B5 Communicable Diseases

Health = state of physical and mental well-being

Communicable disease = infectious disease caused by pathogens that can be passed on from one person to the next. e.g. TB and flu

Non-communicable disease = disease that cannot be transmitted e.g. heart disease

Factors causing ill health

Diet- eating too less, not getting nutrients - starvation, rickets, anaemia. Eating too much - obesity. type 2 diabetes

Stress - too much stress = increased risk of heart disease, some cancers and mental health problems

Life situations - where you live, gender, financial status, ethnic group, health care, sewage and rubbish disposal

Health problems often interact in the real world, making one another worse ---> examples

Health problem interactions

Viruses living in cells can trigger changes that lead to cancers - HPV virus can cause cervical cancer

Defects in immune system - more likely to suffer from communicable diseases

Immune reactions caused by pathogens can trigger allergies - rashes, asthma

Bad physical health - depression and mental illness

Malnutrition = deficiency diseases, weak immune system, obesity, cardiovascular, type 2 diabetes and cancer

Communicable disease = infectious and spreadable

Pathogens = micro-organisms that cause disease e.g. bacteria, viruses, protists and fungi

Communicable diseases caused by pathogen or pathogen toxin

How pathogens cause disease

• Bacteria divide rapidly by splitting in two - binary fission. Produce toxins that make you feel ill

• Viruses take over cells of body - live and reproduce inside the cells, damaging and destroying them.

High temperatures, headaches and rashes are caused by the body's response to the pathogen's effects.

Air

• Bacteria, viruses and fungal spores are carried and spread in the air. 
• Droplet infection - ill people sneeze and pathogens fly out of them. People inhale them and pick up the pathogens. E.g TB, flu and common cold

Direct contact 

• Direct contact of an infected organism with a healthy one.
• In plants, infected piece of plant material can infect a new crop. In humans, syphillis and chlamydia are spread by direct contact of skin. HIV/AIDS enter through cuts, scratches and direct sexual contact.

Water

• Fungal spores carried in splashes of water carry plant diseases
• Eating raw, undercooked or contaminated food or water can spread diseases e.g. cholera and salmonella

An uncontaminated culture of micro-organisms are needed for investigating the action ofdisinfectants and antibiotics.

Growing micro-organisms in the lab

• Culture medium (agar gel) - containing nutrients, carbohydrate as energy source, nitrogen to make proteins 
• Warmth
• Oxygen
• Sterilise solutions and equipment to kill pre-exisisting bacteria
• Contamination can come from skin, soil or water. Mutations can produce a dangerous pathogen.

An uncontaminated culture of micro-organisms can be grown using sterilised Petri dishes and agar. You sterlise the inoculating loop before use and secure the lid to prevent unwanted micro-organisms coming in. 

Cultures should be incubated at 25 degrees Celsius (max) in schools to reduce risk of growing harmful pathogens. 

Bacteria reproduce by binary fission - splitting in two. With the right conditions, enough nutrients and temperature, they can divide every 20 mins.

Preventing bacterial growth

• Raise or lower the temperature
• Use chemicals 
• Disinfectant - chemicals used to kill bacteria in the environment around us
• Antiseptic - disinfectant safe to use on human skin
• Antibiotics - chemicals that can be used to kill bacteria inside our bodies

Disinfectants and antibiotics

A clear zone indicates bacteria have been killed or cannot grow = called zone of inhibition.

Preventing the spread of communicable diseases 

Hygiene

• Handwashing after using the toilet, or after being in contact with an animal or infected person.
• Using disinfectants on surfaces in the kitchen and bathroom
• Keeping raw meat away from uncooked food
• Maintaining hygiene of agricultural machinery to prevent plant disease

Isolating infected individuals - People with serious infectious diseases are kept in isolation. The less people that come in contact with them, the less likely it is that the pathogen will be passed on. 

Destroying or controlling vectors  - Vectors = passers on of diseases e.g mosquitoes. Controlling number of vectors reduces spread of disease

Vaccination - Introducing a small amount of harmless pathogen into body prepares it for the next time it may come into contact with you. Vaccinating large numbers of humans against disease is good protection.

Viruses - live and reproduce in cells, damaging and destroying them. Scientists have not developed medicines to cure viral diseases, so it's important to stop them spreading. 

Measles

• Spread by inhalation of droplets e.g. coughs and sneezes
• Symptoms = fever and red skin rash
• Can be fatal, no cure
• Isolation and vaccination prevents spread

HIV/AIDS

• Initially causes mild, flu-like illness. Attacks immune system and remains hidden until the immune system is so badly damaged it cannot deal with infections = AIDS
• HIV spread by sexual contact, exchange of bodily fluids e.g. blood
• Can be prevented by using condoms, not sharing needles
• Antiretroviral drugs prevent development of AIDS for many years however, it is not available to everyone. 

Tobacco mosaic virus 

TMV causes pattern of discoloration on leaves as the virus destroys them. 

Leaves cannot photosynthesise and so affects their growth

Reduces yield of a crop

Spread by contact and vectors (insects)

Prevented by field hygiene and pest control

Salmonella food poisoning

• Salmonella = bacteria found in raw meat, poultry and eggs. If they get into our bodies, natural gut bacteria is disrupted
• Spread through eating undercooked food when bacteria hasn't been killed by heat and from poor hygiene in cooking conditions
• Symptoms = abdominal cramps, diarrhoea and vomiting caused by toxins produced by the bacteria. 
• Prevention = poultry vaccinated against salmonella, keep raw chicken away from uncooked food, avoid washing raw chicken, wash hands thoroughly and cook chicken thorougly.

Gonorrhea

• STD - spread by unprotected sexual contact with an infected person. 
• Symptoms = discharge from genitals and pain on urination
• Treated using antibiotics, however, many strains are now resistant 
• Prevention = using condoms, limiting sexual partners.

Bacterial disease in plants 

Bacterial diseases in plants usually found in tropical climates

AT bacterium causes crown galls - mass of unspecialised cells that grow between the root and the shoot in infected plants. 

Bacteria inserts plasmids into cells and causes a mass of genetically modified cells to grow. 

Rose black spot

• Causes black spots on roses leaves. Cannot photosynthesise properly so plant weakens and rose dies
• Spores of fungus carried by wind and rain splashes it from one leaf to another.
• Spread is controlled by removing affected leaves and chemical sprays - not very effective

Protists - usually involve a vector that transfers the protist to the host. 

Malaria

• Caused by parasitic protists and is spread by the bite of female mosquitoes
• Damages blood and liver cells, causes fevers and shaking and can be fatal
• Drugs effective if given early enough, but protists becoming resistant
• Spread reduced by: preventing vectors from breeding, using mosquito nets, using insecticides

Skin defences 

• Acts as a barrier - prevents bacteria and viruses reaching tissues beneath
• Cuts in skin are restored by platelets in blood that form a clot - stopping pathogens from entering
• Antimicrobial secretions
• Healthy skin covered with micro-organisms that act as an extra barrier

Respiratory and digestive defences 

• Nose - full of hairs and mucus that trap particles in the air that may contain pathogens
• Trachea and bronchi - secretes mucus that traps particles. Cilia lined. 
• Stomach - produces acid which destroys pathogens in food, drink and mucus 

Immune system

• Producing antibodies - chemicals that target specific bacteria or viruses and destroy them.
• Ingesting micro-organisms - ingesting pathogens destroys them, stopping illness
• Producing antitoxins - antitoxins counteract the toxins released by pathogen

Aphids and nematodes 

• Bacteria, viruses, fungi and insect pests
• Aphids = insect pest that penetrates the phloem tissue and sucks up the sugar-rich sap
• Attack in huge numbers, depriving plant of the products of photosynthesis
• Aphids = vectors transferring viruses, bacteria and fungi into healthy plants
• Destroyed using: pesticides, releasing aphid eating insects like ladybirds to control numbers
• Nematodes = worms that feed on plant roots. Plants cannot absorb minerals and water.

Mineral deficiency - non communicable diseases in plants 

• Nitrate ions needed to convert sugars into proteins for growth
• Lack = stunted growth
• Magnesium = to make chlorophyll
• Lack = leaves become yellow, slow growth - chlorosis

Detecting disease

Sooner, a disease can be detected the more likely it is that it can be treated and reduce spread.

Symptoms: 

• stunted growth - nitrate deficiency
• spots on leaves - e.g. rose black spot
• areas of decay - black spot on roses 
• growths - crown galls caused by bacteria
• malformed stems and leaves - aphid, nematode infestation
• discoloration - chlorosis, magnesium deficiency
• visible pests

Treatments: Pesticides, antifungal treatments, removing diseased plants.

Detections: Gardening manuals, DNA analysis of diseased material and testing kits using monoclonal antibodies

Detecting disease

Sooner, a disease can be detected the more likely it is that it can be treated and reduce spread.

Symptoms: 

• stunted growth - nitrate deficiency
• spots on leaves - e.g. rose black spot
• areas of decay - black spot on roses 
• growths - crown galls caused by bacteria
• malformed stems and leaves - aphid, nematode infestation
• discoloration - chlorosis, magnesium deficiency
• visible pests

Treatments: Pesticides, antifungal treatments, removing diseased plants.

Detections: Gardening manuals, DNA analysis of diseased material and testing kits using monoclonal antibodies

Physical barriers

• Cellulose cell walls - strengthen plant cells to resist invasion by micro-organisms
• Waxy cuticle - barrier to pathogen entry
• Bark, layer of dead cells on stems - layer that is difficult to penetrate. Shedding causes pathogens to fall off
• Leaf fall - pathogens fall off leaves of deciduous trees

Chemical barriers

• Antibacterial chemicals - protect them against invading pathogens
• Poisons - deter herbivores

Defence against herbivores 

Poisons, thorns, hairy stems - hard for the herbivore to eat, drooping or curling frightens the animal, mimicry- acting as a dead plant so animals don't eat them