Question 30-37

Question 1

Definitions of pathogenicity, virulence, infection, contagiosity, transmissibility

Answer 1

Pathogenicity
- Qualitative term, property to generate a local or systemic infectious disease

• Dependent on a certain host-pathogen system

Virulence
- Quantitative term, degree of disease-inducing potency of a pathogen

• Related to virulence factors (e.g. formation of a capsule, production of toxins in bacteria)

Infection
- Invasion (active, passive), adhesion, propagation of a pathogen on its host → immune response

• Stages: Invasion + primary propagation, generalization, manifestation at major target organ, healing or further proliferation + death

Transmissibility
- Property of an infectious agent to invade a host of the same or a different species

• Transmissibility is the basis for contagiosity
• Pathogens may be monophageous (only one host species) or polyphageous (two or more host species)
• Direct excretion (e.g. faeces) or indirect excretion (e.g. carcasses) is a precondition of transmission
• Direct or indirect transmission (e.g. insects) and horizontal or vertical within a susceptible population

Contagiosity
- Power of contagion or the transmissibility of a pathogen, its ability to be transmitted

• Contagiousness is highly dependent of pathogen concentration in an infected individual or in their body secretions
• Includes transmissibility and pathogenicity

Question 2

What is an endemic, epidemic, pandemic diseases?

Answer 2

Endemic
- Without limitations in time

• In a certain region, country or climate (limited in location)
• No tendency for wide-distance spread
  Frequency of disease is mostly low

Epidemic
- Cumulation of the same disease in a certain region

• Limited in time and location
• Tendency to spread within a susceptible population
• Frequency of the disease is mostly high

Pandemic
- Epidemic without limitations in location

• Spreads over a longer time with increasing numbers of infected individuals

Prevalence = proportion of existing cases in a giben population at certain moment

Incidence = number of new cases in a population over a specified period of time

Question 3

Henle-Koch-postulates

Answer 3

Henle-Koch-postulates describe connection between microorganisms as pathogens and infectious diseases

For monocausal infectious diseases:
1. Suspected pathogen should be present in all cases of the disease and absent from healthy individuals.
2. Suspected pathogen should be isolated and grown in pure culture.
3. Cultured pathogens should cause disease in a healthy experimental animal showing the same clinical signs.
4. Pathogen should be re-isolated from the reinfection and proofed as the original one.

Question 4

Principle aspects of epidemiology

Answer 4

Epidemiology
- Scientific discipline dealing with the appearance, spreading and accumulation of infections in humans and animals, analyse cause/spread/consequence of a disease

Qualitative aspects
- Prerequisite for the transmission of pathogens is their excretion by the infected host, direct (secrets from mucosa) or indirect (carcasses, blood)
- Direct introduction via: smear/contact/droplets/lesions/sex/into mouth, nose, eyes, skin or other mucosa …
- Introduction via contact to: food, feed, faeces, water, soil, air, tools …
- Indirect introduction via living sectors: ecto- and endoparasites, pests, animals, humans (surgery)

Quantitative aspects
- Prevalence (represents the fraction (proportion) of existing cases in a given population)
- Incidence (describes the number of novel cases that arise in a population over a specified period of time).

Question 5

Eradication of poliomyelitis virus

Answer 5

Acute viral disease, transmission person-to-person via fecal-oral route

3 serotypes (slightly different capsid proteins), all very virulent, PV1 most common, PV2 wild type (eradicated), humans are only natural host, PV survives in body and contaminated water

Symptoms: majority none, upper respiratory symptoms, nausea, vomiting, abdominal pain, fever …
- 3%: PV enters CNS → non-paralytic aseptic meningitis or acute flaccid paralysis AFP

Prognosis: generally very good, 50% of spinal polio patients are left with some disability
- Mortality (paralysis of breathing muscles): children 2-5%, adults 15-30%

Treatment: no cure, only to increase comfort, speed recovery and prevent complications

Prevention: Vaccine!!
- Salk vaccine (IPV): inactivated PV, trivalent, intramuscular - 2-3 doses necessary

• Sabin vaccine (tOPV): live attenuated viruses, trivalent, oral
• • replicates efficiently in gut → excellent immunity in intestine, cannot replicate well in nervous system tissue
• 3 doses necessary, VAPP (vaccine associated paralytic poliomyelitis), cVDP (circulating vaccine-derived poliovirus)
• Bivalent oral polio vaccine (bOPV): live attenuated viruses of type 1+3
• • targets two remaining types of wild PV, reduce type 2 cVDPV, 30% more effective than tOPV → 2016 global switch

Eradication: humans = only host + sufficient vaccine = prerequisite

• Today only endemic in Afghanistan and Pakistan
• Problem 1: wild PV (type 1) → vaccinate all children < 5
• Problem 2: cVDPV (type 2) → use bOPV
• Problem 3: eradication plan until 2020 didn’t work, infection numbers are rising

→ Global Polio Eradication Initiative GPEI (2022-2026), childhood immunization and surveillance

Question 6

Foodborne viral diseases: examples (you should be able to give and describe an example for foodborne viral diseases, e.g. Hepatitis)

Answer 6

Norovirus:

• Caliciviridae, small (27-35nm), non-enveloped, icosahedral capsid, ssRNA (+), genome in 2-3 open reading frames
• Transmission: fecal-oral (contaminated food/water), person-to-person, airbone and fomite
  !large shedding amounts, very low infectious dose (< 100 particles), resistant to inactivation in environment!
• Symptoms: gastroenteritis with fever and headache, !dehydration!
• Incubation 12-48 hours, lasts 12-60 hours, sereve illness and death very rare
• Outbreaks: nursing homes, medical and child care facilities, cruiseships, restaurants and catered events
• Close living/incontinence/poor personal hygiene/poor sanitation/raw or semiliquid foods

Prevention and control:

• Don’t let infectious people handle food
• Keep water clean (good waste water management)
• Interrupt person-to-person transmission by hand washing, face masks, clean soiled surfaces and bedding appropriately
• – no vaccine

Question 7

Bacterial waterborne diseases

Answer 7

• Botulism: Clostridium botulinum
• Cholera: Vibrio cholera
• E.coli infection: Escherichia colia
• Dysentery: Shigella (dysenteriae) and Salmonella
• Salmonellosis: Salmonella ssp.
• Typhoid fever: Salmonella typhi

Question 8

What are typical pathogenicity factors of bacteria (examples, kind of action)?

Answer 8

Adhesins like Pili and Fimbriae
→ host and tissue specific, cause adhesion to glycoproteins or complex lipids

Antiphagocytosis factors/Evasins: capsule, protein a of S. aureus (IgG can’t work), antigenic variation/ mimicry to protect against immune reactions

Invasins: force non-phagocytic cells to engulf bacteria
- Hyaluronidase, Flagellae, Protease, DNAse, Lipase

Endotoxinsfrom LPS of G-
→ inflammation, septic shock, influence on coagulation

Exotoxins from living bacteria
Lipase, pore building, neurotoxins, endotoxins (diarrhea)