Is mold an issue in houses?

Unlike wood framed houses in Europe / North America, houses in Mauritius are made of bricks and mortar.  There is no real chance for moisture to collect in walls unless there is a water leak in the wall itself.

But yes, mold can happen - but it will be in an extremely moist environment like in the bathroom or kitchen.  If you keep the house dry inside, either by keeping it well vented or with air conditioning, mold should be minimal / not present.

You should check for water leaks and / or where water collects - and get rid of those conditions in any house.

However, you can expect some green mold in or near water storage tanks - and the way to handle those is to clean those storage tanks with chlorine based solution periodically.

In summary, mold can happen but with proper precaution, this should not be a problem.

As above, mold will happen with humidity. If you keep things clean & ventilated, there are no issues. Houses here don't have air vents, so you just need to keep windows open & clean bathroom regularly.