Unit 2 - Lecture 12 Viral Epidemiology Flashcards
What are the terms of Epidemiology?
- Study
- Distribution
- Determinants
- Health-related states
- populations
- control
Define Study?
Study: epidemiology is a highly quantitative discipline based on principles of statistics and research methodologies
What is Distribution?
Distribution—frequencies and patterns of health events within groups in a population (“when”, “where”, and “whom”).
What are Determinants?
Determinants—search for causes or factors that are associated with increased risk or probability of disease (“how” and “why”).
What are health-related states?
Health-related states—applied to the whole spectrum of health-related events, which includes chronic disease, environmental problems, behavioral problems, and injuries in addition to infectious disease.
What are populations?
Populations— epidemiology deals with groups of people rather than with individual patients.
What is a control?
Control—data steers public health decision making and aids in developing and evaluating interventions to control and prevent health problems.
What is an Endemic?
Endemic—diseases that persist at a moderate or steady state level within a given geographic area.
ex: Chicken Pox in US
- malaria is not endemic to US
What is Epidemic?
Epidemic—an unusually high number of cases in excess of normal expectation of a similar illness in a population, community or region.
Ex: Seasonal influenza, yellow fever (1793), cholera (1865) dengue in bolivia (2009)
What is pandemic?
Pandemic: a worldwide epidemic
ex: 1918 influenza, HIV and smallpox
What is Sporadic?
Sporadic—disease outbreaks that have no pattern of occurrence in a given time or location.
What is incidence?
Incidence—measurement of morbidity; the number of new cases of a disease that occurs in a specified period of time in a susceptible population; usually expressed per 1000 persons
There is an equation!
Incidence rate = number of new cases of a disease in a population during a specified time frame / number of persons exposed to risk to developing disease during a specified time frame x1000
What is Prevalence?
Prevalence—measurement of all individuals affected by a disease at a specified time; also recorded per 1,000 persons
Equation:
Prevalence = number of cases of disease present in a population during a specified time frame / Number of persons at risk of having disease at a specified time frame
What is Morbidity?
Morbidity: refers to an illness or disease state
What is Mortality?
The number of deaths correlated with a particular disease during a given time frame
Mortality rate:
Mortality rate = Number of deaths in a population during a specified time frame / number of persons in the population during a specifiied time frame
What is the Incubation period?
Incubation period is the time between infection with a virus and the onset of symptoms.
What is the prodromal period?
Prodromal period - first appearance of mild or nonspecific signs and symptoms of an illness.
What is Mode of Tranmission?
Mode of transmission—how an infectious disease is spread or passed on.
What is Etiological agent/pathogen?
Etiological agent/pathogen—disease causing agent.
What is the Reservoir?
Reservoir—where the etiological agent lives, grows, and multiplies (e.g., human, animal or arthropod).
What is a Case definition?
Case definition—a standard set of criteria that is used to identify who has the disease being studied.
What is Communicable Period?
Communicable period—time period when an infected individual or animal is contagious and he/she can directly or indirectly infect another person, animal, or arthropod.
What is convalescence?
Convalescence—the recovery period after an illness
What is Zoonosis?
Zoonosis—any infection or infectious disease transmissible from animals to humans.
What is the History of Epidemiology?
Pioneers of epidemiology
Their important observations and actions led to disease prevention:
Edward Jenner (1796, smallpox)
John Snow (1854, cholera)
Florence Nightingale (1855, mortality rates of wounded British soldiers during the Crimean War)
Who is John Snow?
John Snow (1813-1858)
- 19th century physican
- Believed in the germ theory of disease during a time period when most people believed in the miasmatic theory
- Miasma: polluted gases from swamps or decaying matter that cause disease
- Groundwork for descriptive epidemiology
Who is Florence Nightingale?
- Credited mostly for her modernizing nursing practices of the times
- Collected statistics and mapped mortality rates of British soldiers during the Crimean War
- Observed unsanitary conditions in the army hospital
- Soldiers were dying of typhus, cholera, and dysentery instead of battle wounds.
- Nightingale believed these infections were preventable.
What are the complexities of disease transmission?
There are many factors associated with increased risk of diease transmission.
What are the host characteristics that are associated is the factors of disease transmission?
Some Characteristics that are involved are:
- Age
- Sex
- Reace and genetic factors
- Immune status (decreased)
- Nutritional status (lack)
- Behavior (e.g. occupation, lifestlye, religion, customs)
- Previous infection or current coinfections.
What are the factors from the pathogen to cause disease?
- Stability is the environment
- virulence factors
- Presence of immune evasion gnes
- Resistance to antiviral therapy
- Enhanced mode of transmission
Within Modes of transmission:
What is direct?
What is indirect?
Direct: person to person
Indirect: Virus is transferred or carried.
What is the Chain of infection?
How do you break the chain of infeciton?
Chain of infection: term frequently used in hospitals with regard to the control and prevention of infectious diseases.
Ways to break the chain:
- Rapid ID of pathogen
- Proper snitation
- Disinfect or sterilize fomites
- Barrier technique
- handwashing
- Proper trash and waste disposal
- Proper food handling
- Aseptic technique
- Recognition of high risk individuals
What is the concept of Herd immunity?
If the majority of population (herd) is mostly protected from a disease through immunization or genetic resistance, the chance of a major epidemic is unlikely.
When a population lacks herd immunity the disease spread very quickly or to many people
What does an epidemiologist want to know?
- Case definition (what)
- Person (Who)
- Place (where)
- Time (when)
- Risk factors (how and why)
When gathering data…
What are descriptive studies?
What is analytical epidemiology?
Descriptive studies
- Performed right after the epidemic occurs
- Short study (e.g., Snow’s 1854 cholera study)
- Published as case reports
- Leads to lengthier, larger analytical studies
Analytical epidemiology
- Determines the “why and how” of the epidemic
- Hypothesis-driven studies
- May involve control group
- Cohort method (2 similar populations)
Surveillance and serlogical epidemiology has several forms:
- Monitor available data from mandated reports on reportable diseases
- Active field surveillance at healthcare facilities
- Serological screening of populations
- antibodies are the “footprints” of disease exposure and protection against disease.
A method of surveillance can be down with chicken. Describe the scenerio of the
Sentinel Chick Surveillance Program
- Canadian health authorities used sentinel chickens along the Canadian/U.S. border to monitor for the presence of West Nile virus in 2000.
- Chickens with West Nile develop a very short viremia without symptoms.
- Scientists draw blood
- looking for WNV antibodies.
How are tracking diseases from outer space done?
- Environmental factors play a role in outbreaks of viral illnesses.
- Use of satellites to monitor changes on land surfaces.
——-Heavy rainfall (more mosquito eggs laid in standing water)
———Temperature changes
———Vegetation changes
How are infectious diseases contained?
What is Quarantine?
- Practice of quarantine is still used today to prevent person-to-person transmission of infectious diseases (e.g., SARS outbreak, tuberculosis)
Individual is thought to have been exposed to another individual suffering from a communicable disease
Animals too
- Isolation: separation of ill individuals from healthy individuals
- Placards
What are things to consider while traveling?
- What arthropod vectors are in the area?
- Is there contaminated food or water (food and waterborne illnesses)?
- What medical facilities exist in remote areas?
What are some Medical facilities?
- 15 percent of the population in rural Kenya is infected with HIV
- Many live in districts with fewer than one doctor for every 15,000 patients
- Clinics lack supplies, medicines, and expertise
- Gov’t, religious groups, and private organizations provide support to remote areas of developing countries
- Travelers should take active steps to minimize the risk of injury and infection
Epidemiology Example: Nipah Virus
How was this virus come about?
- Based on seroprevalence data and virus isolations, the primary reservoir for Nipah virus was identified as Pteropid fruit bats
Pteropus vampyrus (Large Flying Fox)
Pteropus hypomelanus (Small Flying-fox)
- Overlap between bat habitats and piggeries in peninsular Malaysia
fruit orchards were in close proximity to the piggery
spillage of urine, feces and partially eaten fruit onto the pigs
What is a Nipah Virus?
What is the structure?
How is it diagnosised?
What are the clinical features?
- Negative strand ssRNA
- Helical, enveloped
Diagnosis:
- serum neutralization
- ELISA
- PCR
- immunofluorescence assay
- virus isolation by cell culture
Clinical features:
- fever, migraine, vomiting, myalgia, and coma
- case-fatality rate of 40%
Continued Nipah Virus
Where and when did this virus come about?
- Outbreak of febrile encephalitis in Malaysia in September 1998.
- Initially thought to be Japanese encephalitis
- Preceded by the occurrence of illness and excessive mortality in pigs in 3 pig-farming areas in same affected suburb
Epidemiology Example: Nipah Virus
Who did it affect?
- Ministry of Health Malaysia recorded a total of 283 cases of viral encephalitis with 109 deaths from 29 September 1998 to December 1999
- 86% of case-patients reported touching or handling pigs before the onset of illness
- Majority of patients were from 21 to 60 years of age (88.1%)
- Largest number of cases (15.9%) occurred in the 40-44 year old age group, followed by the 30-34 and 25-29 age groups (13.8% and 13.1%, respectively)
What is the prevention and control of the Nipah Virus?
- Nationwide campaign to educate people on the dangers of JE and its mosquito vector
—-fogging of pesticides were carried out on 18,586 pig farms and 403,837 houses in the vicinity of the pig farms
- Phase I: Immediate eradication by mass culling of pigs
—–1 million swine; significant impact pig industry in Malaysia
- Phase II: Antibody surveillance of high-risk farms to prevent future epidemics
- Additional actions: ban on transporting pigs within the country
—-No US imports from Malaysia during 1999 epidemic
What are the fundamental Concepts?
- Epidemiology is the branch of science that deals with how diseases affect groups (whole communities or populations).
- —-Disease diagnostics,trends, prevention, and control measures
- —Common terms
- —-Pioneers in the field include Snow and Nightingale
- Vaccination is an effective way to create herd immunity to prevent further spread of infectious disease
- Two types of epidemiological investigations:
- Descriptive= provides the “what, when, where, and who” of an outbreak
- Analytical= provides the “why” and “how” of an outbreak
- Surveillance programs and reporting systems play a fundamental role in public health
- —Gov’t and private organizations
- —Quarantine and isolation techniques
- Medical clinics established globally to met the needs of travelers
—–Lack of proper supplies, medicines, and experienced staff
- Changes in environment may set the stage for new diseases.
- Nipah virus epidemiology
