Disease Epidemiology and Microbial Pathogenicity: Transmission, Outbreaks, and Host Defenses

What is the difference between symptoms and signs of a disease?

Symptoms are subjective experiences felt by the patient (e.g., fatigue), while signs are objective changes that can be measured or observed by a medical professional (e.g., fever).

What is a syndrome?

A syndrome is a way to characterize a condition using specific signs and symptoms, such as Irritable Bowel Syndrome (IBS).

What is a communicable disease?

A communicable disease is one that is spread from one human host to another, such as influenza or chicken pox.

What is a noncommunicable disease?

A noncommunicable disease is not spread from one human host to another and often includes microbes that only cause disease when introduced to the body, like tetanus.

What is a reservoir in the context of infectious diseases?

A reservoir is the habitat of a pathogen where it can survive, which may include living reservoirs (humans/animals) or non-living reservoirs (water, soil).

What is a carrier in infectious disease transmission?

A carrier is a living organism that harbors a pathogen and can shed it into the environment, potentially infecting susceptible humans.

What are the three main routes of contact transmission?

The three main routes are direct transmission, droplet transmission, and indirect transmission.

What is direct transmission?

Direct transmission occurs through physical contact without an intermediate host or object, such as touching or kissing.

What is droplet transmission?

Droplet transmission involves microbes spread from respiratory droplets over short distances (less than 1 meter) through sneezing or coughing.

What is indirect transmission?

Indirect transmission involves the transfer of pathogens via non-living items known as fomites, such as bedding or surgical instruments.

What is airborne transmission?

Airborne transmission occurs when infectious agents are dispersed via dust and remain suspended in the air, traveling over distances greater than 1 meter.

What is waterborne transmission?

Waterborne transmission occurs when untreated water allows pathogens to replicate, leading to disease.

What is vector transmission?

Vector transmission involves living organisms, such as insects, that transfer pathogens from one host to another.

What is mechanical transmission in vectors?

Mechanical transmission is a passive transport mechanism where a vector, like a fly, carries a pathogen on its body and transfers it to food.

What is biological transmission in vectors?

Biological transmission is an active transport mechanism where a vector, like a mosquito, picks up a pathogen from an infected host and injects it into another host.

What is epidemiology?

Epidemiology is the study of the occurrence, distribution, and determinants of health and disease in populations.

What is descriptive epidemiology?

Descriptive epidemiology involves the collection and analysis of data to provide a general overview of health and disease.

What is analytical epidemiology?

Analytical epidemiology analyzes specific diseases to determine their probable causes.

What is experimental epidemiology?

Experimental epidemiology includes hypothesis testing and controlled experiments, such as clinical trials.

Who is John Snow and what is he known for?

John Snow is known for mapping the occurrence of cholera in London during 1848-1849.

Who is Ignaz Semmelweis and what did he contribute to epidemiology?

Ignaz Semmelweis tested the theory that improved hand sterilization among doctors could reduce the death rate from infections.

What did Florence Nightingale observe regarding typhus?

Florence Nightingale observed that individuals treated in hospitals with better sanitation had a lower incidence of typhus.

What is an outbreak in epidemiology?

An outbreak is defined as numerous cases of a disease occurring over a short period of time, often in an area where cases are minimal.

What is incidence in epidemiology?

The number of new cases of a disease during a particular time, indicating the spread of disease.

What does prevalence refer to?

The number of new and existing cases at a particular time, indicating how long a disease can persist in a population.

How is mortality calculated?

Mortality rate = (deaths/population) * 100.

Define endemic disease.

A disease that is constantly present at a low incidence in a population, e.g., common cold.

What characterizes an epidemic?

A disease that infects an unusually high number of individuals in a population, e.g., influenza.

What is a pandemic?

A widespread epidemic, usually worldwide.

Describe human host-to-human host epidemics.

Epidemics that start with one infected individual and spread to susceptible persons over a longer time period.

What are common-source epidemics?

Epidemics that originate from a contaminated common source, causing many people to become sick at the same time.

What are the stages of disease progression?

1. Infection, 2. Incubation, 3. Prodromal period, 4. Acute period, 5. Decline period, 6. Convalescent period.

What is a primary infection?

The infection that causes the initial illness.

Define secondary infection.

An opportunistic infection that occurs after a primary infection.

What are predisposing factors in disease susceptibility?

Factors controlled by the host that increase susceptibility, such as gender, inherited traits, and lifestyle.

What is an acute disease?

A disease with symptoms that develop rapidly but last for a short time, e.g., influenza.

Define chronic disease.

A disease with symptoms that develop slowly and often last for a long time, e.g., type 2 diabetes.

What is a latent disease?

A disease where the causative agent is inactive for a time but can activate later, e.g., tuberculosis.

Why do infectious diseases spread rapidly in hospitals?

Diseased patients are reservoirs, patients share rooms, healthcare workers move between patients, and surgical procedures expose organs.

What are healthcare-associated infections (HAIs)?

Infections acquired while receiving treatment in a healthcare facility.

How common are HAIs in the USA?

Affect 1 in 38 hospital patients; approximately 518,000 infections per year and over 99,000 deaths.

What measures can reduce healthcare-associated infections?

Handwashing, disinfecting instruments, using disposable bandages, and infection control committees.

What is E. coli?

Part of the intestinal normal microbiota; some strains can cause illness, particularly food-borne illness and urinary tract infections.

What is enterohemorrhagic E. coli?

A strain of E. coli that causes foodborne illness, often transmitted through contaminated food/water.

What are the symptoms of enterohemorrhagic E. coli infection?

Key symptoms include bloody diarrhea, and 5-10% of cases can lead to kidney failure.

What does the 'O157:H7' designation in E. coli indicate?

'O' refers to the specific sugar composition of the O antigen; 'H' refers to a specific structural protein in the flagella.

What is infection?

The growth of a microbe in a host.

What defines a disease in the context of pathogens?

When the pathogen affects the normal functioning of the host.

What is pathogenicity?

The potential ability of a pathogen to cause disease in a host.

What is virulence?

The actual ability of a pathogen to infect or damage a host.

What are the three portals of entry for microbes into a host?

Mucous membranes, skin, and parenteral routes.

How can microbes penetrate mucous membranes?

Through inhalation, consumption of contaminated food, or sexual contact.

What is the significance of the number of invading microbes?

A low number of microbes can often be stopped by the host immune system, depending on virulence.

What does ID50 represent?

The number of microbes/viruses required to produce an infection in 50% of healthy humans.

What is adherence in the context of microbial infection?

The process of pathogens attaching to a host cell at the portal of entry.

What are adhesins?

Surface molecules used by pathogens to enter a host cell.

What is phagocytosis?

The process by which host cells recognize, engulf, and destroy invading pathogen proteins.

How do microbes evade host defenses through capsule formation?

Capsules reduce phagocytosis effectiveness, increasing pathogen survival.

What role do coagulases play in microbial evasion?

They form blood clots to hide inside the host, evading phagocytosis.

What is antigenic variation?

The ability of some microbes to change their surface antigens, preventing antibodies from binding.

What are siderophores?

Microbial proteins that bind iron in the host, essential for bacterial growth.

How do toxins affect the host?

Toxins are microbially produced substances that negatively affect the host.

What are exotoxins?

Toxins produced internally and excreted into the environment by both Gram-positive and Gram-negative bacteria.

What are endotoxins?

Part of the bacterial cell (lipopolysaccharide layer) released by Gram-negative bacteria.

What happens to host cell nutrients when bacteria invade?

Bacteria use host cell nutrients and excrete waste products, potentially leading to host cell lysis.

What is the role of enzymes released by bacteria in evading host defenses?

They can form blood clots to hide inside the host and later digest these clots to escape.

What is the impact of siderophores on host iron concentrations?

They decrease host Fe concentrations while increasing microbial growth.

What is the relationship between microbial growth and host cell damage?

Increased microbial growth can lead to the production of waste products and ruptures in host cells.

How do microbes typically enter through the skin?

Through hair follicles, as unbroken skin is impermeable to microbes.