Rabies Virus - Lecture Notes PDF

Rabies virus (Rhabdovirus) **ABUNU MARIAM OHUNENE** **23/12517** **CUL-MCB 205** **BASIC CONCEPTS IN VIROLOGY** **LECTURER: Dr. CHINYERE BAKPA** Due date: Monday 27^th^ January 2025 **TABLE OF CONTENTS** **INTRODUCTION...............\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.....

Rabies virus (Rhabdovirus) **ABUNU MARIAM OHUNENE** **23/12517** **CUL-MCB 205** **BASIC CONCEPTS IN VIROLOGY** **LECTURER: Dr. CHINYERE BAKPA** Due date: Monday 27^th^ January 2025 **TABLE OF CONTENTS** **INTRODUCTION...............\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...1** - **History and significance of the Rabies Virus** **CLASSIFICATION\.....................\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...2** - **Taxonomy, family and genus** - **Distinguishable characteristics** **STRUCTURE AND MORPHOLOGY\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.......\...\...\...\...\.....3** - **Viral structure and Genetic Material** - **Protein Composition** - **Electron Microscopy images** **CHARACTERISTICS\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\....4** - **Stability in different environments** - **Modes of Transmission** - **Pathogenicity** **CULTIVATION\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.....5** - **Methods used to grow** - **Cell culture techniques** **REPLICATION\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...6** - **Host Cell Entry and Release of viral DNA** - **Transcription and Translation** - **Replication and Assembly** - **Budding and Spreading** **DIAGNOSIS\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.....7** - **Methods used to diagnose/Laboratory Techniques** - **Clinical signs and symptoms indicative of rabies** **PREVENTION AND TREATMENT\...\...\........................\...\...\...\...\...\...\...\...\...\...\...\...8** - **Strategies for prevention and treatment** - **Post -- Exposure Prophylaxis (PEP)** - **Vaccination Methods** **CONCLUSION...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\....9** **REFRENCES\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\...\.....10** **Introduction** Rabies is caused by the rabies virus, which is a member of the Lyssavirus genus. It is a vaccine-preventable, zoonotic (a disease transmitted from animals to humans), viral disease affecting the central nervous system. In up to 99% of the human rabies cases, dogs are responsible for virus transmission. Children between the age of 5 and 14 years are frequent victims. Rabies infects mammals, including dogs, cats, livestock and wildlife. It spreads to people and animals via saliva, usually through bites, scratches, or direct contact with mucosa (e.g. eyes, mouth, or open wounds). Once clinical symptoms appear, rabies is virtually 100% fatal. It is a neglected tropical diseases (NTD), predominantly affecting marginalized populations. Although effective human vaccines and immunoglobulins exist for rabies, these are often inaccessible or unaffordable to those in need. Louis Pasteur is a very important figure in the history of rabies. He developed the first rabies vaccine, which was a major breakthrough in the fight against this deadly disease. Pasteur's work on rabies began in 1881, when he was asked by the French government to investigate the disease. He developed the ground-breaking technique of **attenuating** the rabies virus." By drying the spinal cords of infected rabbits", he weakened the virus, making it less virulent. This process laid the foundation for the creation of a vaccine that could stimulate the body's immune response without causing the disease. In 1885, Pasteur made the momentous decision to administer his experimental rabies vaccine to a young boy named **Joseph Meister**, who had been bitten by a rabid dog. The vaccination was successful, and Meister did not develop rabies. Marking a turning point in the fight against the disease and established the principle of vaccination as a powerful tool for disease prevention. The rabies virus, with its unique properties and complex interaction with host immune systems, not only highlights the intricate mechanisms of viral evolution and transmission but also underscores the importance of understanding viral behaviour in developing effective prevention and treatment strategies." **CLASSIFICATION** Rabies virus belongs to the **Order Mononegavirales**, a diverse group of viruses characterized by their: - **Negative-sense, single-stranded RNA genome:** This means the viral RNA has a complementary sequence to the messenger RNA (mRNA) that is used to produce viral proteins. - **Bullet-shaped virions:** The virus particles have a distinctive bullet-like shape, a characteristic feature of the Rhabdoviridae family. Within the Rhabdoviridae family, rabies virus is classified in the **Genus Lyssavirus**. This genus includes several other related viruses, such as Lagos bat lyssavirus and Mokola virus. Key features of the Lyssavirus genus includes; - **Neurotropism**: These viruses have a strong affinity for the nervous system, infecting and damaging neurons. - **Zoonotic potential:** Many lyssaviruses can infect both animals and humans, posing a significant public health threat. - **Diverse host range:** Lyssaviruses can infect a wide range of mammals, including bats, dogs, and other carnivores. The specific **Species** within the Lyssavirus genus is **Rabies lyssavirus**, which is responsible for the vast majority of human rabies cases worldwide. The distinguishable characteristics of the rabies virus include; - Bullet-shaped virion   - Negative-sense, single-stranded RNA genome - Neurotropism - Long incubation period(few days to several years) - Zoonotic potential - High mortality rate **STRUCTURE AND MORPHOLOGY** The structure of the rabies virus includes; 1. **Bullet-shaped:** Rabies virus particles have a distinctive bullet-like shape, a characteristic feature of the Rhabdoviridae family.   2. **Enveloped:** The virus is surrounded by an envelope derived from the host cell membrane.   3. **Glycoprotein spikes:** The envelope is studded with glycoprotein spikes, which are crucial for attaching to and entering host cells.   4. Nucleocapsid: Inside the envelope, the viral genome (RNA) is tightly coiled within a helical nucleocapsid.   - **Single-stranded RNA:** Rabies virus possesses a single-stranded RNA genome.   - **Negative-sense RNA:** The viral RNA is "negative-sense," meaning its sequence is complementary to the messenger RNA (mRNA) that is used to produce viral proteins.   - **Genome size:** The rabies virus genome is relatively small, containing approximately 12,000 nucleotides. Rabies virus is composed of five major proteins:   **Nucleoprotein (N):** - Encapsulates the viral RNA genome.   - Forms the core structure of the nucleocapsid, a helical structure within the virus particle.   **Phosphoprotein (P):** - Acts as a cofactor for the viral polymerase (L protein), essential for viral RNA replication and transcription.   **Matrix protein (M):** - Located between the nucleocapsid and the viral envelope.   - Plays a crucial role in virus assembly and budding. **Glycoprotein (G):** - Forms the surface spikes of the virus particle. - Responsible for attaching to host cell receptors, initiating the infection process. - A major target for the immune system and a key component of rabies vaccines. **Large protein (L):** - The viral RNA-dependent RNA polymerase.   - Responsible for both transcription (creating mRNA from the viral RNA genome) and replication (creating new copies of the viral RNA genome).   These proteins work together in a coordinated manner to allow the virus to infect host cells, replicate its genome, and assemble new virus particles. Understanding the structure and function of these proteins is crucial for developing effective diagnostic tests, vaccines, and antiviral therapies against rabies. **CHARACTERISTICS** The characteristics of the rabies virus includes; A. **STABILITY IN THE ENVIRONMENT** The rabies virus is relatively fragile outside the host and can be inactivated by various environmental factors. Here's a breakdown of its stability:   1.T**emperature** Heat: Rabies virus is heat-sensitive, elevated temperatures can rapidly inactivate the virus.   Cold: Low temperatures can slow down viral activity but may not completely inactivate it. 2\. **Drying:** Desiccation, drying conditions are detrimental to the virus. The rabies virus is susceptible to desiccation and typically does not survive for long in dry environments.   3\. **Sunlight:** UV radiation, Ultraviolet radiation from sunlight can inactivate the virus. 4.**Disinfectants:** Many common disinfectants, such as bleach solutions, can effectively inactivate rabies virus. 5\. **pH:** Extreme pH levels (both acidic and alkaline) can inactivate the virus. **B. MODES OF TRANSMISSION** Rabies is primarily transmitted through the bite of an infected animal, but the other modes of transmission include; **Animal Bites:** This is the most common route of transmission. The saliva of an infected animal, containing the rabies virus, is introduced into the victim's bloodstream through a bite wound.   **Scratches:** Deep scratches from an infected animal can also transmit the virus if the saliva contaminates the wound. **Contact with Mucous Membranes:** In rare cases, the virus can be transmitted if infected saliva or brain tissue comes into contact with mucous membranes (eyes, nose, mouth) or open wounds. C. **PATHOGENICITY** The rabies virus exhibits a unique and devastating pathogenicity:   **Neurotropism**: This is the hallmark of rabies. After entering the body through a bite wound, the virus travels along peripheral nerves to the central nervous system (CNS). It exhibits a strong affinity for neurons, infecting and destroying them.   **Long Incubation Period:** The time between infection and the onset of symptoms can vary widely, from a few days to several years.  This long incubation period makes diagnosis challenging. **Progressive Neurological Disease:** Once the virus reaches the CNS, it causes a progressive and ultimately fatal neurological disease. **Immune Evasion:** Rabies virus has evolved mechanisms to evade the host immune response, allowing it to replicate and spread within the nervous system. **CULTIVATION OF THE VIRUS** The rabies virus can be cultivated using the following methods: 1. **Cell Culture:** Rabies virus can be grown in various cell culture systems, such as Vero cells (derived from African green monkey kidney cells) and neuroblastoma cells. These cell lines provide a suitable environment for the virus to replicate. 2. **Animal Models:** Historically, the rabies virus was cultivated in the brains of laboratory animals, such as mice and hamsters. This method is less commonly used today due to ethical and practical considerations. **REPLICATION** The replication of rabies virus occurs within the host cell and involves several key steps:   1. **Attachment and Entry:** The rabies virus attaches to specific receptors on the surface of the host cell, primarily neurons, through its glycoprotein (G) spikes. The virus enters the cell through receptor-mediated endocytosis. 2. **Uncoating:** Once inside the cell, the viral envelope fuses with the endosomal membrane, releasing the viral nucleocapsid into the cytoplasm. 3. **Transcription:** The viral RNA-dependent RNA polymerase (L protein) transcribes the negative-sense RNA genome into messenger RNA (mRNA) molecules. Each viral gene is transcribed individually, resulting in five distinct mRNA molecules. 4. **Translation:** The mRNA molecules are then translated by host cell ribosomes into the five viral proteins: nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), and polymerase (L). 5. **Replication:** The viral polymerase also synthesizes a full-length positive-sense RNA strand, which serves as a template for the synthesis of new negative-sense RNA genomes. 6. **Assembly**: The newly synthesized viral proteins and RNA genomes assemble into new virus particles within the infected cell. 7. **Release:** Mature virus particles are released from the infected cell through a process called budding.   **DIAGNOSIS** The diagnosis of rabies infection primarily relies on detecting the presence of the virus or viral antigens in infected tissues. Here are the main methods used; 1. **Direct Fluorescent Antibody (DFA) Test:** This is the gold standard for rabies diagnosis. It involves staining tissue samples (typically brain tissue) with fluorescently labelled antibodies specific to rabies virus antigens. It is rapid, sensitive, and relatively easy to perform. 2. **Direct Rapid Immunohistochemistry Test (dRIT):** Similar to DFA, but uses an enzyme-linked antibody instead of a fluorescent one. It Can be performed in laboratories without access to fluorescence microscopy. 3. **Reverse Transcription-Polymerase Chain Reaction (RT-PCR):** This highly sensitive technique detects the presence of rabies virus RNA in tissue samples. It is highly sensitive and specific, can detect very low levels of virus.   4. **Mouse Inoculation Test (MIT):** This older method involves inoculating laboratory mice with suspect brain tissue. It is less commonly used today due to ethical concerns and the availability of more rapid and efficient diagnostic methods. **Clinical signs and symptoms indicative of rabies** 1. **Prodromal Phase (Early Symptoms)** - Flu-like symptoms: Fever, headache, malaise, muscle aches   - Discomfort at the bite wound: Tingling, itching, burning sensations   - Changes in behaviour: Anxiety, irritability, restlessness   2. **Neurological Phase** - Agitation and Excitability: Restlessness, aggression, confusion, hallucinations   - Dysphagia: Difficulty swallowing, excessive salivation ("foaming at the mouth")   - Hydrophobia: Fear of water due to painful spasms of the throat when attempting to drink   - Aerophobia: Fear of drafts or air movements   - Seizure - Paralysis: Progressive muscle weakness and paralysis can occur in some cases. **PREVENTION AND TREATMENT** The strategies for prevention and treatment include; 1. **Animal Vaccination** - **Mass Dog Vaccination**: This is the cornerstone of rabies prevention. Widespread vaccination of dogs significantly reduces the incidence of rabies in both animals and humans.   - **Vaccination of Other Domestic Animals:** Cats, livestock, and other domestic animals should also be vaccinated according to local guidelines. 3. **2. Post-Exposure Prophylaxis (PEP)** - Prompt Medical Attention: If exposed to a potentially rabid animal (bite, scratch, or contact with saliva or brain tissue), seek immediate medical attention. PEP Regimen: PEP typically includes: - Wound Care: Thorough cleaning and washing of the wound with soap and water.   - Rabies Immunoglobulin (RIG): Infiltrated around the wound and administered intramuscularly.   - Rabies Vaccine: A series of rabies vaccinations is administered over a period of 14 days. **3. Public Health Education** **Raising Awareness:** Educating the public about rabies transmission, prevention, and the importance of vaccination is crucial. **Promoting Responsible Pet Ownership:** Encouraging responsible pet ownership, including proper vaccination and leash laws, helps reduce the risk of rabies transmission.   **Wildlife Management: I**mplementing strategies to reduce human-wildlife interactions can also help prevent rabies transmission. **TREATMENT** **No Cure for Established Infection:** Unfortunately, there is no effective treatment for rabies once clinical symptoms appear.   **Supportive Care**: Treatment focuses on supportive care, such as managing fever, providing respiratory support, and addressing neurological symptoms. **Experimental Treatments:** Some experimental treatments, such as antiviral medications, are being investigated, but their efficacy remains uncertain. **CONCLUSION** The rabies virus, a member of the Rhabdoviridae family, presents a unique set of challenges due to its neurotropic nature and the long incubation period. Its bullet-shaped virion, enveloped structure, and negative-sense RNA genome contribute to its ability to infect and replicate within neurons, ultimately causing devastating neurological damage. Ongoing research into novel antiviral therapies and improved diagnostic tools is essential to further combat this formidable pathogen. **REFRENCES** (WHO) World Health Organisation -- Rabies Rhabdoviruses: Rabies Virus - Medical Microbiology - NCBI Bookshelf The history of the first rabies vaccination in 1885 \| Institut Pasteur "Louis Pasteur." History of Vaccines Susceptibilities of CNS Cells towards Rabies Virus Infection Is Linked to Cellular Innate Immune Responses -- PubMed Central Morphogenesis of Bullet-Shaped Rabies Virus Particles Regulated by TSG101 -- PubMed Classification -- Rabies -- Bulletin -- Europe Components and Architecture of the Rhabdovirus Ribonucleoprotein Complex -- PMC Structure of Recombinant Rabies Virus Nucleoprotein-RNA Complex and Identification of the Phosphoprotein Binding site Interaction of Rabies Virus P-Protein With STAT Proteins is Critical to Lethal Rabies Disease Overexpression of the Rabies Virus Glycoprotein Results in Enhancement of Apoptosis and Antiviral Immune Response -- PMC -- PubMed Central Matrix protein of rabies virus is responsible for the assembly and budding of bullet-shaped particles and interacts with the transmembrane spike glycoprotein G -- PubMed Rabies -- TN.gov /Rabies: Human Rabies Immunoglobulin (HRIG) -- GOV.UK \[Survival of rabies virus under external conditions\] -- PubMed Pathogen Safety Data Sheets: Infectious Substances -- Rabies virus -- Canada.ca An inactivated recombinant rabies virus chimerically expressed RBD induces humoral and cellular immunity against SARS-CoV-2 and RABV -- PMC -- PubMed Central The Immune Escape Strategy of Rabies Virus and Its Pathogenicity Mechanisms -- MDPI African green monkey kidney (Vero) cells provide an alternative host cell system for influenza A and B viruses -- PubMed Figure 3. Rabies virus life cycle. A simplified rabies virus life cycle in an infected cell digitalcollections.lrc.usuhs.edu Research Advances on the Interactions between Rabies Virus Structural Proteins and Host Target Cells: Accrued Knowledge from the Application of Reverse Genetics Systems -- MDPI Structural and Evolutionary Insights Into the Binding of Host Receptors by the Rabies Virus Glycoprotein -- Frontiers Everything you always wanted to know about Rabies Virus (but were afraid to ask) -- PMC Rabies -- Diagnosis & treatment -- Mayo Clinic Responsible Pet Ownership is crucial in reducing the rise in Rabies cases -- FOUR PAWS in South Africa -- Animal Welfare Organisation Clinical Overview of Rabies -- CDC