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Chapter 26
Infectious
Diseases
a LANGE medical book
Pathophysiology
of Disease
An Introduction
to Clinical Medicine
Seventh Edition
CHAPTER 4
Infectious Diseases
Infection and the
Body’s Defense Mechanisms
• There are several microorganisms that live on
and in the human body that do not produce
signs of illness
• Referred to as indigenous flora, these bacteria
can also be helpful
• Pathogens are microorganisms that produce
signs of illness
Infection and the
Body’s Defense Mechanisms
• The innate immune system
– Structural barriers
• Skin and mucous membranes
– Inflammatory response
• The acquired immune system
– Humoral system
– Cellular immune system
– Immunization
Most Frequent and Serious Problems
• Bacterial Infections
– Secondary infections, sexually transmitted
infections
• Viral Infections
– Upper respiratory illnesses
– Gastroenteritis
– Cold sores
– HIV
Most Frequent and Serious Problems
• Rickettsial Infections
– Rocky Mountain Spotted Fever
• Fungal Infections
– Candida
Most Frequent and Serious Problems
• Protozoal Infections
– Malaria
• Helminth Infections
– Roundworms
Symptoms, Signs, and Tests
• Rapid onset of muscle aches, fatigue, fever,
malaise
• Physical exam
– Many lesions are characteristic enough to
be diagnostic
Symptoms, Signs, and Tests
• Laboratory testing
– Culture: most commonly used for bacteria
• Once the bacteria is identified, it is tested
for susceptibility to various antibiotics
– Gram stains
• Allow for an “educated guess” about
antibiotic coverage while waiting for the
organism to be identified
Specific Diseases
• Staphylococcal Infections
– S. aureus can develop into Methicillin
Resistant S. aureus and cause serious illness
in some patients
Specific Diseases
• Group A Streptococcal Infections
– Strep A is the most virulent, and common in
upper respiratory infections
– Scarlet fever
– Necrotizing fascitis
Specific Diseases
• Streptococcus pneumoniae
– Common cause of pneumonia
• Neisseria meningitidis
– Meningococcal Menigitis
Specific Diseases
• Haemophilus influenzae
– Common cause of ear infections and
sinusitis
– Other serious illnesses caused by this
bacteria have been eliminated through
immunization
Specific Diseases
• Legionellosis
– Gram negative bacteria that thrives in water
reservoirs and cooling towers
– A common cause of community acquired
pneumonia
Specific Diseases
• Nonfastidious Gram-Negative Rods
– Enteric bacteria
– When these bacteria cause sepsis, they
often lead to septic shock with a mortality
rate of up to 50%
Specific Diseases
• Anaerobic Bacteria
– Bacteria that grow with little oxygen
• Sexually Transmitted Infections
Specific Diseases
• Anaerobic Bacteria
– Bacteria that grow with little oxygen
• Sexually Transmitted Infections
Specific Diseases
• Bacterial Infections Mediated by Exotoxins
– Clostridium Family
• Tetani (tetanus)
• Botulinum (botulism)
• Difficile (entercolitis, not exotoxin
mediated)
• Perfringens (gas gangrene)
– Diptheria
Specific Diseases
• Bordetella pertussis (whooping cough)
– Not as prevalent in young children due to
immunization, though resurgence in older
children and adults suggests the vaccine
needs to be re-administered
Specific Diseases
• Mycoplasma Disease
– Common cause of atypical pneumonia
• Lyme Disease
– Tick borne disease
Specific Diseases
• Plague
• Tularemia
• Brucellosis
• Leprosy
Specific Diseases
• Viral Infections
– Do not respond to antibiotic therapy and
are best treated with supportive
mechanisms
– Few anti-viral medications are available to
decrease the duration of illness
– Immunization has decreased the number of
viral infections
Specific Diseases
• Measles, Mumps, Rubella, and Varicella
– Young children are immunized against these
with one vaccine (MMRV)
• Smallpox
– No longer found in the U.S. due to
successful vaccination
Specific Diseases
• Influenza A
– Causes wide-spread respiratory disease
yearly
• Mononucleosis
– Epstein-Barr Virus
Specific Diseases
• Herpes Simplex
– Type I—mostly oral lesions “cold sores”
– Type II—genital lesions
• Human Papillomavirus
– Some strains associated with the
development of cervical cancer
Specific Diseases
• Cytomegalovirus
• Human Immunodeficiency Virus
– Causes AIDS
• Rickettsial Infections
Specific Diseases
• Protozoal Disease
– Malaria
– Toxoplasmosis
– Cryptosporidiosis
• Helminthic Infections
– Various “worms”
– Trichinosis