L60 - Outbreak Investigations and Mechanisms of Disease Transmission

Why are Communities Important in Outbreak Investigations?

Disease develops through connections among people, animals, plants, and their environment

What are the Seven Basic Questions of an Outbreak Investigation?

1. Who

2. What

3. When

4. Where

5. Why

6. How

7. What do we do now?

What is an Outbreak?

Disease cases or health events clearly exceeding normal expectations for a population, time, and place

• Synonymously with “epidemic”

How does the Outbreak Threshold vary by Disease?

One Ebola case may trigger an investigation → common diseases may require a larger increase above baseline

What caused the Mass Die-Offs of Saiga Antelope?

Hemorrhagic septicemia associated with Pasteurella multocida type B

Which Environmental Factors were associated with Saiga Die-Offs?

High temperature and high humidity

Why was identifying the Bacterium Insufficient to explain Saiga Outbreaks?

Investigators also needed to explain why mass mortality occurred under particular environmental conditions

What is the Main Goal of Early Outbreak Detection?

Shorten the time between detection and intervention to reduce cases and deaths

What is the Difference Between Patient Zero and the Index Case?

• Patient zero is the first infected individual

• Index case is the first recognized case

Why is the Left Side of the Epidemic Curve Important?

It represents early detection and response, when interventions may prevent extensive transmission

What are Three Examples of Outbreak Interventions?

• Treatment

• Vaccination

• Restrictions on animal movement

What is the Primary Outbreak Focus of USDA APHIS?

Rapid animal disease control and mitigation of local, national, and international economic impacts

Why are Economic Impacts Important in Veterinary Outbreak Responses?

Outbreaks can disrupt livestock movement, agricultural production, business continuity, and trade

What are the Major CDFA Outbreak Response Activities?

Detection, quarantine, surveillance, epidemiological investigation, control, eradication, and recovery

What is the Primary Focus of WHO Outbreak Responses?

Human public health through coordinated surveillance, investigation, case management, and prevention

Which Additional Components are Important in WHO Outbreak Responses?

Health education, social mobilization, media, logistics, security, coordination, and vector control

How do Veterinary and Public Health Outbreak Priorities differ?

• Veterinary responses emphasize animal health and agricultural impacts

• Public health emphasizes human health

What is the Epidemiological Triad?

The interaction of agent, host, and environment in disease occurrence

What is the One Health Approach to Outbreak Investigations?

An integrated approach considering human, animal, and environmental health

Why is Multidisciplinary Collaboration Important in Outbreak Responses?

Different specialists contribute complementary expertise needed for investigation, control, and communication

What was the Major Transmission Route of Ebola Between Humans?

Direct contact with infectious bodily fluids from infected individuals

What is Zoonotic Spillover?

Transmission of a pathogen from an animal source into humans

How did Human Movement contribute to the West African Ebola Outbreak?

Movement across communities and national borders allowed the virus to spread widely

What was the Significance of the 2013–2016 West African Ebola Outbreak?

It caused 28,652 cases and 11,325 deaths, severely disrupting health systems and economies

What did Genomic Epidemiology reveal about the West African Ebola Outbreak?

Viral genetic changes helped reconstruct geographic spread following a single inferred wildlife spillover.

How can Pathogen Sequencing support Outbreak Investigations?

It helps identify:

• Related cases

• Possible transmission chains

• Geographic spread

Which Leadership Roles did Veterinarians hold during the Ebola Response?

• Epidemiology and laboratory task force leads

• Scientific officers

• Field laboratory leads

• Response leaders

Why are Veterinarians Valuable in International Outbreak Responses?

Their training in infectious diseases, diagnostics, epidemiology, and population health supports investigations

What were Major Challenges during the Sierra Leone Ebola Response?

• Limited resources

• Poor communication

• Uncertain case locations

• Shortages of supplies and personnel

What are Three Key Tools for Organizing Outbreak Data?

1. Line lists

2. Geographic maps

3. Contact or exposure tracing diagrams

What is Contact Tracing?

Identifying and investigating contacts or exposure connections among cases

What is the Purpose of a Contact Tracing Diagram?

To visualize possible links and transmission relationships between individuals or herds

Which Patterns should Investigators seek in Contact Tracing?

• Shared contacts

• Exposures

• Locations

• Species

• Timing of disease

What is a Line List?

A table organizing information about individual cases or herds, usually one case per row

Which Information belongs in an Outbreak Line List?

• Case ID

• Species

• Age

• Onset date

• Clinical signs

• Location

• Test results

• Possible exposures

Why are Line Lists Useful in Outbreak Investigations?

They organize large amounts of case data and help reveal patterns before formal analysis

How are Geographic Maps Useful in Outbreak Investigations?

They reveal spatial clustering, possible exposure locations, and geographic spread

How do Line Lists, Maps, and Contact Tracing differ?

• Line lists organize case details

• Maps show locations

• Contact tracing shows connections

What were Major Community Impacts of the West African Ebola Outbreak?

School and business closures, food shortages, quarantine, healthcare disruption, and economic instability

Why were Healthcare Workers Especially Vulnerable during Ebola Outbreaks?

Limited PPE, unfamiliar disease presentations, and inadequate resources increased occupational exposure

How did Ebola-Related Fear affect Animal Welfare?

Fear of dogs as possible sources of infection contributed to abandonment and increased stray populations

What is the Veterinary Role in Outbreak Risk Communication?

Provide accurate scientific information to prevent misinformation and unnecessary harm to animals

How can Veterinarians help prevent Outbreaks Before They Occur?

• Vaccination research

• Surveillance

• Management changes

• Preventive education

What are the Major Roles of Veterinarians in Population Health?

• Lead investigations

• Study zoonotic threats

• Develop interventions

• Communicate with stakeholders

Outbreak Investigation Basics SUMMARY

Question	What Investigators Need to Determine
Who?	Which individuals, species, or populations are affected?
What?	What disease or health event is occurring?
When?	When did cases begin and occur?
Where?	Where are the cases geographically located?
Why?	What risk factors or conditions contributed to the outbreak?
How?	How is the disease transmitted or spreading?
Now what?	What interventions are needed to control the outbreak?

Key concept: Outbreak investigations identify disease patterns, sources, transmission pathways, and appropriate interventions.

Outbreak Response Organizations SUMMARY

Organization	Primary Focus	Main Priorities
USDA APHIS	National animal health	Rapid disease control, limiting economic losses, protecting agricultural trade
CDFA	California animal health	Disease detection, quarantine, surveillance, eradication, recovery
WHO	Human and international public health	Epidemiological investigation, case management, health education, logistics, coordination
One Health Teams	Human, animal, and environmental health	Multidisciplinary investigation, zoonotic disease control, prevention

Remember:

• USDA and CDFA emphasize animal disease management

• WHO emphasizes human health

• One Health integrates all three health sectors

Veterinary vs. Public Health vs. One Health Responses SUMMARY

Category	Veterinary	Public Health	One Health
Primary Focus	Animal populations	Human populations	Humans, animals, environment
Major Concern	Animal disease, welfare, economic losses	Human illness, transmission, community safety	Interconnected disease risks
Investigation	Herd surveillance, animal diagnostics, movement tracing	Human case surveillance, contact tracing	Integrated animal-human-environmental surveillance
Interventions	Vaccination, quarantine, animal management	Vaccination, education, infection control	Coordinated interventions across sectors
Example	Saiga antelope die-offs	West African Ebola response	Rift Valley fever control

Key distinction: Veterinary and public health responses have different primary populations, while One Health combines their perspectives to address shared disease risks.

Epidemiological Data Organization Tools SUMMARY

Tool	Purpose	Information Collected	Example
Line List	Organizes individual case data	Species, age, clinical signs, onset, location, exposures	Comparing cattle with similar symptoms
Geographic Map	Identifies spatial disease patterns	Case locations, geographic clusters	Mapping affected farms
Contact Tracing Diagram	Identifies connections between cases	Contacts, exposure relationships, possible transmission links	Tracing animal movement between farms

How to Differentiate the Three Tools

• Line list = WHO and WHAT: Who is sick, and what characteristics do cases share?

• Map = WHERE: Where are cases occurring?

• Contact tracing = HOW: How might cases be connected?

All three tools can also help analyze when cases occurred and identify possible disease sources.

Veterinary Contributions to Outbreak Investigations SUMMARY

Veterinary Role	Contribution	Example From Lecture
Disease Surveillance	Detect unusual disease patterns early	Rift Valley fever monitoring
Epidemiological Investigation	Identify sources, risk factors, and transmission pathways	Saiga antelope outbreaks
Laboratory Diagnostics	Identify causative pathogens	Ebola laboratory task force
Outbreak Leadership	Coordinate epidemiological and field response teams	Veterinarians leading Ebola response teams
Disease Prevention	Develop vaccines and other interventions	Rift Valley fever vaccination research
Risk Communication	Educate communities and reduce misinformation	Addressing fears about dogs during Ebola
One Health Collaboration	Integrate animal, human, and environmental perspectives	Rift Valley fever prevention

Key concept: Veterinarians are not limited to treating individual animals. They can lead outbreak investigations, coordinate responses, conduct research, and develop population-level interventions.