Lecture 9: Epidemiology and Diagnosis of viral Diseases Flashcards
What is epidemiology?
Epidemiology: ‘’Study of the distribution and determinants of health-related states among specified populations and the application of that study to the control of health problems’’ CDC
What is the viral life cycle?
Execration from infected animal -> transfer to new susceptible host -> replication within new host -> Execration from new host
Cycle repeats over and over.
What are the factors that affect disease potential?
What are the host factors that impact viral diseases?
- Age, Gender
- Immune status
- Vaccination status
- Reproductive status
- Genetics
What are the environmental factors that impact viral diseases?
- Geography
- UV light
- Climate
- Organic matter
- Season
- Ammonia concentration
- Water activity
What are the the agent (pathogen) factors that impact viral diseases?
- Dose
- Virulence
- Infectivity
- Pathogenicity
What are the objectives of studying viral epidemiology?
To identity the causative agent of viral disease and the relevant risk factors
• To assess the severity of viral disease appeared in certain animal/human population
• To study the natural history and outcomes of some viral disease of interest
• To evaluate the efficacy and potency of some preventive and therapeutic strategies against
some viral diseases
What is the benefit of using epidemiology in viral diseases?
- To study the cause (or etiology) of disease(s), or conditions, disorders, etc.
- To determine the primary agent responsible for some viral diseases
- To determine the characteristics of the viral diseases or and other causative factors
- To determine the mode of transmission of viral diseases
- To determine the contributing factors to viral infection
- To identify and determine geographic patterns of the viral diseases
What is this photo in reference to?
Iceberg concept of diseases
What is this photo in reference to?
Iceberg concept of diseases
What is an endemic?
What is an epidemic?
• Epidemic = Epizootic: The peaks in diseases incidences which exceed the endemic base line or expected incidence of diseases
What is a pandemic?
• Pandemic = Panzootic Ve r y extensive worldwide epidemic (SARS-CoV-2, H1N1, etc)
What is an incubation period?
Incubation period: the time intervals between the infection and the appearance of the clinical signs on the affected host
What is sero-epidemiology?
Sero-epidemiology: using serological data as basis for epidemiologic investigations
What is molecular epidemiology?
Molecular epidemiology: using molecular data as basis for epidemiologic investigations
What is morbidity rate?
Morbidity rate: the percentage of animals in population that develop clinical signs out of the total number of the population
What is mortality rate?
Mortality rate: the percentage of dead animals from viral infection in relation to the total number of population
What is descriptive epidemiology?
-Studies that generate hypotheses and
answer the following questions
-Who?
-What?
-When?
-Where?
is the disease or infection
-Person, Animal, Place, and time
What is analytical epidemiology?
-Studies that carried out to test for
hypotheses and to generate conclusions
on the particular disease.
-answer the following questions
-Why
-How
is the disease or infection
-Use to identify the cause of a viral
disease or an outbreak with virus
What are the aims of epidemiological surveillance in viral diseases?
- To help in the discovery and controlling the transmission of viral infectious diseases
- To help in the prevention and control programs for the viral infectious diseases
What is active public health surveillance types?
Local or state health departments initiate the collection of information from laboratories, physicians, health care providers, or the general population.
Achieves more complete and accurate reporting than passive surveillance Ex: Youth Risk Behavior Surveillance
surveys
What are passive public health surveillance types?
Laboratories, physicians, or others regularly report cases of disease or death to the local or state health department
Examples
-A doctor’s office reports 2 cases of measles
-A nursing home reports an unusual number
of older patients with unexplained rashes
What are syndromic public health surveillance types?
The ongoing, systematic collection, analysis, interpretation, and application of real-time indicators for disease that allow for detection before public health authorities might otherwise identify them
Example:
Hospital admittance records
What are the types types of epidemiologic investigations?
Case-control studies (retrospective)
Cohort studies (prospective or longitudinal)
Cross-sectional studies
Long-term herd studies
What are case control studies?
- Investigation starts after the diseases episode starts
- Used to identify the cause of disease outbreak
- Use the existing data and less expensive
- Requires careful selection of the control groups matching the subject group
- Unit of interest is individual animals or aggregates (herds/flocks)
What are cohort studies?
-Investigation starts with a presumed diseases episode
-Requires creation of new data and records
-Requires careful selection of control group to be as similar/close to the exposed group with absence of any
contact with the causative agent
-Very expensive due to long term followup until disuses is detected in the population
-Proof of cause-effect relationship is very strong
-It may progresses into cross sectional or longitudinal studies
What are cross- sectional studies?
- The cause of specific diseases is known
- Can be carried out relatively quickly by the serology or virus identification
- Provides data on the prevalence of virus infection in a population in specific area
What are long-term herd studies?
-Provides info about presence and continued activity of
virus in given area
-Could be run as series of cross sectional studies
-Can be designed to produce data on the efficacy of some vaccines and drugs
What are the sources of virus’?
- Clinical cases
- carriers
- animal products
What are the routes of viral shedding?
Oral
Fecal
Milk
Skin
Urogenital tract
Respiratory
What is an example of oral viral shedding?
Oral
-Rabies execrated in saliva of infected animal
What are virus’ that sheds in the feces? What is an example?
-Enteric viruses execrated in high titters in faeces
Ex: BCoV
What are some viruses shed in milk?
Milk
-Some viruses excreted in milk during viremia
EX-1 FMDV EX-2 BLV
How can virus’ be transmitted via skin? What is an example of a virus that sheds this way?
Skin
- Scabs from skin lesions very rich with virus in case of Poxvirus
- Feather follicles of chickens are very rich with MDV
How can virus’ be transmitted via the urogenital tract? What is an example of a virus that sheds this way?
Urogenital tract
-Some viruses excreted in urine and genital secretions during viremia Ex: Herpesviruses
How can virus’ be transmitted via the respiratory tract? What is an example of a virus that sheds this way?
Respiratory
Coughing, sneezing, halation of discharges from nose and mouth of infected animal
Particles larger than ____ um fall out of suspensions and contaminate the environment. Smaller particles rapidly dehydrated to form droplet nuclei of 10 um or less, which remain airborne which can be inhaled by a susceptible animal
100
visualization using light refraction caused by
differences in air density) of a human cough
Flash photo of a human sneeze
What are the modes of transmission of viral disease? What are some examples?
Direct: Direct contact, droplet spread
Indirect: Airborne, vehicle borne, vector borne
vector borne: mechanical, biological
What are the epidemiological based antiviral control strategies?
- Quarantine procedures
- Sanitation procedures
- Wildlife control
- Vector control
- Vaccines
What is the goal of quarentine procedures?
I- Quarantine procedures: restriction of the source of virus infection including
A- Prohibition/restrictions importation of livestock and animals from certain areas where exotic diseases spread
B- Quarantine and testing of the imported livestock at the portal of entry
C- Restrictions of the animal movements during the epidemics
D- Keep the closed herds strategies to avoid the introduction of any viral infections
What are the common methods of viral inactivation?
Heat
UV irradiation
Ionizing irradiation
pH extremes
Desiccation
How heat can inactivate a virus?
- High temp has deleterious effects on most viruses
- Low temp has preservation effects on viruses
How can UV irradiation can inactivate a virus?
Some viruses destroyed when exposed to sunlight
while UV irradiation has weak penetration effects
How can how ionizing irradiation can inactivate a virus?
Inactivates viruses rapidly and has very strong
penetration Ex: Gamma irradiation used to sterilize
disposable syringes and needles
How can desiccation can inactivate a virus?
Most viruses rapidly destroyed by drying except Poxvirus
How can pH extremes can inactivate a virus?
Most viruses inactivated by pH less than 4 and greater
than 9
What are the common chemical viral disinfectants?
Chlorine and iodine
Formaldehyde
Phenolic compounds
Caustic Soda
70% alcohol
Chlorohexidine hibitane
Detergents
How does chlorine and iodine kill viruses?
- Hypochlorite: cheap but rapidly inactivated by organic matters
- Iodophores: more stale, less corrosive, more expensive
How does formaldehyde kill viruses?
Reliable antiviral but hazardous due to toxicity
-Glutraldhyde: useful but more expensive
How do phenolic compounds kill viruses?
-Although widely used commercial disinfectants, it is not
reliable in case of enveloped viruses
How does caustic soda kill viruses?
- Effective against many viruses
- Relatively inexpensive
- Corrosive
How does 70% alcohol kill viruses?
- Good antiviral disinfectant
- its use restricted by the coast to small scale procedures as disinfection of instruments
How does chlorohexidine hibitane kill viruses?
-Unreliable against nonenveloped viruses
How do detergents kill viruses?
-Useful as cleaning agents but are effective against enveloped viruses only
What are the objectives of sanitation procedures?
Objectives: To reduce the spread of viral infections including
A- Slaughtering then safe disposal of the carcases by incineration or burial of the infected animals
B- Hygienic disposal of the foodstuffs, bedding and animal manures
C- Disinfection of buildings and surfaces
What are the objectives of wildlife control?
Objectives: To restrict the sources of infection by reducing the risk of exposure of domestic animals to the
reservoir hosts
A- Keeping the live stocks in houses
B- Fencing of pastures
C- Destruction/vaccination of the wildlife (Ex: Rabies virus)
What are the objectives of vector control?
Objectives: To reduce the potential risk of spread of viral infections by insect vectors
A- Apply insect proofing an control barns
B- Dipping or spraying of animals with appropriate insecticides to control ticks, fleas, and lice
C- Environmental spraying with larvicides to control mosquitoes
Surveillance of animal diseases provides ?
information about the diseases (prevalence, incidence, epizootic spread etc)
What is a notifiable disease?
-Veterinarians have to report the prevalence of some viral disease to the local veterinary authorities.
-Local veterinary authorities/country must inform the World Organization for Animal Health (OIE) about the prevalence of
some viral diseases
- The OIE may notify the neighbouring countries and the world community about the prevalence of some diseases in certain
region/country
• The OIE has listed the notifiable diseases on its website and in regular brochures
What are sources of surveillance data?
- Notifiable diseases reports
- Laboratory based surveillance
- Population based surveillance
What occurs in the early phase of the discover to control continuum?
- Identify the major parameters of epizootic potential (mortality rates, severity, transmissibility)
- Discovery of new diseases in its host population
- Zoonotic diseases handled by Vet Practitioner
- Epidemiologic field investigation
- Etiologic investigation: to identify the causative virus of the outbreak
- Diagnostic development: to develop some laboratory tests that enable the sensitive, accurate and specific detection of the causative virus
What occurs in the intermediate phase of the discover to control continuum?
-Expansion of many elements
Focusing research about the etiology of this outbreak (vector biology, zoonosis)
-Training, outreach, continuing education and public education
-Risk communication using the common methods as internet, TV, radio, media
Technology transfer (diagnostic, vaccine sanitation and vector control) vaccine sanitation and vector control)
-Commercialization of diagnostic and vaccines from research to production in large scale
What occurs in the late phase of the discover to control continuum?
- Animal health development system
- Special clinical system
- Development of public infrastructure system
- Largest epidemic may require test and slaughtering, restrict movement
- Involvement of international agencies
What are the steps of a viral disease outbreak investigation?
- ) Confirm occurance
- ) identify causative agent
- ) build case definition and how to identify cases
- ) Describe the epidemic (time, place, and animal identification)
- ) Build up + test hypothesis
- ) Conduct environmental epidemiological studies.
- ) Come up with conclusions
- ) Suggest appropriate control measure
- ) Suggest some relavent appropriate control measures
- ) Distribute the recommedation to the stockholders.
For example: Avian influenza
What is the standard quarentine zoning measures?
- Infected Zone: Minimum 3 km radius of the infected premises
- Buffer Zone: The area between 3 km and 10 km of the infected premises will be considered the buffer zone
- Control Zone: Infected and buffer zone
- Surveillance Zone: at least 10 km and may be wider
What are the recommended measures for the control of HPAI-Farm level?
- Keep poultry away from areas frequented by wild fowl
- keep control over access to poultry houses by people and equipment
- Maintain sanitation of property, poultry houses and equipment
- Appropriate disposal of manure and dead poultry
- Generally ‘stamping out’ (culling) to eradicate the disease
- Appropriate disposal of carcasses and all animal
What is the HPAI-Control Poultry Carcass Management strategy?
Burial : fast and cheap, but concerns about environment
increasing
-Burry the dead carcasses and overlaid with lime stone
Incineration: several types of incineration units were used with
varying degrees of success
