Principles of Infectious Diseases

What is an microorganism or microbe?

Any organism this is invisible to the naked eye

Who observed first microbe?

Antonie Van Leeuwenhook

What are microorganisms in order of smallest to largest

smallest: prions

viruses

bacteria

fungi

protozoa

largest:multicellular parasites

What are the three ecological niches of microorganisms?

Freeliving (in enviroment)

commensal (live inside another but dont cause disease)

Pathogen (disease causing)

WHAT IS A MICROORGANISMS ECOLOGICAL NICHE?

where microorganism has capacity to multiply

What is microbiome?

a diverse collection of fungi,bacteria,archaea,viruses and mites that cover animal tissues

WHat is an infectious disease?

Disorders caused by organisms such as bacteria,viruses,fungi or parasites

what is a communicable disease?

any infectious diseases that spread from individual to individual in indirect or direct routes

Are all infectious diseases communicable?

No as there are dead end hosts

WHAT IS A CONTAGIOUS DISEASE?

infectious diseases that spread easily from an individual to another individuak by air or physical touch

What is a zoonotic pathogen?

A. microorganism that is a commensal or pathogen on animals but can be transmitted to humans and cause disease through vectors or by direct contact with the animal or its by products

What is reverse zoonosis?ex?

Human infects an animal and causes disease

-tuberculosis

What is a notifiable disease?

It is legally mandated that the disease is reported to the public health authorities for the purpose of controlling and/or preventing disease spread

when call reportable disease instead of notifiable?

reportable is at local and state level where notifiable is national level

Are all foreign animal disease notifiable? why?

yes as can impact agriculture and public health if spread

what is example of notifiable disease?

STDs

Are all notifiable disease inefectious diseaes?

no. Cancer, lead poisoning and congenital diseases are notifiable but not infectious

Are all contagious diseases communicable?

yes

are all comunicable doeseases contagious?

no

are all infectious diseases transmissable?

no

what is the infectious diseases triad?

Infectious diseases are determined by pathogen,enviroment and susptible host as all three interact in some form for the infectious disease to exist

does exposure always lead to infection?

no

does infection always lead to disease?

no

What are the steps to infectious agent disease?

exposure,infection,disease then invasion

What are the two out comes of exposure?

no infection or infection

what are the two outcomes of infection?

clinical infection or subclinical infection

what happens if subclinical infection?

Have little to no symptoms and either become carrier or eliminate pathogen to have immunity or no immunity after elimination

what happens if have clinical infection?

develop symptoms and either die,become carrier, or elimante pathogen to gain immunity or not gain immunity upon elimination

What are the two types of carriers?

active and latent

What are 3 reasons why epidemiology matters?

-modern animal production has created new challenges as systems have intensified so have interactions among disease,host sand environmental factors

-Emerging diseases are predominantly zoonotic

-Traditional approaches focusing on individual are insufficient

What is epidemiology?

The study of patterns and causes of disease in populations

What is the core purpose of epidemiology?

Provide tools to investigate disease occurance in populations and for developing control strategies often before biology of the causitive organism is fully understood

What is the key distinction between epidemiology and clinical medicine?

Clinical focuses on individual sick animals while epidemiology examine spoulations of animals

What do epidemiologists use the term disease for?

Any health related condition of intrest,not just clinical illness

Why is integration of individual and population medicine important?

Molecular understanding helps design interventions while population thinking guides where,when and how to apply the preventions effectively

What is the key idea of population medicine?

Populations have emergent properties beyond individual animals

Do population characteristics exist at the individual level?

no

populations are ___ systems

complex

What are 3 population level phenomena?

-Herd immunity

-Transmission patterns

-Economic threshold effects

What is herd immunity?

protection occurs when enough animals are immune, reducing the spread of disease and protecting susptible animals

What is transmission patterns?

Pathogens spread through contact networks shaped by mixing,housing,movement and behavior

What is economic threshold effect?

the point where disease losses justify intervention costs, driven by herd-level productivity and economics

Why may treatments that work at individual level fail at population level?

due to factors like compliance,cost, or unintended consequences on disease synamics

Is disease random?

no

What does disease result from?

Interactions between host,agent and enviroment (the epidemiologic triad)

Disease only occurs when ___ ___ ___ of the epidemiologic triad align

all three factors

WHat can break the chain of disease?

Prevention that targets any of the three factors of the epidemiologic triad

What are the 8 core functions of epidemiologists in practice?

-detect disease occurrence

-identify causes

-estimate risk

-understand disease ecology

-quantify impact

-plan control strategies

-monitor prevention programs

-acess economic implications

Is policy driven solely by evidence?

NO

What 4 things do effective interventions need to be?

-scientifically sound

-politically feasible

-socially acceptable

-economically viable

What does epidemiology translate scienc einto?

Decisions that can be implemented

What are the 3 pillars of epidemiological practice?

-Cognitive analysis framework

-valid data collection and analysis

-effective communication

What does vaild data collection and analysis require attention to?

bias, confoun di ng and correct interpretation

For effective communication what do you need to be explicit about?

What is known,unknown and inferred

What are the 3 classes of epidemiological studies?

-Observational studies

-Intervention Studies

-Theoretical studies

What is theoretical studies?

Model to predict outcomes and scenarios

What is intervention studies?

Experimental studies where test treatments and preventions

What are 4 types of observational studies?

-Descriptive

-Cross sectional

-Case control

Cohort

What is an observational study?

Study with no intervention

What is a descriptive study?

Systematically document disease occurence without testing a specific hypothesis to generate a hypothesis

What are 3 strengths of descriptive studies?

fast, inexpensive, uses readily available data

What are 3 limitations of descriptive studies?

cannot prove causation, risk of ecological fallacy, may miss key factors not captured in available data

What is ecological fallacy?

When try to make an assumption about an individual based on data from a population

What is a cross sectional study?

Measure disease status and exposure at a specific point in time to determine current prevelence of disease and make associations between factors and disease presence

What is the 3 key limitations of cross sectional studies?

-exposure and disease meausred simultaneously

-you cant be sure weather disease or exposure came first

-best for fixed factors or chronic conditions

What is a case control study?

Start with disease and look back in time for exposures for both control groups and case groups. Compare the distributions of exposed and unexposed for both the control groups and case groups to reveal associations between disease and exposure

What are 4 advantages of case control studies?

-excellent for rare diseases

-resource efficient

-can evaluate many exposures in same study

-uses existing data

What are 4 disadvantages of case control studies?

-Control selection is crucial

-can not calculate incidence

-Recall bias

-Temporality can be unclear

What is a cohort study?

Select anf follow animals based on exposure status to observe who develops disease and compare incidence between exposed and unexposed groups

What are two types of cohorts used in cohort studies? describe

-prospective (follow groups forward in real time)

-historical (use records to define past exposure and follow outcomes to present)

What can calculate/determine from cohort studies?

-risk

-relative risk

-attributable risk

What are 4 advantages to cohort studies?

-temporal sequence is clear

-true incidence can be calculated’

-multiple outcomes

-natural disease progression is followed

What are 5 practical limitations of cohort studies?

-resource intensive

-time consuming

-costly

-loss to follow up

-limited exposures

What is the gold standard study for evidence?

intervention studies

What is best type of intervention study?

Randomized control study

What is randomized control study?

Researchers randomly assign treatment and control groups to reduce selection bias and with bliding and standardized protocols can answer if an intervention works

What are 5 critical design elements of randomized control studies?

-randomization

-control group

-blinding when feasible

-standardized protocols

-field trial realities

What is a theoretical study?

Use mathematical modeling to explore impossible, unethical or too expensive scenarios to provide insights into disease dynamics and predict outcomes

What are 3 benefits of theoretical studies?

-cost effective

-test extreme situations safely

-provide rapid answers

What are 3 limitations of theoretical studies?

-only as good as assumptions and input data

-may oversimplify complex biological systems

-requires validation with real world data

What are 6 pitfalls to avoid? describe each

-selection bias (study doesnt represent target population)

-confounding (a third variable influences both exposure and outcome creating false associations)

-information bias (systematic errors in measuring exposure or disease)

-ecological fallacy (apply population level findings to individuals)

-overinterpretation (generalizing beyond study population or drawing causal conclusions from observational studies)

-ignoring practical constraints (recommending interventions that are scientifically sound but practically impossible)

A small animal veterinarian wants to understand why some dogs in her practice develop diabetes. Rather than just treating each diabetic dog, she starts recording information about age, breed, weight and diet for all her patients. What primary function of epidemiology is she beginning to preform?

A study finds that farms with higher average milk production report more disease. A manager concludes that his individual high yielding cows must each be at an elevated risk. Which pitfall has he committed?

ecological fallacy

The three components of the epidemologic triad are?

host,agent and enviroment