hey Mehnaz - not to turn this into a religious discussion but here are some Hadith that should help you better understand the concept of illness and disease in Islam. So the next time the ignorant people say something stupid, you can teach them a thing or two 
Abu Hurairah also reports that Allah’s Messenger, peace be upon him, said: “For every misfortune, illness, anxiety, grief, or hurt that afflicts a Muslim -even the hurt caused by the pricking of a thorn - Allah removes some of his sins.” Ibn Mas’ud said: “I visited the Messenger of Allah, peace be upon him, while he had a fever. I exclaimed: 'O Messenger of Allah! You have a high fever! ’ He said: 'My fever is as much as two among you [might have]. ’ I asked: ‘Is it because you have a double reward?’ He replied: ‘Yes, that is right. No Muslim is afflicted with any hurt, even if it is no more than the pricking of a thorn, but Allah wipes off his sins because of it and his sins fall away from him as leaves fall from a tree’.”
'Ata ibn Rabah related that he heard Ibn 'Abbas say: "Shall I show you a woman of Paradise?"I said: “Yes, indeed.” He said: “A black woman came to the Prophet, peace be upon him, and said: 'I suffer from epileptic fits, and because of these, (at times) my body becomes uncovered. Would you invoke Allah, the Exalted One, to cure me of this disease? ’ The Prophet, peace be upon him, said: ‘If you wish, you can be patient and you will attain Paradise (for this suffering). But if you prefer, I will pray to Allah, the Exalted, to cure you of it?’ The woman said: ‘I will be patient,’ then added: 'I become uncovered (when I have fits), so invoke Allah for me that I do not become uncovered. ’ So the Prophet, peace be upon him, prayed for her.”