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Microbiology with Diseases by Body System, 4e (Bauman) Chapter 14 Infection, Infectious Diseases, and Epidemiology 14.1 Multiple Choice Questions 1) Which of the following is NOT an example of symbiosis? A) bacteria in the human colon B) tapeworm in the human intestine C) tuberculosis in the human lung D) protozoa in termites E) microbes passing across the placenta to the fetus Answer: E Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.1 2) A bacterium inhabits the human nasal cavity where it obtains nutrients from secretions. It neither harms nor benefits the host. The relationship is therefore a(n) ________ one. A) commensal B) mutualisitic C) parasitic D) neutral E) antagonistic Answer: A Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.1 3) A protozoan and its resident bacteria invade the body of a worm. The bacteria release toxins and exoenzymes that immobilize and digest the worm, and the protozoan and bacteria absorb the nutrients produced. The relationship between the protozoan and the bacteria would best be described as A) commensalism. B) mutualism. C) parasitism. D) both commensalism and parasitism. E) a nonsymbiotic relationship. Answer: B Bloom's Taxonomy: Application Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.1 1 Copyright © 2015 Pearson Education, Inc. 4) The fungus Pneumocystis jiroveci is found in the lungs of most people in low numbers, but in immunocompromised people it overgrows, resulting in severe respiratory problems. The fungus is best described as A) a parasite. B) resident microbiota. C) a mutualist symbiotic partner. D) transient microbiota. E) both resident microbiota and opportunistic pathogen. Answer: E Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.2, 14.3 5) Chagas' disease is transmitted by a bug with mouthparts that penetrate blood vessels. Which type of exposure does this represent? A) mucous membrane portal B) parenteral route C) skin portal D) contact E) fomite Answer: B Bloom's Taxonomy: Application Section: The Invasion and Establishment of Microbes in Hosts: Infection Learning Outcome: 14.7 6) Symptoms are A) subjective characteristics of a disease that only the patient can feel. B) objective manifestations of a disease that can be measured. C) objective manifestations of a disease that can be observed by others. D) characteristics of a disease, such as sweating. E) laboratory tests used to diagnose a disease. Answer: A Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.11 7) The close contact between newborns and family members allows them to become ________ with microbes that become established as their microbiota. (Choose the most accurate term.) A) infected B) parasitized C) colonized D) contaminated E) infiltrated Answer: D Bloom's Taxonomy: Comprehension Section: The Invasion and Establishment of Microbes in Hosts: Infection Learning Outcome: 14.6 2 Copyright © 2015 Pearson Education, Inc. 8) A person licks a needle before injecting a drug into a vein. The person later develops a bacterial infection of the blood. This is an example of A) a disruption of the normal microbial population of the blood. B) a member of the microbiota gaining access to an unusual location in the body. C) immune suppression leading to disease. D) microbial antagonism. E) microbial synergism. Answer: B Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.4 9) Which of the following statements regarding the demonstration of the etiology of disease is FALSE? A) The suspect agent must be present in all cases of disease. B) The suspect agent must cause the disease under investigation when introduced into a susceptible host organism. C) The suspect agent must be isolated and cultured in the laboratory. D) It must be possible to reisolate the suspect agent from the infected experimental host. E) The suspect agent must be the only potential pathogen present in disease cases. Answer: E Bloom's Taxonomy: Application Section: The Nature of Infectious Disease Learning Outcome: 14.13 10) Which of the following situations is NOT a way in which a baby acquires normal microbiota? A) The baby acquires the residential microbiota in the colon after the first meal. B) Staphylococcus epidermidis is transferred from the hospital staff to the newborn after delivery. C) Microbes cross the placenta during pregnancy. D) Microorganisms grow in the respiratory tract after the baby's first breath. E) Microbes enter the nose and mouth when the baby is in the birth canal. Answer: C Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.3 3 Copyright © 2015 Pearson Education, Inc. 11) Which of the following situations might cause normal microbiota to become opportunistic pathogens? A) growth of microbes on the surface of intact skin B) growth of microorganisms on the excreted cellular wastes and dead cells in the large intestine C) treatment of a cancer patient with radiation D) growth of Lactobacillus on the surface of teeth E) presence of Entamoeba in the lumen of the colon Answer: C Bloom's Taxonomy: Application Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.4 12) Which of the following is considered part of the resident microbiota of the female reproductive system? A) Candida B) Lactobacillus C) E. coli D) Bacteroides E) both Candida and Lactobacillus Answer: E Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.3 13) Bacterial contaminants grow in food in a closed container. The food is heated after the container is opened, but a person develops food poisoning after eating it. The bacteria were producing A) an exotoxin. B) endotoxin. C) an exoenzyme. D) antiphagocytic factors. E) capsules. Answer: A Bloom's Taxonomy: Knowledge Section: The Nature of Infectious Disease Learning Outcome: 14.14 4 Copyright © 2015 Pearson Education, Inc. 14) Among the virulence factors produced by Staphylococcus aureus are hemolysin, coagulase, hyaluronidase, and enterotoxin. Which of these factors contribute(s) to the ability of S. aureus to invade the body? A) coagulase B) enterotoxin C) hemolysin D) hyaluronidase E) coagulase and hemolysin Answer: D Bloom's Taxonomy: Application Section: The Nature of Infectious Disease Learning Outcome: 14.14 15) During which stage of disease should an infected person be considered contagious? A) the incubation period B) all stages C) the illness stage D) the decline stage E) the convalescence period Answer: B Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.15 16) Which of the following is transmitted by the parenteral route? A) ringworm B) warts C) gonorrhea D) yellow fever E) pertussis Answer: D Bloom's Taxonomy: Application Section: The Invasion and Establishment of Microbes in Hosts: Infection Learning Outcome: 14.7 17) Which of the following is considered a mechanical vector transmission? A) cockroach transmission of Shigella B) mosquito transmission of Plasmodium C) flea transmission of Yersinia D) tsetse fly transmission of Trypanosoma E) louse transmission of Rickettsia Answer: A Bloom's Taxonomy: Comprehension Section: Modes of Infectious Disease Transmission Learning Outcome: 14.18 5 Copyright © 2015 Pearson Education, Inc. 18) Vomiting is a common sign of food poisoning. The corresponding symptom would be A) fever. B) cramps. C) nausea. D) pain. E) diarrhea. Answer: C Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.11 19) Which of the following might result in a nosocomial infection (HAI)? A) being bitten by an infected insect B) eating contaminated food C) using a contaminated needle D) a hospital aide forgetting to wash his or her hands before tending a patient E) having unprotected sexual intercourse Answer: D Bloom's Taxonomy: Comprehension Section: Epidemiology of Infectious Diseases Learning Outcome: 14.28 20) Diseases that are induced by modern medical procedures are referred to as ________ infections. A) iatrogenic B) exogenous C) opportunistic D) endogenous E) subacute Answer: A Bloom's Taxonomy: Comprehension Section: Epidemiology of Infectious Diseases Learning Outcome: 14.26 21) The bacterium that causes tuberculosis can be expelled from the lungs by a cough and remain viable in the air for an hour or more. If a person inhales the bacteria from the air, what type of transmission has occurred? A) indirect contact B) airborne C) waterborne D) foodborne E) bodily fluid Answer: B Bloom's Taxonomy: Comprehension Section: Modes of Infectious Disease Transmission Learning Outcome: 14.17 6 Copyright © 2015 Pearson Education, Inc. 22) A person is exposed to desert air containing fungus spores and develops valley fever as a result. Valley fever is an example of a ________ disease. A) contagious B) subacute C) chronic D) noncommunicable E) latent Answer: D Bloom's Taxonomy: Application Section: Classification of Infectious Diseases Learning Outcome: 14.21 23) In early spring 2009, the CDC reported several dozen cases of novel H1N1 influenza ("swine flu") in the United States. By the summer, the number of confirmed cases was reported as over 40,000. The pattern of novel H1N1 cases in the United States represents a(n) ________ disease. A) epidemic B) endemic C) sporadic D) pandemic E) opportunistic Answer: A Bloom's Taxonomy: Application Section: Epidemiology of Infectious Diseases Learning Outcome: 14.24 24) The incidence of tuberculosis in the year 2000 in the United States was 12.43/100,000 cases. This means A) 12.43 in every 100,000 people in the United States had tuberculosis in the year 2000. B) 12.43 of every 100,000 people died of tuberculosis in the U.S. in the year 2000. C) there were 12.43 new cases of tuberculosis for every 100,000 people in the United States in the year 2000. D) there were 12.43 tubercle bacilli per 100,000 microbes in the United States in the year 2000. E) 12.43 of every 100,000 cases of tuberculosis were treated in the United States in the year 2000. Answer: C Bloom's Taxonomy: Application Section: Epidemiology of Infectious Diseases Learning Outcome: 14.23 7 Copyright © 2015 Pearson Education, Inc. 25) A strain of Neisseria gonorrhea has a mutation which has caused it to lose the ability to produce fimbriae and become less virulent as a consequence. What function has this pathogen lost? A) the ability to adhere to cells of the body B) the ability to move from one location in the body to another C) the ability to produce an endotoxin D) the ability to establish a latent infection E) the ability to prevent phagocytes killing it Answer: A Bloom's Taxonomy: Comprehension Section: The Invasion and Establishment of Microbes in Hosts: Infection Learning Outcome: 14.8 26) Ten months after the 2010 earthquake in Haiti, there was a sharp increase in the number of cases of cholera. What was the most likely source of disease? A) direct contact with infected individuals B) indirect contact with contaminated equipment C) airborne D) waterborne E) foodborne Answer: D Bloom's Taxonomy: Application Section: Modes of Infectious Disease Transmission Learning Outcome: 14.16 27) Which of the following types of epidemiology applies Koch's postulates to study a disease? A) experimental B) descriptive C) analytical D) systemic E) retrospective Answer: A Bloom's Taxonomy: Comprehension Section: Epidemiology of Infectious Diseases Learning Outcome: 14.25 28) What is the relationship between prevalence and incidence for an acute disease like influenza? A) The incidence and prevalence are essentially equal. B) The incidence is always greater than the prevalence. C) The prevalence is always greater than the incidence. D) The incidence rises while prevalence declines. E) There is no predictable relationship. Answer: A Bloom's Taxonomy: Comprehension Section: Epidemiology of Infectious Diseases Learning Outcome: 14.23 8 Copyright © 2015 Pearson Education, Inc. 29) An example of direct contact transmission is A) the bite of a kissing bug. B) a door knob contaminated with respiratory secretions. C) saliva exchanged during a kiss. D) fecal contaminates on the hands of a restaurant worker. E) inhalation of respiratory aerosols. Answer: C Bloom's Taxonomy: Comprehension Section: Modes of Infectious Disease Transmission Learning Outcome: 14.16 30) Which of the following pairings of microbe and disease was disproven using Koch's postulates? A) HIV and AIDS B) Mycobacterium leprae and leprosy C) hepatitis B and D and liver cancer D) varicella-zoster virus and chickenpox E) Haemophilus influenzae and the flu Answer: E Bloom's Taxonomy: Application Section: The Nature of Infectious Disease Learning Outcome: 14.13 9 Copyright © 2015 Pearson Education, Inc. 31) The pattern of new cases reported in North America represented in this graph is consistent with ________ transmission. A) airborne B) fecal-oral C) mosquito vector D) direct contact E) housefly Answer: C Bloom's Taxonomy: Application Section: Modes of Infectious Disease Transmission Learning Outcome: 14.16, 14.18 32) Which of the following is the correct sequence of a disease process? A) convalescence, incubation, prodromal period, illness, decline B) prodromal period, convalescence, incubation, illness, decline C) incubation, convalescence, prodromal period, illness, decline D) incubation, prodromal period, illness, decline, convalescence E) illness, convalescence, incubation, prodromal period, decline Answer: D Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.15 10 Copyright © 2015 Pearson Education, Inc. 33) Two children attend the same daycare, but one child is at the facility in the morning and the other child attends the facility in the afternoon. Both children become ill with fifth disease within one day of each other. How might the pathogen have infected both children? A) fomite transmission B) droplet transmission C) vector transmission D) direct contact transmission E) vertical transmission Answer: A Bloom's Taxonomy: Application Section: Modes of Infectious Disease Transmission Learning Outcome: 14.16 34) Treatment with high doses of antibiotics may lead to which type of health care associated infection? A) iatrogenic disease B) exogenous infection C) latent infection D) endogenous infection E) zoonosis Answer: D Bloom's Taxonomy: Comprehension Section: Epidemiology of Infectious Diseases Learning Outcome: 14.28 35) Which of the following combinations of pathogen and virulence factor is CORRECT? A) Neisseria gonorrhoeae and endotoxin B) Streptococcus pyogenes and protein M C) Staphylococcus aureus and neurotoxin D) Gram-positive bacteria and lipid A E) Escherichia coli and cytotoxin Answer: B Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.14 36) A true pathogen may also be described as A) a component of the microbiota. B) highly virulent. C) opportunistic. D) very common. E) easily transmitted. Answer: B Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.10 11 Copyright © 2015 Pearson Education, Inc. 37) Microbes known as transient microbiota are A) microorganisms that remain with the person throughout life. B) microorganisms that may cause a disease under certain circumstances. C) organisms that remain in the body for a short time. D) unsuccessful microbial invaders because of the presence of preexisting microbes. E) sources of microbial contamination. Answer: C Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.3 38) The taxonomic approach to classifying disease is based on the A) type of host for the microbe. B) means of transmission. C) organs or organ systems affected by the disease. D) type of microbe that causes the disease. E) severity and duration of the disease. Answer: D Bloom's Taxonomy: Comprehension Section: Classification of Infectious Diseases Learning Outcome: 14.19 39) Organisms that are resident microbiota are best described as A) microorganisms that remain with the person throughout life. B) any microorganisms that cause disease. C) organisms that remain in the body for a short time. D) microorganisms that may cause a disease under certain circumstances. E) microorganisms that never cause disease. Answer: A Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.3 40) A new influenza strain appears and is spreading rapidly. What measures might be taken by public health agencies to stop the spread? A) Facilitate access to vaccines. B) Identify and treat people who are infected. C) Educate members of the public about ways to protect themselves. D) Educate the public, promote vaccination, and treat those who are infected. E) Shut down public transportation. Answer: D Bloom's Taxonomy: Application Section: Epidemiology of Infectious Diseases Learning Outcome: 14.29 12 Copyright © 2015 Pearson Education, Inc. 41) Several days after a walk in the woods, Cheryl develops a localized rash. It is not painful and soon fades so she thinks nothing of it. Several months later she experiences increasing fatigue, low-grade fever, and pain in the joints. These symptoms persist for months before she seeks medical attention. This description is most consistent with a(n) ________ infection. A) acute B) chronic C) subclinical D) asymptomatic E) latent Answer: B Bloom's Taxonomy: Comprehension Section: Classification of Infectious Diseases Learning Outcome: 14.20 42) The condition called parasitism is characterized as a(n) A) relationship between two organisms where only one member benefits and the other is unharmed. B) relationship between two organisms where both members benefit. C) nonsymbiotic relationship. D) unsuccessful microbial invasion due to the presence of preexisting microbes. E) relationship between two organisms where one member harms the other. Answer: E Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.2 43) An axenic environment is one A) in which microorganisms remain with the person throughout life. B) that is free of microbes. C) that is a source of contamination. D) in which microorganisms remain present only for a short time. E) contaminated by microbial toxins. Answer: B Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.3 44) The condition known as microbial antagonism may be defined as A) microorganisms that remain with a person throughout life. B) a relationship between two organisms where one member harms the other. C) a relationship between two organisms where only one member benefits. D) an unsuccessful microbial invasion due to the presence of preexisting microbes. E) a relationship between two organisms where both members benefit. Answer: D Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.4 13 Copyright © 2015 Pearson Education, Inc. 45) The dots on the map represent reported cases of a disease. This distribution is a(n) ________ pattern. A) endemic B) epidemic C) pandemic D) sporadic E) emerging Answer: A Bloom's Taxonomy: Comprehension Section: Epidemiology of Infectious Diseases Learning Outcome: 14.24 14.2 True/False Questions 1) Both members of a symbiotic relationship benefit from each other. Answer: FALSE Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.1 2) Normal microbiota may cause disease if they are introduced into an unusual site in the body. Answer: TRUE Bloom's Taxonomy: Knowledge Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.4 14 Copyright © 2015 Pearson Education, Inc. 3) A syndrome is a group of symptoms and signs that collectively characterize a particular disease. Answer: TRUE Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.11 4) All infections go through the stages known as incubation period, prodromal period, and illness. Answer: FALSE Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.15 5) Botulism is transmissible by direct contact. Answer: FALSE Bloom's Taxonomy: Comprehension Section: Modes of Infectious Disease Transmission Learning Outcome: 14.16 6) A common cold is an example of a chronic disease. Answer: FALSE Bloom's Taxonomy: Comprehension Section: Classification of Infectious Diseases Learning Outcome: 14.20 7) Biofilms provide an alternative means for bacteria to attach to surfaces within the body. Answer: TRUE Bloom's Taxonomy: Comprehension Section: The Invasion and Establishment of Microbes in Hosts: Infection Learning Outcome: 14.9 8) Bacterial cells with capsules are resistant to killing by phagocytes. Answer: TRUE Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.14 9) Koch's postulates can be applied to every infectious disease to identify its causative pathogen. Answer: FALSE Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.13 15 Copyright © 2015 Pearson Education, Inc. 10) An infection always leads to disease. Answer: FALSE Bloom's Taxonomy: Comprehension Section: The Invasion and Establishment of Microbes in Hosts: Infection Learning Outcome: 14.10 14.3 Short Answer Questions 1) Toxins that affect the lining of the gastrointestinal tract are (endotoxins/enterotoxins/exotoxins). Answer: enterotoxins Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.14 2) The degree to which a microbe is able to cause disease is known as its (morbidity/virulence/toxicity). Answer: virulence Bloom's Taxonomy: Knowledge Section: The Nature of Infectious Disease Learning Outcome: 14.10 3) Rubella, or three-day measles, passes through the (parenteral/placenta/mucous/skin) route to establish congenital infection of a fetus. Answer: placenta Bloom's Taxonomy: Comprehension Section: The Invasion and Establishment of Microbes in Hosts: Infection Learning Outcome: 14.7 4) Nervous system function may be impaired by the action of (endotoxins/neurotoxins/cytotoxins). Answer: neurotoxins Bloom's Taxonomy: Knowledge Section: The Nature of Infectious Disease Learning Outcome: 14.14 5) The (incubation/morbidity/prodromal) period is the time between infection and the occurrence of the first symptoms or signs of the disease. Answer: incubation Bloom's Taxonomy: Knowledge Section: The Nature of Infectious Disease Learning Outcome: 14.15 16 Copyright © 2015 Pearson Education, Inc. 6) Some of the bacteria in the human gut do not survive well outside of that environment, and produce vitamin K among other nutrients. This situation is an example of (commensalism/mutualism/parasitism). Answer: mutualism Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.1 7) Lipid A is a(n) (cytotoxin/endotoxin/exotoxin) that stimulates the body to release chemicals that cause fever, inflammation, diarrhea, hemorrhaging, shock, and blood coagulation. Answer: endotoxin Bloom's Taxonomy: Comprehension Section: The Nature of Infectious Disease Learning Outcome: 14.14 8) Persons with asymptomatic infections may be (contaminants/reservoirs/zoonoses) of disease. Answer: reservoirs Bloom's Taxonomy: Comprehension Section: Reservoirs of Infectious Diseases of Humans Learning Outcome: 14.5 9) Spread of pathogens from one host to another by fomites is an example of (vehicle/direct/indirect) contact transmission. Answer: indirect Bloom's Taxonomy: Comprehension Section: Modes of Infectious Disease Transmission Learning Outcome: 14.16 10) Biological (sources/vectors/carriers) not only transmit pathogens, but also serve as hosts for the manipulation of the pathogen during some phase of the pathogen's life cycle. Answer: vectors Bloom's Taxonomy: Comprehension Section: Modes of Infectious Disease Transmission Learning Outcome: 14.18 11) The bacterium that causes cholera is capable of living independently in freshwater. As a consequence, cholera epidemics primarily involve (nonliving/animal/zoonotic) reservoirs. Answer: nonliving Bloom's Taxonomy: Comprehension Section: Reservoirs of Infectious Diseases of Humans Learning Outcome: 14.5 12) The study of the cause of disease is known as (epidemiology/etiology). Answer: etiology Bloom's Taxonomy: Knowledge Section: The Nature of Infectious Disease Learning Outcome: 14.12 17 Copyright © 2015 Pearson Education, Inc. 13) The hepatitis C virus normally establishes a (latent/chronic/subclinical) infection and may be asymptomatic for a decade. Answer: latent Bloom's Taxonomy: Comprehension Section: Classification of Infectious Diseases Learning Outcome: 14.20 14) The study of when and where diseases occur is known as (analytical/descriptive/experimental) epidemiology. Answer: descriptive Bloom's Taxonomy: Comprehension Section: Epidemiology of Infectious Diseases Learning Outcome: 14.25 15) Virions attach to target host cell by means of (capsules/receptors/ligands). Answer: ligands Bloom's Taxonomy: Comprehension Section: The Invasion and Establishment of Microbes in Hosts: Infection Learning Outcome: 14.8 16) Lyme disease is (communicable/contagious/noncommunicable) among humans. Answer: noncommunicable Bloom's Taxonomy: Comprehension Section: Classification of Infectious Diseases Learning Outcome: 14.21 14.4 Essay Questions 1) What are the different types of symbiosis? List and give a short definition and an example for each. Answer: There are three types of symbiosis: (1) mutualism, which is the relationship between two organisms in which both benefit; (2) commensalism, in which one organism benefits and the other is not significantly affected; and (3) parasitism, in which one organism, the parasite, derives benefit while harming the other, the host. An example of mutualism is the relationship between intestinal bacteria and humans. Lichens, which are a symbiosis between fungus and a photosynthetic microbe, also represent a mutualistic relationship. The presence of Staphylococcus bacteria on skin and in nasal cavities is likely a commensal relationship, as well as Malassezia fungus infection of the epidermis. Tapeworms, the fungi that cause ringworm, and the protozoan that causes malaria are all examples of parasites. Bloom's Taxonomy: Comprehension Section: Symbiotic Relationships Between Microbes and Their Hosts Learning Outcome: 14.1 18 Copyright © 2015 Pearson Education, Inc. 2) Researchers have proposed that the herpesvirus responsible for the childhood illness roseola may cause a type of T cell leukemia. Ninety percent of the population has been infected by the virus by two years of age, but the T cell leukemia is relatively rare. The virus can be cultured in the laboratory in tissue culture, but not in mature organisms. Discuss the obstacles to applying Koch's postulates to the etiology of this disease. Answer: Koch's first postulate, that the suspect agent must be present in every case of disease, is met, but far more people have the virus than have the disease. This suggests that more than the presence of the virus is necessary for the leukemia to develop, and the additional factors may be difficult to identify. The third postulate states that the isolated suspect agent must cause disease when introduced into a host. This situation presents two difficulties in satisfying the third postulate. The first is that it is unethical to deliberately expose humans to an agent that may produce life-threatening disease (the leukemia). Additionally, ethical concerns aside, because such a large percentage of the population has been exposed to the virus, a large pool of potential uninfected subjects does not exist. Bloom's Taxonomy: Analysis Section: The Nature of Infectious Disease Learning Outcome: 14.13 3) Describe three types of reservoirs of infection in humans. Give an example disease for each type of reservoir. Answer: For a pathogen to enter a new host, it must survive in some site from which it can infect the new host. These sites are considered reservoirs, which include the following: 1. Animal reservoirs, such as domestic or wild animals. Examples: rabies, West Nile fever 2. Human carriers, which are individuals who are infectious and may be either asymptomatic or symptomatic. Examples: AIDS, tuberculosis 3. Nonliving reservoirs, such as soil, water, and food. Examples: cholera, tetanus Bloom's Taxonomy: Application Section: Reservoirs of Infectious Diseases of Humans Learning Outcome: 14.5 4) In 2012 a new kind of fungal meningitis (infection of the nervous system) was discovered. Disease occurred among patients who had received steroid injections into spinal joints. Discuss whether these were HA (nosocomial) infections. Defend your answer. Discuss the route of transmission and what measures public health agencies could take to reduce disease. Answer: The fungal meningitis of 2012 was an HAI (nosocomial infection), of the iatrogenic type. It was introduced by the parenteral route. Public health agencies can educate health care providers about the source of the infections and how patients should be accessed and treated. They can stop the distribution of the suspect steroids and determine what production standards may need to be enforced. Bloom's Taxonomy: Analysis Section: Epidemiology of Infectious Diseases Learning Outcome: 14.7, 14.28, 14.29 19 Copyright © 2015 Pearson Education, Inc. 5) Compare and contrast endotoxins and exotoxins. Answer: Both endotoxins and exotoxins are produced by Gram-negative bacteria. Exotoxins are also produced by Gram-positive bacteria. Endotoxins and exotoxins differ in their mechanism of release and composition: exotoxins are proteins or peptides that are secreted, leaving the cell intact, whereas endotoxins are lipids released only when the cell dies because they are a part of the outer membrane. The toxicity of exotoxins is higher than that of endotoxins, but both can be fatal. Both are heat stable, but endotoxins can survive an hour of autoclaving at 121°C, whereas exotoxins are not stable above 60°C. Exotoxins produce a strong immune response, and therefore toxoid immunization is possible. Endotoxins produce fever, but only a weak immune response, so toxoid immunization is not an option. Bloom's Taxonomy: Analysis Section: The Nature of Infectious Disease Learning Outcome: 14.14 20 Copyright © 2015 Pearson Education, Inc.