Class 9,10,11

Bacteria

• A major pathogen 

• Single-celled organisms that grow and reproduce inside and outside the body

• examples: tubercle bacilli, cholera, strep, staph, some pneumonia, E.coli

Viruses

• Major pathogen 

• Not complete cells. Reproduce by taking over other cells (plants, animals, even other bacteria)

• ex: smallpox, polio, hepatitis, HIV, rabies, common cold, yellow fever, influenza, measles, coronaviruses

Parasites

• major pathogen

• single-celled animals. protozoa

• example: malaria, tapeworms, giardia, other worms

Prions

• strand of protein but no nucleic acid

• source for mad cow disease

Contagious

Spread from one person or organism to another by indirect or indirect contact

Herd immunity

General immunity in a population based on the acquired immunity by a high proportion of the members over time

Endemic

regularly found in a certain area or among particular people

Epidemic

widespread occurrence in a community at a particular time

Pandemic

worldwide or countrywide spread

Transmission pathways for infectious diseases

• passed from person to person 

• transmitted via bites from insects or animals 

• acquired by ingesting contaminated food or water or other exposures in the environment

Methods of transmission

• direct contact (airborne, aerosols, parasites)

• fecal-oral route

• sexually transmitted

• vector born (insect or animal)

Epidemiological triad

• Model that studies disease causation and transmission consisting of 3 interacting components: host, agent, and environment

• Agent = pathogen/cause of disease

• host = individual or organisms that can get sick

• environment = physical, social, cultural context in which the disease occurs including factors like climate, access to healthcare,  sanitation, and human behavior

Malaria Epidemiological triad

Host: Humans

Agent: Parasite plasmodium

Environment: stagnant water (breeding sites for mosquitoes)

Vector: anopheles mosquito

Chain of Infection

Pathogen → Reservoir → Place of Exit → Method of Transmission → Port of Entry → Susceptible Host

• control of an infectious disease is accomplished by interrupting the chain of infection

COVID Epidemiological Triad

Host: Humans 

Aget: SARS - CoV -2

Environment: Contaminated droplets/surfaces

Long COVID

• a chronic condition resulting from a COVID-19 infection

• More likely to occur in those who had more sever lines, underlying conditions, aging population, or unvaccinated

CDC Framework for Prevention of Infectious Disease

• Element 1: Strengthen public health fundamentals, including infectious disease surveillance, laboratory detection, and epidemiological investigation

• Element 2: Identify and implement high-impact public health interventions to reduce infectious diseases 

• Element 3: Develop and advance policies to prevent, detect, and control infectious diseases 

Measles

Rash, fever, can cause serious complications, especially in young children

Symptoms show up 7-14 days after contact

Highly contagious, mainly among those unvaccinated

Eliminated in the U.S.

Malaria Epidemiological Triad

Host: humans

Agent: Plasmodium falciparum (most common parasite)

Environment: Humid climate, mosquito breeding ground

Vector: Anopheles mosquitos

Malaria Prevention

• Individual prevention of mosquito bites (nets, repellants, protective clothing)

• Vector control (insecticide-treated nets, indoor residual spraying)

• Medication (primarily for travelers)

• Vaccination

Genetic Diseases

Diseases caused by abnormalities in an individual’s DNA - can be inherited or due to new mutations

• types include single-gene disorders (cystic fibrosis, sickle cell) - not visible under microscope

• chromosomal abnormalities (Down syndrome) - visible under microscope

• multifactorial disorders (interaction of genes + environment → like heart disease in children with no family hx)

• X-linked Disorders: defective gene on x chromosome 

Chronic Disease

Diseases of long duration and generally slow progression

• heart disease, stroke, cancer, chronic respiratory diseases, and diabetes

• leading causes of mortality