An Insidious Case of Pigeon Fever - The Horse Owner's Resource

An Insidious Case of Pigeon Fever

A lump on a gelding"s chest ends up being more than just swelling as his owner learns the facts about a type of infection that"s growing in frequency.
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The brisk autumn weather was perfect for riding on that Sunday afternoon last November, so I pulled on my boots and crunched through the colorful fall leaves out to the pasture, where my 7-year-old mustang gelding, Wesley, stood at the gate. But about 10 feet out, I stopped. Something was wrong. Wesley's head didn't pop up to greet me, and he didn't offer his usual low, grunting nicker.

herd feeding

Moving closer I spotted a swelling on his chest, in front of his left shoulder. I stepped through the gate and ran my hand over the protuberance: It was firm but not hot, and it covered his left front chest and extended down between his front legs.

"What happened, Wes?" I asked, rubbing the star on his forehead. "You get kicked?"

Wesley is pastured with two other geldings, and these boys do get rowdy. My horse Zeke had once been kicked in the chest, and the injury had produced a hematoma, a blood-filled swelling, the size of a grapefruit. That must be it, a hematoma, I thought.

I slipped the halter over Wesley's head, and we headed toward the barn. He was moving sluggishly, reluctant to bear much weight on his left front leg.

My brow furrowed. This could be more than a hematoma. Was it a shoulder fracture? A tumor? I'd lost my first mustang to an aggressive sinus cancer, and I am forever fearful of seeing equine cancer again. Taking a deep breath, I reassured myself that it was probably not cancer and Wesley would be OK. I stroked his neck and encouraged him to come along.

I put Wesley in a stall with hay and water and gave him two grams of phenylbutazone (bute), which I stock for my arthritic horse, to control his pain. In the meantime, my husband hitched up the trailer so we'd be ready to take Wesley to our local veterinary clinic first thing in the morning.

Wesley's swelling looked about the same the next day, and he had trouble climbing into the trailer because his shoulder and leg made the step up painful. But he's a good horse, and once he was loaded, we drove to see Steve Shideler, DVM.

Not so simple
"That looks like an injury. Could be a hematoma," Shideler said as Wesley backed off the trailer. Walking slowly to accommodate Wesley's pain, we led him to the treatment area.

The veterinarian palpated the swelling, then he cleaned the center of the mound and inserted an 18-gauge needle to see if he could aspirate (draw out) any fluid. Nothing. Shideler said Wesley had probably experienced some trauma. He administered a dose of penicillin in case some infection was present and prescribed daily warm compresses and continuing the bute as needed, but he said he would expect the swelling to go down over time as the injury healed. Relieved, we loaded Wesley and returned home.

Alone in a paddock, Wesley stood quietly for the application of warm compresses. He's a mild-mannered horse, and he appreciated the attention and the head rubs. We gave him two grams of bute for three days and then tapered him off of it by day five. Bute can cause gastric ulcers, so I didn't want to keep him on it too long.

But once the bute was stopped, Wesley's pain seemed to increase. And, instead of shrinking as we expected, the swelling on his chest grew bigger. Now his head bobbed when he walked, a telltale sign of how painful weight-bearing had become. I put him back on the bute.

The Monday after Thanksgiving, I called Shideler to report that Wesley wasn't feeling better and the swelling was getting worse. We discussed alternative diagnoses. The possibility of cancer came into the conversation; my heart sank. Shideler recommended taking Wesley to the university clinic, where a specialist could ultrasound the swollen area to get a better idea what lurked beneath that ballooning skin.

A different diagnosis
Worried, I emailed a photo of Wesley to Alison Eddy, DVM, at Mississippi State University's College of Veterinary Medicine; she's treated our other horses before. Eddy replied that, although she couldn't diagnose the problem without examining the horse, she thought the swelling looked like pigeon fever---an infection that causes large pus-filled abscesses under the skin. Also called dryland distemper or false strangles, pigeon fever gets its name because the swellings, which often appear on the front of a horse's chest, mimic the bulging profile of a pigeon's breast.

She explained that pigeon fever is caused by the bacterium Corynebacterium pseudotuberculosis and is more common in arid regions of southern California and the Southwest. However, she added, they'd been seeing more of this infection in Mississippi this year than they had in the past. Eddy assured me that pigeon fever isn't usually life threatening, but it does require treatment. I made an appointment at the university for the next morning.

With Eddy's permission, I gave Wesley two grams of bute one hour before loading to help reduce his pain, and he gamely climbed back onto the trailer. Eddy and the other equine veterinarians were waiting and ready to examine Wesley as soon as we arrived at the hospital. All his vital signs were normal---no fever---and he was bright and alert. His only sign of trouble was the classic hallmark of pigeon fever: pectoral swelling and pain from that king-size abscess. All of this pointed toward that diagnosis---most horses with pigeon fever eat well and have no fever. Eddy told us that an ultrasound of the swelling, to look for the pus pocket, would help confirm their diagnosis.

The swelling was shaved for the ultrasound, and Wesley's dark-tipped ears flicked forward momentarily with concern as the equipment was wheeled toward him. He stepped back, but after being allowed to sniff the apparatus, he sighed and settled.

A hypoechoic area--one that is dark on the monitor, because it isn't solid like normal tissue--was found two centimeters (almost one inch) below the skin. This was the abscess. The good news was that draining the pus would start Wesley on the road to recovery. But there was some bad news, too: The abscess didn't appear to be well encapsulated; that is, it was ill defined and spread out somewhat. If it were opened, the pus might not drain completely, and the abscess would only return. If instead the abscess was left to mature, or "ripen," the body would wall off the infection into a distinct area that would drain more readily. They couldn't fix my horse that day.

Eddy estimated Wesley's abscess might be ready to open in two or three days. Because draining an abscess is a routine veterinary procedure, we had the option of taking our horse home and letting Shideler take care of it when the time came. However, Shideler was heading out of town, so we chose to leave Wesley at the clinic, where he could be monitored until the abscess was ready for lancing.

Crash course
I knew nothing of pigeon fever, so Eddy took a few minutes to explain it to me. Caused when C. pseudotuberculosis enters cuts or wounds as small as fly bites, pigeon fever can take three forms. About 90 percent of the time, the disease causes abscesses, most often on the chest but sometimes under the belly or in other areas, usually near the lymph nodes. In a second type of pigeon fever, the bacterium is carried to the liver, lungs, kidneys or other organs and internal abscesses form; these cases are more likely to be fatal. A third type, called ulcerative lymphangitis, affects the lymphatic system on the lower legs and is much more serious and slower to heal. This type is extremely rare in the United States.

I gave thanks Wesley had the most common and treatable form of pigeon fever. But I wondered how my horse had contracted this infection. Eddy said that C. pseudotuberculosis resides in the soil, and it thrives in arid or droughty conditions. The bacteria enter the skin either directly, when a horse with a cut or abrasion lies down, or indirectly, when he is bitten by a fly carrying
the pathogen.

The disease is common in California and the Southwest because the bacteria flourish in the hot, dry climate. Eddy commented that Mississippi had seen an increase in cases over the past two years. Most of the South has been parched from reduced rainfall those years, and large swaths of the Midwest have been experiencing droughts; in fact, the whole country has seen warmer temperatures. These conditions have enabled pigeon fever infections to sweep eastward and northward in recent years, and veterinarians who had never seen a case in their careers are now treating horses with the illness.

We left Wesley munching horse treats offered to him by the staff. Eddy called me the following evening. The overstretched skin covering Wesley's voluminous abscess was threatening to split. The veterinarians now believed the lesion was mature enough to make the procedure successful. I gave the go-ahead.

Well-mannered Wesley required no sedation, only the local injection of anesthetic (Carbocaine) to numb the area. Eddy told me that while the process of draining a pigeon fever abscess may be relatively straightforward, it is an extraordinarily messy spectacle. After piercing Wesley's skin where it was stretched so tight an exudate was beginning to ooze, the veterinarians had guided a 14-gauge catheter into the abscess until pus was aspirated. With the abscess location confirmed, a scalpel was guided alongside the catheter to drain the abscess.

Copious amounts of tan, odorless exudate spilled from the opening; this characteristic appearance of the pus helped confirm the diagnosis of pigeon fever. Because the abscess wasn't quite fully encapsulated, the veterinarians made a second incision to open another pocket of infection. Wesley fared well during the procedure, and with the wounds left open, he was ready for discharge.

Healing at home
I had to work the next day, so my husband picked up Wesley and received our discharge wound-care instructions. Because the drainage from his wounds might be able to infect other horses, we were advised to isolate Wesley until all the exudates appeared to have exited and the swelling had diminished. Some experts even recommend burning all bedding or hauling it to a landfill, then bleaching all hard surfaces in tHe'stall and any tack that's come in?contact with the horse.

More recent evidence and expert opinion suggest that isolation of a horse with pigeon fever and disinfection of equipment may not be necessary. However, we decided it was just good hygiene to keep this horse with a draining wound away from the others. We also wore disposable exam gloves to treat him and washed our hands after touching him.

Wesley's daily wound care involved inserting a soft rubber catheter into the open cavities and flushing the pockets with a saline solution. Eddy told us how to make our own saline, using distilled water and table salt. She also advised us to coat Wesley's chest area below the wounds with petroleum jelly to help protect his skin from the oozing exudate.

Ever the stoic gentleman, Wesley tolerated the treatments well. In less than two weeks, his wounds healed, the swelling resolved and he was released to return to his herd and his duties as a riding horse. We did elect to disinfect his halter and the stall, and I washed the saddle pad

I'd been using on him, too.

Pigeon fever has been around for a long time in the Southwest, yet I'd never heard of it happening here. However, cases have been on the increase in Texas and the South, and the disease has appeared as far east as Florida and Kentucky. The hot, droughty summers we've seen in recent years could make the infection more common in states where it had never been before. I hope that my experiences help you recognize the signs of pigeon fever sooner should the infection appear in your area. Finally, Wesley and I are off for that ride.

For more information, see "On Watch for Pigeon Fever" (EQUUS 368).

This article first appeared in EQUUS issue #426.

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