infectious disease epidemiology seminars

Epidemiology

1. Topic : infectious disease epidemiology By YOANNES BUTI MAYIK program: MPH in Epi/Bio IDNO: PRPGMHS/025/17 Moderator: ABAYNEH TUNJE ( PhD ) Seminar Presentation

2. INFECTIOUS DISEASES EPIDEMIOLOGY Introduction Epidemiological Pattern Epidemiological Indicators Dynamic o f Disease Transmission Mode of Disease Transmission Prevention and Control Infectious Disease Model 10/23/2025 infectious disease epidemiolgy 2

3. Learning Objectives: Infectious Disease Epidemiology By the end of this seminar, learners will be able to Define the concept of infectious disease epidemiology. Describe the epidemiological patterns of infectious diseases. Identify and interpret key epidemiological indicators used in infectious disease studies. Explain the chain of disease transmission and its components. Differentiate the modes of disease transmission. Discuss prevention and control strategies for infectious diseases. Understand the basic principles of infectious disease modeling. 10/23/2025 infectious disease epidemiolgy 3

4. Infectious disease epidemiology Epidemiology is the study of the distribution and determinants of health related states or events in specified populations, and the application of this study to control health problems ( Last, 2023 ). Infectious Diseases are an illness caused by a pathogenic microorganism such as bacteria, viruses, fungi , or parasites that can be spread directly or indirectly from one person (or animal) to another. 10/23/2025 infectious disease epidemiolgy 4

5. Infectious disease…. Infectious disease epidemiology is the study of the distribution, patterns, and causes of infectious diseases in populations to control their spread and mitigate their public health impact (Elsevier, ScienceDirect Topics, 2025) Its answer question like who gets sick , where , and when By using method like outbreak investigations, modeling and data analysis to understand disease dynamics.   10/24/2025 infectious disease epidemiolgy 5

6. Infectious disease terminology Infection : Process in which a pathogenic organism enters, establishes itself, multiplies and invades the normal anatomical barrier of the host resulting in disease Colonization : Pathogenic organism enters, multiplies but does not invade, and neither causes disease nor elicits a specific immune response Unlike normal flora colonizers have pathogenic potential 10/23/2025 infectious disease epidemiolgy 6

7. Infectious disease terminology Infestation : Inhabiting the surface of the body of the host without penetrating into the tissues ( ecto -parasites). Acting as important vectors to transmit the pathogenic microbes such as louse, fleas , mites and ticks , etc 10/23/2025 infectious disease epidemiolgy 7

8. Communicable vs. Infectious Diseases Infectious diseases are illnesses caused by germs (such as bacteria, viruses and fungi) that spread from person to person, are transmitted by insects or other animals, or are present in the air, water, food, or soil. Communicable disease spread from person to person, or from animal to person (e.g., through body fluids or droplets). All communicable diseases are infectious. Note : not all infectious diseases are communicable (e.g., tetanus is infectious but not communicable). 10/23/2025 infectious disease epidemiolgy 8

9. Epidemiological pattern Epidemic : the occurrence of a disease in a population at a level that exceeds what is normally expected in a specific time and place . Outbreak: sudden rise in the number of cases in a limited geographic area Endemic : disease that is constantly present in a population or region at a predictable level. 10/23/2025 infectious disease epidemiolgy 9

10. Epidemiological pattern.. Sporadic disease : a disease that occurs infrequently and irregularly in a population , with no predictable pattern . Pandemic : an epidemic of a disease that spreads across multiple countries or continents, affecting a large number of people . Exotic disease : a disease that is rare or absent in a particular country or area, often imported from another region. 10/23/2025 infectious disease epidemiolgy 10

11. Epidemiological pattern.. Z oonotic diseases: infectious diseases that are naturally transmitted between animals and humans . Epizootic : a disease that appears suddenly and spreads rapidly among animals in a particular area, thread to human. Nosocomial infection: an infection acquired by a patient during their stay in a hospital or healthcare facility, 10/23/2025 infectious disease epidemiolgy 11

12. Epidemiological pattern… Notifiable diseases : disease that must be reported to the public health authority in the pertinent jurisdiction when the diagnosis is made Elimination : Interruption of transmission of disease in a given geographical area or region Eradication : Termination of an infection from the whole world, so that disease will no longer occur in the world 10/23/2025 infectious disease epidemiolgy 12

13. Epidemiological indicators 10/23/2025 infectious disease epidemiolgy 13 Incidence proportion (or attack rate or risk ) Secondary attack rate Incidence rate (or person-time rate ) Point prevalence Period prevalence Case fatality ratio Mortality rate Morbidity indicators Mortality indicators

14. Dynamics of disease transmission 10/23/2025 infectious disease epidemiolgy 14

15. Agent factors Infectious microorganism such as a virus, bacterium, parasite, or fungus that is responsible for the causation of the disease Presence of those agents alone are not always sufficient to cause the disease variety of agent related factors influence whether the exposure to an organism will result into disease 10/23/2025 infectious disease epidemiolgy 15

16. Agent factors… Organism’s Pathogenicity : Ability of the organism to cause disease Infective Dose : Infective dose is the minimum inoculum size that is capable of initiating an infection Source: Refers to a person, animal, or object from which the microorganism is transmitted to the host Reservoir : Natural habitat in which the organism lives and multiplies 10/23/2025 infectious disease epidemiolgy 16

17. Reservoirs Human reservoir Animal reservoir Non-living things as reservoir 10/23/2025 infectious disease epidemiolgy 17

18. Human reservoirs Human sources may be either cases or carriers Cases or patients : Persons in a given population having a particular disease Carrier : Persons who harbor the infectious agent in the absence of any clinical symptoms and shed the organism from the body via contact, air or secretions 10/23/2025 infectious disease epidemiolgy 18

19. Types of carriers Incubatory carriers: Shed the organism during the incubation period of the disease Healthy carriers : Subclinical cases who develop into carriers without suffering from overt disease Convalescent carrier: Who has recovered from the disease and continues to harbor and shed the pathogen from his body Temporary/ chronic carriers : Depending on the duration of carriage 10/23/2025 infectious disease epidemiolgy 19

20. Animal reservoirs Animal may be case or carriers The diseases transmitted from vertebrate to human being are called zoonosis e.g Rabies, influenza and yellow fever etc. Wild birds are important hosts in transmission cycle of the most mosquito borne encephalitis 10/23/2025 infectious disease epidemiolgy 20

21. Non-living thing as a reservoirs Soil and inanimate matter can also act as reservoir/source of infection for example, soil may harbor the agents of tetanus, anthrax and some intestinal helminthes such as Trichuris, hookworm and Ascaris 10/23/2025 infectious disease epidemiolgy 21

22. Mode of transmission Direct contact Inoculation into skin contact with soil Droplet infection Vertical/ Tran-placenta Vector borne: biological/ Mechanical Airborne: droplet nuclei/dust Vehicle borne Fomite borne unclean hand and fingers Direct transmission Indirect transmission 10/23/2025 infectious disease epidemiolgy 22

23. Susceptible Host Host : A person or animal including birds or arthropods that affords subsistence or lodgment of an infectious agent under natural conditions . Obligate host : Means the only host. Eg : Measles Definitive host : Hosts in which parasites attains maturation or passes it’s sexual cycle Intermediate host : Host in which parasite in asexual or larval state 10/23/2025 infectious disease epidemiolgy 23

24. Susceptible Host Age Gender Nutritional status Immunity Immunization Behavioral factor Literacy Marital status Obligate host Definitive host Intermediate host Host factors in communicable disease Type of host 10/23/2025 infectious disease epidemiolgy 24

25. Successful parasitism Four stages: Portal of entry Site of election Portal of exit Survival capacity in external environment 10/23/2025 infectious disease epidemiolgy 25

26. Environmental factors Many diseases are common in winter such as influenza and meningococcal meningitis Vector-borne diseases such as malaria, dengue are more common in rainy season which parallels with mosquito breeding Organisms which are more resistant to the action of disinfectant can survive in the environment for longer . 10/23/2025 infectious disease epidemiolgy 26

27. Infectious disease modeling Infectious disease modeling is the use of mathematical and computational approaches to understand how diseases spread predict future trends, and assess control strategies . It helps public health decision making by simulating disease dynamics 10/23/2025 infectious disease epidemiolgy 27

28. Important of infectious disease modeling Provide information that can be used to understand disease transmission and compare control option Predicts disease outbreaks and epidemic peaks Assesses effectiveness of interventions (e.g., vaccination, quarantine) Guides resource allocation and policy decisions 10/23/2025 infectious disease epidemiolgy 28

29. Basic model types Deterministic models : used fixed parameters (e.g., SIR, SEIR ) Stochastic models : its include randomness to simulate variability( e.g , Chain binomial models, (CTMC) Models) Agent based models : its simulate individual interactions Network models : its represent transmission through contact networks 10/23/2025 infectious disease epidemiolgy 29

30. Sir models β : transmission rate γ: recovery rate d : the rate of change(differential) t: time 30

31. Infectious disease prevention and control Disinfection Treatment Isolation Quarantine Immunization Notification 10/23/2025 infectious disease epidemiolgy 31

32. Conclusion Infectious disease epidemiology plays a crucial role in detecting, monitoring, and controlling infectious threats. It combines surveillance, field investigation, and data analysis to guide public health interventions and improve global health outcomes. Infectious disease models are essential tools in public health planning and response, offering insights for prevention, control, and preparedness 10/23/2025 infectious disease epidemiolgy 32

33. Acknowledgement I would like to express my heartfelt gratitude to ABAYNEH TUNJE ( PhD ) for granting me the opportunity to deliver this seminar presentation on the topic of infectious disease epidemiology . It has been a truly enriching learning experience and I am sincerely thankful for the chance to engage in academic discourse through this presentation. 10/23/2025 infectious disease epidemiolgy 33

34. References Last, J. M., Spasoff , R. A., Harris, S. S., & Thuriaux , M. C. (Eds.). (2023). A Dictionary of Epidemiology (6th ed .). Elsevier, n.d. Infectious disease epidemiology – an overview . ScienceDirect Topics . Available at: https://www.sciencedirect.com/topics/medicine-and-dentistry/infectious-disease-epidemiology [Accessed 14 Oct. 2025 ]. Hethcote , H. W. (2000). “The Mathematics of Infectious Diseases.” SIAM Review, 42(4), 599–653. https://doi.org/10.1137/S0036144500371907 10/24/2025 infectious disease epidemiolgy 34