Please help! Insect bites causing large amounts of edema and pain

[emipou]

My trainer and I have been scouring every google search we can think of, we’ve talked to numerous vets, we are still scratching our heads a little on this.

My 21 yo PRE gelding has started getting these bites, starting in 2021 which cause severe edema in his barrel and chest region. The edema is so heavy, he can barely walk in the more extreme occurrences due to the pain.

We treat with a wide variety of medications (zyrtec, banamine, dex, this most recent round) to help target pain and swelling.

I’m wondering if anyone else has experienced this and might know what’s causing it…

Important things to note:

• stalled 24/7
• we live in an urban area near a large river
• we are located in the southwest
• i’ve ruled out black widow and brown recluse, but haven’t ruled out brown widow which has become more prevalent in the region in recent years (mostly because I can’t find any examples of such bites with horses, vet today didn’t know what a brown widow was)
• the bite heads surface within 24-48 hours after the bite and while they have a head, it remains fairly small, with swelling 3" in diameter
• fever, swelling, pain are the main symptoms
• happens mostly in the spring, today was our first fall appearance
• we’ve previously ruled out pigeon fever. Lyme disease isn’t really an issue here. Waiting for bloodwork, but previous work done has shown nothing of concern.

Looking for possible bee, wasp, spider type response.

We know definitely not from flies.
Everything I’ve googled for hypersensitivity with insect bites on horses seems to return hives or necrotic skin lesions, neither of these apply to my boy.

I’ll attach some photos of the edema to show how severe it gets.

[NaturallyHappy]

Gosh-that’s awful. What about Benadryl? I don’t know the dosage…

[emipou]

We have been giving Zyrtec instead of benadryl.

[JB]

Cetirizine (Zyrtec) would be more for preventing the histamine reaction, Benadaryl (diphenhydramine) would be more useful for dealing with histamine reaction after it happens

I would test for PPID, to be honest. Test this week if you can, next week is ok, it’s the tail end of the seasonal rise in North America

[IPEsq]

My vet says that Benadryl doesn’t work for horses. It’s not bioavailable in ingestible form. (see https://pubmed.ncbi.nlm.nih.gov/34921427/)

Those are pretty bad! Have you tried allergy testing? I think unless you can totally change his environment for some time, you are stuck treating symptoms unless you can get any success from some sort of immunotherapy. That does look like something where I’d reach for the steroids.

[emipou]

We did a ppid test a few months ago and it came back negative.

[emipou]

Yeah, an allergy test might be our last option, but in all honesty, what would it fix? We’re spraying, adding d-earth to his bedding, covering him when it’s cool enough… it would be nice to know. It was my reason for posting here and I do want to know what is causing this. I’m 99% positive it’s from an insect. We find a bite every time. I’m not sure the allergy test would list what type of insect?

The crazy thing about all this is that although he has had a rather not normal medical history, these bites weren’t an issue until 2021 (incidentally, 2 months after he was mine funny right? It’s the irony of horse ownership- and previous owner is still very involved in his care so it wasn’t just a hidden issue). He developed these allergic reactions just in the past couple years. It seems so extreme to.me.

[BlueDrifter]

wow. Since it is on the lower half, I am going to ask if he is in pasture/turnout where insects could jump up and reach those areas to bite?

[cilla1]

OP says stalled 24/7, what about his bedding? Once our haflinger had a bad dermathitis, turned out it was a batch of bedding contaminated by parasites which name I can’t recall. It was flax straw bedding by the way

[endlessclimb]

Is your bedding fluffy, or does it have little “sticks” in it? My young mare would react if any of the bedding even kind-of got stuck to her etc.

Can you switch the bedding as a test, put him on sand or something?

[Marla_100]

Just some food for thought here-
We live in Fl. where strange insect related bites happen frequently.
My mare was over reacting to normal overnight
fly or mosquito bites.
Also we suspected possible PPID and mild neuro.
She had 2 areas, one open raw spot and a weird
swollen spot near her eye. Neither would heal despite trying dozens of potions for almost a year.
Out of desperation I bought some MVP Eclipse Pm to try for the neuro symptoms.
Well surprise, surprise, the lesions actually started healing
and totally went away.
Then I went back and read the ingredients which
are also for “immune support” and saw all the
great vitamins and minerals in it.
Might be worth a try, also I believe many skin and immune problems are related to deficiencies.

[trubandloki]

I would look into things other than bugs.
Did you change fly sprays? Or coat conditioners or shampoo?
Has the bedding or the hay changed at all?

[2DogsFarm]

I’m going to suggest you ask your vet about naquazone for the edema.
Many years (30+) my TB got bitten/stuck in his knee on a Sunday trail ride. Leg was swollen from shoulder to hoof by Tuesday, you could wring out fluid like a teabag.
Vet put him on ABX, but this BB suggested the diuretic. Worked a charm.
We never did find out what caused the reaction, even with an exploratory surgery of the knee.
He recovered completely in a month or so, most of that time for care of the surgical site.

For your boy, is any turnout possible?
Movement can sometimes help reduce edema.

[Simkie]

Are you sure there’s not a bigger systemic issue at hand here? Like…heart failure contributing to this edema? Melanoma compromising his lymph system?

Have you brought in a boarded veterinary internist? Or been seen at a large referral or teaching hospital?

This is such an out of scope response to bug bites, especially given that he doesn’t seem to be responding to steroid and anti histamines. I would look very hard at the whole horse, and that may need a team of people, or a very focused specialist, and involve a lot more than just bloodwork to assess his general state of health.

[IPEsq]

Horse allergies can get worse as they age. My horse is allergic to all of the bugs as well as dust mites. He gets small hives but is super itchy. He started developing sweet itch in 2022 for the first time ever (he is 11 now). It was even worse this year. He was so itchy, he ripped a chunk of eyelid off accidentally while rubbing his neck. Thankfully his eye is ok. The eye emergency was the last straw for me, so I did the testing and now am in the middle of the shots. The hope is that the allergy shots will help him not have such bad reactions in the future.

[Posting_Trot]

Lots of great suggestions in the thread. It might be worth changing the bedding (from shavings to straw, for example) for a good month to see if that gets you any relief.

Mites are also a possibility–some animals have dramatic reactions to mite bites, although I think the bites usually cause lesions as well as swelling.

[emipou]

This is what’s been nagging me a little… we know that some bug is involved because we’ve been able to trace each occurrence to an insect bite, but I have yet to find another occurrence online of a horse having such extreme edema/pain from a bite (without the necrotic lesions).

[endlessclimb]

How do you know for sure the bump you found is an insect bite? Can’t it be from a host of other things, too?

[Chall]

Since you’ve had the vet out, so he’s covered medically, here’s what popped into my head

1. Call the feed company to see if they variable ingredients (where substitutes are routinely made) or if they recently changed the formula. Ditto any supplements
2. Change the bedding once a week: straw, pellets etc and monitor
3. Take his temperature twice a day and log it.
4. Check neighboring stalls to see if someone has changed flyspray, and if any cleaners are being used on the floor that have been switched

I am not a medical person, but It looks like pictures I have seen of pigeon fever.

Where are you located?

Can he be hand walked in the aisle or is he required to be immobile?
Sorry this is happening! Keep us updated.

P.S. if you just got ownership, can you ask the previous owner what bedding, food he had before, when this wasn’t showing up.

[CindyCRNA]

We are in the midwest and my guy gets infested with chiggers every year about July on all 4 legs. His legs blew up and wept something aweful. We had to wrap and give IV DMSO. This year we sprayed his fly boots with 10% permetherin and this was our first year we had no issues. But I don’t think you all have chiggers (kinda like mites) down there.