Microbial Diseases of the Cardiovascular, Lymphatic, and Respiratory Systems

Microbial Diseases

Review

• Using key terms in conversation is helpful for retention.
• Example: Someone on the bus rubs their eye, which now feels itchy; this could be conjunctivitis (pink eye) from a bacterial or viral infection, a contagious/communicable disease like trachoma caused by Chlamydia trachomatis, which may require antibiotics.

Cardiovascular and Lymphatic Systems

• Cardiovascular system: Circulates blood, delivering substances to and removing them from cells. Includes the heart, arteries, veins, and capillaries.
• Lymphatic system:
  • Plasma becomes interstitial fluid after leaving blood capillaries.
  • Lymph capillaries transport interstitial fluid (lymph) to lymph vessels (lymphatics) and lymph nodes.
  • Picks up microorganisms and infectious agents.
  • Lymph nodes contain fixed macrophages, B cells, and T cells.
  • Buboes: Swollen lymph nodes.

Cardiovascular System Highlights

• Key anatomical parts: Heart, Veins, Arteries.
• Three tissue layers of the heart:
  • Inner: Endocardium
  • Middle: Myocardium
  • Outer: Pericardium
  • Endothelium: Innermost tissue layer of veins and arteries.

Lymphatic System Highlights

• Fluid leaks from the circulatory system into tissues; the lymphatic system collects and returns this fluid.
• Lymph nodes are primarily located where limbs attach.
• The lymphatic system is a completely closed system, entered through wounds or parenteral entry.

Interconnected System

• The circulatory and lymphatic systems are interconnected, facilitating the transport of fluids, nutrients, and immune cells throughout the body.
• Lymph nodes contain lymphocytes and macrophages for immune surveillance.
• Bacteria should not be present in these systems.

Infections of the Blood

• Septicemia: Acute illness due to pathogens or their toxins in the blood.
• Sepsis: Systemic inflammatory response syndrome (SIRS), the body’s excessive reaction to infection causing full-body inflammation.
  • Damages blood vessels, causing fluid leakage.
  • Gram-positive vs. gram-negative sepsis.
• Lymphangitis: Inflamed lymph vessels.
• Severe sepsis: Decreased blood pressure and dysfunction of at least one organ.
• Septic shock: Advanced sepsis with uncontrollable decreased blood pressure, heart palpitations, and lightheadedness.

Gram-Negative Sepsis

• Also called endotoxin shock.
• Endotoxins (lipopolysaccharides [LPS]) cause a severe drop in blood pressure.
• Klebsiella spp., E. coli, and Pseudomonas aeruginosa are most frequently involved.
• Antibiotics can worsen the condition by killing bacteria and releasing more LPS.
• Treatment involves neutralizing the LPS components and inflammatory cytokines.

Gram-Positive Sepsis

• Potent exotoxins cause toxic shock syndrome.
• Hospital-acquired infections:
  • Enterococcus faecium and Enterococcus faecalis:
    • Inhabit the colon.
    • Colonize wounds and the urinary tract.
    • Resistant to many antibiotics.
  • Group B streptococci (GBS):
    • Streptococcus agalactiae, most common cause of neonatal sepsis.
    • Exposure during birth, mortality rate is 10-20%.
    • Symptoms can present in infants from 6 hours old – 28 days old.
    • One of the leading causes of infant death

Puerperal Sepsis

• Also called puerperal fever and childbirth fever.
• Caused by Streptococcus pyogenes.
• Transmitted to the mother by the environment and attendants.
• A common cause of death for women due to childbirth.
  • Most common are cardiovascular-related conditions and hemorrhaging.
• Infection of the genital tract:
  • Infects the uterus and progresses to an infection of the abdominal cavity, may occur up to 42 days after birth (six weeks).
• Ignaz Semmelweis noted a high mortality rate in women due to puerperal sepsis and established hygienic principles for hospital care.

Bacterial Infections of the Heart

• Endocarditis: Inflammation of the endocardium (inner lining of heart chambers).
  • Subacute bacterial endocarditis: Impairs the function of the heart valves.
    • Alpha-hemolytic streptococci from an oral or tonsil infection.
• Pericarditis: Inflammation of the sac around the heart.
  • Streptococci.

Rheumatic Fever

• An autoimmune complication of S. pyogenes infections.
• Only occurs in untreated GAS infections.
• Inflammation of the heart valves.
• Immune reaction against streptococcal M protein.
• Subcutaneous nodules at the joints.

Tularemia

• Caused by Francisella tularensis (Gram-negative rod).
• Zoonotic disease transmitted from rabbits, ticks, and insects (deer flies).
• Highly infectious and can be used in bioterrorism.
• Bacteria reproduce in phagocytes.
• Enlarges the regional lymph nodes.
• Penetration of skin results in less than 3% mortality; respiratory infection can result in pneumonia with mortality usually <30%.
• Inflammation of air sacs in lungs, may be filled with fluid or pus.

Anthrax

• Infectious disease caused by Bacillus anthracis (Gram-positive, endospore-forming aerobic).
• Occurs naturally in soil, primarily affects grazing animals.
• Bacteria enter the bloodstream and release toxins.
• Contracted by working with infected livestock or animal products.
• Endospores can be weaponized; inhaling them leads to almost 100% mortality.

Key Terms: Effects on Tissue

• Ischemia: Loss of blood supply to tissue.
• Necrosis: Death of tissue.
• Gangrene: Death of soft tissue.
  • Gas gangrene: Caused by Clostridium perfringens (Gram-positive, endospore-forming anaerobic rod).
    • Grows in necrotic tissue.
    • Treatment includes surgical removal of necrotic tissue and/or use of a hyperbaric chamber.

Diseases Transmitted by Bites/Scratches

• Cat Scratch Disease:
  • Caused by Bartonella henselae (Aerobic, Gram-negative).
  • Inhabits cat RBCs; carried in the blood of 50% of cats.
  • Multiplies in the digestive system of cat fleas.
  • Cat claws contaminated with flea feces scratch humans.
  • Forms a papule at the infection site and swollen lymph nodes.
• Rat Bite Fever:
  • Caused by Streptobacillus moniliformis (Filamentous, gram-negative, pleomorphic).
  • Fever, chills, muscle pain; mortality rate of 10%.

Plague

• Contagious bacterial disease characterized by fever and delirium.
• Caused by Yersinia pestis (Gram-negative rod).
• Transmitted by the rat flea (Xenopsylla cheopis).
• Endemic to rats, ground squirrels, and prairie dogs.
• Bacteria blocks the flea’s digestive tract.
• Flea bites the host, and ingested blood is regurgitated into the host.
• Bacteria enter the bloodstream and proliferate in the lymph tissue.
• Cause intense swellings called buboes.

Categories of Plague

• Bubonic plague: Bacterial growth in the blood and lymph.
  • Transmitted by bites.
  • Most common form; 50-75% mortality rate.
• Septicemic plague: Septic shock due to bacteria in the blood.
• Pneumonic plague: Bacteria in the lungs.
  • Easily spread by airborne droplets.
  • Near 100% mortality rate.

Plague Cases

• 1000-2000 cases of plague each year worldwide.
• 30-60% death for bubonic plague.
• Always fatal for pneumonic plague when untreated.
• Antibiotics are effective early on.

Lyme Disease (Lyme Borreliosis)

• Caused by Borrelia burgdorferi (gram negative).
• Most common tickborne disease in the United States.
• Field mice are the most common reservoir.
• Nymphal stage of deer ticks feeds on mice and infects humans.
• Possible to avoid contracting disease if the infected tick is removed within 36-48 hours.
• Most cases are cured within a 2-4 week course of antibiotics.
• Some patients experience post-treatment Lyme disease syndrome:
  • Chronic symptoms of pain, fatigue, and brain fog.

Symptoms of Lyme Disease

• First phase:
  • Bull’s-eye rash; flu-like symptoms.
• Second phase:
  • Irregular heartbeat; encephalitis; facial paralysis; memory loss.
• Third phase:
  • Arthritis due to an immune response.
• Treated with antibiotics.
• More difficult to treat in later stages.

Typhus Disease

• Any disease caused by bacterial Rickettsia spp.
• Obligate intracellular parasites:
  • Infect the endothelial cells of the vascular system.
  • Block and rupture the small blood vessels.
  • Spread by arthropod vectors.

Typhus Disease Types

• Typhus fever (epidemic louseborne typhus):
  • Caused by Rickettsia prowazekii.
  • Carried by the body louse (body lice).
  • Common in unhygienic living conditions.
  • Prolonged fever and a rash of red spots due to subcutaneous hemorrhaging.
  • Can cause more severe reactions that lead to pneumonia, meningitis, or kidney failure.
• Rocky Mountain spotted fever (tickborne typhus):
  • Caused by Rickettsia rickettsii.
  • Spread by wood ticks (Dermacentor andersoni) and dog ticks (Dermacentor variabilis).
  • Measles-like rash, except the rash also appears on the palms and soles.
  • Without early diagnosis, the mortality rate is approximately 20%.
  • Treatment with tetracycline and chloramphenicol.

Viral Infections of the Circulatory/Lymphatic System

• Burkitt’s Lymphoma: Tumor of the jaw; most common childhood cancer in Africa.
  • Due to Epstein-Barr virus (human herpesvirus 4).
  • Malaria suppresses the immune system response to the virus.

Infectious Mononucleosis

• (“Mono”) is caused by the Epstein-Barr virus.
• Highly infectious.
• Childhood infections are often asymptomatic.
• Transmitted via saliva; incubation of 4 to 7 weeks.
• Fever, sore throat, swollen lymph nodes, enlarged spleen.
• Usually dormant, may reactivate with a weakened immune system.

Epstein-Barr Virus and Other Diseases

• Associated with:
  • Multiple sclerosis: Autoimmune attack on the nervous system.
  • Hodgkin’s lymphoma: Tumors of the spleen, lymph nodes, and liver.
  • Nasopharyngeal cancer

Climate Change and Chikungunya Fever

• Originally transmitted by Aedes mosquitoes in Tanzania.
• High fever, severe joint pain, rash, blisters.
• Low death rate.
• 2013: First case in the Western Hemisphere.
• Asian tiger mosquito:
  • One of two vectors for chikungunya; feeds all day.
  • Moving further north in the United States.
  • Changing climate has expanded its habitat.
  • Could occupy 50% of the land in the northeastern United States by 2080.

Chikungunya Fever Challenges and Control

• Challenges:
  • Insecticides do not work well.
  • Bed nets are ineffective because Asian tiger mosquitoes feed all day.
• Some methods of control:
  • Water storage covers.
  • Biological control.
  • Mosquito dunks.

Yellow Fever

• Yellow fever virus is injected into the skin from Aedes aegypti, a mosquito vector.
• Fever, chills, headache, nausea, vomiting.
• Jaundice due to liver damage.
• Endemic in tropical areas.
• No treatment; attenuated vaccine available.

Dengue and Severe Dengue

• Milder than yellow fever; transmitted by A. aegypti.
• Endemic to the Caribbean and tropical environments.
• Asymptomatic and mild (dengue) to severe bleeding and organ impairment (severe dengue).
• Antibody enhancement may occur, where antibodies against previous dengue infections help a new infection gain access to host cells.
• No animal reservoir.
• No vaccine or effective drug treatment.

Protozoal Disease of the Circulatory System

• Chagas Disease: Caused by Trypanosoma cruzi (flagellated protozoan).
  • Reservoir in rodents, opossums, and armadillos.
  • Vector is the reduviid bug (kissing bug).
  • Death due to heart damage.
• Malaria: Caused by Plasmodium parasites.
  • Plasmodium falciparum: most deadly; severe anemia; blocks capillaries; affects the kidneys, liver, and brain.

Structure & Function of the Respiratory System

• Upper respiratory system: Nose, pharynx, middle ear, and Eustachian tubes.
  • Saliva and tears protect mucosal surfaces.
• Lower respiratory system: Larynx, trachea, bronchial tubes, and alveoli.
  • Ciliary escalator moves particles toward the throat via ciliary action.
  • Alveolar macrophages destroy microorganisms in the lungs.
  • Respiratory mucus protects mucosal surfaces.

Microbial Diseases of the Upper Respiratory System

• Pharyngitis (sore throat)
• Laryngitis (infection of your voice box/larynx)
• Tonsillitis (infection of your tonsils)
• Sinusitis (usually self-limiting)
• Epiglottitis (most life-threatening disease of the upper respiratory system)

Streptococcal Pharyngitis and Scarlet Fever

• Streptococcal pharyngitis (strep throat):
  • Caused by group A streptococci (GAS), Streptococcus pyogenes.
  • Resistant to phagocytosis.
  • Local inflammation, fever, tonsillitis, enlarged lymph nodes.
  • Can be infected with strep throat multiple times.
• Scarlet fever:
  • Erythrogenic toxin produced by lysogenized S. pyogenes.

The Common Cold

• Over 200 different viruses.
  • Rhinoviruses (30-50%):
    • Thrive in temperatures lower than body temperature.
  • Coronaviruses (10-15%)
  • Enterovirus D68 (EV-D68)
• Sneezing, nasal secretion, congestion.
• Can lead to laryngitis and otitis media (middle ear infection).
• Not accompanied by fever.
• Antibiotics are of no use.
• Relief via cough suppressants and antihistamines.

Whooping Cough

• Pertussis (Whooping Cough) is caused by Bordetella pertussis (Gram-negative coccobacillus).
• Produces a capsule allowing attachment to ciliated cells in the trachea.
• Stage 1: catarrhal stage, like the common cold.
• Stage 2: paroxysmal stage, violent coughing, gasping for air.
• Stage 3: convalescence stage, may last for months.
• Prevented by DTaP vaccine, required by many schools.

Microbial Diseases of the Lower Respiratory System

• Caused by many of the same bacteria and viruses as the upper respiratory system.
• Bronchitis
• Bronchiolitis
• Pneumonia: Pulmonary alveoli are involved.

Respiratory Issues: Pneumonia

• Inflammation of the air sacs in one or both lungs.
• Filled with fluid or pus, causing wet coughs.
• Many microorganisms can cause pneumonia.
• Can spread from infected individuals or develop due to flu or COVID infection.
• Treated with antibiotics and pain/fever reducers.
• May be fatal depending on circumstance and time of detection.

Bacterial Pneumonias

• Typical pneumonia:
  • Caused by Streptococcus pneumoniae (Pneumococcal Pneumonia).
  • Infected alveoli of the lung fill with fluids and RBCs; interferes with oxygen uptake.
• Mycoplasmal Pneumonia:
  • Also called primary atypical pneumonia or walking pneumonia.
  • Caused by Mycoplasma pneumoniae (no cell wall).
  • Mild but persistent respiratory symptoms; low fever, cough, headache.
  • Common in children and young adults.

Legionnaires’ Disease

• Legionellosis is caused by Legionella pneumophila (Aerobic, gram-negative rod).
• Severe form of pneumonia.
• Grows in water and evaporative air conditioning, biofilms, and soil.
• Transmitted by inhaling aerosols; not transmitted person to person.
• Symptoms: high fever and cough, gastrointestinal issues, vomiting, diarrhea.

Tuberculosis

• Caused by Mycobacterium tuberculosis (Acid-fast rod; obligate aerobe).
• Symptoms include a persistent cough and fever, pain in the chest, weight loss, and loss of appetite.
• Primarily affects lungs but may affect bones and brain.
• Other causes:
  • Mycobacterium bovis (Bovine tuberculosis; < 1% of U.S. cases).
  • Mycobacterium avium-intracellulare complex (Infects people with late-stage HIV infection).

Tuberculosis Statistics and Prevention

• 10 million develop TB annually; 2 million die.
• Leading cause of death for those with HIV.
• BCG vaccine: live culture of avirulent M. bovis.
• Not widely used in the United States due to questionable effectiveness.

Diseases Caused by Chlamydophila

• Psittacosis (Ornithosis): Caused by Chlamydophila psittaci (Gram-negative intracellular bacterium).
  • Transmitted to humans from bird droppings transmitted through air.
  • Fever, headache, chills, disorientation.
• Chlamydial Pneumonia: Caused by Chlamydophila pneumoniae.
  • Transmitted person to person.
  • Mild respiratory illness common in young people; resembles mycoplasmal pneumonia.

Viral Diseases of the Respiratory System

• Respiratory Syncytial Virus (RSV):
  • Most common viral respiratory disease in infants and life-threatening pneumonia in older adults.
  • Almost all children are infected by age 2.
  • 14,000 deaths annually, mostly in older adults.
  • Coughing and wheezing for more than a week.
• Influenzavirus (Flu):
  • Chills, fever, headache, and muscle aches.
  • No intestinal symptoms.
  • 3,000 to 50,000 deaths in the United States annually.
  • 1% mortality; usually the very young and very old.

Influenza (Flu) Details

• Hemagglutinin (HA) spikes: Recognize and attach to host cells.
• Neuraminidase (NA) spikes: Help the virus separate from the infected cell.
• Antigenic drift: Minor antigenic changes in HA and NA.
  • Allow the virus to elude some host immunity.
• Antigenic shifts: Changes great enough to evade most immunity.
  • Lead to pandemics.
  • Involve the reassortment of the eight RNA segments.

Fungal Diseases: Histoplasmosis

• Caused by Histoplasma capsulatum (Dimorphic fungus).
• Yeast-form grows intracellularly in macrophages.
• Forms lung lesions; 0.1% of cases become a severe, generalized disease.
• Symptoms include fever, cough, and fatigue.
• Acquired from airborne conidia in areas with bird or bat droppings.

Fungi and Respiratory Diseases: Aspergillus

• Aspergillus fumigatus:
  • Commonly inhaled every day.
  • Weakened immune system, asthma, and lung disease at higher risk of infection.
• Causes aspergillosis.
• Airborne conidia:
  • In soil, compost, rotting plant debris, dust, damp buildings, air-conditioning systems.

Mold Intoxication

• Mold poisoning is caused by exposure to toxic fungal spores (mycotoxins).
• Immune reaction results in allergy-like symptoms (runny nose, itchy eyes, shortness of breath, etc.).
• Chemical and inflammatory reaction caused by immune response to mycotoxins.
• Cognitive difficulties, unexplained weight gain or loss, metallic taste in mouth, vertigo, ringing ears, digestive issues, chronic fatigue, dehydration, etc.
• Treatment is to remove the source of mold and use binders to remove toxins.