Essentials of Anatomy and Physiology

524 An Introduction to Microbiology and Human Disease

Table 22–8 ARTHROPOD VECTORS

Arthropod Disease (Type of Pathogen)*

Mosquito

Flea

Body louse

Tick

Tsetse fly

Deer fly,

horse fly

*These diseases are described in previous tables.

Malaria (protozoan)

Encephalitis (virus)

Yellow fever (virus)

Plague (bacterium)

Endemic typhus (rickettsia)

Epidemic typhus (rickettsia)

Tularemia (bacterium)

Relapsing fever (bacterium)

Lyme disease (bacterium)

Rocky Mountain spotted fever (rickettsia)

Tularemia (bacterium)

African sleeping sickness (protozoan)

Tularemia (bacterium)

Classification of Microorganisms

1. Bacteria—unicellular; some are pathogens.


2. Viruses—not cells; all are parasites.


3. Protozoa—unicellular animals; some are pathogens.


4. Fungi—unicellular (yeasts) or multicellular
   (molds); most are decomposers.


5. Worms—multicellular animals; a few are parasites.


6. Arthropods—insects, ticks, or mites that are vec-
   tors of disease or cause infestations.

• Binomial nomenclature—the genus and species
  names.

Normal Flora—see Table 22–1

1. Resident flora—the microorganisms that live on or
   in nearly everyone, in specific body sites; cause no
   harm when in their usual sites.


2. Transient flora—the microorganisms that periodi-
   cally inhabit the body and usually cause no harm
   unless the host’s resistance is lowered.

Infectious Disease

1. Caused by microorganisms or their toxins.


2. Clinical infections are characterized by symptoms;
   in a subclinical infection, the person shows no
   symptoms.
   3. Course of an infectious disease: Incubation
   period—the time between the entry of the
   pathogen and the onset of symptoms. The acme is
   the worst stage of the disease, followed by recovery
   or death. A self-limiting disease typically lasts a cer-
   tain period of time and is followed by recovery.
   4. Types of Infection
   
   
   • Localized—the pathogen is in one area of the
     body.
   
   
   • Systemic—the pathogen is spread throughout
     the body by the blood or lymph.
   
   
   • Septicemia (bacteremia)—bacteria in the blood.
   
   
   • Acute—usually severe or of abrupt onset.
   
   
   • Chronic—progresses slowly or is prolonged.
   
   
   • Secondary—made possible by a primary infec-
     tion that lowered host resistance.
   
   
   • Nosocomial—a hospital-acquired infection.
   
   
   • Endogenous—caused by the person’s own nor-
     mal flora in an abnormal site.
   
   
   
   

Epidemiology—see Fig. 22–1

1. The study of the patterns and spread of disease.


2. Portal of entry—the way a pathogen enters a
   host.


3. Portal of exit—the way a pathogen leaves a host.

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