Viral Diseases of Humans and Animals - Assignment Example

Question 1: Describe, with specific examples the Baltimore system for the classification of human and veterinary according to whether the direction of translation of viral mRNA(s) is positive or negative in relation to their genomes. Answer: Baltimore classification is a system that places viruses into one of seven groups and this will largely depend on a combination of their Nucleic acid (RNA or DNA), sense, strandeness, and method of replications. These groups in the Baltimore classification are usually designated by Roman numerals and discriminate viruses depending on genome type and their mode of replication. As in other classifications are usually determined by the disease caused by the virus, neither of which are satisfactory due to different viruses causing the same illness or looking very similar. In addition, the viral structures have been found to be difficult to be determined even under the microscope. By convention, mRNA is usually defined as positive (+ve) strand because it is the template for protein synthesis. A strand of DNA that is equivalent sequence is also called the +ve strand. DNA strands and RNA that are complementary to the +ve strand care called negative (-ve) strands. Question 2 Describe briefly the overall structure of the major antigens that determine immunity to influenza A and B viruses. How do changes to these antigens give rise to "antigenic shift" and "antigenic drift"? Answer The constant region determines the mechanism used to destroy antigen (Alberts et el, 2002). Antibodies are divided into five major classes, IgM, IgG, Iga, IgD, and IgE, based on their constant region structure and immune function (Parham, 2009) There are two ways in which influenza virus changes- these are called shift and drift. Antigenic shifts, is an abrupt change in virus, which produces a new combination of the NA proteins and HA proteins (Parham, 2009). Such viruses have not been seen so they can be easily be transmitted from one person to another, a pandemic may occur. Antigenic drift is the gradual, continuous change that happen when the virus make small “mistakes” when copying its genetic information (Alberts et el, 2002). His can result in a slight difference in the HA or NA proteins (Alberts et el, 2002). Although the changes may be small, they may be significant enough so that the human immune system will no longer recognize and defend against the altered proteins. Question 3 Viral diseases of humans and animals can be diagnosed using similar techniques. Detail generic techniques that can be used for the detection of viral antigens, nucleic acid and antibodies elicited following viral infection. In your answer ensure that any diagrams used are labelled. Answer Serum, blood on filter paper and saliva, but not urine, can be used for detection of IgM if samples are taken within the appropriate time frame (five days or more after the onset of fever). Serum specimens may be tested at a single dilution or at multiple dilutions. Most of the antigens used for this assay are derived from the virus envelope protein. MAC-ELISA has good sensitivity and specificity but only when used five or more days after the onset of fever. Different commercial kits (ELISA or rapid tests) are available but have variable sensitivity and specificity. A WHO/TDR/PDVI laboratory network recently evaluated selected commercial ELISAs and first-generation rapid diagnostic tests, finding that ELISAs generally performed better than rapid tests. Question 4 Describe the strategy you would use to quickly develop a vaccine for a newly emerged highly pathogenic virus. Answer Recombinant protein vaccines are made up of protein antigens that have been produced in a heterologous expression system or it has been purified from large amount of the pathogenic organism (Anderson et el, 2009). A vaccinated person is able to produce antibodies to the protein antigen, thus he will be able to protect himself from the outbreak. Recombinant protein vaccines is developed from the concept that humoral immune responses mounted to an infection are often targeted toward specific localized regions on the surface of the protein antigens known as epitopes. A particular vaccine will be produced through expression of immunogenic proteins using the heterologous expression systems. The immunogenic protein antigens are then purified, and once these immunogenic protein antigens have been purified, they are recombinant and endogenous; they can then be administered with adjuvant to boost the immune system in persons. This strategy has been found to eliminate the risk of active infection that may occur with live attenuate vaccines or in cases where inactivation is incomplete. Question 5 Describe the principles underlying development of antiviral drugs, and give some examples of the mechanisms of action of antiviral drugs in relation to either herpes simplex virus or HIV. Answer In Principle a molecule can act as an anti-viral drug if it is able to inhibits some stage of the virus replication cycle, and should not be toxic to the human body’s cells (Anderson et el, 2009). The possible modes of action of anti-viral agents would include being able to 1. Prevent viral attachment and/or entry 2. Inactivate extracellular virus particles 3. Prevent synthesis of specific viral proteins 4. Prevent replication of the viral genome Antiviral treatment of herpes simplex virus or HIV at earliest stage in the course of the disease is made to decrease the length of recurrences (Flint, 2009). However there is not satisfactory treatment remedy for herpes simplex virus or HIV infection, as long as the virus remains in in the body (Flint, 2009). The development of agents capable of preventing HSV-1 production of microRNAs would cause the virus to become active (Anderson et el, 2009), rendering it susceptible to existing antiviral agents that could then cure infection. Question 6 How does HIV cause disease? What are the main stages of disease caused by untreated HIV infection in humans? Answer Human immunodeficiency virus (HIV) if left unchecked or untreated can lead to diseases. Unlike other viruses, the human body cannot be able to get rid of HIV completely. HIV will attack the immune system of a human being, specifically the T cells or CD4 cells, which helps the immune system in the human body to fight many infections. When HIV is unchecked, it reduces the number of CD4 cells in human body, making the victim to be more likely to get infections. There are 3 stages/phases of HIV infection: 1) Acute HIV infection; 2). Chronic HIV Infection; and 3) AIDS. AIDS is the final stage of Human immunodeficiency virus (HIV) infection that occurs when a person immune system is badly damaged and the person become vulnerable to opportunistic infections. Because HIV has severely damaged the immune system, the body of a affected person will not be able to fight off those opportunistic infections (opportunist infections are infections related cancers or disease infections that occur may times or are more sever in HIV victims that have weaker immune system than HIV victims with healthy immune systems.) the affected person with HIV will be diagnosed with AIDS if their CD4 count in the body is less than 200 cells/mm3 , they have one or more opportunistic infections, or both. Without treatment, people with AIDS typically survive about 3 years. Question 7 Describe briefly the pathogenesis of herpes simplex virus infection of the genital tract including latency and reactivation. Include in your answer diagnostic methods available and treatment options and their mechanism of action. Answer Pathogenesis of Herpes Simplex Viruses (HSV) Infection a. Primary Infection: Male species of human being are the only natural host of HSV, and the HSV virus is usually spread by contact, the usual site for the implantation is mucous membrane or skin (Boos and Kim, 2006). The basal and intermediate undergo acantholysis that lead to vesicle formation. In mucous membranes, the vesicle roof collapses to form a attributes of herpetic ulcer. During infection, the HSV virus will spread locally and will then short lived viraemia occurs, where it will be disseminated in the human body. b. Latency: HSV will escape the immune response and persists in a latent state in tissues. It has been reveal that the HSV virus in 50 per cent of normal human trigeminal ganglia and, in sacral and vagal ganglia, and cervical (Boos and Kim, 2006). This will be irrespective of an individual herpetic history. HSV virus may either be:- i). true latency- HSV virus is non-replicative and is seen to be maintained within the cell either integration in an episomal form or into the cellular chromosome (Brown et el, 2004). ii). Virus persistence- this is used to describe the dynamic latency, where there is a tight controlled low grade productive virus that does not lead to the lysis of the cells (Cesario, 2000). c. Reactivation:- it is known that may triggers can provoke the recurrence of HSV. These triggers can include: fever; menstruation; irradiation, including sunlight; stress-psychological or physical; meningococcal infection, pneumococcal infection; and others (Brown et el, 2004).   Question 8 Describe the protective benefit of the human papilloma virus vaccination strategy, when it should be given, and why cervical screening by PAP test is still required Answer Vaccinating against human papilloma virus provides protection against development of human papilloma virus related diseases and cancers caused by human papilloma virus types 18, 16. 11 and 6 (Choi, 2007). Vaccinating males have been found to protect them from anal and penile cancers, some cancers of the neck and head, and genital warts (Kahn and Burk, 2007). In addition its helps to protect unvaccinated females from cervical cancers and other human papilloma virus related cancers by reducing the spread of the virus from male to female during intercourse (Brabin, 2008). The right time for this vaccine to be given before an individual becomes sexually active. If an individual has started engaging with sex then they may have been infected with some of these human papilloma virus types (Brabin, 2008). And if they have been infected with any of these 4 types, their protection against HPV related disease and cancers may be reduced. Regular pap test for female species in human being is still required because the human papilloma virus vaccine doesn’t protect against all cancers of the cervix (Brabin, 2008). References Brabin L, Roberts SA, Stretch R, Baxter D, Chambers G, Kitchener H, et al. Uptake of first two doses of human papillomavirus vaccine by adolescent schoolgirls in Manchester: prospective cohort study. BMJ2008;336:1056-8. Brown Z. A., Benedetti J., Ashley R., et al. Neonatal herpes simplex virus infection in relation to asymptomatic maternal infection at the time of labor. N. Engl. J. Med. 2004;324:1247–1252. Boos J., Kim J. H. Biopsy histopathology in herpes simplex encephalitis and in encephalitis of undefined etiology. Yale J. Biol. Med. 2006;57:751–755. Choi YH, M Jit, N Gay, A Cox, G Garnett, and WJ Edmunds. Developing a model of the transmission of HPV and development of HPV-related diseases. 24th International Papillomavirus Conference and Clinical Workshop, Beijing, China, 2007. Cesario T. C., Poland J. D., Wulff H., Chin T. D., Wenner H. A. Six years experiences with herpes simplex virus in a children’s home. Am. J. Epidemiol. 2000;90:416– 422. Kahn JA, Burk RD. Papillomavirus vaccines in perspective. Lancet2007;369:2135-7. Anderson J, Schiffer C, Lee SK, Swanstrom R (2009). "Viral protease inhibitors". Handb Exp Pharmacol. Handbook of Experimental Pharmacology. 189 (189): 85–110 Flint, O. P.; Noor, M. A.; Hruz, P. W.; Hylemon, P. B.; Yarasheski, K.; Kotler, D. P.; Parker, R. A.; Bellamine, A. (2009). "The Role of Protease Inhibitors in the Pathogenesis of HIV- Associated Lipodystrophy: Cellular Mechanisms and Clinical Implications". Toxicol Pathol. 37 (1): 65–77. Parham, Peter. (2009). The Immune System, 3rd Edition, pg. G:2, Garland Science, Taylor and Francis Group, LLC. Alberts B, Johnson A, Lewis J, et al. (2002). "24. The Adaptive Immune System". Molecular Biology of the Cell (4th ed.). New York: Garland Science. Read More