A disease is a particular abnormal condition that negatively affects the structure or function of part or all of an organism, and that is not due to any external injury. Diseases are often construed as medical conditions that are associated with specific symptoms and signs. A disease may be caused by external factors such as pathogens or by internal dysfunctions.
This would depend on the recommendation of a veterinarian or evaluation of a qualified person, as to whether the animal should be put down or not. If they believe that the animal pet should be put down, then it would be permitted to do so.
And Allah knows best.
Accountability is determined by the exercise their own free will and understanding of what they are doing. So for example a 4 year old child hitting another child or stealing is wrong but does the child fully understand yet- the implications of their actions. Are they held accountable in the eyes of Allah swt- the answer is no. This is also because their aql and rational/intellectual faculty is not yet developed fully.
Hence those suffering with serious mental illness in which their aql is severely affected such as severe bi-polar or severe mood disorders, or forms of schizophrenia my have entire breaks from reality, they may for example even think "they are the president of the United States" and actually believe it. These are cases in which such a person is not rational whatsoever and hence would most likely not be held accountable by Allah. Otherwise we are expected to control ourselves and not attribute excuses to simply being "crimes of passion" whereas we are expected to control our passions/impulses and not be controlled by them as human beings that is what distinguishes us from other creatures on this Earth.
wa Allahu al-'Alim,
And Allah is all knowing,
SHAFAQNA – Imam Sajjad (AS) had severe stomach ache in Karbala to an extent that he could not carry weapons or fight [1,2,3]. The illness started in Karbala and not from the time Imam Hussain (AS) started his journey towards Iraq. Of course his illness was a divine plan so that one child would remain from Imam Hussain (AS) to undertake the Imamate and the leadership of Muslims.
 Basaerul Darajat, Saffar Qomi, Pages 148 and 163.
 Alershad, Sheikh Mofeed, Page 114.
 E’alammul Wara, Tabarsi, Page 246.
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Thank you for your question. Illness, as well as other types of ordeal, covers a variety of purposes including the forgiveness of sins, an increas in thawab and an increase in stations.
For a discussion of some of
the ahadith in this regard please see the following podcast episodes:
May you always be successful
Imām Sajjad (alayhi salam) taught us a number of different supplications. They are all found in The “As-Sahifa al-kamilah al-Sajjadiyya”, and also available at https://www.al-islam.org/sahifa-al-kamilah-sajjadiyya-imam-zain-ul-abide....
Imām ’Ali (alayhi salam) recited the following dua when he was sick:
In the name of Allah the Beneficent the Merciful.
O Allah! Whenever You bestow a bounty upon me, my thanks is always less and whenever You have tried me in calamities, my patience was always less.
Then O the one who never made my thanksgiving being low, and O the one who, when sent the calamities my patience was very less inspite of which
He never deprived me of anything and O He who sees me doing sins but never degraded me.
And O He who saw me openly committing sins but never punished me.
Send blessings on Mohammad and his progeny, and grant me cure from this sickness without a speck of doubt You have power over all things.
You may find his supplications at the “As-Safiha Alawiya” .