Chapter 26Infectious Diseases

Pathophysiologyof Disease

An Introduction to Clinical Medicine

Seventh Edition

a LANGE medical book

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