Instructor: Welcome to Module 2: Rabies.
Rabies is a very interesting disease
because of its high case fatality rate, close to 100%.
So it has a great impact on local
and state health departments trying to deal
with rabies exposures.
And the healthcare cost to try
to prevent human cases is high.
So these are the topics that we're going
to be covering in this slide presentation.
And be sure when you review the slides
that you look at the notes under each slide,
where additional information is provided.
So the rabies virus is an RNA virus
in the Rahbdoviridae family, the Lyssavirus genus,
is transmitted primarily through the saliva
of infected animal.
All mammals are susceptible to infection.
There's been an occasional bird
that had antibodies, indicating exposure,
but apparently, the virus doesn't migrate
to the brain in birds.
So there's no clinical infections documented.
It infects the central nervous system,
and it's invariably fatal after the onset of clinical signs.
This is a picture of the bullet-shaped rabies variant.
In the United States,
most of the US acquired cases are due to bats.
And that's because bats have tiny teeth.
And so people may not interpret that they were bitten.
Or even if they realize they were bitten,
the wound isn't bad enough to seek wound care.
And so they're not thinking about rabies.
There's about a handful, usually, on average,
about three human cases reported annually in the US,
and nearly all of them are fatal.
Worldwide, a larger number of cases.
59,000 to 70,000 per year estimated.
And 99% of them are caused by dog bites
and the dog variants outside the United States.
This is the United States from 1928 to 2018.
The solid line here is domestic animals
and the dotted line are human cases.
And you can see that the number of cases were high,
you know, as high as 10,000 each year,
in the United States through the 1940s,
and then there was a mass vaccination
of dogs against rabies, which was started in 1947.
And you can see the number of cases dropping,
both in domestic animals and humans.
Worldwide, the green countries, like North America,
do not have the dog variant of rabies.
Now, dogs can occasionally still be infected
by other variants,
but at least we don't have the dog variant,
which is so easy to be transmitted to people
because how close dogs live in the human environment.
The red countries are those
that have dog-mediated human rabies,
and the other countries are kind of in between
in regards to perhaps not having human rabies,
but the dog variant is present.
The World Health Organization has
three different categories of exposure.
The United States does not.
Just has either exposure or non-exposure.
Be sure to look at the ACIP document on rabies
to make this clear.
Basically, in the United States,
they tend to combine these category two or three exposures.
So category one, no exposure,
just touching or petting a rabid animal,
feeding a rabid animal.
Even licks from an animal
that's shedding rabies virus in its saliva,
if it's on intact skin,
is not considered a rabies exposure.
Category two is more mild exposures,
where the rabid animal's nibbled uncovered skin,
and there's minor scratches or abrasions without bleeding.
And then definite bites or broken skin contact
with the saliva of a rabid animal is a severe exposure.
And any bat contact because of this issue of being bitten
and not realizing it.
Other transmission.
There really is not good evidence
for other routes of transmission.
There have have been cases related
to aerosolized virus in the laboratory.
There was thought to be some cases related
to inhalation of the virus in a bat cave, a small bat cave.
But when they looked back at those cases further,
they concluded it was likely due to bat bites.
And there's no human-to-human transmission except
for transplantation of infected tissues.
Signs and symptoms.
Highly variable incubation period.
So the incubation period is the time period
between when the person is exposed, or the animal exposed,
and when they start showing symptoms.
Usually one to three months. Varies by bite location.
So if the bite is in the head,
where the virus is closer to the brain,
then it can be a shorter incubation period.
The symptoms, non-specific prodrome,
so fatigue, fever, and headache, are not specific.
Could be all kinds of other diseases.
But then it will progress to CNS symptoms
because the viruses in the brain can either be furious
or paralytic in humans or animals.
And it can vary by species.
For instance, cat species tend
to be the more furious type of rabies,
where they're attacking other animals and people,
whereas dogs and raccoons may more often be just
the paralytic, where they're not able to move.
They're just stumbling around.
The symptoms typically last anywhere from 2 to 10 days,
ending then in coma and death.
Diagnosis and testing.
So before death, the saliva,
skin biopsy, serum, and CFS can be tested
in both animals and humans.
However, there can be false negatives.
So depending on how the test is done,
the virus may be intermittently shedding in the saliva,
there can be false negatives.
So you really need to follow up with confirmatory tests
on the brainstem and cerebellum postmortem.
We cannot rely on the accuracy of antimortem tests
to determine if an animal is rabid,
because we wanna know with 100% certainty
whether the person who was bitten needs rabies treatment.
And so that's why confirmatory tests require euthanasia.
Now, there are ways to determine in certain species,
like dogs and cats, where it's been determined
that if they have rabies virus in their saliva,
they can't survive more than 10 days.
And so you can confine a dog or cat after a bite,
and if it stays healthy for 10 days,
then you know that it wasn't rabid,
at least at the time of the bite.
But otherwise, antimortem testing doesn't help you
with dogs and cats that have bitten somebody.
Okay, treatment. There's no antiviral treatment.
There is post-exposure prophylaxis, or PEP,
that's administered as a series of four to five doses
as soon as possible after exposure.
So first of all,
the most important thing is to wash thoroughly the wound.
And then if the post-exposure vaccine is given,
it can help fight off the virus
and prevent it from migrating up to the brain.
Another important component
is human rabies immune globulin, HRIG.
And that is given in the wound.
And again, it's fighting off the virus in the wound
and preventing it from going up to the brain.
About 60,000 people
in the US receive PEP each year due to exposure,
and it's nearly 100% effective
if it's given properly, with immunoglobulin,
and given in time.
So prevention.
PrEP, pre-exposure prophylaxis,
for high-risk individuals like veterinarians,
animal control officers, people working with wildlife.
So that's an injection, a vaccine.
You can also distribute wildlife rabies vaccine bait.
And that's what's pictured here with a quarter
to show the size of them.
There've been different formulations of baits,
but these are the ones being used now.
So there's a liquid vaccine inside.
This is often a fish meal polymer
or some other kind of polymer that smells good,
particularly to raccoons, and tastes good.
And these are distributed by hand in a city,
where you toss them behind dumpsters or in bushes,
anywhere where you think raccoons might be hanging out.
And when they eat these,
they get vaccinated through the mouth.
You can also distribute these by plain or by helicopter
in more rural or mountainous areas.
There is approved vaccine for dogs, cats, ferrets,
horses, cattle, and sheep.
You can see a picture here of a dog being injected.
Raccoons, if they're caught in traps,
can also receive a parenteral injection as well.
But often you're catching the raccoons
in traps afterwards to draw blood
in order to see if they have antibodies
to determine whether your bait campaign worked.
There are dog import regulations
to prevent dog variant rabies from being imported
into the United States.
Often there's a conflict,
particularly with service people overseas,
who adopt wild dogs and make them into pets
while they're overseas,
and then they want to bring them back to the United States.
And so there are regulations
to try to prevent dog rabies
from being imported into the United States,
but occasionally it still comes through that way.
Okay, animal reservoirs.
The rabies virus is adapted to specific animal hosts
in different geographic areas.
And if the virus is adapted to the primary animal host,
often that animal will not show symptoms right away
or for a period of time.
And in 2022, in the United States,
most reported animal rabies cases were in bats.
And bat rabies is worldwide. And in raccoons.
And cats represent the most domestic animal rabies cases.
They tend to not be vaccinated quite as well as dogs.
The US was declared canine rabies variant free in 2007,
but dogs can still be infected with other variants.
And I'll show you a picture in a minute of the variants
that we have in the United States.
Okay, so here's the picture.
And you can study this more at your leisure.
FX stands for fox.
So we have the Arctic fox variant up here in Alaska.
We've had fox variant at different times
down in the continental United States.
Currently we have a fox variant in Arizona.
The green area is a raccoon variant.
And the raccoon variant keeps trying to spread north.
In fact, there have been some cases
in the Canadian provinces bordering here,
Quebec and Ontario.
It's trying to spread west.
That's particularly why we do
those vaccine baiting campaigns for raccoons,
is because once a geographic area gets raccoon variants,
the number of animal rabies cases skyrocket,
because raccoons interact when they're rabid
with a lot of other wild and domestic species.
And then you have increased exposures to people
whenever you have the raccoon variant.
We've got some skunk variants here
in the central part of the United States.
And remember, the bat variant is not depicted here.
It's throughout.
Okay, the impact of climate change.
This is just one example.
The common vampire bat is one
of the main wildlife species responsible
for transmitting rabies to domestic animals,
dogs and livestock, and humans in Latin America.
In Latin America,
in places where they don't have window screens,
the vampire bats will come fly in at night
while people are sleeping and feed on their toes,
and the people will get rabies that way.
They'll also feed on cattle,
flying in to feed on the cattle legs.
So as the time has been passing,
you find that the range of the vampire bats is moving north.
And in fact, that range is expected to extend
into the continental United States within 27 years.
So that would be really problematic,
if we end up with vampire bat rabies
in the continental United States.
This last slide has some links
that are important for you to check out.
And I hope you enjoy learning more
about this complex and fascinating disease.