Sudden Death in Otherwise Healthy Mare
I am posting this with the intent of gaining the opinion of an equine veterinarian, veterinary student, or anyone else who has experienced something similar. Although the event that I will describe happened months ago, it has continued to haunt me, and I am determined to find out what happened to cause this incident.
This summer, I managed a horse training and boarding facility in southeastern Kansas. One morning, I was turning out horses, and noticed that one of the mares had strange marks on the sides of her jowls and neck, and also near her forehead. They looked almost as though the skin had been rubbed off of them. (Similar to a "rug burn") I asked the barn owner about the marks, and he said he had never seen anything like them, but assumed it was some sort of allergic reaction, since the mare's fly mask had been washed recently. I kept the mare inside, with the intention of keeping an eye on her during the day.
While I was cleaning stalls, I began hearing kicking and sounds of distress coming from the mare's stall. I monitored her for about three minutes, and noticed that she had become frantic, pacing in her stall, kicking the boards, and breathing heavily. She did not, however, roll, look at her stomach, or show any typical signs I would associate with a colic case. After a few minutes, the mare went into a sort of "trance". She stood facing the back of her box stall with her head hung.
The farm owner had left the farm at this point, and I was alone for the day. With nobody else to consult regarding the issue, I called the veterinarian who the mare's owner used. I explained the signs that the mare was showing, including the marks on her head/neck, the period of excitability, and the "trance"-like state. I explained that I had never seen anything like it, and thought it might be an emergency. The receptionist that I was speaking to then put me on hold, saying that she'd ask the veterinarian what to do. She put me on hold for five minutes.
In that five minutes, the mare walked over to the corner of her stall and placed her head against a board. She then began head pressing, and I noticed that this must have accounted for the hairless patches on her head and neck. (I confirmed this later, when I found patches of hair stuck in the boards of the stall.) Then, it appeared that she became incredibly weak, and attempted to support herself against her automatic waterer. Her legs then appeared unable to support her, and she fell to the floor. She appeared to go into convulsions, with her legs becoming stiff, her muscles twitching, eyes rolling back, and tongue lolling out of her mouth. After about one minute, the seizing appeared to slow, and I entered the mare's stall. Her breathing became very shallow. I checked her gums, and they appeared extremely pale. Her eyes were bloodshot to the extent that the sclera was completely red. The receptionist picked up the phone at this point, and told me that a veterinarian would be there shortly. I told her that it was probably too late.
The mare's breathing became sporadic. I tried to get her up, or even to keep her "awake", to no avail. Her breathing slowed to a stop a few minutes before the veterinarian arrived.
The veterinarian entered the stall, asking me, "Is she alive?". I told her that her breathing had stopped a few minutes ago, as she checked the mare's clinical signs. She informed me that the horse was dead, as if I hadn't known this. She checked the mare's gut, and said simply, "The mare colicked.". I was appalled. However, I didn't want to argue with the just-graduated "professional", and thanked her for hurrying out to the farm.
After the incident, I went home and contacted other veterinarians, researched information in books and on the internet, and spoke to other professionals in the horse industry. I believe that this mare may have suffered hepatic encephalopathy, or something very similar. Afterwards, I went out and checked all of the pastures on the farm. I identified Nightshade, as well as several other toxic plants, along the fencelines of several paddocks. (I had this brought to the owner's attention, and they removed them promptly.) I also suspected a possible aneurysm, or stroke, judging by the signs.
She was an 8 or 9 year old Dutch Warmblood mare. She had never had any medical conditions, to my knowledge. She was rarely exercised. She was ridden once every two weeks. She spent half of her days on pasture, and half in a box stall.
No other horses on the farm became ill or produced similar signs.
This mystery has kept me guessing for months now. I have consulted several other equine veterinarians, all of whom have their own opinions as to what may have happened to the mare. I would very much appreciate any input that others may have. This was a truly traumatizing experience for me, as a pre-veterinary student, and has highly influenced my desire to become an equine veterinarian.
Thank you in advance for your help. It's much appreciated!
I'm not a vet but I had a mare who showed similar symptoms that also died. The vet wasn't available and so we never had him out or a necropsy done, so I'm just tossing out guesses. My mare was in her 20's so I suspected a possible stroke. She was also in foal and had had a Caslick suture put in, and since she'd slipped previous foals, wondered also if she perhaps had slipped this foal but couldn't fully abort due to the Caslick and it possibly could have become necrotic and caused a systemic infection that killed the mare.
I'll never know for sure either way, but it's certainly made me think twice about putting a Caslick in another mare.
I'm not a vet, but based on your description of her symptoms I'd be thinking cerebral hemorrhage (bleeding of the brain) from an aneurysm. They happen pretty rapidly and involve "ballooning" of an artery in the brain (which would cause a considerable headache, hence the rubbing/pressing of her head). It then bursts, which causes the artery to bleed out. The horse will collapse and it is almost always fatal. A key sign is pale mucous membranes (hence the pale gums) when the horse collapses (caused by a lack of blood).
Merck Veterinary Manual
^This might be what you need to read.....as soon as you said head pressing...
There are three strains of equine encephalomyelitis and each is caused by a virus that is spread by mosquitoes. Eastern** and** western** equine encephalomyelitis (EEE and WEE) occur in North America and Venezuelan equine encephalomyelitis (VEE) occurs in Central and South America and occasionally, in parts of the United States. In general, infected horses develop fever, loss of appetite, depression, elevated heart rate, abnormalities in white blood cell counts and diarrhea (in VEE). The horses become unresponsive or irritable and exhibit head-pressing, leaning on walls or fences, compulsive circling and in some cases, blindness. Death is usually preceded by coma and convulsions. Horses that survive often have residual neurologic defects.
Humans can become infected with the EEE virus, the WEE virus and some subtypes of the VEE virus. The clinical signs in people vary from a mild flu-like illness* to* severe brain disease. Deaths have been reported primarily in children and the elderly.
Dr. Laura Kramer, an associate research virologist with the UC Davis Center for Vector-Borne Diseases, provided the following information regarding encephalomyelitis in California.
“The numbers of epizootic (disease that affects many species of animals) incidences of equine encephalitis cases during the 1930s and 1940s devastated agricultural production in the Central Valley and culminated in the discovery of western equine encephalomyelitis (WEE) virus as the causative agent. Research quickly developed an effective vaccine and in Kern County from 1943 to 1952, only* 168 cases of equine encephalomyelitis which resulted in a 29 percent *fatality rate were reported by veterinarians, attesting to the efficacy of prevention by vaccination. All cases occurred from May to October in horses that were reportedly unvaccinated. Few cases have been recognized in recent years. WEE, like several other arthropod borne viruses, is transmitted in nature by the mosquito, Culex tarsalis, in a cycle involving wild birds as reservoir hosts. A secondary cycle involving Aedes mosquitoes and rabbits may develop during summer, but the infection of humans and domestic animals, including horses, is accidental and a dead end for the virus.
“In the past decade, there has been increasing public awareness of newly emerging diseases which present a threat to equines and man. In 1992, the 12th International Symposium on New and Emerging Infectious Diseases was held at the UC Davis School of Veterinary Medicine. At this symposium, one topic of discussion was arthropod borne viral infections which have the potential to become serious problems in California. Researchers determined that of the cases of equine encephalitis in California during 1965-1978, five arboviruses (viruses transmitted by insects such as mosquitoes and flies) in addition to WEE were implicated as causative agents, including St. Louis encephalitis (SLE). Additional arboviral infections of equines have been documented, but currently there is no indication that these cause clinical illness.
“Arboviruses have also caused epidemics in California, the largest of which was centered in the San Joaquin Valley in 1952 with 375 WEE and 45 SLE confirmed cases. Expanded preventive mosquito control, water management projects on the western slope of the Sierra Nevadas, and improved agricultural irrigation methods have essentially eliminated WEE and SLE as a significant cause of human illness in California. There is little evidence that mosquito-borne arboviruses other than WEE and SLE are the cause of a significant number of human cases in California. However, to date, the causative agents of 95 percent of aseptic meningitis and viral encephalitis cases are not diagnosed, and the possible role of one or more vector-borne viruses as the causative agents of these diseases remains an important issue.”
Thank you both for your input. An aneurysm was one of my guesses as well. I just can't account for the loss of motor control and apparent CNS disruption.
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Encephalomyelitis was my other guess. However, the onset seemed much too abrupt, and there had been no reports of the disease in the region at the time.
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Interesting stuff about EEE, Muppet! Scary that it is transferable to humans :shock: I'm not as familiar with local American diseases and I can't remember hearing about this one before - interesting reading!
I have learned about the various strains of encephalomyelitis in classes, and have done research related to the disease. It is certainly interesting, and I would be surprised if it was the cause of the mare's death. I'm just disappointed that the veterinarian didn't perform a necropsy.
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