Infection 1

Body Defenses

• Physical barriers include skin (keratin layers) and mucous membranes in areas like the nose and GI tract.
• Phagocytosis involves neutrophils, monocytes/macrophages, NK cells, eosinophils, and cytotoxic T cells.
• Inflammatory mediators initiate and sustain inflammation.
• Interferons & Interleukins (IL) are immunogenic proteins (cytokine family) secreted by WBCs to stimulate immune responses.
• The body has specific immune responses, including memory B and T cells.
• Fever is a pyrogen-activated increase in body temperature.

Blood Components: WBCs

• Hematopoiesis is the process of blood cell formation.
• White blood cells (WBCs) are key components of the immune system.

WBCs in the Immune Response

• Neutrophils make up around 70% of WBCs and are the first to arrive at tissue damage sites, with a lifespan of up to 1 week in blood and tissues, and immature forms are called band cells.
• Lymphocytes are involved in innate and adaptive immunity, including NK cells, B cells, and T cells.
• Monocytes mature into macrophages in tissues and can be specific to certain tissues, like hepatic Kupffer cells.
• Eosinophils respond to allergies by releasing enzymes/chemical mediators to destroy allergens and parasites.
• Basophils contribute to allergy responses by being pro-inflammatory and anticoagulating.

Immunizations and Memory Cells

• Immunizations form B&T memory cells and boost immunity.
• Passive immunity is transferred from one person to another (e.g., fetus, medications).
• B cells present antigens, clone themselves into millions of copies (plasma cells), and secrete circulating antibodies (immunoglobulins, most commonly IgG) at a rate of, for example, 2000 per second.
• Antibody functions include neutralizing or marking pathogens for destruction by phagocytic cells.
• Memory B cells remember antigens, leading to immediate and faster responses upon next exposure.
• T cells include T helper and cytotoxic T cells, which create T memory.
• T helper cells activate B cells and secrete cytokines (interleukins, interferon, TNF, tumor necrosis factor, perforin).
• T memory cells develop post-exposure and recognize antigens to respond quickly in the future.

Causes of Decreased WBC Numbers

• Autoimmune diseases (e.g., IBD) cause systemic inflammation which decreases synthesis and proliferation, leading to depletion due to chronic inflammatory requirements.
• Chronic infections/inflammation (e.g., viral mononucleosis, HIV) can cause long-term infections, resulting in depletion due to chronic requirements.
• Immunodeficiencies can be researched for during patient care for inborn errors (e.g., DiGeorge syndrome- malformed thymus)
• Cancer (e.g., lymphomas, leukemias) destroys production organs and interferes with the maturation of normal WBCs.

Causes of Infection

• Host susceptibility influences infection.
• Pathogenicity depends on an organism's ability to evade or overcome body defenses.
• Pathogens include bacteria, viruses, fungi, and parasites.
• Virulence is the power to produce disease (e.g., COVID-19's high virulence).
• Portals of entry allow pathogens to bypass endogenous defenses.
• Infections use strength in numbers and toxin production.
• Prevention decreases infection numbers, with 80% of infections spread by hands, emphasizing hand washing with soap and water for 15-20 seconds to prevent infections such as streptococcus septicemia.

General Info on Microorganisms

• Microflora are microorganisms present on or in the human body.
• Commensalism is when the host is not negatively affected by microflora.
• Bacteria provides the host with an environment but causes no harm
• Mutualism is when the host & bacteria benefit.
• A good example is Intestinal flora (Vitamin K formation).
• Infectious diseases happen when pathogens attack the host.
• Opportunistic microorganisms cause disease under certain conditions.
• Intestinal infection is seen often in immuno-suppressed hosts.
• Illness is more common in high-risk patients with chronic diseases, the elderly, newborns, those on drug treatments, and those with malnutrition.

Parasites

• Parasites belong to the 'animal' kingdom.
• Parasites can be in three main groups: protozoa, helminths, and arthropods.
• Protozoa examples malaria.
• Helminths include tapeworm.
• Arthropods include lice, ticks, mites (scabies), and fleas.

Fungi

• Fungi are eukaryotic with an organized nucleus.
• Fungi freely reproduce through sexual or asexual reproduction.
• The two groups of fungi are yeast and mold and, for example, candida albicans.
• Fungi thrive in dark, moist environments.
• Severe disease is rare in a non-compromised person.
• Disease can be superficial mycoses (e.g., athlete's foot, thrush, ringworm) or systemic (lung, GI), which are rare, serious, and difficult to treat.

Viruses

• Viruses lack a cell structure, containing only a protein coat and nucleic acid (DNA or RNA).
• Retroviruses have only RNA and require reverse transcription into DNA.
• An example is HIV (cause of AIDS).
• Viruses require hosts to survive and replicate.
• A virus may alter or lyse the host cell or destroys host cell during replication.
• HPV may alter host cells => oncogenic, which transforms host cells into malignant cancer cells.
• Viruses are generally more common and contagious than other pathogens.
• Examples of common viral infections are: Covid-19, influenza, common cold, and laryngitis.
• Treatment (Tx) includes symptom management with antivirals, immune system support via IVIG, and prevention through immunizations.

Bacteria

• Bacteria lacks organized nucleus and is also known as prokaryotes
• Bacteria also contains DNA and RNA.
• Plasmids aid in antibiotic resistance.
• Bacteria often reproduce autonomously
• Fastidious means the bacteria prefers specific temperatures, darkness, and oxygen or no oxygen
• Bacteria are less contagious than a virus
• Bacteria secrete toxins (exogenous pyrogens) that contribute to inflammation and disease
• Gram-negative and gram-positive results classify bacteria through iodine staining
• Antibiotics treat bacteria, but resistance is increasing.

Portals of Entry

• Main modes of entry include Direct contact with the infected host (e.g., STIs, diseases causing a wound/rash, such as chickenpox)
• Inhalation of airborne pathogens can cause respiratory diseases, common cold, pathogens causing meningitis, and childhood diseases (measles, mumps).
• Ingestion of contaminated foods can lead to food poisoning and parasitic infections (commonly the eggs), foodborne viruses (e.g., Hepatitis A).
• The source of infection is labeled and is known as acquired (nosocomial is acquired in hospital whereas community acquired is outside of hospital)

Site of Infection

• The suffix "-itis" indicates an infected/inflamed body part, such as appendicitis or laryngitis.
• The suffix "-emia" indicates the presence of a pathogen in the blood, like bacteremia (bacteria in blood) or fungemia (fungi in blood).
• Pathogens may infect multiple body areas/organs.
• Pathogens may spread from one area to another.
• A body area/organ may be infected by a variety of pathogens.
• Diagnoses can be complex and should be done imperatively

Course of Infection

• There are distinct stages of infection.
• During the incubation period, the pathogen is present and replicating, but there are no symptoms, but the host has the ability to infect others.
• During the prodromal stage, initial symptoms like malaise, mild fever, headache, and myalgia are generic and difficult to differentiate.
• The acute stage includes a maximum presence of pathogen, maximum response by the host, maximum impact of infection and more specific symptoms arise.
• The convalescent period is when the pathogen decreases in numbers, and the host progressively repairs damages.
• Resolution is when there is no sign of disease.

Antibacterial Treatment Process

• Antibiotic Empiric treatment is when to attack the "suspected" bacterial infections and provides guidance on clinical presentations when making decisions.
• Antibiotic focal treatment is when to use culture and sensitivity tests to create a focused treatment based on the results
• 'Bugs and Drugs' app provides guidance. -A respiratory infection is mostly caused by Streptococci
• Tx choice: Penicillins (Pen G)

Treatment E.g. (Streptococcus pyogenes, group A strep)

• The first step is to treat according to the clinical presentation and the patient's medical history. (Empiric Therapy)
• Then confirm with Culture & Sensitivity is it fact that is in Streptococcus is pen G best?

Diagnosing a Disease

• First step, figure out where the illness location to determine treatment
• Second, identify what is causing the illness: perform a viral and bacterial test, CBC & Differential, look at what is happening through the patients history, and use a culture from a source(body)
• Third step, administer an antibacterial (abx) treatment