Clinical Microbiology HW#5

Chapter 14

1. One effect of washing regularly with antibacterial agents is the removal of normal microbiota. This can result in

Increased susceptibility to disease

2. During a six-month period, 239 cases of pneumonia occurred in a town of 300 people. A clinical case was defined as fever 39°C lasting >2 days with three or more symptoms (i.e., chills, sweats, severe headache, cough, aching muscles/joints, fatigue, or feeling ill). A laboratory-confirmed case was defined as a positive result for antibodies against Coxiella burnetii. Before the outbreak, 2000 sheep were kept northwest of the town. Of the 20 sheep tested from the flock, 15 were positive for C. burnetii antibodies. Wind blew from the northwest, and rainfall was 0.5 cm compared with 7 to 10 cm during each of the previous three years.
 

The etiologic agent of the disease in the situation is

Coxiella burnetii

3. Transient microbiota differ from normal microbiota in that transient microbiota

Are present for a relatively short time

4. Which of the following definitions is INCORRECT?

Epidemic: a disease that is endemic across the world

**TRUE:

incidence: number of new cases of a disease

sporadic: a disease that affects a population occasionally

endemic: a disease that is constantly present in a population

pandemic: a disease that affects a large number of people in the world in a short time

5. The rise in herd immunity amongst a population can directly attributed to

Vaccinations

6. Which of the following is NOT a communicable diseases?

Tetanus

**Communicable disease: tuberculosis, malaria, typhoid fever, AIDS

7. A disease in which the causative agent remains inactive for a time before producing symptoms is referred to as

Latent

8. Which of the following is NOT a reservoir of infection?

None of the answers is correct; all of these can be reservoirs of infection.

**Reservoirs of infection: sick animal, healthy person, hospital, sick person

9. A cold transmitted by a facial tissue is an example of which form of disease transmission?

Indirect contact transmission

10. Which one of the following is NOT a zoonosis?

None of the answers is correct; all of these are zoonoses

**Zoonosis: tapeworm; Hantavirus pulmonary syndrome; rabies; cat-scratch disease

Microbiology Animation: Nosocomial Infections: Overview

1. According to the animation, surgical infections account for what percentage of nosocomial infections?

20%

2. What type of nosocomial infection is likely to arise from intravenous catheterizations?

Bacteremia

3. How might a patient who is not being treated with an antibiotic still be exposed to an antibiotic?

Antibiotics can be used in aerosols, thereby entering the environment.

4. Why are invasive procedures likely to increase the risk of nosocomial infections?

These procedures allow microbes from the skin to enter the bloodstream of the patient.

5. How can health care workers reduce the occurrence of nosocomial infections?

Practice more stringent aseptic techniques

Chapter 14

1. Which of the following does NOT contribute to the emergence of infectious diseases?

The emergence of infectious diseases can be attributed to all of these

**The emergence of infectious diseases can be attributed to all of these:

Antibiotic resistance

Climatic changes

New strains of previously known agents

Ease of travel

Microbiology Animation: Epidemiology: Occurrence of Diseases

1. Expected prevalence of a disease is

the expected occurrence of a disease based on past observations

2. In the sixth segment of the animation, why is the disease epidemic in North America?

The disease occurs at a higher rate than what would normally be expected in this region.

3. In the last segment of the animation, how many regions of the world experience the pandemic during April of year four?

Five

4. In the last segment of the animation, when does the first epidemic occur?

January of year three

5. If a disease occurs at a fairly stable rate, it is said to be

Endemic

Chapter 14

1. The science that deals with when diseases occur and how they are transmitted is called

Epidemiology

2. Both normal and transient flora can become opportunistic pathogens

TRUE

3. MMWR is a publication by the CDC that reports on only emerging diseases

FALSE

4. For a particular disease at a specific time period, morbidity rates should always be equal or greater than mortality rates.

TRUE

Chapter 14 – Reading Questions

1. Malaria is an infectious disease caused by infection with a protozoan. In certain tropical regions, malaria is constantly present. We would say that malaria is a(n) _________ disease in these regions.

Endemic

2. As a health care worker, I am keenly aware of how important it is to avoid harming my patients. I worry about inadvertently transmitting an infectious disease to an already compromised individual. According to the CDC, what is the MOST important thing I can do to avoid this?

Wash my hands before interacting with any patient

Don’t Be in Denial, It’s Just West Nile

Dr. William Stevens is discussing West Nile virus with his microbiology class. He tells them of a personal experience he had with the virus as a graduate student.

The year was 2003. Bill was a 24-year-old graduate student attending his first virology class. His instructor, Dr. Donaldson, informed the class that their lab project for the semester was to attempt to isolate West Nile virus from birds obtained on the campus grounds. Recently, there had been an increase in the number of West Nile virus (WNV) cases reported in the local community. Campus security had found two dead crows and a dead blue jay on university property. They brought the birds to Dr. Donaldson, who preserved them by placing them in freezer in the science building. *If this had happened today, the birds would have been given to the local health department, and the students would not have access to them because West Nile virus is a Centers for Disease Control and Prevention (CDC) reportable infectious disease.*

Before actually working with the specimens, the students were required to research West Nile virus. Bill found out that West Nile virus was first identified in 1937 in the West Nile district of Uganda. It made its first appearance in the United States in 1999 in New York City. He found that the virus is an arbovirus, with a high mortality rate in infected crows, ravens, and blue jays. Most human infections are subclinical and do not result in a noticeable illness, however in immunosuppressed individuals, the disease can progress to a variety of neurological effects, the most severe of which is fatal encephalitis. The CDC considers West Nile virus to be an emerging infectious disease. Image A shows a transmission electron micrograph of the West Nile virus.

The students were instructed to wear gloves, aprons, and goggles while working with the birds. All work was performed in a biological safety cabinet (a hood) within a negative-pressure room. The students took every possible precaution to ensure that the samples did not transmit the infection to anyone.

1. Which of the following best describes why West Nile Virus is considered to be an emerging infectious disease?

West Nile virus outbreaks have increased in number and affected areas since 1937

**West Nile virus was originally identified in 1937, when it caused a significant outbreak in Uganda. Following this initial outbreak, only minor occurrences in Egypt and Israel had been observed until 1999, when the virus reappeared with a significant outbreak in New York City. This appearance was important because it was the first time West Nile virus had been observed in the United States. Since then, West Nile virus has been declared an important pathogen to public health officials and those involved in veterinary medicine. In fact, in 2009, the CDC declared West Nile virus to be endemic in the United States.

2. During his research on West Nile virus, Bill learned that this virus is placed within a functional grouping known as arboviruses. What is meant by the term arbovirus?

An arbovirus is an arthropod-borne virus.

An arbovirus is maintained in nature through biological transmission.

**Arboviruses get their name because they are typically arthropod-borne viruses that remain in nature because of biological transmission between susceptible hosts by blood-feeding arthropods, such as mosquitoes.

3. If mosquitoes are the mode of transmission for West Nile virus, why did the students in Bill’s virology class focus on finding the virus in the dead birds rather than collecting mosquitoes to examine?

The students tried to isolate and identify West Nile virus from birds because they are an amplifying host for the virus, making it more likely that the virus can be isolated from these animals.

**The students tried to isolate and identify the West Nile virus from the birds because there is a high probability that the birds were infected with the virus. Birds are considered to be an amplifying host for the West Nile virus, which means that the number of viral particles is increased dramatically within this host. Although house sparrows seem to be tolerant of this amplification process, studies had shown that crows and blue jays, both of which were specimens, were susceptible to death from this virus.

4. Dr. Stevens continues telling his story to his students.

The brain tissue of two of the birds was intact, with some indication of encephalitis, so it was used in a commercial reverse transcriptase polymerase chain reaction (RT-PCR) kit to verify the presence of West Nile viral RNA. This kit utilizes an enzyme known as reverse transcriptase, which transcribes RNA into DNA, along with PCR, to amplify any virus RNA that might be found in the brain tissue. RT-PCR results for both the crow and the blue jay were positive for West Nile virus. Other possible detection techniques would involve testing blood or tissues for the presence of antibodies against the West Nile virus.

The brain tissue of the birds indicated the possibility of encephalitis. What is encephalitis, and why should this type of infection cause concern among health care professionals?

Encephalitis is an inflammation of the brain tissue. It is a concern to health care professionals because an infection in the brain means the virus has breached protective measures.

**Encephalitis is an inflammation of the brain tissue. It is a concern to health care professionals because an infection in the brain means the virus has breached protective measures of the blood-brain barrier. Brain infections are serious because many are fatal because it is difficult to treat them with antimicrobials. Antimicrobials must be lipid-soluble in order to cross the blood-brain barrier. There is an exception, however. In some infections of the brain, the inflammation alters the permeability of the blood-brain barrier and may allow some antimicrobials to cross that would not be able to cross if the infection were not present.

5. Dr. Stevens continues his story.

Dr. Donaldson discussed the details of West Nile virus infection with his class. They discussed how it is transmitted via arthropods, the infections it causes in its respective hosts, the difficulty in treating nervous system infections, and necessity to develop a vaccine for West Nile virus. The class determined that preventing the infection was the best route of action until a vaccine could be developed.

Which of the following is the best mode of controlling the spread of West Nile infections?

Limit exposure to mosquitoes to prevent the transmission of West Nile virus

**The best way to prevent West Nile virus infections is to limit exposure to the mosquitoes. This can be accomplished by using bug sprays, by staying indoors during times when mosquitoes are out (particularly in the summer months), and by wearing protective clothing outdoors if mosquitoes are present. Another preventative measure is to eliminate sources of water, especially stagnant water, where mosquitoes lay their eggs. This will help to decrease mosquito populations, reduce the possibility of exposure to the mosquito, and as a result limit the chance of infection with West Nile virus.

6. What features of West Nile virus make it an emerging disease of special concern?

West Nile virus is an arthropod-borne virus transmitted by mosquitoes.

West Nile virus has a high mortality rate in immunosuppressed humans and infects many species of birds in southern Europe, the Mediterranean basin, and North America.

West Nile virus is maintained in nature through biological transmission between susceptible hosts by blood-feeding arthropods.

**Emerging infectious diseases are defined as ones that are new or changing, have increased in incidence in the recent past, or show a potential to increase in the near future. Given the increase in number of cases of West Nile virus encephalitis and avian death since it appeared in New York City in 1999, this virus meets the definition of an emerging infectious disease. Over half of known emerging infectious diseases are zoonotic, mainly of viral origin, and are likely to be vector-borne. West Nile virus is all of these things, and infections with this virus must be reported to the CDC for tracking. The CDC works along with the National Institutes of Health (NIH) and the World Health Organization (WHO) to address issues related to emerging infectious diseases. Together, these agencies have set goals for investigating, monitoring, and controlling emerging infectious diseases worldwide.