of this tapeworm. They pick up the eggs, which progress to larvae but no further. The larvae sit inside the cysts in the tissues.
Infected livestock rarely have any major health issues related to their infections, as the animals are often slaughtered before the cysts grow large enough to cause a problem (cysts in a sheep are around 2-6cm in size). In older animals, production may be affected as the cysts impact on the function of the organ they are in (most commonly the liver). A farmer is usually made aware of the infection by the abattoir when affected organs are condemned.
In humans the infection is called Hydatid disease (Echinococcosis), which can be fatal if untreated. In humans, cysts usually develop in the liver or lungs, leading to liver or lung dysfunction. If the cysts rupture they can cause a fatal allergic reaction.
The only control method available is to break the lifecycle in dogs. This can be achieved in the following ways:
- Regular worming of all working and visiting dogs for tapeworm (use a product which contains praziquantel)
- Consider fencing off footpaths
- Don’t feed dogs with raw offal or allow them to scavenge on carcasses
- Only feed dogs proprietary pet food
- Pick up dog faeces where possible and encourage walkers to do this in fields with footpaths
- Collect carcasses from the field as soon as possible
- Practice good hygiene when handling your dog
The habit of feeding pet dogs a raw meat diet has expanded rapidly in the last few years, increasing the risk of Echinococcus granulosus infection. We’d recommend not feeding these products to your dog unless they have been frozen below -20°C for at least 3 days, stopping the cysts from being infective. There are also other issues with raw meat, including bacteria which can survive freezing and still make your pet (and you) ill.
If you send your animals straight to slaughter it is always worth asking the abattoir for a report. These reports are highly valuable sources of information for your farm. There may be a wide range of infections present which aren’t severe enough for condemnation, but which allow you to adjust management to improve productivity.