Articles with the names of illnesses

The definite article the is sometimes used before the names of some common illnesses. Examples are: the measles, the flu etc; others have no articles. Examples are: cancer, stroke, jaundice.

A few illnesses take the article a/an before them. Examples are: a cold, a headache, an earache, a backache

I have a bad headache. (NOT I have bad headache.)

Measurements

Measuring expressions beginning with by usually take the article the.

They sell mangoes by the dozen. (NOT They sell mangoes by dozen.)
Can I get paid by the week?

Also note the expressions 40 miles an hour, twice a week, sixty pence a kilo etc.

Place names

The definite article the is used with the names of seas, mountains, islands, rivers, deserts, big hotels, theatres, museums and art galleries.

Examples are: the Atlantic, the Himalayas, the West Indies, the Thames, the Sahara, the British museum etc.

No articles are used with the names of continents, countries, states, towns, streets and lakes.

Examples are: Asia, France, India, Oxford, Chicago, Lake Victoria etc.

Exceptions

Articles are used with places whose name contains a word like state, union, republic, kingdom etc.

The United States of America
The United Arab Emirates
The People’s Republic of China
The United Kingdom

In British English, the is not usually used with the names of important public buildings and organizations.

Oxford University (NOT the Oxford University)
Salisbury Cathedral

In American English, the is usually used in such cases.

The Harvard University
The Chicago City Council