Hawzah News Agency – If the blood of a human being, or of an animal whose blood gushes out when its jugular vein is cut, is sucked by an animal that is commonly known to have no blood, such that it may be absorbed in that animal’s body – like when a mosquito sucks blood from a human being or from an animal – then that blood is pure. This is called ‘transfer’. As for the blood that a leech sucks from a human being for the purposes of treatment, as it is not known whether or not that blood becomes part of its body, it is impure.
If a person kills a mosquito that had sat on his body and the blood sucked by the mosquito comes out of it, that blood is pure – even if the time that elapsed between the sucking of the blood and killing the mosquito was very little – because the blood was in the process of becoming food for the mosquito. However, the recommended precaution is that in this situation, one should avoid the blood [i.e. it is better not to treat it as being pure].