Contrary to popular mythology, and Mickey Mouse aside, rodents are a nuisance that can damage your home and endanger your family. These dangers can be as minor as damage to your wainscoting or as severe as life threatening illnesses, particularly if you live in a city that's a port town, where mice (and especially rats) can carry parasites from around the globe. Don't think of mice in the attic as being cute - think of them as a potential threat to your home value and your family.
The most common effect of rodents (mice, rats and the like) is physical damage. They all have incisors that grow constantly, and they've got instincts that drive them to gnaw to keep them worn down. They'll gnaw their way through plumbing walls, the walls of your home, the main support beams and more to get to where food is. Worst of all is what they do to cables, which to them seem to be roots...and can cause short circuits or house fires.
In addition to chewing holes everywhere, rodents can also ruin your home through the stench of their droppings. They drop as they walk and many times this will be in highly inaccessible areas, like your walls, appliances, and crawl spaces. While it takes a serious infestation to create this problem if you note the insane rapidity with which they breed it does not take that long to become seriously infested.
While there are very few diseases that transfer directly from rodents, rodents carry mites and fleas and other parasites that DO carry diseases that can cross over to humans.
Rickettsial Pox - A disease similar to chicken pox transmitted from the mites commonly found on rodents.
Food poisoning - If food comes into contact with rodent droppings or urine infections such as salmonella become a serious possibility.
Tapeworms and trichinosis - These parasites and many others thrive under the conditions found in a rat infested house.
Hantavirus - Once thought to be rare this disease is showing up in rodents all over Australia. This serious and potentially fatal disease is spread through inhalation of dust that contains urine, saliva, or droppings. Direct infection from bites is also possible.
Rat-bite fever - As suggested by the name this rare disease is transmitted through rodent bites.
The plague (pneumonic and bubonic) - This disease, carried by fleas and other mites that live on rodents, is thought by many to have been eradicated centuries ago; however cases are still reported today.
Let's look at some things that you can do to help keep these diseases away from your house.
First, there's keeping them out in the first place, or making your home unappealing. Look for any cracks or holes or loose plumbing fittings at about two feet or less from the ground; rats and mice can squeeze through improbably small spaces, and their usual avenue into the home is climbing the plumbing. Taking some time with a caulking gun can pay major benefits.
If you've got direct infestation evidence, get a cat, or a ferret, something that naturally preys on rodents. Even the most heavily infested house can be made free of rodents with a couple of adolescent to early adult cats, and they'll do it very quickly - about a week or so.
The next best option, if you can't bring in a predator, is a sticky trap, or a spring-trap. Sticky traps have glue on them to catch rodents; spring traps will try to snap their necks very quickly and humanely. If you need to bait traps, yogurt covered peanuts are the best kind of bait; also good candidates are peanut butter and bits of bacon. (In general, if it's high in fat and salt, a rodent will love it.)
If you have seen one or two rodents then you have a minor issue that you should be able to take care of on your own, however if you have a larger infestation or live in an area of Sydney that is prone to other pests like termites you might want to consider seeking professional help and having your house checked for other pests at the same time.