Histoplasmosis in Cats: A Personal Story

I remember it clearly: I was standing in the exam room at my vet’s office. Across the table stood my vet, and between us sat Mick, the cat who had deviled us for the past six months. She was now just a shell of her former Psycho Demon Cat self – and I had just learned she’d lost even more weight in the past week, taking her to a scant 4.8lbs. We’d tried everything. She’d been seen by top internalists at Oklahoma State University. She’d been scoped, prodded, stuck, injected, treated, tested. And nothing was working. I could feel her spine and ribs through her short fur. I looked down at her and realized this was probably the end of the line, and even opened my mouth to ask the vet if that was the case – at the same moment he said, “I want to try one more thing.”

A week later, in my kitchen, I got the phone call. “I have good news and bad news,” the vet said, and I could hear the excitement in his voice. “The good news is, it’s histoplasmosis. The bad news is, it’s histoplasmosis.”

“There is no bad news,” I said.

My vet said he’d already ordered the antifungal drugs, and within 48 hours of being on them, Mick was eating normally and acting more like her Psycho Demon Cat self.

Anyone who owns animals – dogs, cats, snakes (blech!), whatever – knows the utter frustration and fear that comes with knowing your pet isn’t well – but you have NO idea why. You take them to the vet, who will examine them and do diagnostics – blood work, temperature check, etc. Sometimes you get an idea of what’s wrong right away. Sometimes past issues get in the way (one time, my cat Rascal wasn’t feeling well, and given his history of bladder issues, that’s what the vet jumped to – until I went to pick up Rascal and discovered he had a huge abscess on his chest). And sometimes, the vet just doesn’t know.

And sometimes, you get lucky. Because you’ve seen the symptoms before.

Nigel (left) with Hammie (remember him? So itty-bitty in June and now he’s the biggest kitty in the house!

That’s was the case a few months ago when one of my barn cats, Nigel, started to drop weight inexplicably. Because it was getting colder, I let him come inside. I also took him to the vet immediately. He had no underlying issues, no real medical past, so we assumed perhaps it was worms (though he’d been wormed just a few months earlier) and he came home. But he kept losing weight. And then he got picky about his food, only licking the gravy from his canned and refusing most things.

And suddenly, I knew what it was. Because I’d seen this before with Mick.

Histoplasmosis is a fungal infection, carried by birds. If a cat ingests it or breathes in the spores, they can’t shed it – it takes root in the body, settling in various areas, including the kidneys, bone marrow, and lungs. There’s some debate about where it’s endemic – it’s actually endemic in the Ohio Valley region – but having had two cats with it, I can tell you that it IS in Kansas, and elsewhere through the Midwest. If there are birds, histoplasmosis is a possibility.

Every cat presents slightly differently, but for me, the major symptoms were:

Weight loss – It’s an insidious weight loss – not sudden, but slow enough that you look at your cat one day and think “Wow, when did you get so skinny?” Because they start to become anorexic (technical term for ‘not eating’) they lose more and more weight. It took Mick about six months to go from a health 10lbs to about 4.8lbs; it took Nigel about three months.

Picky about food – for both Mick and Nigel, the tell-tale sign was this one, and it’s very specific. The cat loses interest in ALL food, but will lick gravy from canned food. You may go through 20 types of canned food to find something they’ll eat once or twice, then abandon. My vet has seen 11 or 12 histo cats in the past ten years, and all of them had this symptom. They eat barely enough to stay alive, and sometimes, not even that much.

Weird blood work results – Mick’s histo settled in her bone marrow and kidneys .Every time we did blood work, the results led us down a different path. Once, her potassium levels were wonky. Another time, it was something else. Every few weeks, it was always something else. With Nigel, we never saw that, but I think that’s because we figured out right away what it was we were dealing with. We didn’t run blood work on him like we had to with Mick while we were trying to diagnose her.

Respiratory issues – with Nigel, the histo settled into his lungs and sinus cavities. He sounded like he had pneumonia, and it affected his sense of smell as well.

Depression – cats with histo feel like hell, all the time. They’re not interested in doing anything. In fact, even when we had Nigel on medicine and I was syringe-feeding him, there were days when I thought we would lose him just to his depression.

I was lucky with both of my cats. I was blessed with a vet who was committed to finding out what was wrong with Mick – she was his first case of histoplasmosis, and it took us about 6 months to diagnose it, from her first symptom of weight loss to the final diagnosis. There’s only one lab in the country that tests for it. Without my vet, I would have lost Mick – and without Mick, I couldn’t have diagnosed Nigel.

It was clear immediately, once I saw Nigel licking gravy and not eating, what we were dealing with, and I instantly called my vet to schedule the histo test. The results came back as I was battling COVID-19. But unlike Mick, Nigel didn’t respond to the usual medication. It made him extremely ill – he became anorexic (more than usual, and I didn’t think that was possible), more depressed, and nauseated. It took a while to figure out that we needed to switch him over to an inject-able antifungal instead. By that time, he was being syringe-fed (a wonderful product from Canada called Critical Care Carnivore saved his life) and weighed just 5.8lbs. There were definitely days when I wondered what I was doing, and it was always in the back of my mind that just because you diagnose something doesn’t mean you can cure it.

Today, almost four months after his first symptoms, Nigel is clear of histoplasmosis. He’s back up to 7.5lbs. He still won’t eat canned food – I think it made him nauseous when he was already ill, and he associates it with that – but he does have a specific dry food he loves. He probably will never again be an outside cat (he won’t drink anything but water from my Brita pitcher now), but he’s happy and healthy, and that’s what matters.

I wanted to share this story because I know there must be dozens – maybe hundreds – of cat owners out there who are struggling, or have struggled, with these symptoms and had no way to know what was causing them. Taken apart, they’re so indistinct that they could indicate almost anything – we tested Mick for FIV, FeLV, even scoped her for ulcers and GI issues and tested her for lymphoma. And unless your vet is familiar with histoplasmosis, they probably won’t even think to test for it. It’s not recognized as endemic in most of the Midwest, after all. Your vet might even point that out. Insist on the test anyway. As I said, only one lab in the country does the test. But a positive result is a POSITIVE result – there are no false positives with this test. And once you know, you can start the treatment. If your cat has a bad reaction to the antifungal, like Nigel did, insist on switching to the injections. They have to be given in subQ fluids – Nigel was on a three-day-a-week schedule – but it’s worth it.

Here’s some good resources and references on histoplasmosis:


https://news.okstate.edu/articles/communications/2019/recognizing_histoplasmosis_in_pet_dogs_and_cats.html – this is a 2019 article from Oklahoma State University. Good to see them recognizing it as endemic now!

https://www.dvm360.com/view/canine-and-feline-histoplasmosis-review-widespread-fungus – a bit older, but still good information.

This is the Carnivore Critical Care that I put Nigel on. You can find it on Amazon. Some cats will eat it just fine; I had to syringe-feed Nigel, but I am convinced this is what bought us enough time for the antifungal meds to start working.

Postscript: I have had so many reactions to this post, but I do need to add a postscript, and a warning.

We lost Nigel last fall to kidney failure. As with Mick, the histo had settled into his kidneys, though we didn’t catch it at the time because we were more focused on his lungs. It’s really important to run those blood panels, and if the kidney levels are even a little indicative of kidney disease, to put them on a kidney diet immediately, and check again in a few months to see if they are improving. Mick had a full recovery; she has been in remission for years with no issues. Nigel was not that lucky, and as cats are wont to do, he showed no real symptoms of kidney failure until he was already at Stage 4, with no chance of recovery. I was heartbroken to have brought him through one life-threatening disease, only to lose him to another in just a few short months. Please run the blood panels.