Unit 4 Study Guide: Infectious Diseases of Major Body Systems

Diseases of the Cardiovascular System

Normal Biota

The cardiovascular system is typically a sterile environment, meaning it does not have a normal resident microbiota. However, transient microbes can enter the bloodstream through minor injuries or medical procedures.

• Transient Bacteremia: Temporary presence of bacteria in the blood, often cleared by the immune system.

• Clinical Relevance: Persistent presence of microbes can lead to serious systemic infections.

Systemic Infections

Systemic infections involve the spread of pathogens throughout the body, often via the bloodstream.

• Viremia: Presence of viruses in the blood.

• Bacteremia: Presence of bacteria in the blood.

• Septicemia: Active multiplication of pathogens in the blood, leading to systemic inflammation.

• Septic Shock: A severe, life-threatening response to infection causing dangerously low blood pressure and organ dysfunction.

• Example: Gram-negative bacteria can release endotoxins, triggering septic shock.

Protozoal Disease: Malaria

Malaria is a protozoan disease caused by Plasmodium species, transmitted by the bite of infected Anopheles mosquitoes.

• Symptoms: Cyclic fevers, chills, anemia, and splenomegaly.

• Life Cycle: Involves both human and mosquito hosts.

• Prevention: Mosquito control, prophylactic antimalarial drugs.

Bacterial Diseases

• Bubonic Plague: Caused by Yersinia pestis, transmitted by flea bites; symptoms include swollen lymph nodes (buboes), fever, and possible progression to septicemia.

• Anthrax: Caused by Bacillus anthracis; can be cutaneous, inhalational, or gastrointestinal; characterized by black eschar (cutaneous), severe respiratory distress (inhalational).

• Rocky Mountain Spotted Fever: Caused by Rickettsia rickettsii, transmitted by ticks; symptoms include fever, headache, and a characteristic spotted rash.

• Lyme Disease: Caused by Borrelia burgdorferi, transmitted by Ixodes ticks; early sign is erythema migrans (bull's-eye rash), followed by joint, cardiac, and neurological complications.

Viral Diseases

• HIV (Human Immunodeficiency Virus): Causes AIDS; attacks CD4+ T cells, leading to immunodeficiency.

• Ebola and Marburg: Filoviruses causing hemorrhagic fevers; symptoms include severe bleeding, organ failure, and high mortality rates.

• Dengue Fever: Flavivirus transmitted by Aedes mosquitoes; symptoms include high fever, severe joint pain, and risk of hemorrhagic complications.

Diseases of the Respiratory System

Normal Biota

The upper respiratory tract harbors a diverse normal microbiota, including Streptococcus, Staphylococcus, Corynebacterium, and others. The lower respiratory tract is generally sterile.

• Role: Normal biota can prevent colonization by pathogens through microbial antagonism.

Pharyngitis: Streptococcus pyogenes

• Cause: Group A Streptococcus (GAS).

• Symptoms: Sore throat, fever, tonsillar exudates, and possible complications like rheumatic fever.

• Diagnosis: Rapid strep test, throat culture.

Colds, Otitis Media, and Diphtheria (Upper Respiratory Tract)

• Common Cold: Usually caused by rhinoviruses; symptoms include runny nose, sneezing, and mild fever.

• Otitis Media: Middle ear infection, often following upper respiratory infections; common pathogens include Streptococcus pneumoniae and Haemophilus influenzae.

• Diphtheria: Caused by Corynebacterium diphtheriae; produces a pseudomembrane in the throat and can cause airway obstruction.

Influenza, RSV, Pertussis (Upper and Lower Respiratory Tract)

• Influenza: Caused by influenza viruses A, B, and C; symptoms include fever, cough, and myalgia; risk of secondary bacterial pneumonia.

• RSV (Respiratory Syncytial Virus): Major cause of bronchiolitis and pneumonia in infants and young children.

• Pertussis (Whooping Cough): Caused by Bordetella pertussis; characterized by severe coughing fits followed by a "whoop" sound.

Tuberculosis & Pneumonia (Lower Respiratory Tract)

• Tuberculosis: Caused by Mycobacterium tuberculosis; chronic cough, weight loss, night sweats; diagnosed by acid-fast staining and chest X-ray.

• Pneumonia: Inflammation of the lung parenchyma; can be caused by bacteria (e.g., Streptococcus pneumoniae), viruses, or fungi.

Diseases of the Gastrointestinal Tract

Normal Biota and GALT

The GI tract contains a vast and diverse microbiota, especially in the colon. The Gut-Associated Lymphoid Tissue (GALT) is an important immune component that protects against pathogens.

• Functions: Digestion, vitamin synthesis, immune modulation, and pathogen exclusion.

Bacterial Diarrheal Illnesses

• Salmonella: Causes gastroenteritis; symptoms include diarrhea, fever, and abdominal cramps.

• Shigella: Causes shigellosis; characterized by bloody diarrhea (dysentery).

• E. coli: Various strains cause different illnesses; EHEC (O157:H7) can cause hemorrhagic colitis and hemolytic uremic syndrome.

• Clostridium and Vibrio: Clostridium difficile causes antibiotic-associated colitis; Vibrio cholerae causes cholera with profuse watery diarrhea.

Viral Diarrheal Illnesses

• Rotavirus: Leading cause of severe diarrhea in infants and young children.

• Norovirus: Common cause of outbreaks of gastroenteritis in adults; highly contagious.

Food Intoxication

• Staphylococcus aureus: Produces heat-stable enterotoxins; rapid onset vomiting and diarrhea.

• Bacillus cereus: Causes emetic (vomiting) and diarrheal syndromes via different toxins.

• Clostridium perfringens: Causes foodborne illness with abdominal cramps and diarrhea.

Other Diseases

• Hepatitis (Viral): Inflammation of the liver; caused by hepatitis viruses A, B, C, D, and E.

• Entamoeba (Protozoal): Entamoeba histolytica causes amoebic dysentery.

• Helminths: Ascaris lumbricoides (roundworm) and Enterobius vermicularis (pinworm) are common intestinal parasites.

Diseases of the Genitourinary Tract

Normal Flora

The genitourinary tract has a normal microbiota, especially in the distal urethra and vagina. Lactobacillus species dominate the healthy vaginal flora, maintaining acidic pH.

UTIs and Vaginitis

• UTIs (Urinary Tract Infections): Most commonly caused by Escherichia coli; symptoms include dysuria, frequency, and urgency.

• Vaginitis: Inflammation of the vagina, often due to Candida albicans (yeast) or Gardnerella vaginalis (bacterial vaginosis).

Leptospirosis

• Cause: Leptospira interrogans, a spirochete bacterium.

• Transmission: Contact with water contaminated by animal urine.

• Symptoms: Fever, muscle aches, jaundice, and in severe cases, kidney or liver failure.

Sexually Transmitted Diseases (STDs)

• Gonorrhea: Caused by Neisseria gonorrhoeae; symptoms include urethritis, cervicitis, and possible pelvic inflammatory disease.

• Syphilis: Caused by Treponema pallidum; progresses through primary (chancre), secondary (rash), and tertiary (gummas) stages.

• Herpes: Caused by herpes simplex virus (HSV-1 and HSV-2); characterized by painful genital ulcers.

• HPV (Human Papillomavirus): Causes genital warts and is associated with cervical cancer.

Strep B Infection in Neonates

• Cause: Streptococcus agalactiae (Group B Strep).

• Transmission: From mother to baby during childbirth.

• Symptoms in Neonates: Sepsis, pneumonia, and meningitis.

HIV and Hepatitis B & C as STDs

• HIV: Can be transmitted sexually; leads to immunodeficiency.

• Hepatitis B and C: Both can be transmitted via sexual contact; cause chronic liver disease.

Additional info: This guide summarizes key infectious diseases affecting the cardiovascular, respiratory, gastrointestinal, and genitourinary systems, as outlined in the provided study materials. For each disease, students should be familiar with causative agents, transmission, symptoms, and prevention where applicable.