what is rabies doing up in that mad dog’s head? do we yet know the specific areas or pathways of the brain that the virus destroys?
on a side note, I was wondering about this as i walked my dog. I realized that early types of rabies, or maybe an ancestor, would have quickly died out if the animal wasn’t driven angry and malicious. So of the earlier infections, a few started producing severe dementia and carried the day. Huzzah!
but some quasi-interesting stuff about rabies:
Rabies is the most highly lethal viral infection known. It has a 100% fatality rate if allowed to reach the brain, though it can be treated if caught early enough.
The virus enters the nerve cell nearest to the entry site (IOW, where the critter bit ya). It then replicates up the nerve until it reaches the brain. This actually isn’t too unusual - herpes does the same thing, except it stops at the first nerve ganglion it hits. Once in the brain, it starts replicating and destroying whatever brain tissue it hits, AFAIK, until death occurs. If there’s a specific pattern to its replication in the brain, we didn’t cover it in my virology class.
Your point about the advantage to the virus of the aggression is interesting. There’s an article in last month’s *Scientific American[\i] (or was it *Discover[\i]?) about how parasites can strongly influence their host’s behavior to their benefit. For example, a parasite that needs to transfer from a fish to the bird that eats it will make the fish flip upside down more commonly that it normally does, exposing its white belly, making it more likely to be eaten. Another parasite forces its host ant to stand on top of a blade of grass all night, waiting to be eaten, instead of going back to the nest. But it doesn’t make it stand on the grass during the day, when it would bake and die.
Preview, dammit, preview!! Curses.
Well, I forgot something anyway: one major reason rabies is so fatal is that because it travels along the nerves, it never enters the bloodstream, so the immune system never gets a shot at it.
[slight hijack]
FTR, the article was in Discover. Kinda creepy when you think about it (the parasites effect on their host, not that the article was in dicover.)
[/slight hijack]
This brings up a question I have wondered about before: if the virus doesn’t enter the bloodstream, how do rabies vaccines work?
Ah, good question. I’ve been thinking about that myself since I posted last. This is an educated guess rather than a definitive answer, but I’m pretty sure it has to do with the fact that the immune system has two sides - the humoral response and the cell-mediated response. I won’t get into all the details, but as I understand it, you need some free antigen in the bloodstream to start the immune response. B lymphocytes only respond to free antigen. Once the process gets started, cytotoxic T lymphocytes are made that recognize native cells displaying viral proteins and destroy them, so they can take care of the infected nerve cells. The vaccine provides the free antigen to start the whole mess up.
The one thing I’m fuzzy on is that maybe T cells can get started merely by seeing the viral proteins - without B cells activiating first. I can’t remember. Even if that’s so, though, there are relatively few infected cells, so it may be difficult to get the right T cell to an infected cell to get started.
I wonder if rabies destroys the nerve cells of the pathway to the brain. If not, then it totally makes sense that the immune system wouldn’t catch on right away.
the T cells respond to human cells that have the viral protein expressed on the membrane. this is basically a signal the T cell reads as “eat me” (we’ll leave the “drink me” protein expression for a later discussion). The T cells get the info from B cells that have picked up stray virus (like from phagocytosis) or that have cleaned up after a lysed cell.
Rabies is not 100% lethal…
There is one documented case of someone surviving an infection of the brain. Not something to take your chances with, though.
The scary thing is that, of the 19 people infected by bats since 1990 (they can tell where it came from from the DNA of the virus), a bite has been confirmed in only several. I forget the details now (knew them very very well a year ago as I was trying to get our health department to recommend shots after finding a rabid bat in our kitchen, with over 100 living in our attic), but the one I do remember is two spelunkers in Texas, I believe, who contracted rabies through breathing aerosolized saliva. Others included a guy whose wife woke up and found a bat sitting on him (he had a shirt on), and a guy who brushed a bat away.
The fact that you don’t have to be bitten to contract rabies is one reason they recommend shots for any children or invalids who are found in rooms with bats, if the bats can’t be tested.
This is one case where you’re better safe than sorry…
Yes, there have been confirmed cases of catching rabies through breathing in infected dander, but it’s extremely rare, and seems to require breathing in a lot. That’s certainly possible when you’re walking in a cave with a few feet of guano on the ground, but I wouldn’t worry about it with just one or two in your attic. If you do have bats, I’d be much more worried about a bite.
'Scuse me? Could you expand on that? Rabies is rabies is rabies. Bats can infect dogs, dogs infect bats, dogs infect racoons, and they all infect humans. And just because a bite can’t be confirmed doesn’t mean there wasn’t one. It’s not uncommon for rabid bats to get into a bed and bite sleeping humans, for instance.
Rabies is not rabies is not rabies (well, yeah, it sort of is, since the end result is the same). Unfortunately, I’ve not been able to find the source of my “19 since 1990,” though I’ll keep looking. Nonetheless, there clearly are different strains of the virus, as suggested below:
[ul][li]Nucleotide sequence analysis of the viral nucleic acid implicated a variant associated with the silver-haired bat, with 99% homology with a variant identified in a previous case of human rabies in Montana in 1996.[/li]
[li]Rabies virus recovered from the five dogs was identified as a variant not previously found in Florida but endemic in coyotes (Canis latrans) in south Texas.[/li]
[li]Rabid raccoons occasionally detected outside of the reservoir area have been found to have non-raccoon variants of the rabies virus, suggesting that they were infected by other species.[/ul][/li]You’re excused.
In addition,
[list][li]the case of the spelunkers is hypothesized to be saliva, not dander;[/li][li]we didn’t have just one or two in the attic, it was a colony of over 100, and we found a rabid bat on our kitchen floor crawling out (the same kitchen, I might add, that our one year old son crawled around on, possibly through rabid bat saliva); and[/li][li]All I said was that bites were not confirmed in all cases (although I think the evidence pretty strongly indicates that you don’t have to be bitten…)[/li]
By the way, the cases found at the bottom of this CDC site make for interesting reading, though not if you think you’ve recently come across a rabid animal.
Again, with rabies, better safe than sorry.
does anyone know exactly how the hydrophobia aspect of rabies expresses itself in humans? do people actually become irrationally afraid of water, or do they just not want to drink, or what?
Found it. Not as detailed as the info I had last year, but it gets the point across.
And JB, the information I’ve seen indicates that the hydrophobic aspect of rabies is probably due to pain when swallowing. Apparently this symptom is not always present. In fact, in at least one of the case studies from the Mortality and Morbidity Weekly of the CDC (very interesting reading, not recommended for hypochondriacs) the diagnosis of rabies wasn’t made until about a month after death–the symptoms can be quite varied.
[QUOTE]
Originally posted by Smeghead
parasites can strongly influence their host’s behavior to their benefit. For example,
Creepy, perhaps. But not hard to understand. It’s a very practical example of Survival Of The Fittest. Stupid parasites die out, and the ones who train their hosts well get to survive.
Johnson where are you living at? :eek: And have you moved yet?
but the bats are gone. This episode would have been worth a pit rant, but I think I’m over it now–time eases the pain. The condensed version (well, ok, not so condensed):
We knew we had bats in the attic, and had for some time, so we had an exterminator over one night at dusk. We counted well over 80 bats coming out. The very next morning, I came downstairs to let the dog out. In my half-awake stupor, I noticed something on the step in between the kitchen and the back porch. I thought to myself “that’s not quite right”–luckily the dog stepped over it and didn’t notice it. I turned on the light, spent literally a minute or two looking for something to put over it, and it barely twitched a muscle–again, I thought something’s not quite right.
We try to call Animal Control, and find out our county has no animal control–the SPCA handles that. No emergency number either. When we get a hold of them, they say they’d be happy to come down and pick it up. We just have to get it in a Tupperware container. Luckily, I’ve had extensive training in handling potentially rabid wild animals–yeah, right (amusingly, Montgomery County’s (MD) Animal Control also tells people they have to contain the animal–even the people who had a 15- or 18-foot anaconda in their back yard trying to eat their dog–don’t we pay them to do these things?). In the end, it’s tested, and has rabies. When the guy picked it up from the house, he asked if we wanted the container back .
I make the mistake of doing too much research (I’ve since sworn off medical research on the web), and determine that I am in fact going to die. The county health official wasn’t to concerned when I told her there was no physical contact, then proceeded to clue me in to those spelunkers who likely inhaled the virus. Now, my brain was telling me there was an extraordinarily miniscule chance that we had contracted rabies, but my brain was also telling me with an incurable fatal disease, why take a chance? Again, it’s not like we saw a bat fly out the window–we had a colony living over us for months, leaving droppings in the driveway, and had a rabid bat in the house. My doctor was reluctant to push the health department until he heard about the numbers involved (he told me a few months later that a woman in his office who broke up a fight between her dog and a raccoon had great difficulty in getting the health department to authorize the shots as well). The doctor at the emergency room was furious at the health department.
That deals with the county bureaucracy. Now we move to the State. Obviously, we want the bats out. The exterminator told us he could exclude them from the house, but they’d most likely roost on the outside of the house and nearby trees–even if he released them several miles away. That didn’t seem like an acceptable option for us, let alone our neighbors. He also informed us that the State won’t allow the extermination of bats. So I call the Department of Natural Resources. The woman responsible for bats tells me that yes, the State does prohibit the extermination of bats, and furthermore, we couldn’t exclude them from the house for two months because the babies were nursing. She also said that studies show that there’s no greater chance that other bats in the colony have rabies (I still find that very difficult to believe, since a scratch can transfer it to humans, and they hang together in clumps, but she’s the expert), and very strongly implied if not outright stated that we should just wait until the winter to bat-proof the house.
I told her that I was living in my mother-in-law’s basement, and that if the bats were paying the mortgage I wouldn’t be so concerned. Unsurprisingly, the bats weren’t paying the mortgage (maybe their check didn’t clear–I don’t know). Her boss was out, and he was the one who would have to sign the papers, so nothing could be done for a week. I asked if it would help if I spoke directly to him, and she essentially told me that wouldn’t be a good idea (in a form that I took to be a threat–there was no “or else,” but…).
After a great deal of back-and-forth, I finally get approval, if we dispose of them in a humane manner–I suggested scientific research. The exterminator sealed up the house except for one area, put a trap over it, and, rather ironically, the bats couldn’t find their way out and died in an inaccessible part of the attic. Still there–I certainly hope the virus can’t survive for long without a host, and that, say, if the roof leaks, it won’t be revived.
We don’t have rabies :), and (I hope) the story’s over. OK, a little longer than I expected.
Now, I would much prefer not to harm any living animals (well, except cows (very susceptible to rabies, by the way–the one thing about this disease I find terribly amusing), chickens, etc.). When they invade my home, however, I get concerned and feel free to take action. When they have incurable fatal diseases that could spread to my wife, child and pet, as well as myself, I’ll damn well do what I have to to get them out. A sluggish uncaring bureaucracy more concerned with a few scores of bats than living breathing humans (and taxpayers, I might add) is infuriating. And I say that as a second generation bureaucrat.
(By the way, the fact that rabies no doubt affected a few brain cells explains any inane/nonsensical posts I might have made, or will make in the future…yeah, I know, just kidding)