Ask the vet: Infectious disease

The summer may be drawing to a close, but the threat of Infectious Disease still lingers. Make sure your horse(s) is still safe. Pose your infectious disease questions to this month's AAEP expert, Dr. Phoebe Smith.

1
Question: Can a horse that has had Potomac Horse Fever (PHF) make a complete recovery? Can they return to their prior job as if nothing has happened or will their performance ability be diminished?
Answer: 
Yes, a horse can recover completely from Potomac Horse Fever (PHF) and return to normal performance. Not all horses do recover to this degree. The severity of clinical signs is quite wide with PHF, and the development and severity of laminitis is often the limiting factor in future athletic endeavors.
2
Question: I have a 19-year-old gelding and a recently acquired 11-year-old mare. I've had the mare for about three months. Three times since I've owned her, I have noticed that she has episodes of short rapid 'puffy' breaths, no nasal drainage and no sweating. Just over the past couple weeks, I have now noticed that my gelding (I have had him since he was a foal) has had the same 'episodes' on about 3 or 4 occasions! The rapid breathing goes away in about 3-4 hours. They receive very little sweet feed (about 2 cups) morning and night and are locked in for the night at 8 pm. I let them out again to graze around 2 pm daily. I've had horses over the years in this same pasture and have never had any problems but am wondering if it is some kind of a new weed growing (we have a 5-way grass mixture) or if I need to be concerned about illness.
Answer: 
The episodes of rapid breathing sound very curious. Unfortunately, without seeing/touching/listening to your horses, I cannot offer much useful information. I'd recommend your veterinarian examine both horses as a starting point. Lab work and an assessment of your pastures may also be useful.
3
Question: I have a beautiful Palomino Quarter horse gelding that I want to show. When I got him last year, they told me not to vaccinate him because he foundered two days after his last routine vaccines. That was back in 2008. He was in the same barn so it was not a problem. Now I own him and the barn that I want to go to, won't let me board him without a flu/rhino vaccine. His previous veterinarian said no...don't vaccinate him as it's not worth the risk. Do you have any suggestions for me? Is there a vaccine that pinpoints herpes? Is there a more mild, for lack of a better word, type of vaccine that I could give? I don't want to risk my horse's life, but just thinking there must be someway to protect horses that have adverse reactions.
Answer: 
This is a very difficult, if not impossible, question to answer. My best advice is to request the specific vaccine type (manufacturer, vaccine trade name) from your horse's previous veterinarian. The previous owner may need to authorize your acquisition of this information. Then discuss with your current veterinarian the options available for vaccination with different products. Each manufacturer uses a different adjuvent (a substance that is added to the vaccine to increase the body's immune response to the vaccine). There are multiple vaccines available targeting herpes virus, both in combination with flu and alone. Ultimately, you and your regular veterinarian are best suited to determine the best preventive care program and living environment for your horse. I apologize that I cannot answer your question more specifically.
4
Question: My 13-year-old pony mare recently showed part of the symptoms of strangles. She had a moderately high temperature and swollen lymph nodes on both sides of the jaw as well as between the lower jaw. I called my veterinarian, but as he was very busy and my pony didn't show any nasal discharge, he told me to wait. The next day, the temperature had gone back to normal and in three (3) days the swelling had decreased without any medication and disappeared in about a week. The mare never lost her appetite yet the lymph nodes were obviously painful when palpated. The other horse, a 15-year-old gelding, never showed any symptoms. My two horses never go out of their pasture and never mix with other horses. Do you think it was benign strangles or could it be something else? Thank you in advance for your answer.
Answer: 
Strangles can cause less severe disease in adult horses than in younger horses, such as the clinical signs you describe. Strangles can also lie dormant in "silent carriers" and cause disease in unprotected and incompletely protected horses. So it is possible that your pony mare indeed had strangles. Additionally, horses can be exposed to the strangles bacteria through contaminated clothing and equipment (called fomites) and develop illness, so direct contact with a sick horse is not required for the development of disease. However, it seems more likely that your mare had another disease causing her short-lived fever and lymph node swelling. We really can't be sure on this one.
5
Question: It's the end of summer and in the 90's with unusual humidity for California. To my frustration, my gelding has presented a fever of 104+/- and a snotty nose. My veterinarian suspects a virus. This horse has been on "bed" rest for the last month due to lameness. How the heck did he contact a virus with no other horses on the property or within nose contact?
Answer: 
Fever and nasal discharge may indeed be caused by viral infection, or by bacterial infection. Equine herpes virus lies dormant in clinically healthy horses until periods of stress, when it becomes re-activated, causing clinical disease. Another possibility in this case is that transmission occurred between a contaminated item, or even person, and your horse. In the early stages of viral infection, there may be no outward signs and thus transmission can occur by fomite (person or item) quite readily. Additionally, it can be difficult to distinguish viral from bacterial infections in the first few days of clinical disease. Viral infections typically resolve within a few days, while bacterial infections are often more prolonged.