1. D O C T R I N E
A B O U T I N F E C T I O N
Tvorko M. S.

3. An infection does not always result in disease!
Infection and disease
What is a pathogen?
A pathogen is a micro-organism that has the potential to cause disease.
What is an infection?
An infection is the invasion and multiplication of pathogenic microbes in an individual or population.
What is disease?
Disease is when the infection causes damage to the individual’s vital functions or systems.
An infection does not always result in disease!

4. How do microbes reach us?
The cycle of transmission involves
Escape from the host or reservoir of infection.
Transport to the new host.
Entry to the new host.
Escape from the new host.
represents the various barriers to infection e.g. the skin
Source/reservoir of infection
HUMAN
HOST
Mode of
transmission
Portal of entry
Portal of exit
represents the target organ e.g. lungs

5. Source of infection: Sick men Sick animal Carrier
Transmission factor: infected food, water, dirty hands, flies, fomites.
Vectors of pathogenic microorganims: ticks, louses, fleas mosquitos.

6. Air-droplet (dust) mechanism of transmission of infection
Stage of penetration of invader
Stage of selection
of invader
Stage of stay of invader in an environment
Tiny
phase
Sneeze
Cough
Breathing
Talks
Sensitive
organism
Source
infections
Aerosol
Drying
Out
settling
Dust
phase

7. Mode of transmission Direct contact – person to person Example: SARS
Vertical – sneezing closer than 1 metre
SARS - associated coronavirus causes severe acute respiratory syndrome (SARS).
SARS is transmitted when an infected person coughs or sneezes infectious droplets onto a nearby person.
The droplets land on another person’s face or hands, and become introduced to the nose or mouth.
Jets of droplets erupt from a man’s nose as he sneezes.

8. Mode of transmission Indirect contact – vehicle borne Example: tuberculosis (TB)
Air/dust
The bacterium Mycobacterium tuberculosis causes tuberculosis (TB).
TB is spread from person to person through the air.
When a person with active TB coughs or sneezes, droplets loaded with the infectious organism are propelled into the air.
The moisture evaporates from these particles to leave droplet nuclei that can remain airborne for days and spread long distances.
The Mycobacterium has a waxy coat, which protects it from drying out allowing it to survive for many months in the air and dust.

9. Fecal-oral mechanism of transmission of infection
Stage of selection of invader
Stage of stay of invader in an environment
Stage of penetration of invader
Factors of transmission
Ways of transmission
Ways of selection
Feces
urine
sputum
(for some
infections)
Food
products
Food
Water
Source
infections
Receptive
organism
Hands
Water
Objects
domestic
use
Contact-
domestic
Soil
Flies

10. Mode of transmission Direct contact – person to person Example: gastroenteritis
Vertical – touching (faecal-oral route)
Norwalk virus causes a type of gastroenteritis.
Norwalk virus is found in the faeces or vomit of infected people. It is highly contagious.
Infection occurs by having direct contact with another person who is infected and not maintaining good hygiene e.g. washing hands.
Human hand contaminated with colonies of bacteria (blue/pink patches).

12. Mode of transmission Indirect contact – vehicle borne Example: food poisoning
Via food
The bacterium Campylobacter jejuni causes a type of food poisoning.
C. jejuni lives in the gut of many warm-blooded animals, particularly chickens, as part of their normal body flora.
The infection is transmitted to humans by eating contaminated food especially poultry and milk.
Campylobacter jejuni bacterium.

13. Mode of transmission Direct contact – person to person Example: cold sore
Vertical – kissing
Herpes simplex virus causes cold sores.
Initial infection occurs through direct skin contact when the secretions from another person’s cold sore, containing the virus particles, come into contact with cells of the skin around the mouth.
A couple kissing.
Cold sores on lip and mouth.

14. Mode of transmission Direct contact – person to person Example: syphilis
Vertical – sexual intercourse
The bacterium Treponema pallidum causes syphilis.
The bacterium enters the body through very tiny cuts on the skin or mucous membranes when there is contact with an infected person or their bodily fluids.
Interlocking gender symbols representing sexually transmitted diseases.

15. Mode of transmission Direct contact – person to person Example: German measles
Horizontal across the placenta or via breast milk
Rubella virus causes German measles.
When infection occurs during pregnancy the virus crosses the placenta in the blood leading to infection of the fetus.
The virus can affect all the organs of the developing fetus.
The risk to the baby is highest in the first 3 months – up to 85% of babies are affected if infected during this period.
Eight week old fetus attached to its placenta by the umbilical cord.

16. Mode of transmission Indirect contact – vector borne Example: malaria
Internal – biological
Malaria is a vector-borne disease caused by a single celled protozoan parasite called Plasmodium, which is transmitted by mosquitoes.
The primary vector for malaria is the mosquito Anopheles gambiae.
Only female mosquitoes transmit malaria when they feed on the human host’s blood.
A. gambiae feeding on human blood.

17. Mode of transmission Indirect contact – vector borne Example: bacterial dysentery
External – mechanical
The bacterium Shigella causes a type bacterial dysentery.
Flies can spread Shigella when they carry infected faecal matter on their feet to drinking water or food.
Symptoms can vary from mild diarrhoea through to a more severe disease with watery or bloody diarrhoea, fever, stomach cramps and vomiting.
Common house flies feeding.

18. HOW DO MICROBES GET IN?

19. Portals of entry
To cause an infection, microbes must enter our bodies.
The site at which they enter is known as the portal of entry.
Microbes can enter the body through the four sites listed below
Respiratory tract (mouth and nose) e.g. Influenza virus
Gastrointestinal tract (mouth oral cavity) e.g. Vibrio cholerae
Urogenital tract e.g. Escherichia coli
Breaks in the skin surface e.g. Clostridium tetani

20. Portals of entry Respiratory tract Example: influenza
Influenza or ‘flu is a highly infectious respiratory tract infection.
It is caused by a virus.
Virus is inhaled into the lungs through the mouth and nose.
The envelope of the virus has around 500 spikes sticking out of it.
Spikes attach to the cells lining the lungs. These help the virus get into the cell.
The respiratory tract.

21. Portals of entry Gastrointestinal tract Example: cholera
Cholera is an acute infection of the intestinal tract.
It is caused by the bacterium Vibrio cholerae.
The infection is spread by contaminated water and food, especially seafood, or from one infected person to another via the faecal-oral route.
The incubation period is hours.
The gastrointestinal tract.

22. Portals of entry Urogenital tract Example: cystitis
Cystitis is the commonest infection of the lower urinary tract.
Strains of the bacterium Escherichia coli, a normal inhabitant of the human intestine, are responsible for 80% of cases of cystitis.
Bacteria enter the urethra and travel up to the bladder.
It is more common in women than in men.
In women the anus and the opening of the urethra are closer to each other.
The urethra is shorter in women so the bacteria have a shorter distance to travel to the bladder.
Artwork of an inflamed bladder (red) caused by cystitis.

23. Portals of entry Urogenital tract Example: Chlamydial infection
Chlamydial infection is the most common sexually transmitted bacterial infection in the world.
It is caused by Chlamydia trachomatis.
About 1 in 10 young people have Chlamydia.
It can’t be caught from kissing, sharing towels or toilet seats.
Chlamydial infection is often known as the silent disease as approximately 75% of women and 50% of men don’t experience any symptoms.
C. trachomatis bacteria (background) with the female reproductive tract superimposed.

24. Portals of entry Breaking the surface of the skin Example: tetanus
Tetanus is commonly known as lockjaw; it is a neuromuscular disease.
It is caused by a toxin (poison), which is produced by the bacterium Clostridium tetani.
C. tetani is found in soil, dust and the guts and faeces of many animals.
C. tetani produces endospores.
The endospores usually enter the body through a puncture wound to the skin.
Splinter in the finger.

25. The dynamics of the development of the infectious process consists of the incubation and prodromal periods, the height of the disease and period of recovery ( convalescence). A certain period of time elapses from the moment of penetration of the pathogenic microbe to the onset of the first sings of the disease, which has been named the incubation period of the disease.

26. Pathogenicity
What makes some bacteria dangerous?

27. degree of pathogenicity
Ability to cause disease
Virulence –
degree of pathogenicity
Bacterial virulence factors
for adherence, colonization, and invasiveness

28. How Bacterial Pathogens
Penetrate Host Defenses

29. Bacterial Adhesion Results in colonisation
One of several pathogenic mechanisms = a virulence factor
Adhesion to host tissues is mediated by:
fimbriae (pili)
cell wall-associated proteins
other cell wall constituents, e.g. lipoteichoic acid
Many adhesins recognize specific sugars on the target tissue

30. Bacterial Adhesion Tropism
Neisseria meningitidis
Neisseria gonorrhoeae
Vibrio cholerae
Bordetella pertussis
Salmonella typhimurium
Helicobacter pylori
Streptococcus pyogenes
Campylobacter jejuni
Mycoplasma pneumoniae
Nasopharyngeal epithelium
Uretral epithelium
Intestinal epithelium
Respiratory epithelium
Gastric mucosa
Pharyngeal epithelium
Adherence of vibrio
cholera
on the mucose

31. Fimbriae of human enterotoxigenic Escherichia coli

32. Spreading factors - enzymes to destroy intercellular cement
Invasiveness
Spreading factors - enzymes to destroy intercellular cement
collagenase,
hyaluronidase,
fibrinolysin,
lecithinase,
streptokinase
Penetration into
the Host Cell

33. Antiphagocytic factors
Capsules, cell wall proteins
leukocidin
coagulase (walls off)
survival in WBC - intracellular parasites (mycobacteria, Listeria)
IgA protease - Neisseria

34. Components of the Cell Wall
Proteins in the cell wall can facilitate adherence or prevent a pathogen from being phagocytized.
M protein of S. pyogenes (cell surface and fimbriae)
Some microbes can reproduce inside phagocytes.
M. tuberculosis

35. Toll like receptors (TLR) respond to bacterial cell wall molecules
Gram negative
Toll like receptors (TLR) respond to bacterial cell wall molecules
And some virus molecules
Pathogen associated molecular pattern (PAMP)
LPS

37. Microbial toxins
According to the nature of production, microbial toxins are subdivided into
exotoxins and endotoxins.

38. Endotoxin

39. Endotoxins

40. Exotoxins They are subdivided into three classes.
Class A includes exotoxins secreted into the external environment: cholerogen (V. cholerae); histotoxin, dermonecrotoxin and haemolysin (Cor. diphtheriae), alpha- and delta-haemolysin and beta and epsilon toxin (C/. perfringens) and others.
Class B includes exotoxins which are partly secreted, partly bound with the microbial cell: alpha toxin (C/. novyi); tetanospasmin (Cl. tetani); neurotoxin (C/. botulinum).
Class C consists of exotoxins bound with the microbial cell; Sh. dysenteriae exotoxin; Cl. perfringens enterotoxin

41. Cytotoxins:
Diphtheria toxin (inhibits protein synthesis)
S. pyogenes erythrogenic toxins (damage capillaries and produce Scarlet fever*).
Neurotoxins:
Botulinum toxin (prevents nerve transmission)
Tetanus toxin (prevents inhibitory nerve transmission or a.k.a muscle relaxation pathway).
Enterotoxins:
affect the intestines induce fluid and electrolyte loss from host cells (S. aureus, V. cholerae, enterotoxigenic E. coli).

42. Mechanism of molecular action of cholerae toxin
Development of vibrio cholerae in the human organism

43. Mechanism of action of toxin of Clostridium tetani
Physiology influencing of tetanospasmin
Child with neonatal tetanus

44. Look of mouth cavity of sick patient with diphtheria
Structural organization of molecule of diphtherial toxin and mechanism of his action on a mew
Look of mouth cavity of sick patient with diphtheria

45. Mechanisms of action of botulinum toxin
Place of neuro-muscle contact
In a healthy organism neuromediator frees oneself
from the nervous ending
in a sinaptic crack
The molecules of botulinum register to the presinaptical membrane and hinder
to freeing of neuromediator