Ross River Virus in Horses with Dr Dave and Kelly

Kelly: So what is the Ross River Virus? 

David: It’s a virus that’s carried by mosquitoes, of various species. It has to be transferred from mossie to horse, so it can’t go from horse to horse, horse to human etc. Therefore, if you have a horse in a herd that could be the only one who gets infected if it’s the only one to be bitten by the wrong mossie. Of course more than one horse or the whole herd could be infected if they’re all bitten.  

Kelly: So what are the symptoms?

David: They can range from:

• stiffness and soreness
• sore joints with possible swelling
• sore muscles with possible swelling
• a cough
• they could have just a temperature, and they usually have a temperature with Ross River Virus. They can get a high temperature that dramatically waxes and wanes for no particular reason. It could rise for an hour then go back to normal. It could then stay normal for half a day, then rise again and go back to normal after an hour (just as an example). During the episode of a high temperature the horse would be pretty unwell but when that episode was over the horse could appear completely normal. They could also display the normal signs associated with a high temperature, and a high temperature doesn't have to be that high, say in the high 39ºC to well up into the 40ºC range
• respiratory signs
• gut signs such as being off their feed, colicy, diarrhoea
• lethargy
• founder, or show signs of lameness (though this would be associated with the high temperature as it is a consequence and not a direct cause)
• nervous signs, such as that the horse is so wobbly that it can’t take a step forwards, or alternatively takes a step forward but then takes 2 steps backwards, or staggers backwards and almost flips over then re-balances.

*Signs are really non-specific, they usually don’t specifically get pneumonia, a gut disease, or a liver problem for examples. But they can get any of the above, singly or in any combination.

Kelly: But, because those signs are similar to Hendra, if we suspect Ross River should we also test a sample for Hendra?

David: It depends on the signs that are showing. The distinguishing fact between the two is that you usually don’t get death within 48 hours (as you do with Hendra). But I guess this doesn’t really help us. We probably need to be aware of Hendra and if there are any symptoms which could indicate Hendra then we need to take those precautions. So this means that we need to look at the time of year, the presence of Bats in the area where the horse is (particularly where are its feed bins).

Kelly: If someone suspects that their horse has Ross River what should they do?

David: First of all, it probably needs to be checked by a vet to eliminate other ailments. Diagnosis requires a fairly close identification of the history, which is very important in making a diagnosis. It could be any number of diseases, viral or bacterial infections. For example, if the horse is showing respiratory signs, it could be Hendra, pneumonia, strangles, etc. You can’t just say, “Oh, it’s crook with these symptoms, it must have Ross River.” It’s one of the things on your list, but it wouldn’t be the first thing you’d go to unless the history and clinical exam suggested it likely.

Kelly: So when you get a vet out, will they treat the horse symptomatically?

David: Yes, treatment is basically symptom-support. A vet would probably administer an antibiotic, particularly if there’s respiratory signs present. In actuality, being a virus, there’s no specific drug that will help. Clinically speaking, colloidal silver has been reported to help in some cases, though there have been no clinical trials to prove its effectiveness in this regard. But it’s something that may help with the symptoms.

Kelly: And what are the long-term effects?

David: The first one is that it may reoccur with stress. Assuming that the horse makes a complete recovery from the virus, and there wasn't any ancillary diseases (pneumonia, brain or spinal lesions, etc) the recovery is usually uneventful. Racehorses I've seen whilst practicing in Victoria who had Ross River sometimes took up to 15 to 18 months to get back to normal.

Kelly: So it's not one of those ailments where they have as many days off as they are sick?

David: No, it's a long recovery. It has been recommended that they go for blood tests periodically, and when the blood dilution level drops low, say around 128, they could possibly start working again. The IgG (immunity level) also needs to be low.

Kelly: And preventative measures?

David: Move away from the coast and live in Toowoomba? That was a joke, but the idea is to reduce your horses' mosquito contact. 

Kelly: So if you treat it a bit like repelling midges for Qld itch (through spraying), will that help?

David: Yes, that would help in keeping mossies away from the horse, by spraying them with FlyAway or an equivalent. But there's no simple fool-proof method of prevention, other than keeping your horse in a mossie-proof enclosure, though this could be difficult. So, if you can prevent your horse from contact with mossies, it won't get Ross River, I guarantee it! And the same works for people of course.

Kelly: So is the strain that affects equines similar to the one that affects humans?

David: It's the same strain. Once again, humans can't catch it from horses or other humans, and horses can't catch it from other horses. In humans there's similar symptoms, all areas of the body can be affected.

Kelly: And what about testing, anything we should know?

David: The tests can determine if it's a recent infection the horse is recovering from or if they were exposed to it a while ago. 

Kelly: So if someone's horse had a virus that they weren't fully recovering from, should they consider getting it tested for Ross River?

David: Yes, but the problem is that you can't guarantee that the reason the horse is unwell is due to the Ross River. You can say that it has been previously exposed, but you can't say it was that exposure which is making the horse sick now.

Kelly: Well, thanks Dave for enlightening us all on this scary virus. If you suspect your horse has Ross River please phone VEVS on 0409 884 377.

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