Infectious Diseases and Pathogens

Infectious Diseases

• Caused by infection via microorganism invasion of a host
• Microorganisms include bacteria, viruses, fungi, and protozoa
• Accompanied by damage to host cells
• Followed by a latent period, the time between infection and symptom development
• Latent period can range from hours to years, but is typically several days

Pathogens: Agents of Infection

• Bacteria are virtually everywhere, but most are harmless
• Bacteria can cause harm by releasing enzymes or toxins
• Bacterial infections can be local or systemic
• Antibiotics are effective in killing bacteria
• Many bacteria have become resistant to multiple antibiotics
• Viruses are acellular pathogens that only survive by invading living cells of a host
• Viruses either kill the host cell or alter its function
• Antiviral drugs can reduce the severity/duration of viral infections
• Fungi include yeasts, mold, and mushrooms
• Fungi absorb nutrients from hosts, causing damage and releasing enzymes
• Protozoa are single-celled organisms
• Protozoa release enzymes or toxins that destroy cells
• Parasitic worms (helminths)
• Attack tissues or organs
• Compete with hosts for nutrients
• Enter through burrowing, undercooked pork/fish
• Adult worms can be meters long

Catching Infections

• Infections can be contracted from people through direct or indirect contact
• Infections can be contracted from food, such as E. coli and Salmonella from raw or undercooked food
• Infections can be contracted from contaminated water, with examples being Vibrio cholera and Giardia
• Animals and insects act as vectors for disease transmission
• Mosquitos transmit Zika virus and malaria
• Rats and fleas transmit the plague

Harmless Bacteria

• Most microbes are harmless
• Trillions of bacteria help with digestion and vitamin absorption in the human digestive tract
• They also compete with and exclude harmful microbes
• Broad-spectrum antibiotics can kill both good and bad bacteria, eliminating the helpful kinds
• Probiotics found in yogurt promote a healthy microbial environment in the body

First Line of Defense

• The skin provides a barrier, unless there is a cut or lesion
• Cilia in the lungs trap pathogens and move them out of the body
• Mucus traps pathogens
• Elevated body temperature inhibits pathogen growth
• Coughing, tears, and saliva remove pathogens from the body

Second Line of Defense

• Immune cells recognize pathogens as foreign due to antigens (proteins/sugars) on their surfaces
• These antigens are different from the host's own
• Specialized cells respond: macrophages, T cells, and B cells launching an immune response to eliminate pathogens

Immune System: T cells and Macrophages

• Macrophages digest foreign matter and engulf antibody-bound pathogens
• T-cells fight parasites, fungi, cancer cells, and infected cells
• Thousands of T-cells work to kill pathogens

Immune System: B cells and Antibodies

• Antibodies (Abs) are made by B-cells
• Abs are proteins that stick to specific antigens on pathogens
• This is called the humoral response
• Abs coat pathogens and make them clump together, so that pathogens cannot infect new cells, and the pathogens are more easily ingested by macrophages

Chain of Infection

• The chain of infection can be broken at any point to prevent disease
• Chain of Infection links:
• Pathogen
• Reservoir
• Portal of Exit
• Means of Transmission
• Portal of Entry
• New Host
• The chain can be broken through: pasteurization, chlorination, disinfectants; medical treatment and testing, insect and rodent eradication, quarantine; condoms, masks, covering mouth while coughing; handwashing, avoiding infected people, sanitary practices, sexual abstinence, condoms and masks, insect repellent; immunization, health promotion, medical treatment

Chain of Infection: Influenza

• Influenza is an airborne virus
• The chain starts with a Human #1 infected with Influenza Virus with a portal of exit of mouth or nose
• Transmitted airborne or indirect transfer on a surface
• The virus enters a portal of entry on Human #2 through the nose or mouth
• With establishment of disease in the New Host

Chain of Infection: Cholera

• Chain of infection to be completed for cholera

Vaccination

• Vaccination involves injecting a small quantity of inactive pathogen
• This creates memory cells (T- and B-cells)
• If, you encounter the actual pathogen, your immune system can fight it off using antibodies
• Vaccination helps prevent disease before symptoms appear
• This method led to the eradication of smallpox, which had a ~35% mortality rate
• A number of other infectious diseases are under control because of vaccines

Infectious Diseases: Globally

• Smallpox has been completely eliminated
• Polio should have been eliminated by now, but hotspots remain
• There were less than 100 cases in 2015, compared to 350,000 cases in 1988
• Measles kills 150,000 people per year
• This is down from 750,000 in 2000
• Malaria kills 500,000 people per year
• This is down from ~1 million in 2000
• HIV/AIDS kills ~1 million per year
• Tuberculosis kills ~1.5 million per year
• Zika is an emerging pathogen
• COVID19 is an emerging pathogen

Measles Case Study

• Measles is the deadliest of all childhood rash/fever illnesses
• Measles causes inflammation of the brain, brain damage, seizures, deafness
• Causes 150,000 deaths per year globally
• In regions with malnutrition, the mortality rate for children reaches 30%
• In pregnant women during the first trimester, the virus can cause miscarriage, stillbirth, deafness, brain damage, heart defects, cataracts
• Widespread use of measles vaccine began in 1980
• Measles killed or maimed several million people a year before this
• The consequences of not vaccinating can be severe
• Recently BC has seen measles outbreaks
• Completely preventable if vaccinated
• Could be eradicated worldwide
• Most people recover after a bad skin rash but severe cases can cause blindness, swelling of the brain, pneumonia, or death
• There's an anti-vaccine movement due to discredited misinformation.
• A retracted study claimed a link between vaccines and autism

Infectious Diseases: Canada

• Common infectious diseases in Canada:
• Colds
• Influenza
• Hepatitis
• Meningitis
• Reproductive & Urinary infections
• Sexually Transmitted Infections

Colds and Flu

• The common cold can be caused by rhinovirus or coronavirus
• There are ~200 types (so you keep getting them)
• Can spread by coughs, sneezes, direct and indirect contact
• Best prevention: hand-washing
• Best cure: your immune system, rest, time, fluids, mild exercise, proper nutrition
• Medications can mask symptoms
• Flu is caused by the influenza virus
• More severe symptoms (aches, chills, dry cough, weakness) that last longer
• Annual vaccine ('flu shot')
• Antiviral drugs available to high-risk patients

1918 Spanish Flu

• The flu killed 50-100 million people
• 50% of the world's population was infected
• Most who died were healthy, 18 to 40 year olds
• Mutations in influenza can recombine with other strains creating deadly flu strains
• Yearly flu vaccination

Hepatitis and Meningitis

• Hepatitis is caused by viruses (A - G)
• Inflammation of the liver
• Symptoms: high fever, headaches, fatigue, aching joints, nausea, vomiting, diarrhea, jaundice
• Hep A/E transmitted by contaminated water
• Hep B/C/D transmitted through sexual contact
• Hep A/B vaccine is available in Canada
• Some infections clear up, others become chronic, spreading the virus
• Meningitis is a viral or bacterial infection that is rarely fungal
• Infection of the membranes surrounding the brain and spinal cord
• Symptoms: fever, drowsiness, confusion, severe headache, stiff neck, nausea, vomiting
• Viral meningitis usually clears up on its own, bacterial and fungal meningitis are more serious and need antibiotic/antifungals immediately

Reproductive and Urinary Tract Infections

• Vaginal Infections:
• Trichomoniasis (protozoan): Itching, burning, discharge
• Candidiasis (yeast infection; fungi): Itching, burning, discharge
• Bacterial vaginosis (bacteria): White/grey discharge, strong odor
• Penile Infections:
• Candidiasis (fungal); epididymitis, orchitis (bacterial or viral)
• Redness, irritation, pain during urination or intercourse, discharge
• Urinary Tract Infections (UTIs):
• Typically caused by bacteria
• Symptoms include burning sensation while urinating, chills, fever, fatigue, blood in urine
• Urethral infections are easier to treat, bladder/kidney infections are more serious
• Common in females (shorter urethra)

Immune System Support

• Wash your hands often with hot water and soap
• Get adequate sleep and exercise
• Eat a balanced diet (fruits, vegetables, quality protein)
• Don't share food or drinks
• Avoid rubbing your eyes and touching your mouth
• Don't bite your nails
• Don't smoke and limit alcohol intake
• Avoid contact with those having a communicable disease
• Limit number of intimate/sexual partners
• Practice safe sex if you are sexually active

Antibiotic Resistance

• Antibiotics kill bacteria, not viruses or fungi
• Penicillin has dramatically decreased deaths from infectious disease
• Natural selection leads to antibiotic resistant bacteria
• Overusing antibiotics pharmacologically and in sanitation/agriculture
• If this trend continues, future generations may face incurable bacterial infections

Preventing Antibiotic Resistance

• Let your immune system do its job
• Finish prescribed antibiotics regimen, even if you feel better
• Don't use leftover antibiotics
• Don't share antibiotics
• Avoid antibiotic soaps and cleansers