M200 Ch. 2 SmartWork

Place the following stages of infectious disease in the order in which occur:

1. incubation period 2. prodromal phase 3. illness phase 4. decline phase 5. convalescent phase

Consider the graph below. What would be the relative virulence of an organism (an "Agent 3") whose LD25 is 600 and LD75 is 1,000?

50% that of Agent 1 A higher LD50 correlates to decreased virulence. Consider, for example, that an LD50 of 10,000 Bacillus anthracisspores has been calculated for inhalation anthrax. It is thus much less virulent than a weaponized strain of which only 2,500 spores are necessary to produce 50% mortality.

One way to measure virulence is to calculate the lethal dose 50% (LD50): the number of pathogens required to kill 50% of an experimental group of animal hosts. Which agent in the figure below is more virulent?

Agent 1 requires fewer pathogens to kill half the animals than does agent 2.

Label the figure of infection cycles with the correct terminology.

As illustrated here, direct transmission is the passing of a microbe from person to person (by touch or aerosolization), whereas indirect transmission is from person to person by way of an inanimate object (called a vehicle) or an animal host. Accidental transmission occurs when a disease that normally does not reach humans does get transferred to humans, such as through an insect bite. Vertical transmission occurs when an infectious agent's host passes the microbe on to its offspring.

What is an infection transmitted from a health care worker to a patient called?

Iatrogenic infection

Imagine that the graph below was derived from a case of undetermined meningitis in a 34-year-old male living in Los Angeles, California. Which of the following conclusions could be logically supported?

If exposed again to this same strain of pathogen, the man is likely to remain healthy. Immunological "memory" is also acquired by vaccination. However, because the effectiveness can decrease with time, boosters (such as recommended for tetanus) may be required to maintain sufficient populations of specific memory cells.

What do we call the collection of bacteria, archaea, and eukaryotic microbes that normally inhabit the human body?

Microbiota Normal microbiota inhabit the host and provide numerous nutritional, developmental, immunological, and even psychological benefits.

The Centers for Disease Control and Prevention (CDC) publishes a weekly report that discusses current outbreaks, statistics, and other health topics. If you wanted to know how many people died from the influenza virus in the past week, which section of this report would provide this information?

Mortality is a measure of how many patients have died from a disease.

In 1884, Yong Ding was a 38-year-old male who worked as a cook in Canton, in southern China. Life was hard, but he still managed to support his family. As he walked to his restaurant each day, he barely noticed the small bands of rats scurrying through the streets. Disease was rampant that year; victims of the Shuyi (rat epidemic) were stacked like firewood in the streets, five bodies high in places, waiting to be taken for burial. Yong Ding knew that the disease started as a swollen gland in the armpit and often had a black appearance (now called a bubo). He checked himself daily for these swellings and, seeing none, always felt relief. Then, one morning, he found one. Within days, Yong Ding began coughing blood as the agent (a mystery at the time) spread though his bloodstream to his lungs. Once that happened, he knew death was not far behind. Within weeks, more than 60,000 people died this way in Canton -- victims of what would be called the Third Pandemic of bubonic plague. Yong Ding's body was one of many lining the street that year. PART 1: More than 60,000 people died from the Third Pandemic of bubonic plague. Where does the name "bubonic" come from? PART 2: What does the term "pandemic" mean? PART 3: Some of the major microorganisms known to have caused pandemics are influenza, Yersinia pestis (bubonic plague), and HIV. Which of the following are reasons why more microbes don't cause pandemics?

PART 1: The swollen lymph node Swollen lymph nodes in the groin and armpit are called "buboes" and can turn a dark color when infected with the plague. PART 2: A worldwide epidemic The term "pan" means "across." PART 3: The agent must require a relatively low infectious dose to cause disease. The organism must be easily transmitted from person to person. Microbes that cause pandemics must have a low infectious dose so that only a few microbes are needed to cause disease. Also, the organism must be easily transmitted from person to person, because humans come in contact mostly with other humans.

What are pathogenic microbes like Shigella flexneri, which causes bacillary dysentery in healthy people, called?

Primary pathogens like Shigella can cause disease in healthy people.

Consider the image shown below. A strain of Listeria monocytogenes that has lost the ability to polymerize actin (perhaps through a mutation in the responsible gene, ActA) would most likely be unable to do which?

Spread from the initial site of infection Listeria monocytogenes produces a pore-forming toxin that it uses to escape host vacuoles. Its actin assembly-inducing protein (ActA) then polymerizes cytoplasmic actin to move through the cytoplasm and into adjacent cells. Accordingly, ActA mutants are restricted to the initial cell they infect. Several other intracellular bacterial pathogens, including Rickettsia and Shigella (the causative agents of Rocky Mountain spotted fever and shigellosis, respectively) also spread among cells using actin-based motility.

Which of the following describes the convalescence phase of an infection?

Symptoms are gone and the patient is recovering. The patient will begin to recover normal health during the convalescent phase.

Which of the following statements are true about the COVID-19 pandemic?

The COVID-19 reservoir is thought to be a bat.

While monitoring the presence of an infectious agent in a population, a clinical microbiologist notices the appearance of a new mutant strain that is associated with increased virulence. Therefore, the researcher decides to measure the LD50 of the mutant strain. Based on the initial observation of increased virulence, what would the researcher expect to see?

The LD50 is decreased. A lower LD50 means that a smaller amount of pathogen is needed to result in death in half of the recipients infected with that pathogen, indicating increased virulence.

Doorknobs, shared utensils, and computer keyboards have the potential to harbor common cold viruses. Under which of the following disease transmission categories does this fall?

Vehicle transmission is a form of indirect transmission whereby an infectious agent is transferred to an inanimate object.