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  • Identify two locations where you would likely find an ICD code.

Part 2

David’s doctor was concerned that his symptoms included prickling and itching at the site of the dog bite; these sensations could be early symptoms of rabies. Several tests are available to diagnose rabies in live patients, but no single antemortem test is adequate. The doctor decided to take samples of David’s blood, saliva, and skin for testing. The skin sample was taken from the nape of the neck (posterior side of the neck near the hairline). It was about 6-mm long and contained at least 10 hair follicles, including the superficial cutaneous nerve. An immunofluorescent staining technique was used on the skin biopsy specimen to detect rabies antibodies in the cutaneous nerves at the base of the hair follicles. A test was also performed on a serum sample from David’s blood to determine whether any antibodies for the rabies virus had been produced.

Meanwhile, the saliva sample was used for reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, a test that can detect the presence of viral nucleic acid (RNA). The blood tests came back positive for the presence of rabies virus antigen, prompting David’s doctor to prescribe prophylactic treatment. David is given a series of intramuscular injections of human rabies immunoglobulin along with a series of rabies vaccines.

  • Why does the immunofluorescent technique look for rabies antibodies rather than the rabies virus itself?
  • If David has contracted rabies, what is his prognosis?

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Key concepts and summary

  • Viruses are generally ultramicroscopic, typically from 20 nm to 900 nm in length. Some large viruses have been found.
  • Virions are acellular and consist of a nucleic acid, DNA or RNA, but not both, surrounded by a protein capsid . There may also be a phospholipid membrane surrounding the capsid.
  • Viruses are obligate intracellular parasites.
  • Viruses are known to infect various types of cells found in plants, animals, fungi, protists, bacteria, and archaea. Viruses typically have limited host ranges and infect specific cell types.
  • Viruses may have helical , polyhedral, or complex shapes.
  • Classification of viruses is based on morphology, type of nucleic acid, host range, cell specificity, and enzymes carried within the virion.
  • Like other diseases, viral diseases are classified using ICD codes.

True/false

True or False: Scientists have identified viruses that are able to infect fungal cells.

True

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Fill in the blank

A virus that infects a bacterium is called a/an ___________________.

bacteriophage

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A/an __________ virus possesses characteristics of both a polyhedral and helical virus.

complex

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A virus containing only nucleic acid and a capsid is called a/an ___________________ virus or __________________ virus.

naked or nonenveloped

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The ____________ _____________ on the bacteriophage allow for binding to the bacterial cell.

tail fibers

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Short answer

Discuss the geometric differences among helical, polyhedral, and complex viruses.

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What was the meaning of the word “virus” in the 1880s and why was it used to describe the cause of tobacco mosaic disease?

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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