Viral Infectious Agents Lecture Notes 2024-2025 PDF

Block 1.2 lectures 2024-2025 lecture Highlighter key Writer 1 Writer 2...

Block 1.2 lectures 2024-2025 lecture Highlighter key Writer 1 Writer 2 Doctor explanation Abbreviation Key information Book >> >> Mohammed Alibrahem Arwa Alzaid 221-222-223 notes References Student explaintion Deleted  Viral infectious agents Dr. Mervat Abdel-Aziz Medical Microbiology, Immunology & Infection Control Code of the module  In general, the Herpesviridae family is known for its latent sequence in viral pathogenesis. Herpes simplex is an example of a virus that causes latent viral infection. Firstly , it presents as a primary HSV infection, which occurs during the rst exposure to the virus, typically in children exposed to it for the rst time. Herpes Simplex Viruses (HSV) type 1 Pathogenesis & Clinical Picture 1) Primary HSV Infections (Exposure to the virus for the first time) Probably transmitted by direct contact. E.g : By saliva, tears Clinically, appears as vesicles on an erythematous base, vesicles rupture and its contents dry forming crusts which finally heal (within 7-10 days) without scarring. This is important because this makes it different from other viruses that heal with scarring.  Clinical Types of HSV-1 Infection Primary : Acute Gingivostomatitis (commonest). Vesicles on the gingiva  Pathogenesis & Clinical Picture Secondary infection : ‫ھﻨﺎ ﻣﻤﻜﻦ ﯾﺠﻲ ﺳﺆال‬ What is the dormant area or site of HSV type 1 (Herpes simplex type one)? 2) Latent Infections :‫اﻻﺟﺎﺑﺔ‬ Dorsal root ganglion of the face ➡ trigeminal ganglion. Virus particles are transported along the axons to the sensory (dorsal root) ganglion where some virus particles are able to establish a latent infection. 9 Explanation: Virus particles travel along HSV-1 latency is in the trigeminal ganglion. the nerve bres (axons) until they reach the sensory dorsal root ganglion, a cluster of Latency remains for the life-time of the host. sensory nerve cell bodies near the spinal cord. Here, some virus particles can The reactivation occur every two enter a dormant state, known years or three, it depends on stressful as latent infection, where condition exposed to the patient and they remain inactive but can immune status of the patient. reactivate later.  Whatever the immune status gets lower, the reactivation of the virus occur. Recurrent herpes labialis (fever blisters or cold sores) : reactivation of the 1ry gingivostomatitis.  VARICELLA-ZOSTER VIRUS Varicella-Zoster Virus (VZV) (VZV) Infection with VZV presents in two clinical forms: ‫الجديري املائي‬ – The primary infection; varicella (chickenpox) is a generalized eruption. ‫الحزام الناري‬ – The reactivation infection; zoster (shingles) is a localized form.  You must to know the differences between these two types because there are questions about them Chickenpox (varicella):1ry infection Shingles(zoster) :reactivation Usually child 4-10 years Adults The virus enters by droplet infection. It results from reactivation of latent varicella infection in the neurons. The virus reaches the ganglion from the periphery by  along nerve axons or About 90% of adult population become  blood during viraemic stage of infected by VZV in childhood but 10% of varicella infection during childhood. young adults remain susceptible. If an adult has not been exposed to Varicella (chickenpox) as a child, then he take the infections… he will take the Varicella rst, though it is relatively rare. 8  It is unilateral because it affects the skin in the dermatome, taking the sensory supply from the dorsal root ganglion where the virus is dormant. The typical rash of varicella Typical rash is unilateral & appears first on the trunk then confined to one dermatome, spread to the face & usually thoracic or lumbar. limbs.(Generalized).(localized) Red area The skin rash is initially macular It manifests as painful vesicular Elevated above the skin papules Clear vesicles eruption Contain uid Contain pus cell pustules which heal without scar formation. “Con ned to one dermatome” means that symptoms, like rashes or pain, are limited to a speci c area of skin that is supplied by a single spinal nerve root, known as a dermatome. Each dermatome corresponds to a segment of the spinal cord, allowing clinicians to pinpoint the affected nerve. This localization is crucial in diagnosing The allegiance at the rst is ( macul) conditions such as shingles, where the rash then raise to be ( papules) then it appears only in the affected dermatome, lled with uid ( vesicles) the uid indicating that the infection is localized to that convert to pus ( pustules) nerve rather than being widespread. Understanding the concept of dermatomes helps in identifying and treating conditions related to speci c nerve roots effectively. Varicella (Chickenpox) Varicella (Chickenpox)  The dermatome supply can be in the back or the trunk, it depends on the innervation. Zoster (Shingles)  Laboratory diagnosis: Although most diagnosis are made clinically , laboratory tests are available Specimen: Smears of vesicular lesions. Direct Virus detection For acute Serology Detection of specific VZV antibodies (IgM or rising titre of IgG) using ELISA can be used to diagnose varicella. Concept of “Titre”: I Titre measures the concentration of antibodies or viruses in a sample through: 1. Serial Dilution: Goal: Reduce concentration to accurately measure antibodies or viruses. 2. Choosing the Last Positive Unit: Goal: Identify the highest concentration showing a positive result to evaluate infection severity or immune response. Interpretation: A higher titre indicates more antibodies or viruses, re ecting the immune response or infection level.  POXVIRIDAE FAMILY The Largest of all viruses Seen by the light microscope because of their large size (300nm). Brick- shaped (complex symmetry). Enveloped Double stranded DNA Members of medical importance: Small pox virus ‫الجدري‬ Small pox no longer exists. In chicken pox the rash is mainly in the center trunk and face, there is a small amount in the peripheral and sometimes not even seen in this area.  HEPATITIS B VIRUS (HBV) HBV is a DNA virus of Hepadnaviridae family that causes serum hepatitis. The complete virus (virion) is called Dane Particle. The patient infected with HBV is detected with viral antigenic substance in the serum in the form of sphere or tubule shape for hepatitis B surface antigen that is why it’s called serum hepatitis.  Double stranded DNA HBsAg=Hepatitis B One part is called hepatitis B core surface antigen HBcAg=Hepatitis B Structure of HBV antigen and the other part is called hepatitis B surface antigen. core antigen In the serum of the patient there is always a sphere and tubule shape for the HBsAg. *not the complete virus particle just the HBsAg is released in the serum and detected during diagnosis.  Modes of HBV Transmission Sexual contact either heterosexual or homosexual. Direct inoculation of HBV by needles especially among parenteral drug addicts. Other percutaneous exposures include tattooing, ear piercing or other injuries from sharp instruments. Perinatally from an infected mother to her infant, most During giving commonly by contact of maternal blood to the infant's birth mucosa at the time of delivery. Once the infant is born it is Mostly concerns doctors, they interact with immediately given HB patients infected with HBV. immunoglobulin (regulate antibody EX:gynecologists during C-section against HBV without antigen) within There’s a chance of a needle prick, in this case the first 24h, later on it is given the the doctor should be cautious and take infectious antigenic. control measures.  Laboratory diagnosis Search for HB surface antigen or antibody in the Hepatitis B virus markers serum of the patient (HBV antigens and antibodies e.g HBsAg, Anti-HBs) Viral DNA: can be detected by probe or PCR. Assess the liver function Liver function tests, because the target of HB is the liver cell. e.g. serum alanine aminotransferase (ALT) and bilirubin, supplement the diagnosis. Any long run virus affects the organ function. The CDA destructs the virus infected cell (destructs the hepatocytes) that is why we always assess the liver function.  HIV is an enveloped virus, easily disinfected when it’s on the surface. HIV It needs to come directly with the blood to infect. gp120=glycoprotein 120 The Envelope gp41=glycoprotein 41 This glycoprotein complex, cleaved by host enzymes to form gp120 and gp41: gpl20- attachment to host CD4+ T cell. gp41- fusion and entry.  The HIV Genome two identical copies of a positive Genome of ssRNA=single stranded RNA sense ssRNA, associated with reverse transcriptase Why did we say two identical single stranded RNA instead of double stranded RNA? Because both of them are positive sense.  HIV Transmission 1. Sexual Transmission. 2. Blood & blood products (e.g. blood transfusion, sharing syringes or accidental needle prick injury). Accidental needle prick injury is very common in the medical personnel. EX: they get infected from emergency patients. 3. Vertical Transmission: during pregnancy, or through lactation. HIV transmission by lactation or during pregnancy is very common. If the mother is infected with HIV she will be directed to not nurse the baby.  For screening we depend on Elisa (less cost). It’s problem is that it’s not specific, there’s a chance of cross reaction with another antigenic substance of another virus. Diagnosis of HIV Infection Screening detects A- HIV antibody screening tests antibodies against HIV HIV-specific antibodies are detectable 3 weeks after infection (i.e., seroconversion). For antibody screening, one should use kits that detect antibodies to both HIV-1 & HIV-2 viruses. Seroconversion: The transformation from seronegative to seropositive for a specific antibody.  If the screening turns out positive we do a confirmatory test called western blot. Western Blot 1 The HIV Western blot consists of a thin nitrocellulose strip in which are embedded HIV protein bands (gp120 (SU), p66/51 (RT), gp41 (TM), p32, p24 & p17). Serum is added to the strip & any existing HIV antibody will bind to the corresponding HIV antigen. We use all of the antigenic part of the virus embedded in a nitrocellulose strip then the patients serum is added after that the development of an antigen antibody reaction will be seen in the form of bands. (The formation of the bands confirms HIV infection). 2- Nucleic acid tests for HIV DNA or RNA: PCR & gene probes. Measurement of HIV viral load. 3- CD4 count The diagnosis of AIDS is also established by the finding of a CD4 count of less than 200 cells/mm3 CD4/CD8 ratio