Why is the rabies virus 100% lethal?

Most diseases, even ones that have very high mortality rates, still have some survivors. However, rabies seems to be the exception with a 100% mortality rate once symptoms appear. Yes, the Milwaukee Protocol has had some success, but apart from that, no human in all of recorded history has ever survived rabies. How is it possible for a disease to have a perfect mortality rate with absolutely no one immune to it?

This article suggests that it’s not 100% fatal after all - it’s extremely lethal, but not invariably. Apart from that, I think that the key to your question is “after symptoms appear”. Rabies is easily survivable if you get treatment after exposure, but before symptoms develop. The reason is that those symptoms, the only symptoms, are themselves fatal. You might as well ask why decapitation is 100% fatal. The symptom - loss of head - is itself fatal, so the only treatment is to prevent that symptom from developing.

That is false. There have been at least three people just in the U.S. who are documented as having survived it, but there may be evidence of antibodies in certain populations:

They also cite that “earlier studies provided weak evidence of past rabies infections in Inuit hunters or fox trappers”. The problem is, if these people have survived infections, it wouldn’t have been diagnosed and documented so we can’t say for sure.

So it’s possible, but yeah, definitely a very tough virus to beat.

It’s not a disease of humans. It is passed to humans from other species of mammals. Transmission from human to human is virtually non-existent. Therefore, there is no selection for reduced virulence to favor transmission.

Some mammals, such as opossums, are virtually immune to rabies, and some bats recover from rabies. When a disease is passed within a species, it will be subject to select for reduced virulence.

The same factor contributes to the virulence of Ebola. It’s mainly acquired from other mammals, and only exceptionally passed from human to human in the recent West African epidemic.

Wikipedia lists 5 other diseases having a mortality rate of 100%, or very nearly, without treatment. Rabies is the only viral disease in this exclusive club.

  1. Prion diseases including mad cow disease, caused by prions
  2. Primary amoebic meningoencephalitis, caused by a protozoon
  3. African trypanosomiasis, caused by a protozoon
  4. Visceral leishmaniasis, caused by a protozoon
  5. septicemic or pneumonic plague, caused by a bacterium

The other factor is that the virus confines itself to the nervous system, effectively “hiding” itself from the immune system, unless we can give it a bit of a prompt with a vaccine. The virus infects the nearest neurons and then slowly spreads up the nerves until it reaches the brain. That’s when very bad things happen.

Also, the reason for low mortality is to give the disease a chance to spread itself. Rabies has a different tactic for that, altering the host’s behavior to ensure more rapid spread. That’s obviously a very neat trick if you can pull it off, and if it’s incompatible with leaving the subject alive, it might still be an effective technique.

Pathogens undergo evolution towards optimal virulence. Obviously, if a pathogen kills its host so rapidly it doesn’t have the opportunity to transmit itself to others, it won’t be able to spread or even persist. Therefore the most highly virulent pathogens gradually become less lethal over time. Influenza is quite virulent when it is transmitted to populations that have not encountered it before such as isolated tribes. Among populations in which it is endemic, it is generally lethal only to weakened individuals.

Interesting. I’m not disputing you; rather hoping to learn more.

If indeed Ebola is rarely passed / passable from human to human, why the insane panic last year about transmissibility all over the planet after a relatively few cases appeared clustered in West Africa? Sound science or media-driven ignorant panic?

Certainly it seems like the treatment / management protocol is heavily laden with precautions to protect the caregivers and nearby patients from any/all transmissions of virus from the infected.

Or is it more the case that the stuff is not human-transmissible in the low-density wild of hunter-gatherers, nomadic tribes, and subsistence farmers, but is much more transmissible in the modern high-density environment of cities, airports, and hospitals? Not to mention in cultures whose death rituals include all but bathing in the blood of the recently deceased?

Genuine curiosity here; no agenda.

On a related note, the old rabies vaccine for humans used to require lots of shots in the stomach. The modern vaccine doesn’t, but why did it ever require such a specific area of injection? Also, I’ve heard that even if you get a preventative rabies vaccine, you still need additional shots if you get bitten, though fewer of them. Why doesn’t the preventative vaccine confer immunity?

Ebola is highly transmissable between humans. It’s its high lethality that previously has prevented it from spreading widely before. Previous outbreaks have been in remote areas with sparse populations in which it “burned itself out” among humans in a relatively short time. There wasn’t enough interchange to keep it going. Once such an outbreak stops, the disease is not present among humans anywhere. New outbreaks are produced by the virus being passed to humans from a non-human host. (What that host is is still not entirely clear.)

In the recent West African outbreak got into high-density cities and areas where there was a lot of travel by bus and truck. Transmission became so rapid that it happened faster than it could burn itself out.

Epidemiologists fear thatEbola could become endemic(continuously present) within human populations by becoming less lethal. Ironically, Ebola might actually kill more people in the long run by evolving to kill them more slowly.

Is increased aggression a symptom of rabies infection in humans?

The immune system is prevented from going into the nervous system?

How does the nervous system, especially the brain, protect itself from infection?

More generally: Do I understand correctly that the most successful virus in humans must be herpes or some other minimally-impactful virus?

Are there viruses that actually help their hosts?

Friendly Viruses Protect Us Against Bacteria

They can attack bad bacteria for us:

It can be. Rabies can manifest as either agitation, aggression, and fury or as lethargy, and both types can be seen in the same person (or animal) with lethargy usually following the aggressive stage.

There is this thing called the “blood-brain barrier” that in general isolates the central nervous system from the rest of the body, which helps prevent the CNS from getting infected, but complicates things when it does get infected.

There are viruses that cause no symptoms in healthy adults, only in the immune-compromised, so arguably those are the most successful.

I think there are some insect viruses that have gotten mixed up in their reproductive habits, you might look there.

I’m not sure, but I believe it was simply a factor of the sheer volume of fluid that needed to be injected.

Not exactly. Think of the brain/nervous system as being behind a moat, consisting of the blood. The immune system (speaking very generally here) patrols the blood, looking for foreign invaders and attacking them. There is an arm of the immune system that also examines cell surfaces, looking for foreign proteins, and that kills any cells showing the wrong shapes. All of our cells, incidentally, routinely chew up proteins and random and display bits of them on their surfaces for the immune cells to inspect.

For whatever reason - and I’m not clear on why - the rabies virus in neurons doesn’t trigger an immune response through this pathway unless we trigger the immune system to be hypervigilant by administering the vaccine. Once it’s activated in this way, it’s able to detect and destroy infected neurons, but without the vaccine, the virus is able to sneak under the radar.

More generally, there’s a strong “blood-brain” barrier that prevents most infectious agents from getting into the brain. Any infection of the brain is a potentially very serious problem.

I’ve never quite understood this stomach bit. When did they stop requiring these shots to the stomach? I must have been sometime well before 1948 (almost seventy years ago) - I had a series of rabies shots then, and they were just like a flu shot. Daily trips to the doctor’s office for fourteen days of painless shots with no side effects, and then it was finished.

This was sort of an interesting story. My family had a Mother’s Day dinner at my grandparents house, and there were thirteen of us there. One of the families in attendance brought their dog, and within days the dog was diagnosed with rabies. So we all had to get the Pasteur series of shots, which were all in the arms as I stated above. Ten of us had not touched the dog, so we got by with only fourteen days of treatment. The three who had come in contact with it were given the full dose of twenty-one days worth. All this must have worked as nobody got rabies - although relations between the family that brought the dog and the rest of us was a bit strained for a time.

This happened in Illinois, and the State provided the vaccine free of charge. However, we had to pay the doctor for administrating the shots. This came to a grand total of $246 for a total of 203 shots, just a bit over a buck a shot. Things were sort of different back then.

If I remember my college virology & immunology courses correctly, the early rabies vaccine as injected into abdominal fat because it was more slowly absorbed. This gave a stronger immune response than an IV or IM injection.

I don’t believe a disease like rabies could exhist without bats. The most common animals to get rabies are foragers like raccoons and foxes. They find a sick bat on the ground and eat it. Once infected the amount of animals they are likley to pass this on to is very limitied and would soon burn itself out in an infected area. Bats are very mobile and are about the only species that could keep reinfecting areas.

Clarification on a couple of things:

It is not surprising that some people in a particular population might have antibodies to rabies virus without having been vaccinated or had the disease. There is such a thing as minimum number of infectious particles needed to cause disease (not sure what this is for rabies). Once someone displays signs of illness after rabies exposure, that’s when mortality is almost certain (even with treatment).

Also, the Milwaukee Protocol is being abandoned because of overwhelming failures.