Thank you for your patience. As you can imagine there are quite a number of things that could be causing Jasper to lose the hair on his back. It is unlikely the hair is just falling out, and more likely he is grooming it to the point the hair is being blunted very short (so it appears as hair loss). Either way here we certain have to consider a range of possible issues including allergies. Typically cats can develop flea, food and contact allergies. I will talk through these possibilities with you now.
Firstly - you need to make sure that Jasper is definitely up to date with flea control. It sounds like your vet has helped with this now which is great to hear. It is also extremely important in this case that you ensure all pets in the household are treated at the same time. I would also recommend washing his bedding and treating the house to ensure any flea larvae are also taken care of. Even if you don't think he has any fleas, or if you think the house is flea-less, as a preventative, this is very important. If he has a flea allergy, it only takes one flea to bite him to make him excessively itchy everywhere!
Because of his symptoms, we also need to consider a food allergy here as well. If you wanted to, you could undertake a diet trial with a hydrolysed protein diet like Royal Canin hypoallergenic or Hill's z/d. This would mean feeding ONLY this (no treats or stealing other pets' food) for 8-10 weeks.
It is also possible that Jasper may have skin mites or lice as they commonly cause this sort of behavior. These could be either Demodex (not itchy) or Sarcoptes mites (VERY itchy) and you should ensure a full Veterinary revisit so that he or she can carry out a physical examination and possibly a skin scrape to check for mites and lice, as well as signs of fleas. The next step would be to double check for fungal disease (such as ringworm) and there are several tests for this including a UV light and a fungal culture.
Finally, we also have to consider that Jasper may be overgrooming due to stress. This is less likely if he seems content at home, but we do have to keep this in mind. This problem is called psychogenic alopecia and you can read more about this here: http://www.petplace.com/cats/psychogenic-alopecia-in-cats/page1.aspx You could try Feliway (a feline pheromone diffuser) to help rule out stress as being a causative factor in this problem. You can get this relatively cheaply from your local pet store or online at www.feliway.com
Given you have just been to your vet and got him some flea treatment, clean his bedding and treat the other cats, then see if that makes any difference. If not, I think a skin scrape and microscopy is definitely a good next step. I hope all of the above makes sense? If you have more questions or if I can help in any other way, please do not hesitate to ask! If you would like to accept my answer, please press RATE OUR CONVERSATION (I am not compensated in any other way). Bonuses are always welcome. Thanks! I hope to work with you again soon!
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