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Title: Transmission of the Rabies Virus
Author: Kerri Kill
Date: 15 May 2009
The rabies virus is a member of the Rhabdoviridae family and the lyssavirus genus. It is made up of a single RNA strand with no proofreading capabilities and contains a spiked envelope. It is transmitted mainly from animal to humans or animal-to-animal through animal bites, however, it has also been spread through organ transplants and from mother to newborn. It is a virus that is more prevalent in developing countries such as Latin America, Africa, and Asia rather than in developed countries, like the United States and Europe, due to having a lack of resources to obtain vaccines. The rabies virus affects people by first multiplying in the epidermis of the host, in which it then spreads to the peripheral and central nervous system where fatal encephalitis usually occurs, and then lastly reaches the salivary glands and organs in order to pass on the virus to a new host.
As a kid I still remember that if you saw a dog or cat or some other animal foaming at the mouth you were to stay away because the animal probably had rabies. I did not know what rabies was, but I knew it was not good if I got it. The idea that contracting rabies was not a good thing is something that has stuck with me throughout the years, but I have not gained any more information about the disease other than that I already knew. While I know it is a disease, I did not know what it was, and what it did to a host other than eventually kill them. With this assignment, I felt that this was the time for me to learn more about the virus that I have always wondered about.
During the research on the transmission of the rabies virus, there were some findings that were more significant than others. For starters, dogs and bats are the two animals that will more commonly be found to have and spread the rabies virus. Developed countries have a lower rate of having animals with rabies compared to the rate in developing countries, mainly due to the countries inability to afford the vaccines. The virus is spread by it penetrating the skin, such as by a bite, and it eventually spreading to the peripheral nervous system where it then goes to the central nervous system.
The prevalence of the rabies virus is one that has been known throughout the world for years but the specifics about the virus, like what family it is from, how it affects the person infected, and animals that can be affected, are not as well known. The rabies virus is in the Rhabdoviridae family and the lyssavirus genus (Tortora, p. 654). It is a virus that affects all kinds of species, in all parts of the world, and causes similar but different responses in the animals that it infects.
The make up of the rabies virus, lyssavirus, and its structure allow for scientists studying the virus to figure out how the virus infects animals and how it is transmitted from animal to animal. The Lyssavirus is made up of “bullet shaped viruses with a spiked envelope” (Tortora, p. 654). The characteristic spiked envelope is made up of carbohydrate-protein complexes that project from the surface of the envelope and allow the virus to attach to host cells (Tortora, p. 389). The virus itself is made up a single strand of RNA that has no proofreading capabilities, which makes it so that mutant strains develop rapidly (Tortora, p. 654). The structure of the virus gives some insight into how the virus attaches to host cells, but it is with how the virus is transmitted from host to host that determines how prevalent the virus is in a given area.
There are a few known ways in which the rabies virus is transmitted from host to host, with new ways still evolving as the virus changes and medical advancements are made. Throughout the world the most likely way of obtaining the virus is from a bite of an infected dog (Tortora, p. 654). However, in the United States, due to continued vaccines and prevention programs, wild animals instead of domesticated animals are starting to be the more likely culprit of transmitting the rabies virus to a person. For this reason, it is raccoons and skunks that are taking over the top spot when it comes to being the main host of rabies over the dogs in the United States (Sterner, p. 163). Bats are another animal that this disease is very prevalent in throughout the world, and are responsible for the transmission of the rabies virus to people throughout the world. It is also bats that are creating new challenges when it comes to rabies in North America, due to bat bites not being recognizable (Haider, p. 562).
Animal bits of infected hosts are the most likely way for a person to contract the rabies virus, however, there are a few other ways in which to contract the disease. One such way is by vertical transmission from an infected mother to her newborn. While this is very rare due to most mothers getting the vaccine once exposed to the disease, it has been seen clinically a few times. For most reports of a mother contracting the rabies virus before giving birth, the “newborns did not contract the infection by vertical transmission from the mother,” however it has been reported at least once in Turkey (Lenle, p. 82). Another unusual way of transmission of rabies is by organ donation. In at least one confirmed case by the CDC, the rabies virus was spread to four organ transplant recipients when the donor was not diagnosed with rabies initially. All four recipients, as well as the donor, were later confirmed by autopsy to have the rabies virus by the CDC (Dietzschold, p. 648). With more medical advancements also comes more ways in which to transmit diseases that would not be thought possible, such as with the cases of transmission from a mother to her newborn and through organ donation.
With new vaccines and prevention programs the prevalence of this fatal rabies disease has decreased greatly in many countries. However, there is a growing concern with new findings that a “rabies antibody has been detected in apparently healthy vector species including mongooses, skunks, raccoons,… “(Warrell). This discovery brings with it the possibility of “transmission of rabies by asymptomatic animals” (Warrell). This is the new research being conducted on the transmission of the rabies virus. It will be interesting to find out if this new evolutionary function of the rabies virus is actually possible.
The prevalence of the virus depends not just on how the virus is transmitted but also where it is more likely to be contracted in the world. The areas of the world where rabies is still common are in Africa, Latin America, and Asia due mainly to the lack of resources to pay for vaccinations (Tortora, p. 655).
This is seen by a high mortality rate of people who are exposed to the virus in India, Philippines, Oceania, Africa, and Latin America (Warrell, p. 1906). This is not to say that countries that do have the ability to pay for widespread vaccinations do not also see the spread of rabies. For these countries, such as the United States, transmission of the rabies virus still occurs due to the prevalence of the virus in wildlife. It is for this reason that countries in Europe and North America are attempting to immunize wildlife by feeding them food mixed with the vaccine (Tortora, p. 655).
Then there are also areas, such as Hawaii, that have no occurrences of rabies due to government regulations of quarantining animals entering the country in the effort to keep the country rabies free. When a person gets bit by a dog or a raccoon, the area in which they were bit will make a big difference in the likelihood of that person contracting the rabies virus.
How the rabies affects a host is different for the species that contracts it. For the most part, the way that the virus affects humans is best known due to more research completed on the topic in order to find vaccines and treatments. When a person is first exposed to the virus, usually by an animal bite, the virus proliferates in both the skeletal muscle and the connective tissue for a time period of anything from a few days to even months. Once the virus has multiplied enough, it then enters into the peripheral nervous system in which it then travels to the spinal cord, the central nervous system. Once the virus has entered the spinal cord it then continues to travel up to the brain. Once the virus has entered the brain, it is not long before the onset of fatal encephalitis takes place. Once the virus reaches the brain it also goes to the salivary glands and organs of the victim, which paired with the resulting erratic, aggressive behavior can result in the transmission of the virus to another host (Tortora, p. 655). How the virus affects other animals besides humans is very similar. It still involves the virus spreading from the skin to the peripheral nervous system to the central nervous system, including the brain, and then to the salivary glands. The fact that the rabies virus not only affects the person, or animals, personality when it reaches the brain as well as the fact that it causes death in its host, is why many developed countries are taking the steps to try to prevent the spread of it.
It is safe to say that I now know more about the rabies virus than that it causes dogs to foam at the moth. It is a virus that results in fatal encephalitis to anyone that comes in contact with it and that does not receive the vaccine. It is virus that is made up of a single strand of RNA, as well as a spiked envelope, that allows for the virus to better attach to host cells. It is a virus that affects many different species in a similar way, which results in death in all of them. It is a virus that is starting to be more known by the science community, yet there is still no known cure. It will be interesting to
see how this
virus changes as the years go on and what scientists will discover about it to possibly find a cure one day.
Microbiology an Introduction
. Pearson Education Inc. United States. 654-6 pp.
Sterner, Ray T. Aug 2006.
Modeling wildlife rabies: Transmission, economics, and conservation
. Vol. 131 Issue 2, 163-179 pp.
Iehlé, Catherine. May 2008.
Journal of Clinical Virology
Delivery and follow-up of a healthy newborn from a mother with clinical rabies
. Elsevier B.V. Vol. 42. Issue 1, 82-5 pp.
Warrell, MJ. "Rabies and other lyssavirus diseases."
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Dietzschold, Bernhard. "Rabies transmission from organ transplants in the USA."
364 (2004): 648-49.
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Haider, Shariq. "Rabies: old diseases, new challenges."
CMAJ: Canadian Medical Association Journal
178 (2008): 562-63.
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: Treatment and Prevention of Rabies
: Noelle Menesini
: May 15, 2009
To determine the treatment and prevention options for the
, also know as the rabies virus. Though it is one of the oldest diseases in the world, Pasteur had discovered the first vaccine in 1885 and unfortunately the treatment options are not as effective as we had hoped.
affects the central nervous system and eventually causes encephalitis, which is inflammation of the brain. After being exposed, mainly through bites, the result is almost always death. The main treatment option involves an active and passive immunization that stimulates white blood cell proliferation and creates an immune response.
Rabies is perhaps one of the oldest recorded diseases of humankind. It “…predates the code of Hammurabi of ancient Mesopotamia
4000 years ago” (Baer, 368).
Pasteur became well-known for his work on the rabies vaccine, initially established by Emile Roux, and later tested on a young boy who was cured in 1885.
I take personal interest in this topic because I find it fascinating that it is in fact the oldest disease in history and that wolves and mankind work together when times of hunting and gathering prevailed. Many years later, some wolves became domestic and are now ‘man’s beat friend’ as the saying goes. It is also appealing to me because to this day rabies is still a common virus and the death is a frequent result. Even though technology has evolved tremendously over the years, the virus is still around, which means se still have a long way to go. Rabies is a virus that affects the central nervous system, and “causes acute
encephalitis in all warm blooded hosts, including humans, and the outcome is almost always fatal
” (CDC). Fortunately, over the years scientists, like Pasteur, have created vaccines and ways to prevent the rabies virus from affecting our every day lives. The goal of my research is to find treatment and prevention options for those who have come in contact with the virus.
The term rabies is “derived from the Latin word rabere (rave; be mad)” (Myetomology.com). The Greeks used the word “lyssa… meaning hydrophobia” (Park, 614), this terminology is used in naming the genus
. The family is Rhabdoviruses and all virions from this family consist of two major components which are “a helical ribonucleoprotein core (RNP) and a surrounding envelope” (CDC). “
Rhabdoviruses are negative strand RNA viruses” (Hunt); which means they have a single strand of RNA that is anti-sense to the messenger RNA needed to code for viral proteins
From the moment of entry the virus travels straight to the CNS through the neural pathways and will perfuse into other organs. Its incubation period can be anywhere from “ten days to one year” (Tortora, 454). The salivary glands in particular receive a high concentration of the virus, which is a biological characteristic to further the spread of the virus to other hosts. The rabies virus is spread by bites and the most common hosts are wild or domestic animals.
There are three main ways in handling prevention for the rabies virus. The first is the Human Diploid Cell Rabies Vaccine, HDCV, which can be administered before a bite has occurred and the second way is the Purified Chick Embryo Cell Vaccine, PCEC. Both of these vaccines are administered in a succession of five to six injections at specific times during a twenty-eight day period and are considered active immunizations.
The rabies vaccine works by stimulating the immune system to produce antibodies that counterbalance the virus.
The third type of prevention is “a passive immunization given simultaneously by injection Human Rabies Immune globulin (RIG)” (Tortora, 656).
Rabies immune globulin contains antibodies from blood donors who were given the rabies vaccine. The antibodies provide temporary protection until the person who was exposed to the virus can build up their own antibodies.
Having these vaccines work together gives an increase chance in survival.
If someone has been bitten by a rabid animal some early symptoms are pretty much flu-like with headache, fever, and fatigue. The exceptions are encephalitis, discomfort, numbness or pain at the point of entry. Progressive symptoms of the rabies virus are more neurological affects including: insomnia, anxiety, confusion, slight or partial paralysis, hypersalivation, hallucinations and agitation; as well as hydrophobia, difficulty swallowing, and possible excitation (
By consulting a physician an exposed person will be able to receive immediate help. During a diagnosis some questions that may be asked to help the physician with the patients past and present history are: where were you when this occurred? What type of species did it involve? How did this occur, meaning was it spontaneous or provoked? Was the animal wild or domestic and was it safely captured? These are important questions to identify when it occurred and how it can be treated. Some tests that might be performed are saliva, blood, and spinal fluid. Another type of test is Polymerase Chain Reaction, PCR testing. This uses a skin biopsy to attain the rabies virus
genetic material by using reverse-transcription
After being bitten there are not many things one can do. “Local treatment is perhaps the single most effective means of preventing rabies” (Baer, 540). This can be achieved by applying iodine or alcohol solutions to the point of entry to reduce the amount of contamination or washing aggressively with soap and water. Other than excessive washing Post-exposure Porphylaxis, PEP, is an option. It is considered “a medical urgency not a medical emergency” (
). This is important because the physician needs to examine every possible exposure to rabies and then make an educated decision on the next step. PEP is a series of injections that is taken simultaneously with RIG to boost the immune response. “Five survivors had received PEP before the appearance of symptoms” (Tortora, 656). Even though this seems like great news the statistics show otherwise.
Baer, George M.
Natural history of rabies
. Boca Raton: CRC P, 1991.
"MyEtymology.com: Latin etymology of rabies."
MyEtymology.com - A universal etymology dictionary
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"Natural History of Rabies | Rabies."
Centers for Disease Control and Prevention
. 11 May 2009 <
Park, William H., Anne W. Williams, and Charles Krumwiede.
Pathogenic Microorganisms: A Practical Manual for Students, Physicians, and Health Officers
. 7th ed. Lea & Febiger, 1920.
Biomedical Sciences Graduate Program
. Ed. Richard Hunt. 11 May 2009 <
Schoenstadt, Aurthor. "Rabies Virus."
Rabies Home Page
. 11 May 2009 <
Tortora, Gerard J., Berdell R. Funke, and Christine L. Case.
Microbiology An Introduction (9th Edition)
. San Francisco: Benjamin Cummings, 2006
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