2. pathogenesis, course, epidemiology of infectious diseases, factors influencing the spread of infectious diseases.

Question 1

Course of an infectious disease?

Answer 1

Course of an infectious disease

1. Local infection (e.g. tetanus, papillomatosis)
   - Lesions at the place of entry
   - Entry ➝ colonisation ➝ replication ➝ alterations
2. Infections of different organs (localised) - e.g. rabies
   - Lesions only in one organ

‣ Entry, getting into the target organ

‣ Colonisation ➝ replication ➝ damage

3. Generalised infections (e.g. anthrax, ASF)
   - Lesions in more organs
   - Incubation: hours (e.g. anthrax) ➝ months (e.g. maedi)

‣ Infection

‣ Colonisation

‣ Start of replication

• Generalisation: viraemia, septicaemia, bacteraemia

‣ Spreading by blood, lymphatic vessels, perineural

• Manifestation

‣ Clinical signs, lesions (virulence factors), intracanalicular spreading in the case of chronic diseases

‣ Foetus (foetopathogenic agents)

๏ Embryonic death, resorption, abortion

๏ Teratogenic

๏ Decreased resistance

๏ Tolerated infections

• Outcome of the disease: healing or death

Question 2

Course of Infectious diseases caused by viruses?

Answer 2

Course of infectious diseases caused by viruses

Replication at the place of entry and in the regional lymph nodes ➝ exceptions: rotavirus, papillomatosis

• Basic system is the same (generalisation)
• Localisation by macrophages
• Replication in infected macrophages, lymphocytes, blood ➝ cell bound viraemia, bacteraemia
• Replication in lymphoid cells ➝ immune suppression (increased resistance) and damage of blood vessels (haemorrhages) ➝

viraemia ➝ organs reached

• Secondary replication in tissues ➝ damage of cells of organ ➝ clinical signs (only partially caused directly by virus, allergic

reaction by host can worsen the clinical signs)

• Reactive inflammation, start of immune reactions, allergic reactions ➝ clinical signs

Question 3

Start and course of infectious diseases: Course of the disease?

Answer 3

Start and course of infectious diseases: Course of the disease

• Incubation time (flexible): between infection and appearance of clinical signs
• Seroconversion time: the time between infection and appearance of immune reaction ➝ important to know the immune reaction

time

• Course of an infection in time

• Peracute
• Acute
• Subacute
• Chronic

Question 4

Outcome of the disease?

Answer 4

Outcome of the disease

• Complete or partial recovery ➝ residual symptoms such as pneumonia, arthritis and infertility
• Death
• Carriage and shedding of the agent
• Temporary or long-lasting (even in case of immunity e.g. TBC)
• Also in case of asymptomatic infection
• Maintains chain of infection

Question 5

Asymptomatic infection?

Answer 5

Asymptomatic infection

• Abortive infection
• Inapparent (subclinical) infection
• Persistent infection (virus) e.g. ASF, Marek’s disease ➝ agent is present in lymphoid cells, antibodies, immune complexes, allergic

processes, tumor transformation

• Latent infection (virus): infection before self-recognition of the immune system
• Tolerated infection (virus): infection before self-recognition of the immune system
• Epidemiological importance of asymptomatic system
• Asymptomatic infections can manifest

Question 6

Epidemiology of infectious diseases?

Answer 6

Epidemiology of infectious diseases

• Data collection using statistic methods

• Susceptible species, vectors
• Characteristics of the populations
• Spreading: geography, time
• Aetiology
• Epidemiological follow-up
• Analysis
• Non-infective diseases as well

Question 7

Characteristics of infectious diseases?

Answer 7

Characteristics of infectious diseases

• Epidemic diseases: spread, disease in larger animal population
• Contagious diseases: fast spread, animal-to-animal
• ‘Dead end hosts’ ➝ e.g. WNV: horse, humans (do not shed the agent, virus does not infected further)
• Soil infections

Question 8

Statistical evaluation of infectious diseases?

Answer 8

Statistical evaluation of infectious diseases

Statistical evaluation of infectious diseases

• Morbidity ➝ diseased/herd (%)
• Mortality ➝ dead/herd (%)
• Lethality ➝ dead/diseased (%)
• Incidence ➝ diseased/whole population/year (%000)
• Prevalence ➝ existing disease cases/whole population (%000)

Question 9

Analysing methods of infectious diseases?

Answer 9

Analysing methods of infectious diseases

• Data collection to diagnostic work

• Monitoring: routine collection of data of a disease
• Screening

‣ Aimed testing of animals

‣ Differentiation of healthy and diseased (infected) ones

• Surveillance: strategy

‣ Recording and analysis of data

‣ Advise the owner

‣ Actions to control a disease

‣ Types: passive and active

• Sampling, sample size

• Statistical methods
• 95% confidence
• 5% precision (1%, 10%)
• Prevalence influences

Question 10

Extension of infectious diseases?

Answer 10

Extension of infectious diseases:?

Extension of infectious diseases

• Sporadic diseases
• Endemic diseases (enzootia) ➝ small, limited area, one stock or a few herds
• Epidemic diseases (epizootia) ➝ spreading disease, larger area
• Pandemic diseases (panzootia) ➝ extended epidemics, continents

Question 11

Factors influencing infections?

Answer 11

Factors influencing infections

• Susceptible hosts

• Number of the susceptible hosts
• Number of the maintaining animals
• Life cycle of susceptible animals ➝ mating, leave of the offspring
• Reservoirs ➝ wild animals, vectors
• Geographical factors
• Island, desert, mountain, river
• Soil
• Transport: road, rail, harbour

• Climatic factors

• Sunshine, temperature, wind, vapour content
• Seasonal diseases (arthropod-borne)

• Management

• Keeping animals indoors or on pasture
• Stable ➝ temperature, draught, NH3
• Overcrowding
• Mixing animals

• Nutrition

• Pasture
• Nutritional deficiencies ➝ quality of feed, starvation, toxins