The short answer- Yes! Rodents such as rats and mice can carry a bunch of diseases such as hantavirus, leptospirosis, tularemia, and the plague. Mice can also carry Lymphocytic chorio-meningitis. Many of these diseases can be spread through breathing in dust contaminated by droppings or urine. This means that you risk getting sick, even if you dont know you have an infestation. According to the Center Of Disease Control (CDC) many people who became ill reported that they had not seen rodents or rodent droppings at all.
First of all, make sure every single entry point is sealed off! Many rats can enter through a hole the size of a quarter, and they have strong enough teeth to chew through most materials to enlarge a hole until its big enough for them to fit. Check places where your exterior siding reaches the ground, where piping or wiring comes out of the house, where two forms of siding meet, where corners meet, soffits, eaves and any place where there is a break or end in material.
Next, evaluate pathways. Trees that overhang onto your roof makes your attic the place to go! Keep shrubbery a few feet away from your roof structure, and at least a foot away from your house at ground level. Rodents like to hide so make it harder for them!. If you see a dirty/greasy spot near a hole or along side piping or wiring, that is likely a path they are using to enter your home.
Even though your home is sealed, it's not guaranteed they won't find their way in. Make sure you keep the house clean and regularly remove debris and old food, otherwise the rats will find out and force their way in. If you have rats in your neighborhood, you are likely to get rats, even if you do everything right. If you hear of neighbors finding rats, it might be a good time to re-check your house, take a peek up in the attic or in the crawlspace, and maybe set a few traps.
Just be careful when putting out poison. The few rats that eat and are killed by the poison may die in your house or even in your walls. This can lead to a terrible odor and a much larger, more expensive clean up project. Poison can also affect many other animals that hunt rats and mice. The predators may become ill, or worse after eating a poisoned rat. This could allow the rat population to grow by reducing the amount of predators. Many neighborhood cats and dogs will go after a rat, so protect your furry friends!
If you do find out that you have rats, it is really important to take care of it sooner rather than later. Not only will you be susceptible to the diseases outlined but they can quickly wreak havoc on your home as well. They can chew through pipes, wires, walls, and leave a not so sweet smell. If you take care of them early, you reduce your risk of damage to your house and heath, and reduce their ability to multiply.