This article does not focus on worms in the stomachs and intestines and airways of grazing stock. Suffice to say these worms are farming’s number one disease in NZ and controlling them is a multi-million dollar business.Maybe the most notorious case of internal parasitism in NZ, which happens to link farm animals with small animals, is hydatids. Thankfully, NZ is now, unofficially, free of this potentially horrible disease but the regulations about feeding meat and offal to dogs remain. The hydatids adult was a tiny tapeworm living in the gut of a dog – not affecting it at all. The adults produced microscopic eggs that come out in the dog faeces. If the eggs were accidentally swallowed by stock or people they turned into golf ball and bigger sized cysts in the host’s liver, lungs or brain. The hydatid life cycle was complete when the host was eaten by a dog. Some of you will remember the hydatids drenching and purging (for testing) dog strips and the regular treatment of all dogs with Droncit. Well, it was worth it. Today we still have sheep measles, which is another little tapeworm living as an adult in dogs, but the only intermediate host is sheep and the cysts are only a few millimetres across, are firm, white and live in muscle.
The common roundworms in our pets can damage intestines and cause ill-thrift. The microscopic eggs pass out into the environment and usually the life cycle is simply completed by another member of the same species accidentally swallowing those eggs. But that is not the whole story…The main roundworm of dogs is Toxocara. When swallowed, the eggs first develop into immature larvae. They ‘want’ to grow up in a dog intestine but they can go AWOL migrating. They can cross into the unborn puppies in a pregnant bitch. They can migrate into the eyes of puppies and, if the eggs are swallowed by people, on rare occasions, larvae can end up in their eyes! So be mindful of hygiene around dogs, especially children handling puppies. If you let dogs lick your face remember where their tongues might have been.Horses can have a roundworm that lives in the rectum and causes an itchy rear end – other domestic species do not. The little rice grain segments you may see on the fur near your pet’s rear end are muscular egg capsules that have broken off a tapeworm further up inside. They don’t tend to cause itch.
Horses often have “bloodworm”. The adults of these worms live in the intestines but their larvae live in the walls of the arteries serving the intestines. This can be a cause of colic and, on rare occasions, cause artery rupture and fatal haemorrhage.
No discussion on internal parasitism would be complete without mentioning liver fluke. There is one in NZ whose adults live as tiny “flounders” in the livers bile ducts in sheep and cattle. The life cycle goes through a phenomenal 12 stages. At one stage there is burrowing into and bursting out of reminiscent of Alien. If you happen to be a freshwater snail you might experience this in person. The final infective stage falls through the water where the snail is living and cements onto firm objects. If this is a blade of grass and stock eat it then the life cycle is complete. If it is a leaf of watercress and you put it in your sandwich without cooking it, then you can personally get involved too.
By David Haugh, Wellsford Vets
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