Welcome! The purpose of this blog is to inform and educate the public regarding the rabies virus. It will go over several elements of the virus including its structure, life cycle, diagnosis, symptoms, treatment, prevention, epidemiology, and public health effects. Rabies is a virus that appears throughout popular culture. It has made cameos in "To Kill A Mockingbird", "Their Eyes Were Watching God", and "Ole Yeller" just to name a few examples. However, despite the public's basic recognition of rabies as a disease, few truly know all about the virus and how to stay safe from it. This blog will teach the reader exactly what there is to fear about rabies and how to avoid infection.
In the US In the United States, the majority of animals infected with rabies are wildlife. These organisms most often include wild carnivores and bats. Rabies rates in domestic animals especially dogs have diminished significantly in the last century. Furthermore, rabies rates in humans have also gone down. In the early 1900s, there were about 100 annually human casualties due to rabies. In 1990s, however, there have only been about one or two per year. The current rabies deaths in the United States most often occur in people who didn't realize they had been exposed to the virus. However, despite the lowered rates of rabies in the US in the past century, prevention and response efforts still play a major role in American life. About 300 million dollars are spent annually on rabies in the US. These funds are spent on animal vaccinations, animal control operation, rabies laboratories, and medical costs associated with treating the disease. Although rabies has been greatly reduced in America, it is still far from eradicated, rendering necessary current prevention methods such as pet vaccination and education efforts. http://www.cdc.gov/rabies/location/usa/index.html Three Above Figures: https://pubs.ext.vt.edu/420/420-036/420-036.html Around the World
Although the rabies vaccination has been available for over 100 years, rabies is far from gone in both the US and around the world. The majority of global rabies deaths occur in countries without strong public health programs and preventative treatment options. One of the greatest obstacles to rabies prevention in developing nations is program costs. Millions of animals would need to be vaccinated each year, which would amount to enormous sums of money. Tragically, there are about 55,000 human deaths from rabies each year, the majority of them occurring in Africa and Asia. The most common source of human infection is actually uncontrolled rabies in dogs. Children in developing nations are make up the population at highest risk for infection because they are more likely to be bitten, less likely to recognize rabies, and more likely to have multiple bites in high risk body areas. The best ways to respond to the global rabies epidemic involve ensuring adequate animal vaccination and control, education efforts, and greater access to medical care in developing nations. Some of these efforts have come to fruition in recent years. In 2006, the Global Alliance for Rabies Control was created along with the World Rabies Day Initiative. http://www.cdc.gov/rabies/location/world/index.html http://www.cdc.gov/rabies/prevention/people.html http://rabiesalliance.org Diagnosis
In Humans In humans, to test for rabies, saliva samples, serum, spinal fluid, and skin samples are taken. Saliva is tested by virus isolation or reverse transcription and polymerase chain reaction. The serum and spinal fluid samples are used to test for rabies antibodies. The skin specimens (taken from the base of the neck) are examined for rabies antigens. In Animals In wild animals, rabies is diagnosed using a Direct Fluorescent Antibody Test. The test looks for the presence of the rabies virus antigens in brain tissue samples of the animal. This test requires the animal to be euthanized. However, the Direct Fluorescent Antibody Test isn't used on all animals. Due to low infection rates among domestic pets such as dogs, cats, and ferrets, these animals often undergo a ten day observation period. About 120,000 animals are tested for rabies each year in the USA alone using DFA tests and about 6% of these tests come up positive for rabies. However, as previously mentioned, the rates vary considerably by species. http://www.cdc.gov/rabies/diagnosis/animals-humans.html Treatment Rabies treatment in humans most often involves general bite treatment. After the wound has been cleaned and bite treatment has been undergone, the individual also needs rabies treatment. The treatment varies on whether or not the individual in question had already received a rabies vaccination. If they had not, they would receive a post exposure anti-rabies vaccination. They would be given four 1ml doses of either HDCV or PCEC vaccines (administered on days 1, 3, 7, and 14 after infection). These vaccines would be given intramuscularly on the arms as shots. Unvaccinated persons would also need to take human rabies immune globulin which would be administered once. The globulin would give the body the immediate antibodies to stave off infection until the vaccine could help. Previously vaccinated people would only need two doses of the vaccine and would not require human rabies immune globulin treatment. It is important to note that rabies, if caught before the emergence of symptoms, is 100% treatable. http://www.cdc.gov/rabies/medical_care/hrig.html
Symptoms The symptoms for Rabies can be broken up into two categories: early and later symptoms. Early symptoms in people are by no means unique to rabies and can include fever, headache, general weakness, and overall discomfort. Later symptoms are more specific and aid in diagnosis. They are insomnia, anxiety, confusion, slight or partial paralysis, excitation, hallucination, hyper salivation, agitation, difficulty swallowing, and (most characteristically), hydrophobia or the fear of water. The Life Cycle of the Rabies Virus involves transmission between a rabid individual and a healthy individual because rabies, like all viruses is an obligate intercellular parasite. In most cases, the virus is transmitted via the salvia of an infected animal (often raccoons, skunks, bats, foxes, or dogs) to another animal or human. The virus is zoonotic as it can infect both humans and multiple species of animals. Rabies is a lytic virus, meaning that it's life cycle is as follows: attachment, entry and degradation of host DNA, synthesis of new viruses, release of new viruses (through the lysis of the cell). More specifically, the life cycle of rabies is illustrated below: http://www.und.edu/instruct/rsweitze/b151/Chapters33-34Notes.html 1. the rabies virus envelope fuses to the host cell membrane (absorption). This absorption is enabled by the glycoprotein trimetric spikes which fuse with host cell surface receptors. 2. the virus penetrates the host cell, enters via pinocytosis via clathrin coated pits. 3. the virions congregate in large cytoplasmic vesicles and the viral membranes fuse to the vesicle membranes, causing the viral RNP to be released into the cytoplasm (un-coating) 4. mRNAs are transcribed for replication because the virus has single stranded negative RNA. 5. Transcription of structural proteins occurs on free ribosomes in the cytoplasm of the host cell. 6. Protein processing occurs, leading to the creation of the five proteins encoded in the virus genome (the N, P, M, G, and L proteins). 7. The viral genome is replicated. In this process, positive strands of the genome are created which serve as templates for synthesis of negative strands of RNA. 8. The proteins and replicated RNA all combine to form a new rabies virus. 9. Newly completed viruses leave the host cell which undergoes lysis. The Rabies Virus has a non segmented, negative stranded, RNA genome and a bullet shape. It belongs to the Mononegavirales order, the Rhabdoviridae family, and the Lyssavirus genus. The Lyssavirus genus also includes the Lagos virus, the Duvenhage virus, the European Bat Virus 1, European Bat Virus 2, and the Australian Bat Virus. http://www.cdc.gov/rabies/transmission/virus.html This is a Diagram of the Rabies Virus which demonstrates its shape and structures. The virus appears to be in the process of synthesizing protein from its genome. Here is another diagram of the Rabies Virus. This diagram demonstrates the location of the five proteins in the virus's genome. http://www.ncbi.nlm.nih.gov/books/NBK8618/ The Proteins Encoded by the Virus Genome
The Rabies Virus's RNA genome encodes for five proteins. The five proteins are nucleoprotein, phosphoprotein, matrix protein, glycoprotein, and polymerase. The glycoprotein is on the surface of the virus and surrounds the ribonucleic protein core. It forms trimetric spikes on the virus's outer envelope. These spikes help for recognition and binding to host cells. The matrix protein gives the virus its bullet shape and helps in the binding of the RNP core and host cell membrane. The nucleoprotein, phosphoprotein, and polymerase all act in the RNP core. The phosphoprotein regulates the nucleoprotein and acts as a cofactor to promote the virus's genome replication. The nucleoprotein phosphorylates a substance called serene residue to help regulate genome replication. Finally, the polymerase encodes over half of the virus's genome for transcription and gene replication. http://cosmos.ucdavis.edu/archives/2010/cluster7/Jaramillo_Couger_Rabies.pdf http://www.cdc.gov/rabies/transmission/virus.html "CHAPTER 33 & 34: REVIEW OF MATERIAL IN CHAPTERS RELEVANT TO THE GENETICS OF VIRUSES & BACTERIA."
University of North Dakota. N.p., n.d. Web. 6 Apr. 2015. <http://www.und.edu/instruct/ rsweitze/b151/Chapters33-34Notes.html>. Davidson University. N.p., n.d. Web. 6 Apr. 2015. <http://www.bio.davidson.edu/courses/immunology/ students/spring2006/jameson/rabies%20structure.bmp>. Dualibra. N.p., n.d. Web. 6 Apr. 2015. <http://dualibra.com/wp-content/uploads/2012/04/037800~1/ Part%207.%20Infectious%20Diseases/Section%2015.%20Infections%20Due%20to%20RNA%20Viruses/188_files/ loadBinary.gif>. Madoff, Larry. "The State of Rabies: Treating a Disease That Often Leads to Death." The Atlantic 2012: n. pag. Print. "Rabies." Centers for Disease Control and Prevention. N.p., n.d. Web. 6 Apr. 2015. <http://www.cdc.gov/rabies/>. "Rabies." National Travel Health Network and Centre. N.p., 2012. Web. 6 Apr. 2015. <https://www.nathnac.org/travel/factsheets/rabies1.htm>. "Rabies: Its Ecology, Control, and Treatment." Virginia Cooperative Extension. Virginia Tech, Virginia St. University, n.d. Web. 6 Apr. 2015. <https://pubs.ext.vt.edu/420/420-036/ 420-036.html>. "RABIES: STRUCTURE & SYMPTOMS." COSMOS UC Davis. University of California Davis, n.d. Web. 6 Apr. 2015. <http://cosmos.ucdavis.edu/archives/2010/cluster7/Jaramillo_Couger_Rabies.pdf>. "Rhabdoviruses: Rabies Virus." NCBI. N.p., n.d. Web. 6 Apr. 2015. <http://www.ncbi.nlm.nih.gov/ books/NBK8618/>. "Understanding rabies can protect pets and their owners." Spotlight: n. pag. Print. |
AuthorMy name is Claire and this blog is a project for my AP Biology Class. I hope you find it informative! ArchivesCategories |