Jon Geller, DVM, offers his farm animal health experience in caring for cows, calves, horses and sheep. This issue includes questions on parasites and skin diseases in farm animals at the county fair.
"You are never truly alone" my parasitology professor used to say. It was as disconcerting a comment in my student days as it was now, especially as I watched three large grubs exiting from several pus-filled holes on an Angus steer's back. When you think about skin diseases in farm animals, always think parasites first, then go down the list from there.
Dermatology Day at the country fair, and the steer in question was suffering from hypodermosis, or grubs. The third-stage larvae, now triumphantly exiting the skin, had started their journey about a year ago when a heel fly had deposited its eggs on the legs of the steer. From there the first-stage larvae penetrated the skin, using flesh-dissolving enzymes to tunnel their way to the esophagus, where they congregated for several months. The enterprising larvae then made their way to the tissues surrounding the spinal canal, where they enjoyed several more molts before emerging.
I was beginning my day as the on-site veterinarian for the Independence Day Stampede, a combination rodeo/county fair/4-H extravaganza, and was looking forward to seeing so many critters in one place for a change, instead of having to drive dozens of miles between farm calls, often desperately behind schedule.
My first order of business was to inform the owner of the steer that there was no risk to other animals or humans, since the emerging grubs simply fall to the ground to pupate for several months until a new heel fly emerges. Then I went about the somewhat grisly task of extracting the rest of the grubs. Using surgical tissue thumb forceps, I extracted 17 more grubs from their hiding places along the steer's back, after which I poured some disinfectant over the holes. Most large-herd domestic cattle are too wild for this treatment and must instead be treated with an insecticide.
Pesky Animal Parasites
Skin diseases caused by parasites are best prevented by treating animals in a herd before the life cycle of the unwelcome insect becomes established. In the case of cattle grubs, all animals should be treated as soon as possible following heel fly season, which in southern states occurs from January to March and in northern states from May to July. Small groups of individual cattle on the other hand, can be monitored more carefully and treated on an as-needed basis.
The list of parasites that cause skin diseases in animals is long, though lice and mites are the most common culprits. Most of these parasites cause hair loss, itching, redness, scaling and occasionally secondary infection. When more than one animal is affected, the possibility of parasites is greater.
The good news is that most can be recovered with a simple skin scraping. This should be done by a veterinarian. Often, there is zoonotic potential, meaning the parasite could infect humans. Always use gloves if you suspect parasites are present.
Fortunately, many different parasites respond to the same treatment. The wonder drug for many skin (and internal) parasites is Ivermectin, made by Merial. It is a potent drug available as a feed additive, oral paste and injectable formulation. Like many other drugs, here is a specific withdrawal time required for food animals, and lactating dairy cows must not be treated.
I filled my coffee mug and was about to head over to the pig barn when my two-way radio crackled; I was needed at the bucking chutes. A young gelding had a swollen eye and the livestock contractor was worried.
Animal Skin Problems Can Be Serious
The black gelding with the swollen eye was a seasoned bucking horse named Terminator. This would have to be one of those cases diagnosed and treated from a safe distance. We ran the horse into a chute to inspect him. I could see his left eye was completely swollen shut and there was a bald spot in the middle of his forehead.
When I tried to touch his head, he reared up and just about crushed my hand against the chute. He settled back down and I was able to shine a light into his good eye, where I noticed some clouding. Right away, I suspected that the roundworm, Onchocerca, was the probable culprit. The offspring of the adult roundworms migrate into the tissues of the eye, causing swelling and other changes. This rank gelding would obviously not tolerate skin scraping or biopsy, so I went ahead and treated him for parasites.
Ivermectin kills parasites quickly. Occasionally, the treated animal will suffer an allergic reaction to the dying parasites before they are cleared from the body. In this case, the offspring from the adult Onchocerca hart invaded the tissues around the eye. Treatment with Ivermectin could make the problem worse and so an injection of steroids would also be needed to control swelling.
Experience has taught me that finesse is not always helpful. I jammed a 2 inch needle into Terminator's hip to give him the injections. The horse's good eye bulged as he tried to turn and destroy me.
"Doc, can this horse perform tonight?" the livestock contractor asked.
"Sure, but I pity the poor soul that draws him,"' I replied.
No sooner had I left Terminator's tent than I was called to see a Suffolk ewe that was losing its wool, The owner reported that the ewe recently had been prone to periods of head tremors and appeared to be itchy over her rump. She had been seen rubbing her back against the fence rails.
Itchiness and hair loss can certainly be caused by parasites, but I didn't know of any that caused neurological signs. I performed a quick skin .scrape using a surgical blade and an angle, and mixed the scrapings with a drop of mineral oil on a slide, which I then checked with my field microscope. There were no mites or lice or any other parasites. Nor, for that matter were there any signs of bacterial infection.
This concerned me because any Suffolk sheep with itchiness, loss of wool on her back and head tremors probably has scrapie, and there is no way to diagnose it while the animal is alive. Scrapie is truly a dreaded disease, similar to BSE, or mad cow disease. In fact, mad cow disease is theorized to have started in Great Britain, when cattle were fed scrapie infected protein supplement that were inadequately processed.
Sheep that have scrapie must be destroyed and the herd they come from identified so that close blood relatives can also be culled. I hated to deliver this news to the owner but the county fair was certainly no place for a scrapie infected suspect.
Hair loss can be caused by a number of things, and it is critically important to sort them out and determine the underlying disease. Some can be as serious as scrapie, others as mundane as a saddle sore.
A Dog's Tail
Back at the arena, a rodeo clown named Roddy asked me to look at his blue heeler, Buck, for yet another skin problem.
"Doc, he's been so itchy he makes my skin crawl just watching him. Look at his tail and face!"
Buck was somewhat pathetic looking, with his tail all scabbed over and hairless, and areas of redness and hair loss around his eyes, ears and nose. But it was Roddy's comments about his own itchiness that piqued my interest.
"So have you noticed any rashes on your own skin?" I asked.
"Now that you mention it, I've got this rash on my arm. I thought it was from scraping against the barrel several nights ago during the bull fighting, but it doesn't want to go away. And it does itch to beat the dickens."
I went ahead and did another skin scraping at the base of Buck's tail, and set up the scope. Staring back at me were a dozen little ovoid critters, each with four pairs of legs. It spooked me some to see them scuttling about on the slide.
Mange is the general name for skin diseases caused by mites, microscopic parasites that infect almost every domestic species of animal worldwide. Although they are generally picky"lodgers" — dog mites prefer to stay on dogs, cattle mites prefer to stay on cattle, and so on — these parasites have been known to spend time on those closely associated with their hosts, especially nearby humans. But because of mites inherent host-specificity, human cases of mites (caused by animal mites) usually clear up on their own; after a couple of days, the mites simply leave. For cases that do not improve within a few days, however, medical attention should be sought.
The other major skin parasites that affect mammals are lice, but these are likely to jump over to humans. Lice are usually found on animals confined in less than sanitary conditions. Like mites, they can be successfully treated with Ivermectin or another medication. The practical options, however, have been reduced in response to concerns over insecticide residues. environmental contamination and human health hazards. Formulations that have the potential for toxicity to plants and other animals should be avoided completely. lvermectin's effectiveness, lack of environmental toxicity and safety of application make it overwhelmingly the drug of choice for treating individual and small numbers of animals.
I gave Buck an injection of Ivermectin, with a plan to repeat it once a week for the next three weeks. Roddy's rash would probably clear up in a few days as the mites moved on in search of another dog. Just then I got a call from a young 4H'er who had brought in a pig suddenly lame and with strange lesions on its skin.
Pig Problems and Lame Lambs
When I arrived at the pig barn I noticed many light purple diamond-shaped areas all over the pig's back and sides, a problem I recognized as "diamond-skin disease." More formerly known as erysipelas, it is caused by a bacterium that triggers arthritis, skin disease and sometimes cardiac valve thickening. In its most severe form, it can lead to septicemia (infection in the bloodstream) and death. However, in more mild cases like the one before me, it can be successfully treated with antibiotics.
Animals contract the disease when the bacteria, shed in the feces of pigs that are carriers, are picked up by young ones that have not yet developed immunity. Penicillin works well as a treatment, so I gave the pig a dose of procaine penicillin. I also told the young farmer about some oral vaccines he could give to his other pigs. The lad appeared relieved when my lecture was interrupted by a call from the other side of the barn.
There I found an older sow that also had some odd changes to her skin, including multiple circular reddened areas and some areas that appeared to have blisters. In the reddened areas, blisters had apparently broken open and a moist, greasy layer of oily excretions covered the pig. Pioneers in the study of pig diseases aptly dubbed this ailment "greasy pig disease," or, more formally, exudative epidermis. It, too, is a bacterial disease (of the staphylococcus type) that attacks the skin.
This pig was also sore around her feet, in this case because of an infection around the coronary band above the hooves. I gave a high dose of penicillin and instructed the owner to isolate the pig and wash her down with warm water and a mild disinfectant such as chlorihexidene.
Greasy pig disease can he prevented by increasing zinc and biotin levels in the diet. There is also a vaccine available for prevention in young animals. After passing this information along to the owner, I realized that I hadn't eaten lunch. All this unexpected work had made me hungry, so I stopped at a nearby stand that was grilling thick, juicy pork chops. What's a man to do?
Later, over in the sheep barn, I took a look at a lamb that had a problem with his mouth. The poor guy had blisters and crusted areas on both lips. He obviously was not eating well; he was thinner than he should have been. I asked if the ewe was around, and when I looked at her udder, I noted the same kind of blistering and crusting of the skin around the teats.
Orf, or contagious ecthyma, is a fairly common disease of young sheep and goats, usually showing up in late summer. The worst part is that it's contagious to anyone working with the sheep, as well as to other lambs.
Because it is caused by a virus, there is no specific treatment. I applied some antibiotic salve to the sores to help prevent secondary infection. Once a lamb gets over orf, in about four weeks, it has lifetime immunity. A vaccine is recommended for all unaffected lambs in a flock with an orf outbreak. Affected lambs,. such as this one, had to be isolated.
Seeing all of these skin diseases reminded me of how challenging dermatology in animals can be. One needs to sort out the hundreds of possibilities by playing the odds, and in farm animals, external parasites are most likely. But internal parasites, ringworm-causing fungi, bacteria, viruses, genetic diseases, nutritional imbalances and skin changes caused by the immune system are all possibilities, as is cancer.
A Final Challenge
As the day came to a close, I gathered up my medical supplies, repacked them into my truck, then indulged in some Indian tacos and roasted corn from a nearby tent. I would be back on the road the next day, with only my lunchbox to look forward to.
My stomach full, there was just one thing left to do. Grabbing a gear bag containing my saddle, pad, spurs, gloves and chaps, I stuffed a wad of shredded bubble gum in my cheek and headed over to check the draw, for the bareback bronc-riding contest. There, next to my name, was the horse I would be riding: "Terminator."
As I peered over into the pens, the cantankerous black gelding was nipping at another horse's flank. Whirling around, Terminator's good eye briefly passed over me with a contemptuous glance. On a positive note, I was pleased that the swelling in the other eye had gone down.
The Usual and Unusual Suspects
Mosquitoes Annoying bites, vectors for other diseases
Flies and gnats Painful bites, infection, larval infestation
Sheep keds Anemia, weight loss, damage to sheepskin
Blowflies Invading larvae destroy host tissues, produce toxin
Bolflies Nasal discharge and bleeding, annoyance
Lice Anemia, intense irritation
Fleas Pruritus in dogs, cats and poultry
Mites Mange, intense pruritus, secondary infection, hair loss
Ticks Disease transmission, weight loss, paralysis
Causes of Hair Loss
Ringworm, fungal infections
Bacterial infection (usually secondary)
Viral infection (often carried by insects)
Mites, many kinds
Lice, chewing and sucking
Onchocerciasis (migrating roundworms)
Immune-mediated diseases (lupus and pemphigus)
What To Do When You Suspect a Skin Disease In a Farm Animal
1. Determine if more than one animal is involved and if any people are affected.
2. Determine if the animal appears sick or has any change in normal habits.
3. Isolate the animal, if possible, prior to veterinary care.
4. Handle only with gloves until diagnosis.
5. Inspect skin carefully for parasites.
6. Do not administer any medications without the instructions of a veterinarian.