Descriptive Epidemiology Project-Rabies
Dr. Carol Hoban
Applied Epidemiology
MPH 510
Cari M. Cooper
February 3,2013
Over 55,000 people die annually of rabies, although mostly in Asia and Africa
rabies occurs in more than 150 countries and territories. More than 15 million
people worldwide receive a rabies vaccine annually. An annual vaccine is estimated
to prevent thousands of deaths every year. Even with this data, according to the
CDC, it is difficult to estimate the global impact of rabies by using only human
mortality data. Rabies vaccinations have been around for more than a 100 years but
because rabies mostly occurs in countries with inadequate public health resources,
few diagnostic facilities and almost no rabies surveillance, it is really hard to define
an absolute significance of rabies worldwide.
Underreporting is a problem with almost every infectious disease in developing
counties but rabies faces a unique problem. Since rabies in the natural sense is not a
disease of humans, we also need to focus our efforts on to what extent the animal
population is affected. We also need to focus most of our attention and expense on
preventing transmission of rabies from animals to humans. Although we have found
great success in animal vaccination and elimination of stray dogs, rabid dogs is still
the cause of over 90% of human exposure to rabies which makes up 99% of human
deaths from rabies worldwide.
In the United States, rates of rabies have drastically changed in the last 100 years.
Unlike the rates of rabies worldwide in the United States, more than 90% of rabies
cases occur in wildlife, mostly bats and wild carnivores. Prior to 1960, the majority
of cases were from domestic animals but due to education and vaccination rates
have declined to about 100 annually around the turn of the century to 1 or 2
annually presently. Although rates of rabies are now a rarity in the United States,
this does not come with out a cost. Public heath efforts which include vaccination of
companion animals, control programs; maintenance of rabies laboratories, and
medical costs, such as those incurred for rabies post exposure prophylaxis (PEP)
cost the United States 300 million dollars annually.
Rabies is a zoonotic disease (a virus or disease that is transmitted from humans
to animals) that causes a deadly viral infection that is usually spread by infected
animals to humans. The rabies virus belongs to the order Mononegavirales, a virus
that is nonsegmented with negative stranded RNA genomes. This virus has a unique
bullet shape and is classified as a animal virus in the Rhabdoviridae family. The
structure of Rhabdoviruses are approximately 180 nm long and 75 nn wide.
Included in the rabies genome are five proteins: nucleoprotein, phosphoprotein,
matrix protein, glycoprotein and polymerase. All rhabdoviruses have two major
structural components: a helical ribonucleoprotein core and a surrounding
envelope. Once within a muscle or nerve cell, the virus undergoes replication. From
the point of entry, the virus is neurotropic traveling quickly along the neural
pathways into the central nervous system and then to other organs. The salivary
glands receive high concentrations of the virus, thus allowing further transmission.
The initial symptoms of rabies can cause a lot of discomfort and can range from
flu like symptoms such as weakness, fever and headache but along with these
symptoms there is usually pain or and unusually tingling pricking or burning
sensation around the wound site. These initial symptoms may last for days. After
this, the person infected with rabies will likely experience cerebral dysfunction,
anxiety, confusion and agitation. If left untreated, the person may experience
delirium, abnormal behavior, insomnia and hallucinations. The acute period of
disease typically ends after 2 to 10 days. Once clinical signs of rabies appear, the
disease is nearly always fatal. To date less than 10 documented cases of human
survival from clinical rabies have been reported. The incubation period for rabies is
typically 1–3 months, but I have found in my research in rare cases can range from 9
days to several years.
Transmission for the rabies virus usually occurs when an infected animal bites a
human. The infected salvia is passed to the man. Although rare rabies can be
transmitted via other routes such as contamination of mucous membranes, aerosol
transmission and ordeal and organ transplantations. Ingestion of raw meat or other
tissues from animals infected with rabies is not a source of human infection. All
mammals are susceptible to the rabies virus, however, in the United States and
Canada bats are the source of most human rabies deaths. Raccoons, skunks, foxes,
and coyotes are other species to watch out for when it comes to the rabies virus.
Rabies can be diagnosed in animals fairly easy but not as easy in the human
population. In animals, rabies can be diagnosed by using a direct fluorescent
antibody test. This test looks for the presence of the rabies virus antigens in the
animal’s brain tissue. No tests are available to diagnose rabies infection in humans
before the onset of clinical disease, and unless the rabies-specific signs of
hydrophobia or aerophobia are present, the clinical diagnosis may be difficult.
Diagnosis in humans can be detected post mortem by finding the viral antigens in
the dead humans brain and skin.
Since the disease cannot be diagnosed in humans, it is imperative to find and test
the animal that potentially infected the human host.
Post-exposure prophylaxis or (PEP) is the most effective treatment after the
suspected exposure to the rabies virus. PEP can prevent the onset of symptoms and
prevent death. Post-exposure prophylaxis consists of: local treatment of the wound,
a course of potent vaccine that is approved by the WHO and administration of rabies
immunoglobulin in needed. It is also suggested to immediately use recommended
first aid procedures if any unknown animal bites a human. Recommended first aids
proceeded include immediate flushing and washing of the wound for a minimum of
15 minutes with soap and water, detergent or providone that kills the rabies virus.
The best way to prevent rabies is through animal vaccination. Those with pets,
especially dogs, cats and indoor ferrets are recommended to visit their veterinarian
regularly to keep vaccination updated. Keeping direct supervision of dogs and
keeping cats in ferrets inside is suggested to reduce the chance of having your pets
infected with rabies. Having your pets spayed or neutered to help reduce unwanted
pets is suggested as well as to call animal control if you notice any stray animals
roaming though your neighborhood. Pre-exposure immunization is recommended
for travelers who spend a lot of time outdoors is suggested along with those who
work in an occupation that has a high risk of potential exposure with the rabies
virus. Children are more at risk; about 40% of those bitten by a suspect infected
animal are children under the age of 15. It may be a consideration to have them
immunized as well, especially if they live or will be vacationing in a rural setting
where potential infected animals live.
It is estimated that 55.000 people die annually from rabies, however, morbidity
and morbidity for rabies worldwide is hard to estimate, as there is major
underreporting of the virus in underdeveloped countries where the majority of
cases are found. Therefore, there is no confirmed estimate of cases but since rabies
can be found in any mammal and therefore spread to humans, we must keep and
eye on this virus and use preventive measures to reduce the risk worldwide. In the
United States, the surveillance of human rabies is fairly well documented. In this
century the mortality rates have gone from approximately 100 to and average
presently of 2 or 3 annually.
Rabies does not care about its host characteristics. Since the viruses are mostly
transmitted through animal bites, it is can occur in any age, sex, marital status or
ethnic group. Because children are more likely to play with stray animals, in general
rabies has its highest rates in children. Nearly half the population of those bitten by
an infected animal are children under the age of 15.
Worldwide rabies is found more in specific geographical regions. Areas that have
the highest rabies rates are documented in the would map below. The highest rates
and risk areas are found in Central America, the upper portion of South America,
Africa all of Asia and the eastern portion of Europe. Intermediate risk and rates of
the rabies virus are Greenland, the lower portion of South America and a small
portion of the Middle East. The lowest rabies risk areas can be found in the United
States, Canada, Australia, New Zealand and Western Europe.
Although my project is on human rabies, it is impossible to study human
rabies when not looking at the rates of rabies in animals. I have included
these maps on animals in the United States.
There are no rabies cases found in Hawaii.
Rabies, in general, is found in countries with lower socioeconomic profiles. These
countries have fewer resources for both prevention and treatment. As stated earlier,
the Untied States spends about 300 million dollars to keep rabies rates low. Many
countries cannot afford this, therefore, higher rates are inevitable in countries with
lower socioeconomics. Inadequate housing in areas with lower socioeconomic that
are open to the elements, can of course, increase the rate of an infected animal
getting inside and infecting people. Occupations where people are outdoors most of
the time increases the risk of getting bit by an infected animal and increasing the
change of the person getting rabies. Education, in itself, has no barring on if a person
will get infected with rabies.
Weather can affect the rate of rabies. According to and article published last year,
United States outbreaks are linked to drought and warm weather. Cities that are
located in drought stricken areas are said to be experiencing more dramatic spikes
in rabies outbreaks in animals. This is due to the warm weather forcing infected
animals to seek food and water in more urban areas. While the number of reported
rabid animals declined nationwide in 2010, according to the most recent federal
data, states such as South Dakota, Kansas and Texas have recently seen a jump in
the number of skunks testing positive. In drought-stricken Texas, more than 1,000
animals last year were exposed to rabid skunks, double the number in 2010. As
global warming continues, this rabies can become more of a threat.
Overall rabies is an interesting virus, one of few who can easily be passed
from an infected animal to a human host. Rabies is especially interesting
because it can be treated and controlled through vaccination as we have found
success in doing so in the United States. Like other infectious diseases, it is sad
that underdeveloped countries do not have the same resources for prevention
and treatment. Because of this, it is unlikely that rabies will ever be completely
eliminated but it is unlikely that it will ever be large scale epidemic since the
infected animal, for the most part, has to bit the human host and the human host
is not contagious to spread the virus to other humans.
References:
American Human Association, (Feb, 2013), Rabies Facts & Prevention Tips
Centers of Disease Control and Prevention, (Feb, 2013),Rabies around the
world. Retrieved by http://www.cdc.gov/rabies/location/world/index.html
Centers of Disease Control and Prevention, (Feb, 2013). The rabies virus.
Retrieved by http:www.cdc.gov/rabies/transmission/virus.html
Thinkprogress, (April, 2012), U.S. Rabies Outbreaks Linked to Drought, Warm
Weather. Retrieved by http://thinkprogress.org/climate/2012/04/06/459614/usrabies-outbreaks-linked-to-drought-warm-weather/?mobile=nc
World Heath Organization, Feb, 2013), Rabies, Retrieved by
http://www.who.int/mediacentre/factsheets/fs099/en/