John Gill Commentary Deuteronomy 28:59

"then Jehovah will make thy plagues wonderful, and the plagues of thy seed, even great plagues, and of long continuance, and sore sicknesses, and of long continuance." — Deuteronomy 28:59 (ASV)

Then the Lord will make your plagues wonderful
Visible, remarkable, distinguishable, and astonishing to all that see them:

and the plagues of your seed ;
for they were to continue, as they have done, With their posterity, age after age:

[even] great plagues, and of long continuance ;
great as to quality and quantity, and firm, sure, lasting, and durable; the word used is rendered "sure" in (Isaiah 55:3) ; sure by prophecy and in the event; and which when inflicted remained, as they have 1700 years; all which might be believed as certain, or what would certainly come to pass, and be depended on:

and sore sicknesses, and of long continuance ;
besides those diseases mentioned (Deuteronomy 28:27Deuteronomy 28:35) ; or however others including them.