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

Question 1

Course of infectious disease

Answer 1

Incubation time: replicates
Seroconversion time: time between infection and immune reaction
Course of infection in time
Peracute: <6hrs
Acute: few days
Subacute: few weeks
Chronic: >4 weeks to several years

Question 2

Outcome of disease

Answer 2

Complete recovery
Partial recovery: following chronic diseases
- Residual symptoms: pneumonia can give abscess in lung or even atelectasis, arthritis, infertility
Death
Carry and shed the agent
- Temporary/long lasting (even in case of immunity, ex. TB, Brucellosis)
- Also in case of asymptomatic infection
- Maintains chain of infection

Question 3

1. Local infection

Answer 3

(tetanus, papillomatosis)
Lesions at place of entry only
Entry - colonization - replication - damage (+ shedding)

Question 4

2. Infection of different organs

Answer 4

(rabies)
Localized - lesions in one organ
Entry, getting into target organ, manifestation - colonization - replication - local damage

Question 5

3. Generalized infections

Answer 5

(anthrax, ASF)
Lesions in more organs
Incubation - infection - colonization - start of replication

Question 6

4. Generalization

Answer 6

Spreading via blood, lymphatic vessels or perineural (rabies)
Viremia, bacteremia, septicemia
In the organ the agent will replicate and damage the host with toxins, EC enzymes etc.

Question 7

Manifestation of a disease

Answer 7

CS, lesions (virulence factors), intracanicular spread (chronic diseases)
Fetus: (fetopathic agents) embryonic death, resorption, abortion, teratogenic, decreased resistance (born with infection, not viable), tolerated infections

Question 8

Course of infectious diseases caused by viruses

Answer 8

Replication at place of entry and regional LN (exceptions: e.g. rotavirus (small int) and papillomatosis)

Localization by macrophages: can enter the blood - frequently cell bound viremia

Replication in infected macrophages, lymphocytes, blood (viremia)

Replication in lymphoid cells (immune suppression, activity of lymphocytes and macrophages will be slightly suppressed, damage of blood vessels: hemorrhages will be present (PM)

CS:
Secondary replication in tissues: damage of cells
Reactive inflammation, start of immune allergic reactions - makes CS worse

Question 9

Asymptomatic infection

Answer 9

Inapparent (subclinical) infection: resistance of host can limit the activation of agent - cannot damage host severely
Difficult to diagnose BUT SHEDDING

Persistent, latent, tolerated infection

Question 10

Persistent infection

Answer 10

Virus
Agent present in lymphoid cells
Antibodies, immune complexes, allergic processes, tumor transformation
e.g. ASF, Mareks

Question 11

Latent infection

Answer 11

Virus
ø complete viral replication
integration of the virus genome into the genome of the cell of hosts
Stress can trigger the activation of the infection so it appears to come out of nowhere - NO SHEDDING
e.g. HERPES

Question 12

Tolerated infection

Answer 12

Virus
Infection before fetal immune recognition
Pregnant animal has disease and agents gets into fetus before immune competence - the agent is regarded as part of the immune system - no response, hard to diagnose STILL SHEDDING
e.g. BVD

Question 13

Epidemiology of infectious diseases, data analysis

Answer 13

Susceptible species, vectors
Characteristics of populations
Spreading (geography, time)
Etiology, predisposing factors
Epi follow up
Analysis --> diagnostic work

Question 14

Dead end host

Answer 14

Has CS but does not shed e.g. WNV, horse and human

Question 15

Soil infection examples

Answer 15

Bacillus anthracis spores, tetanus spores

Question 16

Morbidity

Answer 16

diseased/herd %= how many sick in a herd

Question 17

Mortality

Answer 17

dead/herd % = how many died in a herd

Question 18

Lethality

Answer 18

dead/diseased % = how many died out of those with clinical signs

Question 19

Incidence

Answer 19

(humans): diseased/whole population/year (%000)

Question 20

Prevalence

Answer 20

(humans): existing disease cases/whole population100.000

(%000) e.g. AIDS, TB – more for chronic

Question 21

Analysing methods of infectious diseases

Answer 21

Data collection for diagnostic work – frequency of the disease

1) Monitoring (passive method) more superficial: routine collection of data on a disease (follow the occurrence of the disease)
2) Screening (active method): testing animals, differentiation of healthy & diseased (infected) ones
3) Surveillance (more complex): collect the data & produce a strategy
- Recording & analysis of data
- Advise the owner
- Actions to control a disease
- Types: passive (collecting the data) & active (looking for the data, sampling)

Question 22

Sporadic diseases

Answer 22

1 farm, maybe have 1 or 2 cases

Question 23

Endemic diseases - enzootia

Answer 23

small, limited area e.g. on a farm

Question 24

Epidemic diseases - epizootia

Answer 24

spreading, larger area, not very fast spreading e.g. CSF

Question 25

Pandemic diseases - panzootia

Answer 25

extended epidemics, countries/continents

e.g. influenza, FMD