B5: Communicable diseases

• Health is a state of physical and mental well-being
• Communicable diseases are infectious disease caused by pathogens that can be passed on from one person to the next. e.g. TB and flu
• Non-communicable diseases are diseases that cannot be transmitted e.g. heart disease

Other factors causing ill health -

• Diet - eating too little, not getting enough nutrients leads to starvation, rickets, anaemia. Eating too much leads to obesity, type 2 diabetes
• Stress - too much stress causes 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

How health problems interact -

• Viruses living in cells can trigger changes that lead to cancers as HPV virus can cause cervical cancer
• Defects in your immune system means more likely to suffer from communicable diseases
• Immune reactions caused by pathogens can trigger allergies causing rashes, asthma
• Bad physical health can lead to depression and mental illness
• Malnutrition links with deficiency diseases, weak immune system, type 2 diabetes and cancer

• Communicable diseases are infectious and spreadable
• Pathogens are 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 caused by the body's response to the pathogen's effects.

How pathogens are spread -

• 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 -  in plants, infected piece of plant material can infect a new crop and 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 and 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 of disinfectants 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.

How to do -

• 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.

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 are 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.

Measles -

• Spread by inhalation of droplets e.g. coughs and sneezes
• Symptoms are 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
• 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 is 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 are abdominal cramps, diarrhoea and vomiting caused by toxins produced by the bacteria. 
• Prevention by poultry vaccinated against salmonella, keep raw chicken away from uncooked food, avoid washing raw chicken, wash hands thoroughly and cook chicken thorougly.

Gonorrhea -

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

Bacterial disease in plants -

• Bacterial diseases in plants usually found in tropical climates
• AT bacterium causes crown galls and 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. 

Fungi - usually in plants

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 however 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 are 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 are vectors transferring viruses, bacteria and fungi into healthy plants
• Destroyed using: pesticides, releasing aphid eating insects like ladybirds to control numbers
• Nematodes are 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 leads to stunted growth
• Magnesium needed to make chlorophyll
• Lack leads to leaves become yellow, slow growth - chlorosis

Detecting disease symptoms-

• Treatments - pesticides, antifungal treatments, removing diseased plants.
• Detections - gardening manuals, DNA analysis and testing kits using monoclonal antibodies
• stunted growth - nitrate deficiency
• spots on leaves and areas of decay - e.g. rose black spot
• growths and malformed stems and leaves - crown galls caused by bacteria or infestation
• discoloration and visible pests - chlorosis, magnesium deficiency

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