infectious disease

• Pathogens are disease-causing organisms; including bacteria, viruses, protozoans, fungi, parasitic worm
• Virulence is the relative ability of a pathogen to cause disease and is determined by: ease with which pathogens enters the body; degree and type of damage to cells
• Bacteria are prokaryotes which lack a nucleus and other membrane-bound organelles; is a cell wall of peptidoglycan
• There are three shapes of bacteria: spherical (cocci), Rod-shaped (bacilli), Spiral-shaped (spirilla)
• Bacteria reproduction: very rapid, asexually, by binary fission (parental cell divides into 2 daughter cells and it happens very quickly and continue the process)
• Bacteria adaptive mechanisms: flagella (allow for movement and spread of infection), Pili (use for attachment), Capsule (used for adherence and evading immune system)
• Beneficial bacteria: in food production (yogurt, cheese), Environment (decomposers, chemical cycles), Genetic engineering, Normal inhabitants of the body that keep harmful organisms in check and produce vitamin K
• Bacterial enzymes and toxins cause direct tissue damage and may allow bacteria to spread; many toxins are released into the bloodstream; disease symptoms depend on what areas are affected by a particular toxin
• Antibiotics are chemicals that inhibit the growth of bacteria; it disrupt processes in bacteria but not in human cells, prevent synthesis of cell walls, and block protein synthesis in the bacteria
• Antibiotic resistance is when bacteria become resistant, antibiotics are no longer effective; made worse by overuse and misuses of antibiotics
• Slowing the spread of antibiotic resistance: use antibiotics responsibly, do not insist on antibiotics against the doctor's advice, take antibiotics exactly as prescribed, reduce risk of infection by washing hands frequently, rinsing fruits and vegetables, cooking meat thoroughly
• Viruses are responsible for many human illnesses, are not considered living organisms
• The structure of viruses: much smaller than bacteria, genetic material (DNA or RNA) surrounded by a protein coat, a capsid, some have an outer envelope studded with glycoproteins
• Steps in viral replication of viruses: attachment (virus attaches to particular receptors on the host cell), penetration (virus enters the host cell and loses capsid), production of viral genetic information (DNA or RNA) and proteins, Assembly of new viruses, release of viruses from the host cell (budding and rupture of host cell membrane)
• Some viruses remain dormant in the host cell for long periods and cause latent infections
• At any time, the virus can begin replicating and cause cell death upon release of new viruses
• Viruses are difficult to destroy: antiviral drugs block a step in viral replication, the best way to prevent viral infections is through vaccination
• Protozoans are single-celled eukaryotic organisms; cause disease by producing toxins and enzymes that prevent the normal functioning of host cells; responsible for many disease including sleeping sickness, amebic dysentery and malaria
• Fungi are eukaryotic organisms. Obtain food by secreting enzymes that digest cells, very few fungi cause human disease
• Examples of fungal infections include histoplasmosis and athlete's foot and ringworm; most can be cured with antifungal drugs
• Parasitic worms are multicellular animals whose life cycle involves a close physical relationship with a host; they usually cause harm to not the death of the host
• Parasitic worms cause disease by releasing toxins, feeding on blood, or competing with the host for food. Examples include flukes, tapeworms, roundworms
• Prions are infectious particles of proteins; misfolded versions of a protein normally found on the surface of nerve cells; prompt host protein to change its shape to the abnormal form
• Prions cause transmissible spongiform encephalopathies (TSEs), which result in brain degeneration and death. Animal TSEs: mad cow disease, scrapie (sheep), chronic wasting disease (deer and elk). Human TSE: Creutzfeldt-Jakob disease (CJD)\
• Disease is transmitted through: Direct contact (STDs), Indirect contact including inhalation (many respiratory infections), contaminated food or water (Hepatitis A, Legionnaire's disease)
• Animal vectors: Lyme disease. Deer ticks are the vectors; caused by bacterium; pain, swelling, and arthritis may develop; cardiovascular and nervous system problems may follow the arthritis
• Animal vectors: West Nile virus. Mosquitoes are the vectors; can cause meningitis and encephalitis; can infect vertebrates including humans, horses, birds and occasionally dogs and cats
• Intravenous (IV) drug use: HIV and hepatitis C can be spread by sharing needles in IV drug use
• Epidemic: large-scale outbreak of an infectious disease (examples include bubonic plague and smallpox)
• Emerging disease is a condition with clinically distinct symptoms whose incidence has increased over the last two decades (examples include HIV, H1N1 influenza)
• Remerging disease is a disease that has reappeared after a decline in incidence (an example is tuberculosis)
• There are four factors that play important roles in the emergence and reemergence of diseases: 1. development of new drug-resistant organisms 2. environmental change that affects the distribution of organisms 3. population growth 4. failure to vaccine
• Factors that determine where new infectious diseases are likely to emerge include: rate of human population growth, density of human population and number of species of wild mamals
• Epidemiology is the study of the patterns of disease occurrence, distribution and control. Epidemiologists try to determine why a disease is triggered at a particular time and place
• Four patterns of disease: Sporadic diseases (occur occasionally at unpredictable intervals, affect a few people within a restricted area), Endemic diseases (always present and pose little threat, common cold is an example), Epidemic diseases (occur suddenly and spread rapidly to many people, measles is an example), Pandemic (global outbreak of disease, covid 19)