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Micro Notes CHAPTER 24 1. Ten unique characteristics of viruses that add significantly to their medical impact and complications include the following: 1) viruses are not cellular; 2) viral multiplication is completely dependent on infection of a living host cell; 3) the viral genome can consist of either DNA or RNA; 4) the viral genome may be either single- or double-stranded; 5) viruses lack the machinery for protein synthesis (i.e. ribosomes); 6) viruses lack enzymes for metabolic processes including ATP synthesis; 7) in their basic structure, virus particles consist of only nucleic acid and proteins; 8) viruses are ultra microscopic in size and typically less than 500 nm; 9) existing viruses infect every type of cell; and 10) viruses can take control of the host genetic material to regulate the synthesis and assembly of new virus particles. 2. a. Specific receptors on the surface of viruses dictate their interactions with host cells. b. The symptoms of viral diseases are a result of damage caused to host cells and the response of the host to viral infection. These symptoms commonly include rashes, fever, muscle aches, respiratory involvement, and swollen glands. c. The pathological effects of viruses vary based on the cell serving as a host, the cytopathic effects of the virus, and the ability or inability of the virus to initiate persistent infection or transformation of the cell. d. During a chronic viral infection, the virus is detectable in tissue samples and is still multiplying at a slow rate, but symptoms of infection are mild or absent. By contrast, in a latent infection, the virus has entered a dormant phase inside the host cell and has become completely inactive. It is not multiplying, generally is not detectable, and does not cause any symptoms. Chapter 24 3. The chart below outlines the target organs and general symptoms of DNA viral infections. Viral Infection Target Organs Symptoms Variola infection (Smallpox) Epidermal cells and subcutaneous connective tissue Fever, malaise, prostration, rash, toxemia, shock, intravascular coagulation Molluscipoxvirus infection (Molluscum contagiosum) Skin cells Skin lesions Herpes simplex 1 and 2 infection Skin cells, rarely sensory nerves Lesions on the face (HSV1) or genitalia (HSV2) Varicella-Zoster virus: Chickenpox (Shingles after reactivation of latent infection) Skin (sensory nerves) Macular, popular, vesicular rash on entire body (vesicular-papular rash on chest and back) CMV (Cytomegalovirus) disease All organs Varies, but severe cases may involve enlarged liver and spleen, jaundice, capillary bleeding, and microcephaly in newborns. Infection in adults can involve fever, diarrhea, hepatitis, and pneumonia. Epstein-Barr virus infection (infectious mononucleosis) Epithelium of oropharynx, parotid gland, B cells Sore throat, high fever, cervical lymphadenopathy Hepatitis B infection Liver Jaundice, decreased liver function Adenovirus infection Respiratory system Fever, rhinitis, cough, lesions of the conjunctiva Human papillomavirus infection Skin and mucous membranes Warts (common and genital) Parvovirus infection Skin cells, erythrocytic stem cells Rash on the cheeks 4. a. DNA viruses (with the exception of Pox viruses) multiply within the host cell’s nucleus while RNA viruses (with the exception of retroviruses) tend to be replicated and assembled in the cytoplasm. b. In addition to active, lytic infection, DNA viruses can be carried in two ways: 1) as chronic infections, in which the virus is multiplying at a slow rate but symptoms of infection are mild or absent, and 2) as latent infections, when the virus is completely inactive, is not multiplying, and causes no symptoms. 5. a. Smallpox is no longer an active disease, but when the virus was present in the population, it was considered one of the world’s deadliest diseases. Smallpox exposure usually occurs through inhalation of droplets or skin crusts and initial symptoms include fever, malaise, prostration, and a rash from which the disease gets its name. Writing to Learn Questions Page 2 of 7 Chapter 24 b. Variola major, the more severe form of the disease, is marked by toxemia, shock, and intravascular coagulation, all part of the high mortality rate seen with smallpox. c. A pock is a skin pustule which leaves a small, depressed scar upon healing. Viral infection first causes a macular rash which in turn becomes popular, vesicular, and pustular before finally crusting over and leaving small unpigmented sites pitted with scar tissue. d. Instead of an attenuated or inactivated strain of variola, the smallpox vaccine actually utilizes vaccinia, a close relative of the smallpox virus. e. The vaccination for the vaccinia virus also provides protection against smallpox and other poxvirus infections for at least ten years. 6. a. Molluscum contagiosum is marked by smooth, waxy nodules on the face trunk and limbs. b. Warts, caused by infection with human papillomaviruses, could be easily mistaken for the nodules of molluscum contagiosum. c. The discontinuation of the smallpox vaccination has led to a population with no acquired immunity to any of the pox viruses. This is unimportant in the case of smallpox, which no longer exists in the wild, but has led to an increase in monkeypox infection. 7. Although members of the herpesvirus family differ in many of their characteristics, they all share the ability to cause recurrent, persistent, and latent infections. 8. a. HSV-1 HSV-2 Skin lesions Type of disease Skin lesions Usually oropharynx, rarely genitalia Body areas affected Usually genitalia, rarely oral mucosa Herpatic keratitis; herpetic whitlows; approximately 30% of cases of neonatal encephalitis Possible complications Approximately 70% of cases of neonatal encephalitis; herpetic whitlows b. Newborns infected with herpes have no acquired immunity and are therefore protected only by passive immunity from their mother. This lack of a robust immune response is responsible for the severity of symptoms in the disease. c. Diagnosis usually begins with observation of symptoms. Both oral and genital herpes manifest one or more small fluid-filled vesicles which burst and crust over. Scrapings from these lesions may be stained and observed with light microscopy to reveal multinucleate giant cells typical of herpes infections. To confirm the diagnosis and determine the type of herpes, subtyping may be performed with fluorescent antibodies and specific DNA testing. The most effective treatments and preventives are the “cyclovirs” such as acyclovir, famciclovir, and valacyclovir. These may be prescribed in topical or oral drug form. Some over the counter ointments may be of some use in relieving pain and shortening the time of infection. d. Recurrent attacks of HSV originate in the tendency of herpes simplex viruses to multiply in sensory neurons during an attack and subsequently enter a latent period in the nerve trunks and ganglia cells. They remain in an inactive state until some stimulus causes them to become reactivated and migrate back to the original site of infection and cause symptoms. Some of the factors that appear to stimulate recurrency are trauma, sunburn, stress, and fever. 9. Writing to Learn Questions Page 3 of 7 Chapter 24 a. Chickenpox is the result of initial infection with the varicella-zoster virus. Shingles is reactivation of the same virus. b. Shingles lesions appear on the skin of the face and trunk as the virus migrates down the trigeminal and thoracic nerves. Lesions appear on the skin of areas innervated by these nerves, producing an asymmetrical rash characteristic of the disease. c. Both ZIG and VZIG are specific immune globulins that work by vastly increasing the titer of varicella-zoster specific antibodies in the blood. They generally lessen the symptoms of infection but do not entirely prevent disease. 10. a. Cytomegalovirus targets the liver, spleen, lungs, blood cells, and retina. b. Transmission of CMV usually involves sexual contact, vaginal birth, transplacental infection, blood transfusion, and organ transplantation c. The three groups at highest risk for disease are fetuses, newborns, and immunodeficient adults. 11. a. The Epstein-Barr virus is associated with infectious mononucleosis, Burkitts lymphoma, and nasopharyngeal carcinoma. b. Burkitts lymphoma is thought to arise as a persistent EBV infection in young children and give rise to transformed B lymphocytes while other chronic infections overwhelm the T-cell effecter response needed to stop the overgrowth of these unhealthy B-cells. c. Due to improvements in sanitation and less frequent and intimate contact with other children, 70% of Americans enter young adulthood never having had HBV infection. The more intimate associations common to adulthood lead to a much greater rate of infection such that 90% to 95% of all people show serological evidence of infection by midlife. Writing to Learn Questions Page 4 of 7 Chapter 24 12. Virus Name HSV-1 / HSV2 Varicellazoster Cytomegalovirus Epstein-Barr virus HHV-6 / HHV-7 Tissue infected Oral (HSV-1) and genital (HSV-2) mucosa Skin, sensory nerves Liver, spleen, lungs, blood cells, and retina Lymphoid tissue and salivary glands Lymphoid tissue and salivary glands Names of diseases Oral herpes, genital herpes Chicken pox, shingles CMV disease Mononucleosis Roseola Special characteristics Complications include whitlows and neonatal encephalitis Shingles is reactivation of latent viral infection Far more virulent in fetuses, newborns, and immunosuppressed Complications include Burkitts lymphoma and nasopharyngeal carcinoma May be linked to development of multiple sclerosis and Hodgkins lymphoma 13. a. Viral hepatitis is an inflammatory disease of the liver in which the death of hepatocytes and the mononuclear response swells and distorts the liver, interfering with the excretion of bilirubin into the intestine. When bilirubin accumulates in the blood and tissue, it lends a yellow tinged appearance (jaundice) to the skin and eyes. Hepatitis (HAV) is an RNA virus responsible for infectious hepatitis, which is spread via contaminated food and water and is the least severe of the three main hepatitis viruses. HBV is a DNA virus responsible for serum hepatitis. It is contracted through close (often sexual) contact and can lead to chronic hepatitis and hepatic cancer. HCV is an RNA virus responsible for post-transfusional hepatitis. It is contracted in the same manner as HBV and leads to chronic inflammation of the liver and cirrhosis. b. The delta agent (hepatitis D virus) is a defective RNA virus that can only cause infection when a cell is also infected with HBV. 14. a. Most of the genome of the hepatitis B virus consists of a double stranded DNA molecule, but a portion of the genome exists as single stranded DNA. b. Because HBV cannot be grown in culture, viral fragments, antibodies, and in some cases entire virions, all of which have been isolated from the blood of infected patients, are used as the primary source of viruses for study. c. People infected with HBV usually have a very high viral load, and, because the infectious dose for the virus is very low, infection is very easily accomplished. Care must be taken not to share items such as toothbrushes or razors. Mosquitoes, too, have been known to serve as vectors. d. People most at risk for contracting hepatitis B include those living under crowded conditions, drug addicts, the sexually promiscuous, and people whose occupation requires them to routinely handle blood or blood products. 15. a. The hepatitis B virus enters the body through a break in the skin or by injection into the bloodstream. Eventually it reaches the liver cells where it multiplies and releases viruses into the Writing to Learn Questions Page 5 of 7 Chapter 24 blood during an incubation period of 4 to 24 weeks. Most people exhibit few overt symptoms and eventually develop immunity to HBV. Others experience malaise, fever, chills, anorexia, abdominal discomfort, and diarrhea. Some of these persons will go on to develop fever, jaundice, rashes, and arthritic symptoms, while an even smaller subset will develop glomerulonephritis and arterial inflammation. The hepatitis B virus can leave the body through bloodletting procedures and can also be passed to neonates during the birth process. b. The most serious complications of HBV infection include chronic liver disease in the form of necrosis or cirrhosis, arthritic symptoms, and a vastly increased risk of liver cancer. 16. a. Two types of vaccines exist for HBV. The first (Recombivax, Energix) contains HBV surface antigens which have been grown in yeast. The second (Heptavax) is made from the purified sterile antigen extracted from the blood of carriers. It is used primarily for people who are allergic to yeast. b. Vaccination is required for medical and dental workers, students, patients receiving multiple transfusions, immunodeficient persons, and cancer patients. It is now strongly recommended as part of the routine childhood immunization schedule. 17. a. Adenoviruses cause conjunctival infections, mild respiratory diseases (colds), and acute hemorrhagic cystitis. b. Adenoviruses are spread via respiratory and ocular secretions. 18. a. Painless, elevated, rough growths on the fingers or other parts of the body are known as common, or seed, warts. Plantar warts are deep, painful papillomas on the soles of the feet. Genital warts have a varying morphology but appear on the genitals. b. Genital warts are most serious because they carry with them a greatly increased risk of cervical and penile cancer. c. Warts are caused by the human papilloma virus (HPV). The lesions of warts are typically fleshy, skin-colored growths that range from flat and smooth to raised irregular masses. To confirm the diagnosis, a biopsy may be done to look for signs of the virus. This may require examination with an electon microsope to identify the virus directly. A pap smear of the cervix can reveal abnormal cells that are often a feature of genital warts. Another useful test involves a DNA probe to detect HPV DNA. This is currently a screening test given as part of the gynecological exam to rule out the presence of HPV in women. d. These are recombinant vaccines carrying a surface antigen from the virus (the whole virus is not used). Both Gardasil and Cervarix contain the antigens of the most common strains of viruses involved in cervical cancer. The vaccines are meant to be a preventive for HPV infections in girls and young women that will protect them against getting cervical cancer. It is effective only if given before they have become infected. 19. The most important human parvovirus is B19, the cause of erythema infectiosum. 20. a. Oncogenic DNA viruses are Epstein-Barr virus, human herpesvirus 8, hepatitis B virus, and humanpapilloma virus (HPV). b. Sexually-transmitted DNA viruses are molluscum contagiosum, herpes simplex, type 2, hepatitis B virus, and some types of humanpapilloma virus. c. Those spread by blood or blood products include EBV, HBV, and HCV. Writing to Learn Questions Page 6 of 7 Chapter 24 d. DNA viruses spread by respiratory droplets, kissing, and other nonsexual intimate contact: Smallpox, molluscum contagiosum, monkeypox, HSV-1, HSV-2, varicella-zoster, cytomegalovirus, EBV, HBV, HCV, adenovirus, HPV. Writing to Learn Questions Page 7 of 7