Suggested Answers for Case Study, Chapter 16, Mechanisms of Infectious Disease

Suggested Answers for Case Study, Porth Chapter 16, Mechanisms of Infectious Disease

1. Novel infectious diseases are becoming increasingly prevalent in the Western hemisphere owing to an expanding global market and international travel. Modes of transmission include birds, mammals, and insects. West Nile virus is a vector-borne illness transmitted by mosquitoes.

2. Antibody titers (or levels) indicate the presence of infection. Certain titers are elevated during the acute phase of a specific illness and tend to decline during convalescence.

3. When Jason was feeling at his worst, he was experiencing the acute phase of the illness. At this time, there is rapid proliferation and spread of the pathogen within the body. Toxic byproducts of microbial metabolism and cell lysis contribute to the specific signs and symptoms of the invading pathogen. The host’s immune response generates inflammation and tissue damage, further adding to the clinical presentation.

4. Viruses have either a single DNA or RNA strand. In order to replicate, they require the genetic material of a host; they cannot replicate outside of a living cell. Once in the host cell, they may replicate and migrate from the cell through “budding” or through cellular lysis. Alternatively, they may lie in a state of latency to create disease at a later time or alter the genetic material of the host cell to create malignant transformation. Suggested Answers for Case Study, Porth Chapter 17, Innate and Adaptive Immunity

1. Macrophages are a component of innate immunity and are responsible for the phagocytosis of microbes and processing of antigen. When working with T lymphocytes, macrophages can act as antigen-presenting cells. After ingesting the microbe, digestive enzymes break down antigen into small peptides and combine it with class II MHC. These complexes are presented on the cell membrane surface to CD4+ helper T cells, which recognize the antigen–MHC II complex by means of a T-cell receptor.

2. Type I interferons are produced by macrophages and fibroblasts. They inhibit viral replication and allow a virally infected cell to be recognized by lymphocytes. IFNs are also responsible for triggering uninfected cells to produce antiviral proteins to inhibit viral synthesis and spread.

3. Antibodies contribute to the agglutination of microbes to prevent their spread, facilitate phagocytosis, and encourage their destruction. They have the ability to neutralize bacterial toxins and inhibit the ability of viruses to invade host cells. Antibodies also contribute to the activation of complement and assist in the adherence of antigen to immune cells. Suggested Answers for Case Study, Porth Chapter 18, Inflammation, Tissue Repair, and Wound Healing

1. Carlton’s signs are typical of acute inflammation. Local vasodilation creates erythema and warmth. The edema is a result of increased vessel permeability and migration of exudate into the surrounding tissue. The engorgement of fluid at the area of injury contributes to the sensation of pain.

Visceral inflammation has a slightly different presentation: heat is less likely to occur because core temperature is preserved at a homeostatic level, and pain becomes apparent only when stretch receptors on the surfaces of viscera are stimulated.

2. In an acute response, leukocytosis occurs to increase the number of circulating white blood cells to support the immune response. The movement of white blood cells to the site of injury occurs as a result of chemotaxis. Margination and emigration are the events that describe the movement of circulating leukocytes from the blood to the injured tissue; local blood stasis allows leukocytes to move to the perimeter of vessels and pass (or emigrate) through capillary walls. Neutrophils arrive early to phagocytize microbes and cellular debris. Monocytes travel in the blood and migrate to injured tissue, where they become macrophages. These cells are capable of engulfing greater quantities of foreign material and are able to move to the lymphatic system, where they prime specific immunity.

3. Although the components of nutritional intake are valuable to all stages of wound healing, some have more specific qualities. Both vitamin A and C assist collagen synthesis, but vitamin C has a direct influence on collagen assembly and the removal of byproducts that result from collagen manufacturing. A deficiency in vitamin C would therefore affect the onset of the proliferation stage and the effectiveness of the remodeling phase, in which collagen production and lay-down is critical. Vitamin A stimulates capillary growth and epithelialization. A deficiency in vitamin A would hinder angiogenesis in the inflammatory phase of wound healing and epithelialization in the latter component of the proliferation phase. Suggested Answers for Case Study, Porth Chapter 19, Disorders of the Immune Response

1. Ahmed demonstrated a type I, IgE-mediated hypersensitivity reaction as indicated by his rhinoconjunctivitis and asthmatic symptoms. The rapid onset of his respiratory symptoms shortly after putting on the gloves is also typical of the type I response. Latex allergy can also be attributed to a type IV, T-cell- mediated response that presents with dermatologic signs and symptoms that are more delayed in their onset.

2. In a type I hypersensitivity disorder, TH2 cells differentiate in response to an allergen and in turn release IL-3, IL-4, and IL-5. IL-3 and IL-5 recruit and activate eosinophils, whereas IL-4 stimulates the differentiation of B cells into IgE-producing plasma cells. The IgE antibodies in turn sensitize mast cells, which subsequently undergo degranulation when exposed to the allergen. Mast cells produce vasodilation and smooth muscle spasm. Both mast cells and eosinophils contribute to the mucosal edema, secretion, and bronchospasm seen in type I hypersensitivity responses.

3. The latex proteins responsible for allergic reactions bind readily with the cornstarch used to coat gloves. In any environment in which gloves are frequently changed, the cornstarch becomes airborne and liberates aerosolized latex. A susceptible individual can react to the airborne proteins without having had contact with the latex material itself.

The proteins responsible for latex allergy reactions have a similar structure to the proteins found in bananas, avocado, kiwis, tomatoes, and chestnuts. Those with latex allergy often show cross-sensitivity to these foods. Suggested Answers for Case Study, Porth Chapter 20, Acquired Immunodeficiency Syndrome 1. A number of factors increase the risk for HIV transmission from mother to infant. A mother who exhibits a low CD4+ count or high viral load during pregnancy increases the risk for transmitting the disease to the unborn child. Delayed delivery after rupture of the amniotic sac is another factor that puts the fetus at risk. Transmission can occur in utero, during delivery, or with breast-feeding.

2. HAART refers to highly active antiretroviral therapy. The treatment protocol involves the administration of two or three antiretroviral medications that collectively destroy the HIV at various stages of replication. The aim of the therapy is to reduce the presence of HIV RNA to an undetectable level while increasing CD4+ cell counts. Zidovudine is a particularly effective antiretroviral medication to be administered to the pregnant woman because it greatly reduces the risk for perinatal transmission to the fetus. Some antiretrovirals, however, are teratogenic and should not be administered to the mother during the first trimester.

3. An opportunistic infection occurs when otherwise benign or common microorganisms cause disease in a compromised host. Individuals with HIV are prone to opportunistic infection because of CD4+ deficiency. The level of CD4+ cells directly correlates with the risk for developing an opportunistic infection. Viral load is another risk factor, and higher HIV RNA levels predispose the individual to opportunistic illness.