This is the 12318th most frequent Turkish word.
hastalığa
"To the illness" or "to the disease."
The word 'hastalığa' in this sentence is the dative form (to/against the disease), showing the direction or target of the action 'fights'.
Bağışıklık sistemimiz hastalığa karşı mücadele eder.
Our immune system fights against the disease.
In this example, 'hastalığa' suggests a resulting state that is invited, connecting the condition to the outcome (to illness).
Uzun süre kapalı bir yerde kalmak hastalığa davetiye çıkarabilir.
Staying in a closed space for too long can invite illness.
Here, 'hastalığa' indicates the target to avoid contracting (to the disease), representing a target state.