The reason I say that is because you mention that the snake strikes at the food and that it is lossing weight. If a snake has an URI then it can not breath while eating like they normally do, so they will strike at the food (normally out of threat posture then feeding response) and then they will try to find cover or avoid the food. I just cleared up two of my Boas from an URI that were doing the same thing and now they are both feeding again!
The weight loss is due to the energy that the snake uses to fight the infection. A male that would normally stop feeding this time of year anyway, would not normally show a visable amount of weight loss. They also normally (at least my boas) won't even strike at food as the are single minded in their thoughts of mating.
Look or feel for raspy congestion when you first pick up your snake, also open the mouth and see if there is clear mucus in it or check the nostrils for clogged or plugged holes or bubbles when breathing.
A URI is not normaly that difficult to get rid of but will normaly require treatment of antibiotic injections.
Good Luck and get the snake to a VET.
Thanks
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Jim Hopkins "Hoppy"
Hopkins Holesale Herps
Hopfam1@aol.com