AS Biology F212: Disease

Health is a state of mental, physical and social wellbeing - NOT just absence of diesease.
If one is in good health they are:

• able to carry out normal mental and physical tasks
• well fed with a balanced diet
• usually happy with a positive outlook
• suitably housed with proper sanitation
• well integrated into society
• free from diseases

What is disease?

• Disease is a departure from good health caused by malfunction of the mind or body
• symptoms can be physical, mental or social
• those caused by living organisms are called infectious diseases - usually physical 

Parasites and Pathogens

• Parasites
• Live on (external) or in (internal) another living thing (host)
• they cause harm to the host by taking nutrients
• they may live all or part of their life on the host
• they can overburden the host and make it more susceptible to secondary infections
• Pathogens
• this is an organism that causes disease
• they live by taking nutrition from their host and cause damage in the process
• includes a wife range of bacteria, fungi, protoctist and viruses

• Bacteria - cholera
• caused by bacterium Vibrio cholerae
• it is a water-borne disease and spreads through contaminated water, food or shell fish
• they act on the walls of the small intestine causing diarrhoea, dehydration and weakness.
• Tuberculosis
• aka TB is an infectious disease that can affect any part of the body although it is usually found n the lungs as these are the first site of infection
• it kills approx 2 million people each year - more than any other infectious disease
• tuberculosis is caued by one of two species of rod shaped bacteria
• Mycobacterium tuberculosis
• Mycobacterium bovis
• Fungi - Athletes foot and ringworm
• Caused by Tinea fungus
• many different species that causes these diseases
• they live in the skin
• cause redness and severe irritation
• Viruses - TMV and HIV
• TMV - tobacco mosaic virus - affects plants
• HIV - human immunodeficiency virus - affects humans 
• also more common diseases such as colds and flu.
• take over the cells genetic machinery and organelles to allow it to reproduce
• Protosctist
• Amoeboid dysentery 
• Malaria
• enter cells and feed on the contents as they grow

TRANSMISSION OF DISEASE

For a micro-organism to be considered a pathogen they must

• travel from one host to another
• gain entry to the host's tissues
• reproduce
• resist the defences of the host
• cause damage to the host's tissues

Forms of transmission

• by the means of a vector (carrier)
• by physical contact
• by droplet infection

• Malaria
• caused by eukaryotic Plasmodium
• Plasmodium falciparum is the most common
• spreads by the female Anopheles mosquito
• these feed on blood
• the parasite lives in the red blood cells and feed on the haemoglobin
• HIV/AIDs
• The HIV virus enters the body and may remain inactive
• This is known as being HIV positive
• once active, the virus attacks and destroys T helper cells in the immune system
• these cells help to prevent infection
• their destruction reduces the person's ability to resist infection
• EFFECT
• you are unable to defend yourself against any pathogen that enters your body
• these are known as opportunistic infections
• it is the effect of these that eventually kills as person with HIV
• AIDS stands for acquired immune deficiency syndrome
• Transmission
• Exchange of bodily fluids such as blood-to-blood contact
• unprotected sex
• unscreened blood transfusions
• use of unsterislised surical equipment
• sharing hypodermic needles
• accidents such as 'needle-stick'
• across the placenta or during childbirth
• from mother to baby during breast feeding
• Tuberculosis (TB)
• TB is an infectious disease that can affect any part of the body although it is usually found in the lungs as these are the first site of infection
• Pulmonary tuberculosis is spread through the air by droplets containing the bacteria, released into the air when infected individuals cough, sneeze or even talk.
• normally takes close contact with an infected person over a period of time rather than a causal meeting in the street to transmit the bacteria
• Symptoms (droplet infection)
• the symptoms of pulmonary tuberculosis initially include a persistent cough, tiredness, and loss of appetite that leads to weight loss.
• As the disease develops, fever and coughing up of blood may occur
• Risks
• some groups are at greater risks of contracting TB than others.
• people who are in close contact with infected individuals over long period e.g. living and sleeping in overcrowded conditions
• work or reside in long term care facilities where relatively large numbers of people live close together e.g. old people's home, care homes, hospital or prisons
• people from countries where TB is common
• have reduced immunity such as
• the very young or very old
• those with AIDS
• people with other medical conditions that make the body less able to resist disease e.g. diabetes, or lung disease such as silicosis
• those undergoing treatment wit immunosuppressant drugs eg. following a transplant surgery
• the malnourished
• alcoholics or injecting drug-users
• the homeless

The World Health Organisation (WHO)

• WHO states that good health is a human riht
• poor health causes a lot of suffering
• Ill health has an economic cost as a result of medical provision and loss of productivity
• worldwide, many peopl have no access to the basic requirements for good health
• contributing factors
• poverty
• lack of proper shelter
• lack of purified water
• poor nutrition
• poor hygiene
• lack of government investment
• poor/inadequate education on disease, it causes and transmission
• civil unrest or warfare

• Malaria
• kills around 3 million people peryear
• about 300 million are affected worldwide
• it is limited to were the vector (Anopheles mosquito) can survive
• 90% of sufferers live in sub-Saharan Africa
• It is difficult to control
• mosquito
• resistant to insecticides/pesticides/chemicals used for control
• build up in food chains/kill predators
• breeds quickly/very common/lays many eggs
• breeds in small bodies of water/inaccessible places
• especially in rainy seasons
• difficult drain/spray/cover
• difficult to encourage everyone to use netswide range of increasing because of climate change
• rests and hides in houses
• Plasmodium
• side effects of (e.g. anti-malarial) drugs/people don't take drugs long enough (think they are well but not)
• many strains and species
• resistant to drugs
• inside red blood cells or liver cells
• antigen concealment
• dormant/in body for a long time/symptomless carriers/long incubation
• different stages in life cycle in the body
• no vaccine/difficult to develop vaccine
• people lose immunity if malaria is eradicated
• HIV/AIDS
• Spreading in pandemic proportions (is an epidemic of infectious disease that is spreading through human populations across a large region)
• 45 million people living with HIV/AIDS at the end of 2005 (>half in sub-Saharan Africa)
• 5 million newly infected each year
• at the end of 2006 30 million died as result of HIV/AIDS related disease
• Epidemiology
• = patterns in the occurrence of the disease in the human population 
• it identifies the cause of a disease
• the risk factors associated with the disease
• determines the incidence of a disease
• determines the prevalence of the disease as well as the mortality and morbidity
• study how quickly it's spreading
• identify countries/part of population at risk
• identify a disease as endemic, epidemic or pandemic
• ENDEMIC: always present in a population
• EPIDEMIC: spreading rapidly to a lot of people over a large area
• PANDEMIC: a worldwide epidemic
• they target education programmes at people at most risks
• target advertisements to raise the awareness
• target screening programmes to identify individuals at risk
• provide specialist healthcare in certain areas
• provide vaccination programme for the major disease
• targeting research to find cures for the major disease