Infectious diseases

• Pharmaceuticals


  Pharmaceuticals are drugs or chemicals prepared for the alleviation and treatment of particular symptoms or diseases. There is a huge range of these drugs, but we will focus on the ones specific for killing or slowing down the function of pathogens. Antimicrobial agents are designed to control infectious diseases caused by microbes. There are 4 main groups:

  
• Viruses


  Antiviral medications are used to control viral infections. They do not kill viruses but inhibit their development inside infected cells. They do not cure the disease but simply slow down its progress, allowing the body’s natural defences to take over. If taken early in the course of the disease, symptoms will be milder and of shorter duration. They stop the spread of viral diseases and therefore are a useful addition to the control of epidemics and pandemics.
• viruses


  viruses

  
• Virus replication

  How viruses replicate:

   The diagram above shows the main stages in viral replication in a host cell. We can see a number of stages where a specially designed molecule could interfere with the life cycle of a virus:

  1. Inactivate extracellular virus particles

  2. Prevent viral attachment and/or entry

  3. Prevent replication of the viral genome

  4. Prevent synthesis of specific viral protein/s

  5. Prevent assembly or release of new infectious viruses
• Viruses


  • Use the host's cells to produce new virus particles
  • Making it very challenging to develop a class of drugs that stops viral replication without killing the host cells
• With the rise of the HIV epidemic in the 1980s, there was a coordinated global medical research effort that led to great advances in our understanding of the biology of viruses
• Efficacy


  The ability of a medication to produce the desired outcome, in this case eliminate the viral infection from the patient
• These drugs have greater efficacy when taken early in the course of the illness
• Widespread administration of these drugs to populations during outbreaks

  Concerns about their safety
• Antibiotics

  “One sometimes finds, what one is not looking for. When I woke up just after dawn on September 28, 1928, I certainly didn't plan to revolutionize all medicine by discovering the world's first antibiotic, or bacteria killer. But I suppose that was exactly what I did.”

  — Alexander Fleming

   

  Alexander Fleming had accidentally discovered penicillin produced by a common mould that had contaminated his agar plate.
• Testing antibiotics

  Penicillin was the first known antibiotic. Antibiotics are used to control bacterial infections. They work by either killing or slowing down the growth of bacteria. Antibiotics are not effective against viruses.

  These small discs have been soaked in different antibiotics and placed on a thin film of bacterial growth. The clear circles indicate the degree of antibacterial action of each sample to this particular bacterium.
• Action of antibiotics


  Antibodies

  
• Antibiotics


  • Most effective when used solely for the treatment of bacterial infections and not viral infections
  • Bactericidal antibiotics are used to kill rather than inhibit growth of the bacteria (penicillins, cephalosporins)
  • Narrow-spectrum antibiotics are chosen that target the specific pathogen
  • They are able to get to the site of infection and kill the bacteria (the blood–brain barrier, necrotic and granulating tissue may be barriers)
  • Therapeutic blood levels are maintained
  • The whole course is taken to reduce the risk of bacterial resistance – although a recent scientific paper has questioned the validity of this central dogma of antibiotic treatment. Doctors will need to wait and see what subsequent studies may find before they change this practice
  • A Gram stain and culture, and sensitivity tests are done to ensure that the appropriate antibiotic has been chosen and that the bacterium has been correctly identified as the causal agent of the disease
• Antibiotic resistance


  Bacterial resistance limits the effectiveness of antibiotics in controlling outbreaks of infectious diseases
• This problem arises as an antibiotic becomes less effective over time in treating a particular bacterial disease
• Rise of MRSA (methicillin-resistant Staphylococcus aureus or 'golden staph')


  • In hospitals
• Selection pressure on a population of organisms


  • In the presence of a mutation or gene (genotype) that confers resistance to an antimicrobial substance, bacteria are able to survive or grow in higher antimicrobial concentrations than most other bacterial strains of the same species (phenotype)
• Overuse of antibiotics during the 20th century has caused this serious problem
• Environmental management methods

  Environmental management is imperative for effective disease control, with many environmental factors such as water supply, air quality, sanitation, facilities and food sources influencing the spread or control of infectious disease. Effective environmental management can limit the spread of disease outbreaks and improve the health of those affected. Conversely, uncontrolled environmental factors can facilitate the spread of an outbreak.

  Some of these methods involve:

  • water supplies
  • food sources
  • sanitation
  • air quality
• Contaminated water


  Can facilitate the growth of water-borne diseases such as cholera
• Unclean water


  Can spread parasites such as cryptosporidium sp., which lead to disease
• Water supplies often become contaminated during emergency situations, such as during natural flooding events, or in less developed countries where water supply infrastructure is not sufficient
• Diseases spread by vectors such as mosquitos can thrive in water supplies
• To prevent or control an infectious disease outbreak, water supplies should be protected by


  1. Boiling water before drinking

  2. Chlorinating water

  3. Importing contained water from safe supplies

  4. Sealing, containing, and/or draining water bodies to control the spread of disease
• Food sources


  • Can become contaminated and act as an agent of transfer for infectious diseases
• Preventing or controlling an infectious disease outbreak through food supplies

  1. Limiting food preparation to those who are not infected by the contagion (and have not been in contact with those infected)

  2. Following proper hygiene practices when handling food (e.g. hand washing)

  3. Importing food from safe supplies

  4. Storing food in sealed, temperature-controlled containers

  5. Disposing of all affected food items and avoiding consumption if food is an agent of disease transfer (e.g. a batch of food contaminated by Salmonella sp.)

  6. Avoiding sharing food with others
• Sanitation


  Adequate sanitation facilities control the outbreak of disease by removing human waste from areas of habitation, as well as hygienically disposing of food and animal waste, along with other rubbish
• In states of emergency, or in less developed countries, sanitation services and infrastructure are often not available
• Adequate sanitation for the control of disease


  • Sealed and functioning sewage systems
  • Safe disposal of animal waste, food scraps, and rubbish (e.g. removal of rubbish from towns to a sealed, secure rubbish tip)
  • Safe, secure disposal of hospital and health services waste
• Air quality


  Poor air quality and ventilation can facilitate the transfer of infectious diseases that are spread by airborne droplets (e.g. Legionnaire’s disease or influenza can be spread by sneezing or coughing). Polluted areas, such as cities with smog, can exacerbate the spread of disease, while contained areas such as buildings should have adequate ventilation to ensure the removal of airborne pathogens. Some infectious diseases are so highly contagious that hospitals will put patients in air-locked rooms with separate ventilation systems.
• Quarantine


  Separates and restricts the movement of people, animals and materials that may spread infectious disease
• Quarantine stations


  • Have the power to detain, medically examine and conditionally release people and animals
• Diseases that trigger automatic quarantine


  • Fatal and highly contagious diseases for humans
  • Agricultural diseases that could have a significant negative economic impact
• Examples of diseases that trigger automatic quarantine


  • Tuberculosis
  • Smallpox
  • Cholera
• Actions taken during epidemics


  Governments may place further restrictions on the movement of people, animals, plants and biological products into and out of the affected countries
• Quarantine occurs for diseases with high transmission rates and those capable of reaching epidemic or pandemic prevalence
• Ebola


  Highly contagious disease
• Fruit bats


  • Believed to be the original hosts of the Ebola virus
  • Land degradation and deforestation possibly causing closer proximity of humans to bat colonies
  • Agriculture now shares land with previously native forests
  • Bat species such as the straw-coloured fruit bat (Eidolon helvum) often feed on fruit crops, possibly leading to transmission of infection when humans eat the crops
• Any contact with a patient's body fluids puts a person at risk of contracting Ebola
• Decontamination of sites where Ebola patients had been cared for


  1. Decontaminate homes and hospitals

  2. Prevent cross contamination of other patients and staff

  3. Monitor the effectiveness of decontamination practices