People need to remember to put things in perspective - risk from nature vs. risk from chemicals. Science can bridge this gap if (a) people are willing to learn a little bit and (b) are aware enough to see the propaganda of the chemical industry that wants to sell you toxins to "protect" your pet.
You can see how this can apply to many other issues - fleas (which now are seen as some super-danger), food, vaccines, snakes, mosquitos, etc., etc. But I digress.
Here's my take on West Nile. It poses very little risk to dogs (a tiny bit more to cats). The main reason is that most dogs will show no ill effects at all, and the rest will show only slight ones. They seem to absorb the virus and develop antibodies easily.
And there is no risk of you or your horse contracting it from your dog, so rest easy on that account.
The following is from Contra Costa County Health Services:
Can West Nile Virus cause illness in dogs or cats?
Yes, West Nile Virus can cause illness in dogs or cats. Most dogs or cats infected with West Nile Virus do not show signs of illness and most will recover from the infection. Experimentally infected dogs showed no symptoms after being infected with WNV, and some infected cats exhibited mild, nonspecific symptoms during the first week after infection.
Can an infected dog or cat become a carrier of the disease?
The evidence suggests that dogs do not develop enough virus in their bloodstream to infect more mosquitoes. Cats develop slightly higher levels of virus in their bloodstream, but it is unclear if this would be enough to infect mosquitoes. It is very unlikely that cats would be important in furthering the spread of the virus.
The information closely matches that from the CDC website.
I find it funny that they say the animals can get sick when they then go on to describe pretty much nothing, especially for dogs. They manage to plant that seed of doubt that people latch onto when they are not comfortable dealing with health naturally.
I'd be way more concerned in my area about Ehrlichiosis, which is much more common (and passed by ticks, by the way). Never heard of it? Yep, neither had I, until last year! This is your chance to do a little internet research, ok. Teach yourself.
So do the usual - fresh food diet, supplements (antioxidents, trace minerals, EFAs, aromatics), and natural pest deterrents and controls as needed (I spray with essential oils when going on a trail in warm months). Don't freak out!