Amphibians Under Threat

Cats and their Parasites

Cats and their Parasites

Jekyll & Hyde

Pets are a good thing. They keep us company and enrich our lives. But not everybody looks after their pets in the best way. Environment groups have long been voicing their concerns about the damage that cats especially can do to wildlife. Regardless of whether you consider the estimates of native animals killed to be accurate, there can be no denying that the modern cat still bears the qualilities of its hunting ancestors: very sharp, retractable claws; fast reflexes and running speed; good vision and hearing. Generations of controlled breeding have yielded some breeds which can be docile but individuals can still vary greatly in their temperment.

An individual cat can also behave one way when it is inside the house and very differently when it is outside. When you play with your cat, especially as a kitten, you use toys or perhaps even a piece of yarn and you drag these around or dangle them up and down to get the cat's attention. This usually works, doesn't it? Once the cat has noticed the item, it becomes curious, chases the item and swipes it with its paws. Outside, there might not be a stuffed toy mouse or some red yarn but there are those long little dark things making abrupt strides across the fence (skinks) and those colourful objects which change shape and flit from grass to branch to clothes line (birds). These can stimulate the cat's attention and playful curiosity just as the yarn and the toy mouse did in the house. Unfortunately, when the cat decides to go and play with these 'toys' outside, they aren't toys - they're alive and they can be severely injured or die in the process.

Some individual cats still have an instinct to hunt or to provide a gift for their human family such as the dead animals that are brought back to the house and left on the front doorstep. The frog hospital has received frogs which were not only attacked but were partially eaten by the cat. Although many owners are convinced their 'sook' on the lounge wouldn't hurt a fly, there are obviously a lot of cats that don't meet this description because the animals they attack keep turning up at rescue centres. The phone calls keep coming in from discouraged home owners who are desperate for ways to keep other people's cats out of their yards and away from the wildlife they've tried so hard to encourage into visiting.

When people talk about the damage done by cats to native animals, they are referring to a direct contact situation where the cat has attacked the bird, lizard, etc. The frog hospital has received quite a few frogs which have been attacked by cats at night and by dogs during the day. Most of the frogs that have been attacked by cats either die from severe injuries or take many months to recover. The photo at right shows how sharp those claws are. This frog had a scratch on the top of its head (as well as other scratches) and looked as if it would heal but died soon after being turned in for care. After the skin on the head was cut away, the cause of death was revealed: a claw had not only scratched the skin, it sliced right through the skull.

To minimise the possibility of contact with nightime wildlife, many people recommend that you simply keep your cats indoors at night. This is a good thing to do but we now know that this is not enough. Since 1998, the frog hospital has been receiving large numbers of sick and dying frogs. Some of the dead frogs have been sent to labs for testing and, while we still have many more pieces of the puzzle to sort out, we have learned some critically important things.

One of the problems the sick frogs are having is severe parasite infestation. The worst parasite is a tapeworm called Spirometra erinaceii. The immature worm can live in many different host animals but, according to researchers, it only reproduces in ONE animal: the cat. We now know that cats can kill frogs even if they never come within a car length of each other. The problem is the cat's faeces. The tapeworm breeds inside the cat and the huge number of eggs are deposited in the faeces. From there, the eggs are washed into waterways.

The first stage of the tapeworm's microscopic larvae can live in waterways and these burrow into tadpoles in the water. So the gradual destruction of the frog is started before the animal has even become a frog! Such tadpoles that begin their lives infested with worms will carry them all their lives. The worms grow as the frog grows and, by the time the frog is an adult, it is plagued with dozens of these worms up to 20cm long!


Once inside a frog, Spirometra is a nasty, long-term predator. The worms migrate through various internal organs, damaging them as they go, and then the worms make their way to the muscle tissues. During inactive times of the year, the worms burrow into the muscles and reemerge during warmer times of the year or anytime the frog is put under stress (because of an injury or dry season food shortages). They can damage lymph sacs, cause internal bleeding and lymph accummulation and they can even penetrate bones, causing them to weaken and break at the slightest jarring. If the tapeworms have occupied the frog long enough, they can liquify the entire thigh muscle making it very difficult for the frog to move properly and catch its food. The skin itself can be dissolved by the worms and open lesions are often seen on frogs with long term parasite infestation. Once these holes in the skin are created, the frog becomes a sponge for bacteria and fungal diseases and dies within days if it doesn't get medical help.

So far, we have not found any medication which kills all the worms without killing the frog. All we have been able to do is bring the infestation under control so that lesions heal and lymph sacs are reduced. The frog will still need to be re-medicated whenever the worms become seasonally active. Even killing Spirometra in a cat requires extra attention.

If you have a cat, be sure you worm the cat regularly.
Some worming products will list spirometra on the package but their product doesn't actually kill spirometra. To kill Spirometra in particular, one of our previous consulting vets has suggested that four times the normal dose be used. These super-doses can be once a year but must be done two months in a row. If you are not sure about the killing efficiency of the parasite medication you are using, discuss it with your vet. You don't want to reduce spirometra in your cat - you want to eliminate spirometra in your cat!
Another drug that is specifically aimed at spirometra is praziquantal (Drontel or Propenol) so you could switch off your usual wormer during Oct and Nov and use praziquantal for those months only so that the worms are cleared out of your cat before the summer frog breeding season starts.
If you allow your cat outside, please provide it with a kitty litter box outside and train the cat to always use that box - not your yard.
Clean up any droppings quickly that your cat has done in the yard and remove some of the adjoining soil with the dropping. Dispose of this in a sealed plastic bag in your garbage bin. Never discard cat faeces into any waterway or area which will drain into a waterway during heavy rains.
If you don't own a cat but your neighbours' cats visit your yard, clean up the droppings as described above as soon as you find them.

There are other cat and dog parasites which also invade frogs and cause problems such as hydatids which live on the skin of animals. Hydatids have been found on the White-lipped tree frog in particular and can only be treated in the early stages - once the infestation is advanced, it kills the frog. Keep your pet properly bathed with medicated shampoos to ensure it is not producing skin parasites that could spread to other animals.

These parasites are a serious cause of decline in some frog species and we hope that if you are a cat owner, you will follow the recommendations on this page which will give you a healthier pet and help save frogs.

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