As you probably know, West Nile Virus is transmitted from birds to mosquitos, mosquitos to horses and, occasionally, humans. I have wondered if the disease can be passed directly from an infected bird to, say, my cat Freckles. Though Freckles is well-fed on Cat Chow, he preys on and eats birds.
It might seem farfetched to worry about my cat getting an exotic disease in central Indiana, but the disease is near. A dead, WNV-infected bird was found in Indianapolis, about 35 miles from here.
Here is a list of species found positive for West Nile exposure. Domestic cats are listed but it is my impression that very few domestic cats and dogs have been found to have died from West Nile. So what are the ways your cat can be exposed to West Nile virus?
Mosquitoes looking for a bloodmeal is the most likely way Freckles would be exposed. Most mosquitoes have a preferred host type: birds, mammals, or herptiles. The cycle for West Nile virus appears to involve primarily avian hosts and avian-seeking mosquitoes and generally involves bridge vectors (mosquitoes that bite both birds and mammals, i.e. humans and horses) only during an outbreak. Well, at least this is what happens in the Old World and in established arboviral cycles like Eastern Equine Encephalitis. But West Nile is an emerging disease presented with immunologically naive populations so there’s a lot of guessing when it comes to predicting the flow of the virus through natural populations. For one thing, it appears that we don’t find much virus (apart from the crows and their relatives) in the wild bird population unless we look near areas of major outbreaks. For example, last year I trapped over 1500 birds, banded them and drew a drop of blood before I released them here in New Jersey. Only 3 non-corvids had evidence of West Nile antibodies. CDC found high levels of seropositive House Sparrows in Queens, NY but low levels in Staten Island in 1999. In the year 2000, they found higher levels on the island, but we found low levels here in New Jersey (5 out of over 900 caught). This was with considerable positive crows and mosquito pools in the area. This may mean that West Nile, like St Louis virus, chugs along at normally low levels in the avian population (but quite frankly, there’s so few of us looking at live birds that it’s difficult to predict at this point).
There is strong evidence that virus can be transmitted from one crow to another (from Bob McLean of National Wildlife Health Centers) without the aid of a mosquito, most likely through the shedding (and aerosolization?) of feces. Crows, as you are aware, I’m sure, are highly sensitive to this virus, with mortality rates well over 95%. Crows may be cleaning virally-laden feces off and exposing themselves to the virus through oral mucous membranes/cuts. But this mode of transmission is thought to play a minor role since the overall death patterns in corvids (crows, ravens, magpies, and jays) screams mosquito transmission.
Finally, there is some evidence that a very few birds may have died also through oral transmission or aerosolization, but without the feces delivery system. In 2000, a Red-tailed Hawk died in February in the NE USA (don’t remember which state). This is not mosquito season. Given that some birds develop very high viremias and that some birds of prey appear susceptible to WN, we suspect that an infected individual was caught by the hawk, torn up and eaten. It would seem less likely that the hawk picked up the virus during the previous mosquito season (ending the previous October) considering how quickly birds go down after exposure.
Is Freckles in any danger? I’d say the chances are very low. If you have a horse, vaccinate it. Like crows, they are at risk. If you have mosquitoes around your house, reduce their breeding areas or call your local mosquito control agency. West Nile can be dangerous to those with compromised immune systems or the elderly. But with a few precautions, you should be able to minimize exposure to it and any other arboviruses that are currently hanging around your place right now.
Boy, have I blathered on!
Thank you, Rhynchar… Brachyrhynchos! The scroll doesn’t work when the bold is engaged. You sure came through! That eases my mind. Young Freckles tends to bag the sparrows and finches. Sometimes, I’ll find a spray of blue jay or mourning dove feathers in the yard, but I think the kestrels got them. The remains that Freck brings home are mostly finchy, from the daft Shakespearian experiments.
This is the wonder of the Teeming Millions! Where else could a midwestern guy who keeps a cat find a Brachyrhynchos with all the answers? Fighting ignorance since 1973, and all that! (I had to take my shirt off to make sure I had the quote right.)
So, brachyrynchos, how quickly is that exactly? I watched this poor bird all day yesterday until I lost sight of him in the neighbours’ yard. Didn’t see him this morning. Feel free to blather some more!
Thanks AskNott for directing me here.
Oops, I should have mentioned this thread:
http://boards.straightdope.com/sdmb/showthread.php?threadid=124516