Should bee activity reduce considerably or to nil it is quite likely that a disease exists in the hive. AFB (American Fowl Brood) is the worst and is fairly prevalent particularly in coastal areas.
Open brood box and cut a sample (approx. 12cm x6cm); place in clip lock bag and label with your registered number; complete "Brood or adult bees specimen advice sheet" (request they email result - ensure you quote your email address) and mail this with specimen to Biosecurity Sciences Lab. - address is on form (postage is about $8). ENSURE THE ENTIRE BOX/BOXES ARE CLOSED SO THAT NO OTHER BEES COULD ENTER THE HIVE TO ROB AND FURTHER SPREAD THE DISEASE (Bees robbing infected hives for "free" honey is the major reason for the spread of AFB).
a "Negative" reply but if positive contact one of the more experienced beekeepers for advice on procedure to sterilize your hive and equipment and take the utmost care that no bees have any access to even a drop of honey (small amounts of honey are present in cappings etc so take care that this infected honey is disposed so that bees do not have any access to it if you melt wax. Our club has a "cooker" for treating equipment.