Reference no: EM132434978

Assignment -

1. Distinguish among helical, polyhedral, enveloped, and complex viruses, and provide one example of each.

2. The following questions pertain to viruses and infectivity:

a. Draw a simple diagram of a bacteriophage, and label the capsid, sheath, nucleic acid, baseplate, and tail fibres.

b. A scientist wanted to test the infectivity of two new bacteriophages (phages) on a strain of E. coli. In doing so, the scientist mixed a sample of the organisms together with each phage and distributed the samples in molten agar after incubating the mixtures for a period of up to three hours. Table 1 describes the results obtained.

i. Draw a clearly labelled and titled graph comparing each sample for each time point given.

ii. Compare the effectiveness of each of the phages used.

iii. Explain why scientists use phages in their research studies.

TABLE 1. Infectivity of phage A and phage B on E. coli over time, represented in plaque-forming units per ml.

Time (hours)	Phage A (pfu/ml)	Phage B (pfu/ml)
1	40	2
2	120	30
3	300	40

3. Outline the major steps involved in the multiplication of Poxviridae.

4. A patient was admitted to hospital with a high fever (40^oC), a headache, and diarrhea. He informed the doctor that he had returned from travelling abroad two weeks earlier. Microbiological examinations indicated that the patient was infected with a species of Salmonella. During the course of hospitalization, the patient was treated with a quinalone antibiotic and the numbers of organisms in the blood were monitored. The graph below shows the infectivity curve. The values shown on this curve are the numbers of organisms/ml over the course of the illness.

a. Use your knowledge of the disease process, the epidemiology, and the information provided to describe the stages of this disease.

b. Identify the disease and the causative agent in this case. Suggest the possible source of this infection and how this illness could have been prevented.

5. Column A lists terms related to epidemiology and diseases. Column B lists descriptions and definitions. For each term listed in Column A, select the answer from Column B.

Column A	Column B
___ pandemic disease	a. early symptoms of infection
___ septicemia	b. symptoms
___ nosocomial infection	c. world-wide effects
___ prodromal period	d. cause of disease
___ acute disease	e. afflicts large numbers of people
___ epidemic disease	f. causes fever
___ pathology of disease	g. non-communicable disease
___ incidence	h. infection that lasts for a brief period
___ etiology of disease	i. hospital-acquired
___ not spread from one host to another	j. number of people infected during a particular time period

6. Foot-and-mouth disease (FMD) is a life-threatening disease of unvaccinated livestock. In a study of this disease, unvaccinated cows were treated with one of five concentrations of viral particle in suspension. Each treatment was administered to 20 cows; 10 received a liquid suspension injected into the tongue, and another 10 received an aerosol suspension. The results of this study are summarized in Table 2.

a. Describe the virulence of this organism by expressing the infectious dose of each mode of inoculation.

b. Compare the results of the two experimental procedures.

c. How would the researchers use the same experimental procedure to test the lethal dose of these organisms?

d. Describe an experiment to test the effects of a vaccine of FMDV.

TABLE 2. Number of infected cows following injection or aerosol administration of Foot-and-Mouth Disease Virus (FMDV).

Concentration (viral particles/ml)	Number of cows infected by injection	Number of cows infected by aerosol
0	0	0
103	2	0
104	5	1
105	7	3
106	10	5

7. Fill in the table below pertaining to microbial mechanisms of pathogenicity.

Virulence Factor	Function or Effect on the Host	Example of a Bacterium that Produces it	Benefit for the Bacterium
Adhesin
Capsule
M protein
Hyaluronidase
Exotoxin

8. Define innate immunity and describe the role of mucous membranes in innate immunity.

9. How does fever contribute to non-specific defense?

10. Where is the complement system found? If a person had a deficiency in any of the complement proteins C5b through C9, what would they be unable to form and what would be the result? From what bacterial species would this person be more likely to develop infections?

11. Draw a diagram of a typical antibody molecule, and indicate the following: heavy chain, light chain, Fc region, variable region, and antigen binding site.

12. Illustrate and explain how a virus-infected cell is killed by a cytotoxic T lymphocyte.

13. Define autoimmune disease and give an example of an autoimmune disease.