At some point of the term, some teachers lose their motivation and desire toward teaching their students. How to overcome such a negative attitude?

Regular routine brings in monotony and thus a loss of interest. Hence to spice up the teaching environment, it is very essential to have the various teaching activities conducted with as much of  different mechanisms as possible. Here the most useful is to make the learning more fun by having interactive sessions, introducing role play aspects while explaining or stressing about communication skills.The feed back from the students will improve their participation and increase the enthusiasm of the teacher and the taught as well.

Avoid routine, use external sources,engage with the students and ask them about their preferences, and  have some fun in the lectures.

I think that the greatest gift that a teacher can get from the students is their feedback, respect, and longing to follow in your footsteps and example in life.  Find ways to motivate the students toward these goals and the teacher will in turn revel in the immense reward that comes with teaching.