B3 Communicable diseases

• What are microbes that can cause disease called?

  Pathogens
• What are the four types of microbe that cause disease?

  Bacteria

  Viruses

  Fungi

  Protists
• How are infectious diseases spread?

  Air

  Water

  Direct contact
• Spread of infectious disease can be reduced by

  Hygiene (hand washing)

  Isolation of infected individuals

  Vaccination

  Destroying vectors (which transmit microbes)
• Bacteria and viruses reproduce rapidly inside the body
• Bacteria release poisonous chemicals called toxins
• Viruses reproduce inside cells causing cell damage leading to cell lysis
• Measles- Virus

  Spread- inhalation of droplets released by coughing and sneezing

  Symptoms- red rash, fever, could be fatal

  Prevention vaccinate young children
• HIV - Virus

  Spread- Direct contact via sexual contact or exchange of bodily fluids

  Symptoms- Flu like , leads to aids ( immune system can no longer deal with other infections)

  Treatment- Anti-retroviral drugs
• Tobacco mosaic virus - Virus

  Spread- Transferred between plants

  Symptoms- mosaic pattern of discolouration on leaves affecting growth due to lack of photosynthesis

  Prevention- Remove affected plant material, washing hands, sterilising tools
• Salmonella - Bacteria

  Spread - eating contaminated food/ preparation of food in unhygienic conditions

  Symptoms - Fever, abdominal cramps, vomiting, diarrhoea

  Prevention - Vaccination of chickens, prepare food in hygienic conditions, cook thoroughly, wash hands
• Gonorrhoea - Bacteria

  Spread - Direct contact via sexual contact STD

  Symptoms - Thick yellow or green discharge from vagina or penis, pain when urinating

  Treatment - Antibiotics such as penicillin

  Prevention - barrier methods of contraception such as condoms
• Rose black spot - Fungus

  Spread - wind or water

  Symptoms - Purple or black spots on leaves that turn yellow and drop, poor growth due to lack of photosynthesis

  Treatment- fungicides, remove and destroy affected leaves by burning
• Malaria - Protist

  Spread - via mosquitos that act as vectors when they bite to feed on blood

  Symptoms - Recurrent episodes of fever, can be fatal

  Prevention - prevent mosquitos from breeding , use mosquito nets, kill mosquitos
• Non- specific defence systems prevent all microbes from entering the body
• Skin

  Forms a barrier (built of layers)

  Produces anti - microbial chemicals
• Nose

  Contains hairs which trap dust which might contain microbes
• Trachea and Bronchi

  Produces mucus - a sticky substance that traps microbes
• Stomach

  Contains hydrochloric acid which kills microbes
• The immune system recognises pathogens and responds to destroy them
• White blood cells engulf pathogens and destroy them.

  This is called phagocytosis
• White blood cells produce anti-toxins that counteracts toxins and stops them from working
• White blood cells produce antibodies that have a complementory shape to the specific antigens so attach and destroy it
• Vaccination protects us from infectious diseases as it makes us immune this means that the white blood cells are able to respond to a pathogen so quickly you don't become unwell
• How does a vaccination work?

  A dead or inactive version of the pathogen is injected into the body

  The white blood cells produce the correct antibody which destroys the pathogen
• Advantage of vaccinating many people against disease

  Lead to virus becoming eradicated

  Lead to herd immunity (unvaccinated are protected by vaccinated)
• Painkillers

  Reducing sensation of pain but do not kill the pathogens
• Antibiotics

  Kill bacteria but they do not kill viruses
• Problems with antibiotics

  Difficult to identify the correct antibiotic to use

  Do not kill viruses as they live inside our cells

  Some antibiotics don't work against some bacteria because of mutation (DNA change) or overuse causes resistance
• Penecillin

  Treats bacterial infection

  Penicillium mould
• Digitalis

  Treats Heart conditions

  From foxglove plant
• Aspirin

  Painkiller

  From willow tree
• New drugs are tested for

  Toxicity (Is it safe and does it have side effects?)

  Efficacy (Does it work?)

  Dose (How much is given?) - optimum dose
• Pre-clinical trials

  Cells + Tissues - Is the drug likely to work? (efficacy)

  Animals (mice and rats) - Is it safe? (toxicity) Does it work (efficacy)

  If the drug is likely to work they move onto the next stage
• Clinical trials

  Small volunteering group of people - Is it safe? Does it work in humans?

  Large group of people-Blind trial

  Large group of people- Double blind trial

  Afterwards peer reviewed by independent scientist
• What is the point of blind trials and double?


  Comparing the effect of the drug with no drug

  This is done by using a placebo a drug with no active properties
• What diseases are viral?

  Measles, HIV, Tobacco Mosaic Virus
• What diseases are bacterial?

  Salmonella, gonorrhoea
• What disease is fungal?

  Rose Black Spot
• What disease is a protist?

  Malaria