Biology of Disease

3.12 Summary

Pathogenic microorganisms cause clinical conditions from infections of
single organs or systems to systemic disease. Infections of the skin may be
caused by viruses, such as papilloma and Herpes simplex types. Skin bacteria
cause boils and abscesses and severe and chronic conditions such as leprosy.
Fungi also cause a variety of skin infections, although these are not usually
severe, unless the patient is immunocompromized. Severe infections of the
eye include trachoma, a chlamydial disease that is the most common eye
infection worldwide. Helminths, such as Toxocara canis can cause blindness.
Viruses and bacteria may cause painful ear infections which, if recurrent,
may damage hearing. Both groups of organisms are capable of infecting
the CNS, sometimes resulting in encephalomyelitis by Herpes simplex or
meningitis by Neisseria menigitidis. A number of viruses and bacteria cause
significant respiratory infections, some of which, for example TB, are chronic.
All varieties of microorganisms can infect the GIT, causing illnesses ranging
from short-term gastroenteritis to stomach ulcers. An extensive number of
microorganisms can infect the genital tract or are transmitted sexually. Several
may cause systemic diseases.

The diagnosis of infectious disease involves a combination of laboratory tests
to identify the microorganism present in specimens typically by culturing
them. However, the presence of antibodies to the organisms in the patient may
be used for identification and to compare levels in acute and convalescent
patients. An increasing number of biochemical and molecular biological
techniques have been introduced, many of which rely on identifying bacterial
or viral nucleic acid in clinical specimens.

Infectious disease may be prevented by vaccination and public health measures
or treatment with drugs. Depending on the infectious agent, these may be
antiviral, antibacterial (antibiotics), antifungal or anthelminthic. Drugs may
be given singly, or in combinations, as, for example, in the treatment of HIV
patients.

QUESTIONS

1. Briefly review the causes of infections associated with the genital
   tract.


2. List some of the methods used in the diagnosis of infectious diseases.


3. A 19-year-old student attended a barbecue to celebrate his brother’s
   21st birthday. He ate a very rare steak. Two days late he began to
   experience pains on defecation, and to suffer from persistent diarrhea
   that rapidly increased in frequency and produced bloody stools. What
   is the student suffering from? Suggest how this condition should be
   treated.


4. ExamineFigure 3.27. To which antibiotics is this strain of Escherichia
   coli resistant?


5. Compare and contrast the actions of griseofulvin and albendazole.


6. In what ways may antibiotics prevent the growth of bacterial
   pathogens?


7. In two words state a major way of delaying the development of
   antidrug resistance in pathogens.

SUMMARY

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