Thank you Clare,
Poor wee Ollie.
Now just to note while worms are well known to siphon nutrition from cats, it is more often the cause for kitten weight loss then adult cat weight loss. So, with that worming experience, I wouldn't advocate worming at this point unless we first checked a fecal sample that told us that there was a worm load worth treating. and even then we'd want to worm with great caution for him.
As well, I would note that the withdrawing and change in behavior are not unsurprising if he feels unwell. Since cats are not actually the top of the food chain they do have some prey-like instincts. Specifically, they often pretend all is well for as long as they can and then withdraw/hide/change behaviors when they cannot pretend. So, his sleeping elsewhere and being short tempered are likely just signs (as much as his lethargy) that he feels rubbish with this.
Now when a cat goes shows appetite decline as Ollie has, we have to consider two potential issues. Specifically, his signs hints that he is either experiencing severe nausea (where they stop eating to avoid vomiting rather then eating and then vomiting like a dog would) or oral/upper GI based discomfort. In regards ***** ***** causes for each, we can see nausea bother older kitties due to bacterial or viral infections, pancreatitis, IBD, cancer (always a concern in older cats), metabolic (ie hyperthyroidism), and organ diseases (ie kidney, liver). For oral issues, the most common are dental based issues (ie gingivitis, tooth decay, fractures of teeth, etc) but we can also see oral tumors and oral ulcers induced by viral and/or kidney disease. In his situation, while both fit and would be a concern here (even without vomiting), I would consider that his behavior may be being triggered by discomfort more so (since these often are the cats that beg for food before turning away like they just cannot eat it).
With all that in mind, we would want to address both angles since he cannot tell us which is bothering him. Therefore, to start, you can cover your bases and rule out nausea as a case by trying him with an antacid. There are a number of antacids that are available over the counter and pet friendly. I would advise only treating with one, but the two I tend to recommend are Pepcid (More Info/Dose) or Zantac (More Info/Dose). This medication of course shouldn’t be given without consulting your vet if he does have any pre-existing conditions or is on any other medications. Ideally, it should be given about 30 minutes before food to ease his upset gut signs. You can then offer his soft food or try tempting him with light diet options like boiled chicken, white fish, scrambled egg, or meat baby food --as long as it free of garlic/onion. And since he is struggling, small frequent meals could be offered to him.
Further to this, with all these potential triggers in mind, since he is already struggling to eat, I am concerned that we do need to be aggressive here to avoid him going off his food and getting even more weaker here. So, on top of the above, I would note that if he isn't tempted with our light diet options, then you can start offering or even syringe feeding him. To do so, you can use a high calorie supportive diet like Hill's A/D (LINK) or Clinicare Canine/Feline Liquid Diet (LINK). You can even offer (or water down to syringe) pate style kitten food to get more nutrition in per bite he takes.
If you use these and he doesn't improve with mild GI settling steps, then oral discomfort will be more of a concern and that would be our cue to consider getting his vet involved (since there are no safe OTC pain medications for cats). And if you do need to get his vet involved, then you'd want to them to perform an oral exam (which cats in his situation don't tend to be particularly amenable to just letting anyone look). Depending in their findings, the vet will be able to access his mouth and address the root of the problem, and will also be able to provide long lasting injectable antibiotics and cat safe pain relief if necessary. If they do find ulcers in the mouth or their examination does suggest those potential nausea inducing issues, then you might consider having a urine or blood sample checked to ensure his organs are functioning as they should. Depending on their overall findings, they can advise you on which of the above are triggering his signs and initiate treatment to soothe those signs and get him back to eating properly before he can become anorexic and just fade away.
I hope this information is helpful.
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All the best,
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