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The Cardiovascular System is responsible for circulating red blood cells and oxygen throughout the body.
The Lymphatic System primarily circulates white blood cells and other immune components, playing a crucial role in the immune response.
Both systems consist of a series of vessels running throughout the body, forming a closed system (no natural portals for entry or exit).
No normal flora (colonizing bacteria) is present in either system, meaning bacteria that enter are usually destroyed quickly.
Important components:
- Cardiovascular System: Heart - pumps blood
- Lymphatic System: Lymph Nodes - collections of lymph fluid and white blood cells responsible for immune responses

Infection in these systems is difficult because pathogens must cross several barriers to enter the bloodstream, including:
- Epithelial cells
- Chemical and mechanical defenses
- Mucous membranes
- Vessel walls and endothelial cells
If a pathogen successfully enters the blood or lymphatic systems, infections can easily become systemic, spreading throughout the entire body, unlike localized infections (e.g., in the lungs).

Definition: A condition characterized by the active multiplication of microorganisms in the bloodstream.
Prefix "emia" means "in the blood."
Types of septicemia based on the type of pathogen:
- Bacteremia: Bacteria in the bloodstream
- Viremia: Viruses in the bloodstream
- Fungemia: Fungi in the bloodstream
Symptoms:
- Fever and chills
- Global malaise or general feeling of unwellness
- Joint aches and pains
- Hallmark symptom: Low blood pressure (septic shock).
Mechanism:
- The entry of bacteria triggers an immune response, which releases cytokines.
- This response causes blood vessels to become leaky all over the body, leading to decreased blood pressure.
- Organs may not receive sufficient blood, risking organ failure and death.

Septicemia typically has no specific causative organisms; rather, it is secondary to other infections, such as:
- Pneumonia
- Urinary tract infections
- Wound infections
- Sinus infections
Example of possible unique bacteria causing underlying infections leading to septicemia:
- Staphylococcus aureus is commonly known for causing soft tissue infections that may lead to septicemia.

Definition: Inflammation of the inner lining of the heart.
Prevalent in individuals with pre-existing heart conditions, such as:
- Scar tissue (previous heart attack)
- Unusual heart anatomy (missing or malformed valves)
- Presence of prosthetic devices (e.g., pacemakers)

HACEK bacilli: A group commonly found as normal respiratory flora in the mouth; significant in causing endocarditis.

Endocarditis generally occurs via micro-tears in the oral cavity, which allow bacteria (HACEK) to enter the bloodstream.
Risk factors include:
- Dental work or procedures increasing risk of oral tears

Types:
- Bubonic plague: Causes swollen lymph nodes (buboes) and may lead to septicemic plague.
- Sepcticemic plague: Involves infection in the bloodstream, leading to severe symptoms and high mortality rates.

Yersinia pestis survives and replicates within white blood cells, particularly in lymph nodes.
Symptoms of bubonic plague include:
- Swollen, necrotic lymph nodes (buboes); lymph nodes can turn black as they die.

Mainly transmitted through flea bites from infected mammals (e.g., rats or squirrels).
Live vectors (fleas) are not infected but serve as carriers of the disease from animal to human.

Commonly known as “rabbit fever”; primarily transmitted through contact with infected rabbits.
Signs and Symptoms: Ultrative skin lesions and extremely swollen lymph nodes.
Highly contagious, with transmission risks from skinning or being near dead rabbits.
Treatment typically involves IV antibiotics due to a high mortality rate (30-40%).

Caused by Bartonella henselae; characterized by swollen lymph nodes (often mild).
Usually self-limiting, requiring only supportive treatment, as death is rare.

Caused by Borrelia burgdorferi; early symptom includes characteristic bull's-eye rash (present in ~20% of cases).
Late-stage symptoms may involve chronic cardiac issues, neurological symptoms, and debilitating arthritis.
Transmission: Vector transmission through tick bites, typically in wooded areas.
Treatment consists of antibiotics, but difficult diagnosis is common due to symptom overlap.

Caused by various viruses (e.g., Ebola, Marburg, Dengue, Yellow Fever).
Characterized by extreme fevers (up to 107°F) and hemorrhaging (internally and/or externally).
Primarily transmitted through mosquito bites and can also spread through person-to-person contact.

Notoriously associated with earlier low-level outbreaks but could escalate without control.
Treatment is largely supportive care, and mortality rates can be as high as 50%.

HIV attacks the immune system, leading to a decline in T cells (immunosuppression).
Late-stage symptoms may lead to AIDS, where patients are susceptible to opportunistic infections.
Transmission primarily occurs through blood and body fluids, including sexual contact and breast milk.

No cure currently; antiviral drugs can extend life and prevent the progression of HIV to AIDS.
PrEP (pre-exposure prophylaxis) available for at-risk individuals to prevent infection.

Caused by Epstein-Barr virus, commonly referred to as the kissing disease; spreads through saliva and body fluids.
Symptoms include fever, swollen lymph nodes, and extreme fatigue.
Treatment involves supportive care since no specific cure exists.

Caused by a protist (eukaryote) from the genus Plasmodium.
Symptoms include severe fever and hemolytic anemia due to the destruction of red blood cells.
Transmission occurs through mosquito bites; prevention targets mosquito control and protective measures.