Old spreading outbreak of lice and nasty bug (1,4)
I believe the answer is:
e coli
'nasty bug' is the definition.
(I've seen this before)
'old spreading outbreak of lice' is the wordplay.
I cannot quite see how this works, but
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is present in the answer.
an anagram of 'lice' is 'ecli' which is within the left over letters.
This accounts for all the letters.
This explanation may well be incorrect...
'and' acts as a link.
Can you help me to learn more?
(Other definitions for e coli that I've seen before include "An infection found in food and water" , "cause of ill-feeling" , "cause of illness" , "Bug that causes food poisoning" , "Gut bugs" .)