Topic 5 - health, disease and the development of medicines

definition of health given by the World Health Organisation (WHO)

“ a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity”

what are communicable diseases

communicable diseases are those which can be transferred between individuals. this might be through air particles from coughing (known as droplet infection), from parasites in faeces (the faecal-oral route) or through bodily fluids including blood, semen and breast milk. these include viral infections such as flu, bacterial infections such as the common cold, and parasitic infections

what are non-communicable diseases

non-communicable diseases are those which cannot be transfered between individuals. these are usually conditions with a genetic component or conditions acquired due to lifestyle factors. some examples are cardiovascular disease, asthma and diabetes

susceptibility to disease

often, the presence of one disease can lead to increased susceptibility to other diseases. for example:

• having HIV means that your immune system is impaired, leaving you at risk to many other ‘opportunistic’ infections, caused by bacteria, viruses and fungi

• having a particular virus called HPV can increase a woman’s risk of developing cervical cancer

definition of pathogen

an organism which causes diseases. they can infect plants or animals, spreading through either direct contact, by water or by air. most pathogens fall into one of several types: viruses, bacteria, fungi, protists

describe viruses

• very small

• they move into cells and use the biochemistry of it to make many copies of itself

• this leads to the cell bursting and releasing all of the copies into the bloodstream

• the damage and the destruction of the cells makes the individual feel ill

describe bacteria

• small

• they multiply very quickly through dividing by a process called binary fission

• they produce toxins that can damage cells

describe fungi

• they can either be single celled or have a body made of hyphae (thread like structures)

describe protists

• some are parasitic, meaning they use humans and animals as their hosts (live on and inside, causing damage)

describe cholera: category of pathogen, name of pathogen, effects, method of spread

bacteria, Vibrio cholerae, diarrhoea, water

describe tuberculosis: category of pathogen, name of pathogen, effects, method of spread

bacteria, Mycobacterium tuberculosis

describe Chalara ash dieback: category of pathogen, name of pathogen, effects, method of spread

fungi, hymenoscyphu s fraxineus, leaf loss, bark lesions, airbone

malaria: category of pathogen, name of pathogen, effects, method of spread

protists, plasmodium falciparum (and other), damage to blood and liver, body fluids

HIV: category of pathogen, name of pathogen, effects, method of spread

virus, Human immunodeficien cy Virus, destroys white blood cells, leads to onset of AIDS, body fluids

helicobacter: category of pathogen, name of pathogen, effects, method of spread

bacteria, helicobacter pylori, can lead to stomach ulcers, oral transmission

ebola: category of pathogen, name of pathogen, effects, method of spread

virus, B.ebolavirus (and others), causes haemorrhagic fever (fever accompanied by severe bleeding), body fluids

how do pathogens spread

• direct contact - touching surfaces

  examples: kissing, contact with bodily fluids, direct skin to skin, microorganisms from faeces, infected plant material left inn field

• by water - drinking or coming into contact with dirty water

• by air - pathogens can be carried in the air and then breathed in (a common example is the droplet infection, which is when sneezing, coughing or talking expels pathogens in droplets which can be breathed in)

how to limit the spread of pathogens

• improving hygiene - hand washing, using disenfectants, isolating raw meat, using tissues and handkerchiefs when sneezing

• reducing contact with infected individuals

• removing vectors - using pesticides or insecticides and removing their habitat

• vaccination - by injecting a small amount of a harmless pathogen into an individual’s body, they can become immune to it so it will not infect them. this means they cannot pass it on to other individuals

lifecycle of a virus, lytic pathway

1. using host cell machinery, the virus replicated its DNA

2. next, these are assembled to form new virus particles

3. once the host cell is full of virus particles, it bursts in a process called lysis

4. the process is then repeated with nearby cells

lifecycle of a virus, lysogenic pathway

1. the virus uses restriction enzymes to insert its DNA into the host cell DNA - or it can insert small circular fragments of DNA called plasmids into the host cell cytoplasm

2. the host cell replicates, and the viral DNA is also copied in this process

3. the lytic cycle (see above) begins at this point, starting with the assembly of new viral particles

what are STI’s and how do they spread

sexually transmitted infections (STIs) are infections which can be spread through sexual contact, including oral and vaginal sex. they are carried in bodily fluids such as semen and vaginal fluid.

chlamydia category of pathogen and symptoms

bacteria, often symptomless but if there are symptoms these can include painful urination or pelvic pain. left untreated it can lead to infertility

HIV category of pathogen and symptoms

virus, increased susceptibility to other infections, severe illness and death if untreated

how can the spread of STIs be reduced

by using barrier methods of contraception (eg. condoms) or abstaining from sexual activity

how do plants guard their cells and tissues against pathogens that cause disease

some methods involve having physical barriers against disease, whereas others use chemicals to defend against attack from pests and pathogens

plant physical barriers examples

• a thick cellulose cell wall, which is impermeable to many pathogens

• a thick waxy cuticle on the surface of the leaf, which acts as a barrier to most pathogens

• some plants are also covered in a layer of bark (eg trees) which prevents pathogens from reaching the cells and tissues inside

• leaves can often close their stomata (pores) to stop pathogens entering the plant

plant chemical barriers examples

• cells of some plants can produce antimicrobial chemicals, proteins and enzymes

• some plants can release compounds that attract larger insects than the pests, which feed on the pests and stop them eating the plant

• often, we can extract antimicrobial compounds from these plants for use in drugs such as antibiotics

how to identify plant disease in the field

plants affected by disease often have a number of visible clues allowing us to identify it in the field:

• Chalara dieback of ash causes malformations and browning of leaves

• tobacco mosaic virus causes discolouration of leaves

• bacterial canker on fruit trees causes loss of leaves, stunted growth and formation of pus-filled lesions on trunk

• aphids can cause serious structural damage to plants

how to identify plant disease in the lab

sometimes, laboratory techniques are needed to accurately identify a disease. plant virologists use a specific method to do so:

1. cuttings are taken from the diseased plant

2. the virus/bacterium causing the disease is grown on a culture medium/agar plate

3. the pathogen is tested and identified using a monoclonal antibody testing kit (known as an ELISA kit)

examples of human body physical barriers

mucus, cilia, skin

what is mucus associated with and its function

• goblet cells in the airway (produce mucus)

• produced by goblet cells in the airway, mucus traps bacteria and other pathogens before they reach the lungs and cause infection

what is cilia associated with and its function

• ciliated epithelial cells (have cilia on their surface)

• wafts away mucus that has trapped pathogens, to be killed by stomach acid

what is skin associated with and its function

• skin cells

• provides a physical barrier against pathogens, protecting the tissues and cells beneath it from infection

human chemical barriers

lysozymes, hydrochloric acid

where are lysozymes found and function (in humans)

• white blood cells

• used by white blood cells to kill and digest bacteria

where is hydrochloric acid found and function (in humans)

• stomach

• used to kill bacteria in food reaching the stomach - to prevent infection

the specific immune response

1. phagocytosis (white blood cells engulfing and consuming pathogens) - this destroys them, meaning they can no longer make you feel ill

2. producing antibodies - each pathogen has an antigen on their surface, which is structure which a specific complementary antibody can bind to. once antibodies begin to bind to the pathogen, the pathogens start to clump together, resulting in it being easier for white blood cells to find them and engulf them in phagocytosis. during this process, the antigens also trigger production of memory lymphocytes (lymphocytes are a special type of white blood cell). if you become infected again with the same pathogen, the specific complementary antibodies will be produced at a faster rate. the individual will not feel the symptoms of the illness. they are said to be immune

3. producing antitoxins - they neutralise the toxins released by the pathogen by binding to them

what do vaccines do

vaccinations involve making an individual immune to a certain disease - they are protected against it before they have been infected. by immunising a large proportion of the population, the spread of the pathogen is reduced as there are less people to catch the disease from (called herd immunity)

explain the body’s response to immunisation using an inactive form of a pathogen

naturally, when you are infected with a pathogen, you feel ill until white blood cells manufacture the correct specific antibody to combat it. upon a secondary infection, the antibodies can be produced much quicker, so the pathogen can be destroyed and the symptoms are not felt. vaccinations replicate the first infection so that when the person is exposed to the real disease they do not feel any symptom, just like in a secondary infection

• the vaccine contains a dead or inactivated form of the pathogen

• this stimulates white blood cells to produced antibodies complementary to the antigens on the pathogen

advantages of vaccination

• they have eradicated many diseases so far (eg smallpox) and reduced the occurrence of many (eg rubella)

• epidemics (lots of cases in an area) can be prevented through herd immunity

disadvantages of vaccination

• they are not always effective in providing immunity

• bad reactions (such as fevers) can occur in response to vaccines (although very rare)

what can antibiotics be used to treat

antibiotics can ONLY be used to treat bacterial infections, and NOT those caused by viruses, fungi or other pathogens

why is this

bacteria are susceptible to antibiotics because antibiotics inhibit cell processes in the bacterium. However, viruses and other pathogens often use cell machinery in host cells to reproduce, and these are unaffected by antibiotics

what does the culture medium contain for scientists to grow microorganisms

carbohydrates for energy, mineral, proteins and vitamins

two ways to grow microorganisms in the lab

1. in nutrient broth solution - involves making a suspension of bacteria to be grown and mixing with sterile nutrient broth (the culture medium), stoppering the flask with cotton wool to prevent air from contaminating it and shaking regularly to provide oxygen for the growing bacteria

2. on an agar gel plate - the agar acts as the culture medium, and bacteria grown on it form colonies on the surface

   making the plate:

   • hot sterilised agar jelly is poured into a sterilised Petri dish, which is left to cool and set

   • sterilised wire loops called inoculating loops are dipped into a solution of the microorganism and spread over the agar evenly

   • a lid is taped on and the plate in incubated for a few days so the microorganisms can grow (stored upside down)

steps and reasons in this procedure

• petri dishes and culture media must be sterilised before use, often done by an autoclave (an oven) or UV light

  • if this step does not take place, they are likely to be contaminated with other microorganisms

  • these could be harmless but will compete with the desired bacteria for nutrients and space, or they could be harmful (for example through a mutation taking place), potentially producing a new pathogen

• inoculating loops must be sterilised by passing them through a flame

  • this kills unwanted microorganisms, which is needed for reasons above

• the lid of the Petri dish should be sealed (but not completely) with tape

  • sealing stops airborne microorganisms from contaminating the culture, but it should not be sealed all the way around as this would result in harmful anaerobic bacteria growing (due to no oxygen entering)

• the Petri dish should be stored upside down

  • this is to prevent condensation from the lid landing on the agar surface and disrupting growth

• the culture should be incubated at 25 degrees

  • if it were incubated at a higher temperature, nearer 37 degrees (human body temperature), it would be more likely that the bacteria that could be harmful to humans would be able to grow as this is their optimum temperature

  • at lower temperatures, colonies of such bacteria would not be able to grow

core practical: Investigate the effects of antiseptics, antibiotics or plant extracts on microbial cultures

it is possible to calculate the cross sectional area of a bacterial culture using the formula for the area of a circle. if we apply an antibiotic to the agar plate, this is a useful calculation - as it allows us to determine the effectiveness of the antibiotic.

growing the bacterial culture

1. take a Petri dish that has been pre-poured with agar gel, and sterilise it in an autoclave before use. use an inoculating loop (sterilised in a Bunsen Burner) to apply the bacteria being tested to the agar. seal the top of the plate using tape (but not completely) incubate the culture at 25 degrees C for 3 days

2. apply a filter paper disc soaked in antibiotic solution to the centre of the agar plate and wait for 24hours, or until there is no further change

calculating the effectiveness of the antibiotic

3. use a ruler to measure the diameter of the circle taken up by the bacterial culture and record this measurement. repeat for the diameter of the clear agar jelly in the centre, where the antibiotic has killed the bacteria

4. divide both diameters by 2 to get the radius of both these circles. use πr² to calculate the area of these circles

5. divide the areas of the smaller circle by the larger, and multiply by 100. this is the percentage of the bacterial culture that has been destroyed by the antibiotic. the higher the percentage, the more effective the antibiotic

we can repeat these calculations for multiple antibiotics and bacteria, in order to determine the effectiveness of different bacteria/antibiotic combinations. this is useful as it allows doctors and scientists to work out which antibiotics are most effective for particular bacterial infections

what do new drugs need to be tested for

toxicity, efficacy (how well they carry out their role) and dose, using preclinical testing and clinical trials

how are plants used in medicine

the chemicals that plants use to kill pests and pathogens can be used to treat symptoms or human diseases

examples:

• aspirin is used as a painkiller (originated from willow)

• digitalis is used to treat heart problems (originated from foxgloves)

how are microorganisms used in medicine

Penicillin

• Alexander Fleming was growing bacteria on plates

• he found mould (Penicillium mould) on his culture plates, with clear rings around the mould indicating there was no longer any bacteria there

• he found that the mould was producing a substance called penicillin, which killed bacteria

how new drugs are tested

• preclinical testing: using cells, tissues and live animals

• clinical testing: using volunteers and patients

  • it is first tested on healthy volunteers with a low dose to ensure there are no harmful side effects

  • the drugs are then tested on patients to find the most effective dose

  • to test how well it works, patients are split into two groups with one group receiving the drug and one receiving a placebo (appears to look like the drug but has no effect with no active ingredient) so the effect of the new drug can be observed

  • these can be single-blind (only the doctor knows whether the patient in receiving the drug) or double blind (neither the patient or doctor knows whether they are receiving the drug, removing any biases the doctor may have when they are recording the results)

• the results then need to be peer reviewed by other scientists to check for repeatability

what are monoclonal antibodies and what can they do

• monoclonal antibodies are identical antibodies, that have been produced from the same immune cell

• as a result of their ability to bind to only one protein antigen, they can be used to target chemicals and cells in the body and so have many different medical uses, eg in pregnancy testing

how are monoclonal antibodies produced

1. scientists obtain mice lymphocytes (a type of white blood cell that make antibodies but cannot divide), which have been stimulated to produce a specific antibody

2. they are combined with tumour cells (do not make antibodies but divide rapidly), to form a cell called a hybridoma

3. the hybridoma can divide to produce clones of itself, which all produces the same antibody

4. the antibodies are collected and purified

examples of uses of monoclonal antibodies

pregnancy tests, in laboratories to measure the levels of hormones or chemicals, in research and in the treatment of some diseases

how monoclonal antibodies are used in pregnancy tests

a hormone called human chorionic gonadotrophin (hCG) is present in the urine of women who are pregnant

• there are two sections of the stick

• the first section has mobile antibodies complementary to the hCG hormone - these antibodies are also attached to blue beads

• the second section has stationary antibodies complementary to the hCG hormone which are stuck down to the stick

• the individual urinates on the first section, and if hCG is present it binds to the mobile antibodies attached to blue beads to form hCG/antibody complexes

• they are carried in the flow of liquid to the second section

• the stationary antibodies then bind to the HCG/antibody complexes

• as they are each bound to a blue bead, results in a blue line

• this indicated that you are pregnant

how are monoclonal antibodies used in laboratories to analyse blood

• they can be used to measure and monitor levels of hormones or chemicals in the blood

• the monoclonal antibodies are modified so that they will bind to the molecule you are looking for

• the antibodies are also bound to a fluorescent dye

• if the molecules are in the sample then the antibodies bind to it, and the dye can be observed

• an example is screening donated blood for HIV infections

how are monoclonal antibodies used in research to find or identify certain molecules on a cell or tissue

• monoclonal antibodies are modified so that they will bind to the molecule you are looking for

• the antibodies are also bound to a fluorescent dye

• if the molecules are in the sample then the antibodies bind to it, and the dye can be observed

• scientists look for a build up of the fluorescence

how are monoclonal antibodies used in the treatment of disease, eg. cancer

cancer cells have antigens on their cell membranes known as tumour markers (not found on normal body cells), which can be targeted. there are three main ways to treat cancers using monoclonal antibodies

a) producing monoclonal antibodies that bind to the tumour markers in order to stimulate the immune system to attack the cell

b) using monoclonal antibodies to bind to receptor sites on the cell surface membrane of the cancer cells. this means growth stimulating molecules cannot bind, stopping the cell from dividing

c) using monoclonal antibodies to transport toxic drugs, chemicals or radioactive substances as they can only bind to cancer cells

advantages of using monoclonal antibodies

• they only bind to specific cells, meaning healthy cells are not affected

• they can be engineered to treat many different conditions

• we are now able to produce mouse-human hybrid cells to reduce the chance of triggering an immune response

disadvantages of using monoclonal antibodies

• it is difficult to attach monoclonal antibodies to drugs

• they are expensive to develop

• as they were produced from mice lymphocytes, they often triggered an immune response when used in humans

what are many non-communicable diseases caused by

eg. cardiovascular diseases, asthma, and diabetes are caused by the interaction of a number of different factors

what is cardiovascular disease caused by

cardiovascular diseases such as coronary heart disease can be caused by high dietary intake of saturated fat, combined with a sedentary (inactive) lifestyle

factors for several forms of cancer

smoking greatly increases the risk of lung cancer, whereas the risk of developing breast cancer is largely due to a combination of age and genetics

factors affecting likelihood for lung and liver diseases

made more likely by smoking and high alcohol intake respectively. however, other factors can play a part - especially age and genetics. an as individual gets older, they are more likely to suffer from these conditions

factors for vitamin and nutritional deficiencies

common in anorexic patients, as well as those who can’t absorb or use nutrients properly (including patients with coeliac disease and anaemia) obesity, on the other hand, is caused by excess caloric intake (food intake), and can again be heavily influenced by genetics - some people are more likely to gain weight than others

non communicable disease and lifestyle factors, obesity

• eating more calories than you burn from physical activity (and everyday metabolism) causes us to put on weight

• eating a very large excess of calories, especially if a high proportion of these calories come from saturated fat, can lead to obesity and related illnesses

• obesity is an important problem worldwide, but especially in developed countries such as the UK

• obesity can lead to developing cardiovascular disease and high blood pressure, as fat (lipid) deposits from inside blood vessels

• obesity can also contribute to developing Type 2 diabetes, as the body cannot use insulin as effectively when there is a high proportion of body fat

• government programs such as ‘sugar tax’ are aimed at reducing obesity across the country. eating fewer processed foods, less sugar, saturated fat and high calorie foods can help reduce the risk of becoming obese

non communicable disease and lifestyle factors, malnutrition

• equally, eating significantly fewer calories than we use can lead to malnutrition, as the body will not be receiving adequate amounts of nutrients and vitamins

• the symptoms can be different depending on the vitamin or nutrient that is deficient

• malnutrition is less of a problem in developed countries like the UK, but more of an issue in underdeveloped countries where many people do not have enough money to eat

how to determine is someone is underweight, a healthy weight, obese or morbidly obese

BMI = mass (kg)/height² (m²)

we can also use the waist-hip ratio, calculated by dividing waist circumference (cm) by hip circumference (cm).

obesity is classified as a waist-hip ratio of more than 0.85 for women, or more than 1.0 in men

liver disease

• a high alcohol intake can lead to liver disease

• a type of liver disease called fatty liver is common in alcoholics. it can lead to liver cancer and impaired liver function

• alcoholics often have vitamin deficiencies (particularly vitamin B6, thiamine)

• the recommended weekly allowance for men and women is 14 units a week. drinking less than this significantly reduces the risk of developing liver disease

lung disease

• smoking dramatically increases the risk of developing several lung diseases

• these include COPD (chronic obstructive pulmonary disease), bronchitis, pneumonia and lung cancer

• cigarette smoke contains over 40 different chemicals, all of which have different effects on the body - for example, tar can cause lung cancer and nicotine can cause high blood pressure and heart failure

• the UK government provide services to help and encourage smokers to quit smoking

treatments available for cardiovascular disease

life-long medication, surgery and lifestyle changes

life-long medication

• there are several medications that will either reduce cholesterol or reduce blood pressure

• people with high blood pressure may have to take multiple medications to reduce it

• they will most likely have to take these for the rest of their life

surgical procedures

• sometimes medication does not work effectively, and surgery may be required

• coronary arteries supply the heart muscle with oxygen, and cover the heart

• if these are blocked, a coronary artery bypass can be performed, where the blocked sections of the coronary artery are ‘bypassed’

• another method involves using a metal stent to widen arteries that have been narrowed by fat deposits (atherosclerosis)

lifestyle changes

• lifestyle changes (changes to exercise, diet and other habits) are very important in preventing and treating cardiovascular disease

• reducing the amount of saturated fat we eat can reduce the risk of developing atherosclerosis (fat deposits in the arteries) and high cholesterol

• maintaining a healthy BMI can reduce strain on the heart

• taking regular exercise ensures that we remain at a healthy weight

• reducing the amount of salt in the diet, and managing stress levels, can prevent high blood pressure from developing