Controlling Pathogens

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Controlling Pathogens
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How can we control pathogens to prevent disease?

• Quarantine
• Hygienic measures/Antiseptic Technique
• Treatment of infections
• Defence at the organism level

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Quarantine

• Biblical times lepers were shunned. There was
  recognition that the disease was infectious.
  Social isolation prevented spread of pathogen.
• Modern day isolation wards in hospitals for
  highly infectious diseases/emerging threats e.g.
  SARS, anthrax
• AQIS Australian Quarantine and Inspection
  service
• Special conditions apply to importation of some
  materials
• Travellers from certain areas will be screened
  for health
• Limitations on animals (including family pets)
  entering Australia to prevent/limit diseases
  including rabies and foot and mouth disease
• Top Watch Northern Australia
• Similar role to AQIS but patrols the Northern end
  of Australia to prevent the spread of disease and
  pests from New Guinea and the Torres Strait
  region into Australia

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Hygienic Measures

• Semmelweis story simple hygienic measures such
  as washing hands or covering your mouth when you
  sneeze can impact on the spread of pathogens.
• Above and beyond this, the use of antiseptics and
  disinfectants have an important role in
  preventing infection.

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Antiseptics and Disinfectants

• Antiseptics used on skin to kill pathogens
• alcohol (70 ethanol) breaks down lipids and
  denatures protein
• hydrogen peroxide oxidizing agent
• detergents disrupt cell membranes
• iodine binds to proteins
• Disinfectants used to kill pathogens on objects
• chlorine oxidizing agent
• phenols denature proteins
• ammonium compounds interact with phospholipids
  in membranes
• copper sulfate precipitates protein

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Levels of cleanliness???

• Sterilization
• is the complete destruction or elimination of all
  viable organisms.
• procedures involve the use of heat, radiation or
  chemicals, or physical removal of cells.
• Disinfection
• reducing the number of viable microorganisms
  present in a sample.
• Sanitization
• cleaning of pathogenic microorganisms from public
  eating utensils and objects.
• Sanitizer an agent that reduces, but may not
  eliminate, microbial numbers to a safe level.
• Decontamination
• Decontamination is the treatment of an object or
  inanimate surface to make it safe to handle.

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Treatment of Infections

• Antibiotics and antimicrobials
• Fungicides and antifungals
• Antivirals
• Antiprotozoan and antihelminthic drugs

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Antibiotics and antimicrobials

• Antibiotics
• Substances naturally produced by microorganisms,
  that are active against other microorganism.
• First antibiotic was penicillin which is produced
  by the fungus Penicillium notatum.
• Antimicrobial agents
• Chemicals that can be used to inhibit microbial
  growth, including antibiotics.
• Key requirement for a antimicrobial is
  selectivity the ability to kill microorganisms
  but not cells of the host.
• Antimicrobials may be broad-range (kill many
  types of bacteria) or narrow-range (only kill one
  or two types).
• Sensitivity tests are often carried out in a
  clinical setting to determine which drug is most
  effective against infecting bacteria.

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Sensitivity Testing
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Types of antibiotics
Drug Spectrum Mode Possible side effects
Erythromycin Narrow (Gram ) Inhibit protein synthesis GI upset Liver damage
Penicillin Narrow (Gram ) Inhibit cell wall synthesis so bacteria cant reproduce Allergic response
sulfonamides Broad (Gram and -) Compete against against bacteria (inhibit folic acid production) Allergic response Kidney and liver damage
tetracyclines Broad (Gram and -, rickettsia and Chlamydia) Inhibit protein synthesis GI upset Teeth discolouration Kidney and liver damage
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Fungicides and antifungals

• Fungicides
• Used to kill fungi.
• Bordeaux mixture (developed in 1870s) a mixture
  of copper sulfate and lime prevents mildew and
  fungal disease in plants).
• Antifungals
• Very few available for treatment of humans (with
  the exception of topical creams).
• Major difficulty is that fungi and human cells
  are both eukaryotic and therefore have similar
  properties.
• Ergosterol is a major target of antifungal drugs
  as it is found in fungal but not human cell
  membranes. Problem is that there is still some
  interference with similar substances in human
  cells.

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Antivirals

• Viral infections are difficult to treat as it is
  difficult to attack a virus without harming its
  host cell.
• Viruses dont have the structures that are the
  usual targets for antibiotics, so drugs need to
  target specific steps in the viral reproduction
  pathway, for example
• Interfering with the uncoating of coated viruses
  such as influenza
• Preventing nucleic acid synthesis (herpes virus
  and HIV)
• Preventing the assembly and release of viral
  particles (influenza and HIV)
• Interferons are a group of antiviral agents
  produced by virus-infected tissues. They
  preparing neighbouring cells to shut down protein
  synthesis in the vent the become infected.

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Example of an antiviral

• The most effective HIV drugs at the moment are
  those that target step 2.
• Nucleoside inhibitors prevent reverse
  transcription which means that ds viral DNA cant
  be made and viral protein cant be produced.
• Not 100 effective.

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Antiprotozoan and antihelminthic drugs

• Antihelminthics are use to treat infection with
  hookworm, pinworm, threadworm, whipworm and
  tapeworm. Some kill the worms on contact. Others
  starve or paralyse the worms, which then pass out
  of the body in the faeces. Think Combantrin!
• Antiprotozoal drugs are used to treat protozoal
  infections, for example malaria, trypanosomiasis
  and leishmaniasis. In general these drugs are
  inadequate.
• Unfortunately, these are largely diseases of
  third world countries and very little research is
  being done in regards to further drug
  development.

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Defence at the organism level

• Organisms must continually defend themselves
  against pathogens of many kinds
• A variety of defence mechanisms have evolved to
  increase the chances of survival in the face of
  these external challenges
• Defence mechanisms operate at all levels
  external and internal, and involve molecules,
  cells and organ systems.
• The ways that organisms protect themselves
  against pathogens fall into two categories
  non-specific and specific.