An Interesting Microscope Slide

D. E. Larsen, DVM

I looked at the pathetic little orange tabby kitten that was on the exam table. It was supposed to be a year old but looked more like six months. It had very little meat on its bones, and it looked like it had some long-standing chronic diarrhea. The diagnosis could be any of a dozen things, but feline leukemia virus was at the top of my list.

I glanced at the older lady who brought the kitten in and was standing at the end of the table, waiting for some glimmer of hope from me. This was going to be tough.

“We are going have to do some tests to find out what is going on with this kitten,” I said, trying to display some genuine concern.

“Tests, what kind of tests are you talking about?” Mrs. Alford asked. 

“With this chronic diarrhea, I need to do a fecal exam to check for worms and other parasites. I should also do some blood work. This kitten looks a little anemic. Feline Leukemia Virus is a possibility, and that requires sending some samples to the lab for a diagnosis.”

“We are not in a position to pay for a bunch of testing for a sick kitten. We moved to town about a year ago, and we are still recovering from the expense of the move.”

“Where did you move from?” I asked.

“We moved from Arkansas,” Mrs. Alford said. “My husband’s brother has been out here for several years. He had a job lined up for my husband. There is a lot more work here than back home, and the money is much better. But still, it takes a little time to get our feet under us again.”

“We can try treating this kitten with some simple testing. I can do a fecal exam here, and I can look at a blood slide. I like to think that I am pretty good at diagnosing Feline Leukemia from a blood slide. I’m not as good as the lab, however. The thing you need to understand is that if this is feline leukemia, this kitten will die. There is no effective treatment for it at this time. If we miss the diagnosis, sometimes we will spend a lot of money on treatment that, in the end, do little or no good.”

“We are interested in doing something if we can help Ginger. Otherwise, we will just have to make some other decision.”

“Can you leave her with us until late this afternoon?” I asked.

“Sure, would four o’clock be okay?” Mrs. Alford asked.

“That would be great. We can have everything done by then, including her initial treatments.”

We put the Ginger in a kennel, and before we could get a little box in the kennel, she deposited a stool sample for us. We collected the sample and started a fecal floatation. 

I used Zinc sulfate as a floatation solution. Mixing it with the sample in a test tube and spinning it in a centrifuge would bring all the worm eggs to the top of the test tube, where they would be collected by a coverslip.

When I put that coverslip on a microscope slide and got it under the microscope, I was shocked at the number of worm eggs on the slide. 

“This poor kitten, she has a massive number of roundworms and hookworms. I wonder if there are other pets at home that came from Arkansas,” I said to Dixie. “She will definitely benefit from some worm medicine.”

Then I collected a couple of drops of blood. We ran a packed cell volume, and Ginger was only slightly anemic. 

“This anemia could easily be from the parasites,” I said. “Ginger might be lucky and not have leukemia after all.”

With one drop of blood, I made a smear on a microscope slide. I stained the smear with a Dip Quick Stain and put it on the microscope as soon as it was dry.

I started scanning the slide, looking for abnormal cells that would suggest a case of feline leukemia. The slide was primarily normal, except for an increase in the number of eosinophils. Eosinophils are a white blood cell that often increases with parasitism. So this was not alarming to me.

Then it came into view. It took me a moment to digest what I was looking at. Here in the middle of the slide, was a microfilaria. This tiny worm had all the anatomy that was consistent with a heartworm microfilaria. 

Heartworm disease in the cat is rare. In areas with heartworm disease, it only occurs about one-tenth the number that it occurs in dogs. In Oregon, in 1977, heartworm disease was rare or nonexistent in native dogs. How in the world did this cat get heartworms.

I called Mrs. Alford. “Mrs. Alford, Ginger is heavily parasitized. She has many roundworms and many hookworms. I also think that she has heartworms. I am going to send a slide over to the diagnostic lab for confirmation on the heartworms.”

“What does it mean for her chances?” Mrs. Alford asked.

“I wished that I could answer that question,” I said. “I have never seen a case of heartworms in a cat. I don’t think we can treat them in the cat, so it just depends on her living with them if she can. The good thing is cats generally only and one to three heartworms when they are infected. Hopefully, she will feel a lot better when we get rid of the other worms.”

“Can we pick her up this afternoon?” Mrs. Alford asked.

“Yes, and when you pick Ginger up, I would like to discuss her life with you. I am very puzzled at how it is that she became infected with heartworms.”

“Well, she does live with our three dogs. All the dogs lived in Arkansas for five to six years.”

“I guess that could do it,” I said. “I will send this slide over for the lab to double-check it, and I will let you know their findings.”


“Good morning, this is Doctor Dale Robertson,” Dale said as I answered the phone. “I am a resident at the diagnostic lab. I am looking at the slide you sent over. That is definitely a heartworm microfilaria. I was wondering how you found this?”

“I was just scanning the blood smear,” I said. “Actually, I thought this kitten had feline leukemia. It is close to a year old and looks to be less than six months. This microfilaria just jumped out at me.”

“Heartworms are thought not to exist in Oregon,” Dale said. “And in endemic areas, they are very rare in cats. How do you suppose this cat was infected?”

“The family is from Arkansas, and they have three dogs in the house that came from Arkansas,” I said. “This kitten was born in Sweet Home. The reservoir is obvious, but the transmission needs to be explained, I guess.”

“The lifecycle change in the mosquito is very temperature dependent,” Dale said. “You hear different times and temperatures. It sort of depends on which expert you read. But it is generally accepted that you need a temperature over fifty-seven degrees for twenty-four hours a day for two weeks for that change to happen. Those are rare temperatures in Oregon. I guess it could happen inside a house.”

“It is my understanding that there is not much to do with the treating heartworms in the cat,” I said.

“Yes, they have to live with the worms, if they can. And just so you know, I am going to write this up for publication. It should be of interest to a few experts.”


When I talked with Mrs. Alford, Ginger was much improved with the deworming. I explained the heartworm infection, and she was not too worried about any treatment.

“Back home, every once in a while, a dog will die from heartworms. The vets say a lot of dogs have them. I’ve never heard of a cat with heartworms. But Ginger is just going to have to live with them if she can,” Mrs. Alford said.

I was able to follow Ginger for another year before I lost track of the Alfords. During that year, Ginger was doing fine.

Photo by Daniel Bernard on Unsplash.

Published by d.e.larsen.dvm

Country vet for over 40 years in Sweet Home Oregon. I graduated from Colorado State University in 1975. I practiced in Enumclaw Washington for a year and a half before moving to Sweet Home to start a practice.

4 thoughts on “An Interesting Microscope Slide

  1. People who have pets should be prepared to pay for their medical bills. Poor little Ginger. At least she had a good year after you found out about the worms eating her up alive. One that we know of, she might have had more. Was she spayed?
    And the dogs – woman, you cannot just let the dogs have heartworm, you do want to kill that parasite to avoid further infestation .. *sigh*

    Tinykittens, that Canadian cat rescue I already wrote about here, has just now a case of a preemie kitten. Panda is a 31 days old, but looks as if she was two weeks. She weighs 249 g – and that is a success story so far! All her siblings were lost, and the mom and one of her sisters were diagnosed with Feline Leukemia Virus. Cleo, the mom, is only 7 months old and had to have C-section for her last two kittens. She had three, before TK came to the rescue (quite literally), one of which died before TK arrived. And the last two were delivered by emergency c-section (she was spayed during the c-section, of course) – and that is when they found out she is FeLV+. She is recovering at TK, at meanwhile 8 months a kitten herself, still. They will find a place for her, somewhere inside.

    As for little Panda, we don’t know. The last kitten to die, Paisley, was positively tested, so the chances are high, Panda suffers, too. She has green specs in her poop – and the poop is quite runny, too. Shelly Roche, from TK, is in contact with a team of vets, as she has never had to deal with so much piled up against one kitten. That is why her being alive and active and even starting teething and gushie food right now is a huge success story.

    Cleo and her kittens came from a complicated, human mental health situation and Cleo and her litter opened up the chance for TK to intervene, spay and neuter the other cats there, even Cleo’s mom got rescued.

    When I read about Ginger and your suspicion of FeLV I had to swallow, hard … and was immediately thinking of Panda.

    If you are still interested in these kind of stories, here is a link to TK Facebook with a video of Panda:


  2. You were always very thorough, and I am not surprised you found the heartworm. I am guessing you saw a few diseases like that one transferred from state to state when people moved with their pets. I remember your story about chiggers most likely being introduced to the area here that way.


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