Equine influenza, a viral disease causes fever, depression and coughing. Influenza is by far the most common disease of horses. Another upper respiratory viral disease of horses which has the potential for creating much greater economic losses is rhinopneumonitis or "rhino."
The symptoms of "rhino" are similar to influenza, except coughing is not common. In adult horses the symptoms are often undetected because they are so mild. Weanlings usually show the classic symptoms more than older horses. A typical case would present the following symptoms: moderate depression, fever, stocked up legs usually worse in back, watery eyes, inflamed conjunctiva, sometimes nasal discharge, and rapid breathing during the fever stage. Yearlings can show these symptoms to a lesser degree and older horses may show fever, watery eyes, and a slight nasal discharge. If rested and sometimes treated with anti-fever medications, the symptoms usually disappear with 3 to 5 days. "Rhino" looks like a relatively mild respiratory disease of short duration. If your horse has "rhino" when using him or transporting him a relatively long distance, the stress can lead to a serious pleuro-pneumonia. The potential for large economic loss is created when infected horses are in proximity to pregnant mares, which are not immunized against "rhino." It can cause abortion which can be sporadic to epidemic and can cause tremendous economic loss. The typical history goes like this. "These mares have not been sick and have had the same good feed and water. They just started losing their foals." On further questioning you find that a month before some of the weanlings had some swelling in the legs for a couple of days. The virus probably infected all the horses in the area and went undetected because of the mild symptoms. A month later the mares started dropping their foals, which can be from 5 months gestation on. Term foals born with "rhino" are weak and die shortly after birth. The diagnosis can be confirmed by laboratory examination of the aborted foal and by testing the blood of infected horses.
Rarely the virus can enter the spinal canal and cause rhinomyelitis. I have seen 4 cases in 26 years of practice which were able to confirm by laboratory tests. The first one was a beautiful TraKehner stallion just ready to be approved for breeding. He was bright and alert and had no fever, but was extremely uncoordinated. He had little control over where he placed his feet at a walk and would often stand cross legged at rest. We confirmed the diagnosis by testing his spinal fluid and he was humanely destroyed after a month of frustrating treatment at Colorado State University.
The second rhinomyelitis was a quarter horse stallion used for breeding. He was wobbly in all four legs and could occasionally breed mares, but with difficulty. He lost control of his bladder and would constantly dribble urine. After a year of frustration the owner had him put down.
The third case was a mare which we thought was a "wobbler." The two diseases are often hard to distinguish except a wobbler is cased by a pressure lesion on the spinal chord in the neck area and not by an infectious agent. The mare was diagnosed by serum tests as having "rhino" and I lost contact with the owner, so I do not know whether she lived or died.
The fourth case was a young barrel horse just coming into his prime. He was extremely uncoordinated and had a fever the first day. In spite of treatment and round the clock good care, he went down on the fourth day and had to be destroyed. His owner was really a nice young lady whose main interest in life was to compete on the barrels. Being a veterinarian is not fun at times like that.
Early in the 1960's the only state that could legally use vaccination to prevent "rhino" was Kentucky and an intra-nasal spray was used to vaccinate horses with live virus. The feeling at the time was using the vaccine outside of Kentucky would spread the disease into other states. Later intra-muscular modified live virus vaccines became available. Some of these were not modified enough. It was felt they caused abortion rather than prevented it. One quarter horse ranch in Montana, had nearly a 100% abortion rate and a standardbred farm in Kentucky has 55 mares abort after using an early type of modified live virus vaccine.
Many people are still afraid to use "rhino" vaccine, but they need not be. The modified live virus vaccines today are very safe and effective. The only company which makes a statement regarding preventing abortion has a killed vaccine. They recommend vaccination of pregnant mares at 5, 7 , and 9 months of pregnancy. I recommend an earlier vaccination as well, if mares are not on a routine yearly springtime vaccination program. The killed vaccine gives an occasional reaction at the injection site, but these are treatable and inconsequential when compared to the possibilities of abortion and of militias if the vaccines are not used. Whether you have a large band of broodmares or one horse with immeasurable sentimental value, vaccination is cheap insurance.
We would like to take this opportunity to thank HARRIS VETERINARY CLINIC, in Grand Junction, Colorado for providing us with this information.
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