Epidemiology Chapter 1

What are some common ways of preventing and controlling vertically transmitted diseases?

Control and prevention of other diseases that are vertically transmitted may be possible by vaccination, separation of breeding animals from those that may have been exposed to diseases, and quarantine of incoming animals.

What are the three levels of prevention?

1. National 2. Provincial/State 3. Local (Farm)

What are the 5 basic catagories of biological (Eitiological) agents?

1. Protazoa 2. Bacteria & Rickettsia 3. Viruses and Prions 4. Fungi 5. Metazoa (Parasites)

Define Contact

A person or animal that has been in such association with an infected person or animal, or a contaminated environment, as to have had an opportunity to acquire the etiologic agent.

Define simple diseases

Diseases where an agent is the main determinant, and host and environmental factors are of relatively minor importance

Define Bacteriophage

A virus that lyses bacteria

Define Antigenicity

Ability of an agent or its products to stimulate the formation of antibodies.

Define Cohort

Any defined group of animals or persons selected for special purpose or study

What does Febrile mean?

Having a fever or showing the symptoms of.

List some environmental factors

Location Climate - Acclimate - Microclimate Husbandry - Housing - Diet - Managment - Stress

What is a silent (innaparrent) infection?

One in which the infected host does not have symptoms

What are acute clinical cases?

Sick animals

Define asepsis

The absence of infectious microorganisms.

What are Chronic carriers?

Those animals which continue to harbour infectious agents for a year or more.

Define Secondary determinants

correspond to, predisposing, enabling or reinforcing factors.

Define horizontal transmission

disease is spread from one individual to another. There are two main forms of horizontal transmission: direct and indirect.

What factors does the host's susceptibility depend on?

genetic factors, general factors of resistance and specific acquired immunity.

What is wrong with this picture?

It is missing management/husbandry

What is epidemiology?

study of disease in populations and of factors that determine its occurrence

What are inapparent infections?

(Type of carrier) Subclincal cases. i.e. Those individuals or animals who have an infection but show no signs or symptoms.

Define Decontamination

. The removal of an etiologic agent (a contaminant) from an animate or an inanimate surface.

Define Anamnestic response

.... The accelerated rise in antibody titre in an animal (or person) which had previously developed a primary immune response to the particular antigen.

Define Droplets

.Liquid particles expelled into the air during the act of talking, spitting, singing, coughing, or sneezing. Droplets are formed through aerosolization of secretions present in the mouth, nasopharynx and bronchi. They can contain infectious microorganisms.

List 7 ways of how you can protect an already infected population?

1) Immunisation 2) Chemoprophalaxis (an antibiotic) 3) Environmental sanitation 4) Vector Control 5) Genetic Engineering and selective breeding 6) Early Detection/diagnosis 7) Public Awareness/education

At what 3 levels are Foreign Animal Diseases controlled?

1) Import requirements and health certificates. 2) Quarantine stations. 3) Veterinarians must recognise and report the disease.

When should you use biological products instead of vaccines?

1) Incidence is widespread or increasing in spite of present control measures. 2) The technology to eradicate is not available. 3) It does not cause subclinical or carrier states and does not interfere with disease detection. 4) The disease is endemic.

What are the four approaches to control of disease?

1) Prevent spread 2) Decreasing communicability 3) Increasing resistance 4) Early detection and diagnosis

What are the ways in which you can eradicate a disease?

1) Selective slaughter (Kill walkers) 2) Depopulation (Kill everyone) 3) Quarentine (Prison) 4) Mass treatment (Finding the cure) 5) Mass immunization (Curing the walkers)

When trying to design an eradication program. You must onsider these points

1) The characteristics of the disease (method of transmission, life cycle, etc). 2) The characteristics of the vaccine. 3) The positive and negative effects that a vaccine could have on an eradication programme.

There are many factors that influence the efficacy of the vaccine (or any bioproduct) when used in field conditions. What are some of these factors?

1) What is the proportion of animals that actually get vaccinated? 2) Is the vaccine given according to label specifications? 3) Is the product maintained under appropriate storage conditions (i.e. temperature, expiration, etc)? 4) What is the proportion of immune-competent animals in the population?

What are the two main SOURCES of infection?

1. Acute clinical cases 2. Carriers

What is the chain of infection comprised of?

1. Causative agent 2. Reservoir of the agent 3. Portal of exit of the agent from the host 4. Mode of transmission of the agent to a new host 5. Portal of entry into the new host 6. Host susceptibility AGENT -> RES -> PORTAL Ex. -> MODE of TRANSM. -> PORTAL En. -> HOST SUSCEPT.

Define the 5 objectives of Epidemiology

1. determination of the origin of a disease whose cause is known; 2. investigation and control of a disease, whose cause initially is unknown; 3. acquisition of information on the ecology and natural history of disease; 4. planning and monitoring of disease control programmes 5. assessment of the economic effects of a disease and analysis of the costs and economic benefits of alternative control programmes.

What are the 3 Classification of determinants?

1. primary or secondary; 2. intrinsic or extrinsic; 3. associated with host, agent or environment.

Define Agent

A biological, physical, or chemical entity capable of causing disease.

Define determinants

A determinant is any characteristic that affects the health of a population.

Define Disease

A deviation from normal health status associated with a characteristic sequence of signs and symptoms and caused by a specific etiologic agent.

Define Antibody

A globulin, found in tissue fluids and blood serum, produced in response to the stimulus of a specific antigen, and capable of combining with that antigen to neutralize or destroy it. Globulins are often referred to as "immune substances".

Define Antibiogram

A list of those antibiotics to which a particular microorganism is sensitive or resistant.

Define Carrier

A person or animal that harbours a specific infectious agent (but manifests no discernible clinical disease) and is a potential source of infection for man or animals.

List some host factors

Age Sex Species and breed Size and conformation Previous Disease Coat colour Heredity Nutrition

Define Confirmed case

An animal or person from whom a disease producing agent has been isolated and identified or from whom has been obtained other laboratory evidence of the presence of an etiologic agent, i

Define Presumptive case

An animal or person with a clinical syndrome compatible with a disease but without laboratory confirmation of the etiologic agent.

Define Pandemic

An epidemic that affects several countries or continents or much of the world.

Define COMMUNICABLE disease

An illness which is caused by a specific infectious agent or its toxic products, and which arises through transmission of that agent or its products from a reservoir to a susceptible host. Such transmission can be either direct, as from an infected person or animal, or indirect, through the agency of an intermediate plant or animal host, vector, or the inanimate environment.

Define case

An infected or diseased person or animal having specific clinical, laboratory and epidemiologic characteristics

Define Clone

An isolate or group of isolates descending from a common precursor strain by nonsexual reproduction exhibiting phenotypic or genotypic traits characterized by a strain-typing method to belong to the same group.

Define epidemic

An occurrence of disease within a geographic area clearly in excess of the normal expectancy (the endemic level), and transmitted either from a common (single) source or from sources propagated from a single source.

Define Antitoxin

Antibody to the toxin of a microorganism, usually a bacterial exotoxin. Antitoxin combines with a specific toxin, in vivo and in vitro, with the consequent neutralization of toxicity.

What is artifically aquired immunity?

Artificial mechanisms of acquiring such antibodies involve the administration either of vaccines or toxoids (active), or of antitoxins or immune serum globulin (passive).

What are the three types of agents of disease?

Biological Chemical Physical

Specific aquired immunity may be obtained naturally or artificially. What is a naturally aquired immunity?

Natural mechanisms involve the acquisition of protective antibodies by experiencing an infection (active) or by means of transplacental transfer from mother to newborn (passive).

What is the difference between prevelance and incidence?

Prevelance = the proportion of cases in the population at a given time Incidence = rate of occurrence of new cases. Thus, incidence conveys information about the risk of contracting the disease, whereas prevalence indicates how widespread the disease is.

Define Cohort study

Propagation of a microorganism on or within a host without causing cellular injury. A colonized host can serve as a source of infection

What are the main portals of exit of the agent from the host?

Respiratory (Most difficult to manage) Genitourinary Alimentary (easy to control) Skin Transplacental

Portals of entry?

Same as exit

Define Antigen

That portion or product of a biologic agent capable of stimulating the formation of specific antibodies

Define Discriminatory Power

The ability of a test to generate distinct and discrete units of information from different isolates, usually at a subspecies level.

Define Chemoprophylaxis

The administration of a chemical, including antibiotics, to prevent the development of an infection or the progression of an infection to clinical disease.

What is proabbly the most major consideration when dealing with a disease with all these factors?

The agent-host-environment factors interrelate in extremely varied combinations to produce disease. Investigators should be aware of this fact to assist them in analysing disease problems and to reach proper conclusions regarding prevention and control measures.

Define Antigenic character

The chemical arrangement of the antigenic components of an agent, which arrangement and components are unique to each species or strain of agents, and which are responsible for the specificity of immunity resulting from infection with that agent.

Define Enzootic

The constant presence or usual prevalence of a disease or infectious agent in animal populations of a given geographic area.

Define Endemic

The constant presence, or the usual prevalence, of a disease or infectious agent in human and animal populations within a given geographic area.

Define Culture

The deliberate propagation of microorganisms on or in substances (media) especially prepared for this purpose.

Define Disinfection

The destruction of infectious microorganisms on the surface of an object, usually by chemical means.

What is direct horizontal transmission?

The direct mode implies immediate transmission as in the case of contact or droplet spread.

Define Droplet Nuclei

The dried residues of droplets which may contain one or more infectious microorganisms. In contrast to droplets, droplet nuclei can remain suspended in the air for long periods

Define Antibiotic sensitivity

The identification of the testing concentration of various antibiotics to which a particular microorganism is sensitive.

what is indirect horizontal transmission?

The indirect mode of transmission may be accomplished through animate or inanimate mechanisms. (Vectors, air, vehicles)

Define Colonization

The interval during which a person or animal that has an infectious disease is a potential source of infection.

Define Contamination

The presence of an etiologic agent on a body surface; also on or in clothing, bedding, toys, surgical instruments or dressings, or other inanimate articles or substances, including water, milk and food.

Define Antisepsis

The prevention of sepsis by inhibition or destruction of the causative organism.

What is the chain of infection?

The process of disease infection.

What is a resevior of an agent?

The reservoir is defined as the normal habitat in which an infectious agent lives, multiples, and/or grows. These habitats include man, animals, and the environment.

Which area of study did epidemiology arise from?

The study of infectious diseases

Define Convalescent Carriers

Those individuals or animals who, after experiencing acute illness, continue to be infectious during and after their return to health.

What are incubatory carriers

Those persons or animals who are capable of transmitting infection prior to the onset of signs and symptoms of the disease.

Should we just vaccinate for everything? Why or Why not?

To vaccinate or not to vaccinate requires some forethought. The characteristics of the vaccine and whether or not vaccination is the best method of control must be taken under consideration. Most large-scale outbreaks of contact transmitted infectious disease could be prevented if 70-80% of the population are immune. This is a very important consideration when a biological product such as a vaccine is licensed for market. The results obtained in controlled research trials are not necessarily what can be expected in the field use of a product. There are many factors that influence the efficacy of the vaccine (or any bioproduct) when used in field conditions.

what is disease control?

a term used to describe all measures used to reduce the frequency of illness already present in the population to what is considered an acceptable level.

How was VEE (Venezuelan Equine Encephalomyelitis) eradicated from USA?

a) Malathion was sprayed from planes to eliminate mosquito vectors. b) Vaccination of all southern horses (~4,5 million).

What are carriers?

animals and people who harbour infectious agents and who have no overt signs and symptoms.

How should you evaluate the efficacy of a vaccine?

by thinking about prevalence, incidence, endemicity, immune-competency of the animal and the relative safety of the vaccine

Define Primary determinants

factors whose variation exerts a major effect in inducing disease. (usually essential)

What are some factors that enhance capabilites of biological agents of disease?

host specificity, ability to survive or multiply outside the host, and virulence.

What are some reasons that it may not be feasible to eradicate a disease?

large wildlife reservoir (i.e. rabies), they persist very well in the environment and for long periods) i.e. Anthrax), or they are too ubiquitous (ie. Toxoplasma).

What are some of the GENERAL factors that affect a host's immunity?

malnutrition, pre-existing ill health, and artificially depressed immunologic response mechanisms which result from excessive stimulation of the immune system in response to other diseases.

When is vaccination likely to cause problems?

may become important at a later stage and vaccination may be discontinued.

Define complex disease

multifactorial nature predominates, and an interaction between host, agent and environment can be identified as being necessary to maintain the disease

What are some of the RESISTANCE factors that affect a host's immunity?

the skin and mucous membranes, gastric acidity, cilia in the respiratory tract, and cough reflex

What are measures of prevention?

those practices used to exclude a disease from a population of unaffected animals.

Define vertical transmission

transmission of disease from one generation to another through the placenta or milk.

What sorts of things could go wrong if you incorrectly choose to vaccinate against a disease?

vaccine will further the chances of spreading disease due to reversion to virulence (in the case of a modified live vaccine) by creating carrier animals? the product will affect the epidemiology of the disease in a manner that would interfere with eradication measures?

What are some common modes of transmission of infectious agents?

vertical transmission or horizontal transmission.

When is a good time to vaccinate a population to a disease and why?

when the incidence of disease is high. During this stage of the programme, an effective vaccine can be used to reduce the rate of spread and incidence of disease. The problems caused in diagnosis and creation of carrier states are usually not significant at this stage when compared with the problems the disease is causing.