Welcome to HCM,
With history you have given ,he is having fever with chills and rigors
,which is intermittent hence he is normal in between.
This may be due to Malaria
or viral fever
or any infection in side body like Viral Hepatitis
, so he must consult a Physician and after proper examination if required investigations may be performed and once diagnosis is made he may be treated accordingly.
In the mean time he can take a paracetamol
tab to keep fever down and even cold sponging may be done to give him comfort.
He should take liquids and keep him well hydrated .
Please take care