Fleas can come from many sources
There are a couple of places where your cat may have picked them up. It can often be hard to tell the source. Fleas are around all year now due to our warm homes. Cats can get fleas from other cats. If your cat is an outdoor cat and meets others this can be a source of fleas. Fleas can jump quite a distance from one animal to another. It is also possible to contract them in boarding or at cat shows.
Other animals can also be the source. There are specific fleas species that tend to live on cats, dogs and rabbits but they can transfer from one species to another. In South Dublin there are a lot of foxes. Foxes can carry fleas and mites. It would be rare to come in direct contact with a fox but foxes dens can be full of fleas, larvae and eggs.
The house can also be a source of fleas. Fleas lay eggs which turn into larvae and then pupae. These pupae can survive a long time in the environment, up to 2 years. Based on vibrations and warmth they can then hatch and jump onto your cat. The house could even be infested before you move in and your cat could trigger a emergence of fleas from pupae. Keeping your cat regularly treated with a long acting product such as bravecto plus can help break the flea cycle. Treating your house with a licensed household flea spray will help eliminate them from the environment.