The Search for Better Health

What is a healthy organism?Difficulties of defining ‘health’ and ‘disease’:

Disease is any condition that adversely affects the function of any part of a living thing. Many diseases are best understood as a disturbance in homeostasis.

Health refers to the overall well-being of an organism, not just the absence of disease.

Different organisms will differ in health and susceptibility in disease. It is possible for a person to be healthy and have a disease at the same time, making it difficult to define both health and disease.

How the function of genes, mitosis, cell differentiation and specialisation assist in the maintenance of health:

The degree to which an organism is healthy depends on whether or not its cells are functioning properly and how well the body can repair a malfunction or imbalance. Gene expression is essential for the maintenance of health.

Genes control the process of protein metabolism. The growth of tissues and the healing of tissues are dependent on protein metabolism.

Mitosis is the cell division that will allow normal growth and repair. If the processes controlling mitosis go wrong, cancer may occur.

Cell differentiation is the process undergone by the cells after mitosis. Each cell differentiates to become a specialised cell. Undifferentiated cells form tumours.

Cell specialisation allows cells to develop the structure to best perform specific functions. Many types of cells have specialised roles in maintaining the health of an organism.

The maintenance and repair of body tissues in relation to gene expression: Gene expression refers to the transfer of information from a gene to produce

a new protein or RNA. It can occur throughout the life of an organism, specifically for repair and maintenance of tissues.

Constitutive genes are expressed continually to maintain normal body functions, e.g. genes that code enzymes in digestion are expressed frequently to produce sufficient amounts of saliva during digestion. Other genes (facultative genes) are only expressed when needed.

There is still much to be understood about the processes of repair of tissues and the switching on of genes to initiate this.

One group of scientists identified a REG (regenerating) family of proteins in the human digestive system lining. These proteins are not normally expressed by appear in large amounts in certain bowel diseases. Their expression is tightly linked with tissue repair and regeneration.

When there are sufficient cellular materials and organelles, mitosis allows cells to divide. The cells may then continue gene expressing to develop specialised structures so that they are differentiated for specific purposes.

Over 3000 years ago, the Chinese and Hebrews were advocating cleanliness in food, water and personal hygieneInfectious and non-infectious diseases:

An infection is the presence of a disease-causing organism in or on the body of a host. Infectious diseases can be spread from one organism to another by direct or indirect transmission. Examples include influenza, chicken pox and measles.

Non-infectious diseases cannot be spread from one organism to another. They can be caused by genetic factors, environmental factors, diet or physiological malfunction. Examples include Down syndrome, haemophilia and skin cancer.

Why control of disease is assisted by cleanliness in food, water and personal hygiene practices:

There are huge numbers of microscopic disease causing organisms, and minimizing the number of such organisms in our food and water reduces the risk of infection.

- Control of disease caused by organisms includes: Ways of preventing contamination of food and water through proper

sanitation, proper food handling, personal hygiene and water treatment processes

Ways to prevent decomposition and spoilage of food Ways to prevent transmission of the disease and infection by using

disinfectants, sterilisation and antiseptics. Crowded conditions, poor sanitation and untreated sewage increase the spread of disease.

Identifying microbes in food and water: Aim: to culture microbes growing on bread or a piece of fruit and to identify

them Method: collect a piece of fruit or old bread that has developed a furry

growth or mould. Sterilise an inoculating loop and use it to collect spores and spread them in a regular pattern over the agar. Close the lid on the agar plate, then incubate and observe the growth of colonies. Generally, shiny, smooth colonies are bacterial and furry colonies that develop spores or spots are fungal.

Conclusion: generally, bacteria have shiny colonies and fungi have furry growths of mycelium and spore-producing structures on agar.

The conditions under which an organism is described as a pathogen: A pathogen is any organism that can produce a disease. If a pathogen is to cause a disease it must:

o Have enough virulence (the number of the particular pathogen needed to cause the disease)

o Live in or on the host without being destroyed by the body’s immune defence

o Escape from one host to another, and survive the transmission from one host to another.

Pathogens cause disease symptoms in a number of ways:o The large number of pathogens present are too many for the host

tissue to function normallyo The pathogens actually destroy cells or tissueso Bacteria produce poisons called toxinso The pathogen may not directly harm the host, but an excessive

immune response by the host may damage tissue

The treatment of drinking water: Contamination of drinking water is a common way for pathogens to enter the

body. Heat, water and detergents can be used to achieve cleanliness, kill or remove pathogens.

Boiling, radiation, chlorine, microfiltration and distillation all destroy microorganisms by breaking down the cell wall.

Proper treatment of water works to remove impurities and microbes that can cause disease. This happens in three steps:

o Coagulation: addition of chemicals to clump all organic matter together as flock. As it settles, it is then removed.

o Filtration: water flows through composed of virus and protozoan removal methods. This includes sand beds and more recently membrane filtration.

o Disinfection: use of chemicals to disinfect water. Reducing the risk of infection from pathogens:

The removal of fine suspended particles by coagulation and filtration is important as these small particles attract and hold bacteria and viruses. This alone removes approximately 99% of bacteria and viruses.

Oxidising substances such as chlorine and ozone kill microorganisms. Ultraviolet light at the correct levels also kills bacteria and viruses, though there is some doubt about efficient protozoan removal.

In NSW, water is filtered, chlorine is added to kill bacteria and samples are tested for the presence of coliform bacteria, giardia and cryptosporidium.

The work of Pasteur and Koch and other scientists stimulated the search for microbes as causes of diseasesThe contribution of Pasteur and Koch to our understanding of infectious diseases:

Pasteur discovered that microbes such as bacteria can cause disease. He disproved the theory of spontaneous generation through his famous swan-neck flask experiment, as well as showing that micro-organisms came from pre-existing microorganisms.

Koch showed that bacteria were the cause of a disease called anthrax in horses, cows, sheep and humans. He also demonstrated that bacteria were the cause of tuberculosis in humans.

During Koch’s work on diseases, he designed rules of procedure for showing that a particular microorganism is the cause of a particular disease. These rules of procedure are called Koch’s postulates. Koch’s postulates can be used to identify the causative organism of an infectious disease.

Koch’s postulates are: Step 1 – all infected hosts must contain the suspect organism Step 2 – a pure culture of the suspect organism must be obtained Step 3 – a healthy organism infected with the pure culture must have the

same symptoms as the original host Step 4 – the suspect organism must be isolated from the second host, grown

in pure culture and prove to be identical to the first culture

Modelling Pasteur’s experiment: Aim: to model Pasteur’s experiment in order to demonstrate that microbes

cause decay Method: Prepare a nutrient broth and place 150mL into two flasks, one with

a straight neck, the other with a swan-neck. Leave the flasks for 5 days. Look for cloudiness, scum, bubbles and mold colonies.

Results: The broth in the straight neck flask went cloudy, developed scum, bubbled and produced unpleasant odours while the broth in the swan-neck flask remained unchanged. Both flasks were open to the air, however the s-shape in the swan-neck was able to trap microorganisms before reaching the broth.

Conclusion: microbes could not grow spontaneously. Fermentation relies on the entry of microbes.

The cause and prevention of malaria: Malaria is a disease transmitted by an insect vector – female mosquitos.

Symptoms include sweats, fever, delirium, headaches and chills. There are different strands of malaria. Ronald Ross’ work on malaria identified insects as vectors of disease. A vector is an organism, usually an anthropod, which acts as a carrier of a pathogenic organism.

It was originally believed that living near swampy areas caused malaria, but in 1880, French army doctor Laveran discovered the protozoan Plasmodium that caused the disease. He searched for a form of protozoan that could show its transmission from human to human without success. He eventually suggested that mosquitos might be the vectors.

In 1987, Ross found cysts in the stomach walls of the mosquito Anopheles and identified the cysts as the malaria-causing parasite. Ross proved that mosquitos transmit malaria and began investigations into transmission and control of the disease.

Life cycle of malaria Anopheles mosquitos act as a vector, carrying the pathogen to the host.

Malaria has a two stage life cycle – one part mosquito, one part human. During the blood meal, the Plasmodium is transferred from the mosquito salivary glands and into the blood system of the host.

Once inside the human blood stream, the parasite travels to the liver and reproduces asexually in the liver cells. These cells burst and the parasite float freely in the blood, feeding on the haemoglobin. The mosquito picks up the parasite when it bites an infected human and sexual forms develop in the mosquito’s gut.

Control and prevention of malaria: Reducing the population of the vector – spraying with pesticides, identifying

and removing breeding sites and introducing surface minnows, a fish that feeds on mosquito larvae, therefore decreasing the population

Reducing the contact between the vector and the host – education programs informing people of the risk of contracting malaria and ways to prevent mosquito bites, such as insect repellent and mosquito netting

Drugs – people are advised to take chloroquine if entering a malaria infested area. Chloroquine interferes with the development of the parasite.

Research is progressing into releasing genetically modified, sterile mosquitoes that will compete with natural mosquitoes for mates, and so reducing the population of mosquitoes.

Another program has produced mosquitoes that have been modified to prevent the development of Plasmodium.

Types of pathogens that cause infectious diseases in plants and animals:

Prion Defective for of a protein molecule Doesn’t contain DNA or RNA Mostly attacks brain or nerve cells

Virus Non-cellular Contains DNA, RNA and protein

coat Requires a living host cell to

replicateBacteria Procaryotic cell

Divides quickly and/or produces toxins

Very simple cell with no internal membrane

Protozoan Eucaryotic cell – single-celled organism with internal membranes

May have a complex life cycleFungi Eucaryotic cell w/ cell wall

Spreads via spores or rapid division Heterotrophic organisms Some infect external skin and nails,

while others enter the host’s bodyMacro-parasites Also called parasites

Eucaryotic cells – multicellular organism

Visible to the naked eye Mostly anthropods or worms

Prions:

Newly discovered infectious agents that consist only of protein (no nucleic acid). The prion hypothesis states that certain diseases are caused not by known pathogens but by a protein that has adopted an abnormal disease-producing form.

Prion diseases are both infectious and hereditary. Examples include scrapie in sheep, mad cow disease and CJD (Creutzfeld-Jacob Disease)

Viruses: Consist of a nucleic acid (DNA or RNA) surrounded by a protein coat. Viruses invade cells and insert their genetic code into the host cell’s genetic

code. Examples include Hepatitis B (viral liver infection), Herpes simplex 1 and 2 (cold sores and genital herpes) and Paramyxovirus (measles and mumps)

Bacteria: Tiny procaryotic cells that can caused disease by secreting toxins, invading

cells and forming bacterial colonies that disrupt normal cell function. Examples include enterobacteria (salmonella diseases and gastro) and bacterial leaf spot (causes rotting of leaves and stems in snapdragons).

Protozoans: One celled organisms, larger than bacteria, with the DNA organized in a

nucleus (eucaryotic cells). Examples include giardia: a flagellate protozoan (diarrhoea) and plasmodium: a sporozoan protozoan (malaria)

Fungi: Simple organisms, similar to plants but without chlorophyll. Examples are

yeast and mould. Fungal diseases include candida (thrush) and tinea (ringworm and athlete’s foot).

Macro-parasites: Multicellular parasites such as roundworms, flatworms (tapeworms) and

flukes (liver fluke) and anthropods such as ticks, mites, lice and fleas.

Infectious diseases (malaria):Cause Protozoan, plasmodiumTransmission Anopheles mosquito (female) salivary

glands human blood cells liver cells human blood cells anopheles mosquito

Host response When in the blood cells, the host produces antibodies against the Plasmodium

Major symptoms Chills, fever, sweating, delirium, headaches

Treatment Anti-malarial drugs such as quinine chloroquine

Prevention Insect repellent, mosquito netsControl Draining swamps, insecticides

How antibiotics assist the management of infectious diseases:

Antibiotics are compounds that kill or inhibit bacterial pathogens. They serve mainly as a treatment but in some extreme conditions, such as burns victims, they may be used to prevent infection.

When taking antibiotics, the full course should be taken to avoid the more resistant members of a population surviving and developing more resistant strains.

The problem of antibiotic resistance: Resistance to antibiotics is an increasing concern. The overuse of antibiotics

has led to the selection of more virulent bacteria that are resistant to antibiotics.

People do not take antibiotics correctly by not taking the full dose, or taking them incorrectly. The problem arising from that is bacteria then becomes increasingly harder to treat, resulting in a more serious infection.

When antibiotics were first introduced, they had a dramatic effect on the pathogens that cause disease. Over time, it became apparent that the effects of the antibiotics were beginning to become less potent. Overuse of antibiotics has resulted in "superbugs". Unless new antibiotics are produced to fight bacteria, common infection will once again be responsible for many deaths.

Defence against disease Our bodies have three types of defence against pathogens. The first consists of several barriers that prevent the entry of pathogens. The second is the action of white blood cells in destroying foreign particles

(phagocytosis). The third is carried out by the immune system, which plays a complex role in

targeting and destroying pathogens as well as helping to make our bodies immune to them.

Defence barriers to prevent entry of pathogens in humans:- Skin:

The skin is a mechanical barrier. Unbroken skin protects other tissues, and collects and holds pathogens.

- Mucous membranes: Cells that line the respiratory tract and openings of the urinary and

reproductive systems that secrete a protective layer of mucous. Mucous is a sticky substance and hence traps pathogens from entering the body.

- Cilia: Hair like projections from cells lining the air passages. They move with a

wave-like motion to push pathogens from the lungs up to the throat. - Chemical barriers:

Chemicals like acid in the stomach, alkali in the small intestine and lysozome in tears destroy pathogens before entering the body.

- Other body secretions: Secretions including those from sweat glands and hair follicles. These

secretions contain chemicals that destroy bacteria and fungi. Saliva and tears may also contain substances that inhibit or destroy pathogens.

Antigens: Antigens are defined as any substance that the body recognises as being

foreign to an organism’s own body. They are protein molecules that trigger an immune response. Each pathogen has its own antigen.

Why organ transplants trigger an immune response: Antigen-antibody responses result in rejection of transplanted tissue. This is

because it is identified by the body as a foreign substance. This triggers the immune response to attack as if it were a pathogen.

Defence adaptations: If foreign substances or microorganisms get past the first line of defence and

enter deeper tissue, they’ll trigger the second line of defence. - Inflammation response:

Inflammation of tissue is designed to isolate and destroy foreign particles and prepares the tissue for healing.

- Phagocytosis: Phagocytes are cells that engulf and destroy microorganisms. This process is

carried out by some white blood cells, neutrophils and macrophages and is important as the body’s immediate defence against infection.

- Lymph system: The lymph system returns intercellular fluid to the blood system, filters cell

debris and produces white blood cells responsible for the immune response. They are found in the armpits, neck and groin and their enlargement is often a sign of infection.

- Cell death to seal off pathogen: After phagocytes have destroyed an antigen, they die. For some pathogens,

macrophages and lymphocytes completely surround a pathogen so that it is enclosed in a cyst, isolating the pathogen from its food supply, resulting in its death.

A disease caused by an imbalance of micro-flora:

Micro-flora is a pathogen, which usually attacks specific parts of the body. Crohn’s Disease is a chronic disease that causes inflammation in the

gastrointestinal tract. It affects the small intestine and the beginning of the large intestine.

The exact cause is unknown however factors include an autoimmune reaction (when a person’s immune response attacks healthy cells), genetics and environmental factors.

Symptoms include diarrhoea, abdominal cramping and pain and weight loss. Symptoms vary depending on the severity of the inflammation and where it occurs along the gastrointestinal tract.

Effects include bowel obstructions, anal fissures and ulcers in the gastrointestinal tract, which can be fatal if they rupture.

MacFarlane Burnet’s work in the middle of the 20 th century contributed to a better understanding of the immune response and the effectiveness to immunisation programs

The ability of an organism to prevent or overcome infection by a pathogen is through natural resistance and acquired immunity.

MacFarlane Burnet developed the theory of clonal selection, which explains how the immune system can defend the body against many different antigens. This developed into the theory that non-self cells could be placed into an organism and the body’s immune system would learn to recognise them as self, paving the way for organ transplants.

Components of the immune response: Antibodies are proteins that the body produces when it detects antigens.

Each different antigen stimulates the production of its own specific antibody. Antibodies join with the antigen so that they are clumped together and can be recognised and destroyed more easily by macrophages.

B-cells are a special kind of lymphocyte produced in the bone marrow. When a B cell recognises an antigen, it divides repeatedly to produce a mass of identical cells that work as antibody producers.

T-cells are another kind of lymphocyte that is passed through the thymus gland. Some T-cells produce toxic substances that destroy cells that have been invaded by a virus. Others help the B-cells to divide rapidly.

The immune response in the human body: - The interaction between B and T lymphocytes:

T cells influence and help B cells. Both B and T lymphocytes interact as they are both attacking the same antigen.

- The mechanisms that allow interaction between B and T lymphocytes: Mechanism 1: the T cell produces a soluble factor after interaction with an

antigen. The B cell reacts with the soluble factor and the specific antigen to become a functional antibody-producing cell.

Mechanism 2: this is based on cell contact between the T cell and the B cell. This close contact comes about because of interaction with the antigen. This contact allows the T cell to signal the B cell to become a functional antibody-producing cell.

- The range of T lymphocytes and the difference in their roles: Killer T cells (Tc cells) produce cytotoxins that destroy or kill the infected cell.

They recognise and bind to antigens, destroying them directly. Helper T cells (Th cells) secrete chemicals that stimulate cloning in B and T

cells, enhancing antibody production by B cells. Memory T cells remain in the body and reactivate quickly with subsequent

infections by the same antigen Suppressor T cells stop the reaction when the antigen is destroyed

How vaccinations prevent infection: Artificial acquired immunity is called immunisation. Vaccinations involve the injection or ingestion of weakened or non-virulent

strains of microorganisms. It stimulates a person’s own immune system to develop resistance.

Vaccinations introduces antigens into the body so that B cells are activated to produce large amounts of antibody and B cells that are stored in the lymph system are ready for a future attack by a particular pathogen.

The effectiveness of vaccination programs: Vaccines are amongst the cheapest and safest methods for preventing

disease. Much of the world however remains unimmunized, with an estimated 6-8 million children that die every year from disease that could have been prevented by early immunisation.

Despite this, vaccination programs, particularly in developed countries, have stopped the spread and occurrence of once common diseases.

Smallpox: In 1796, Edward Jenner developed a vaccine against smallpox through

transferring the cowpox virus (less severe cousin of smallpox) from a dairy milkmaid to an 8yr old boy, developing immunity to the deadly disease.

By 1980, the World Health Organisation had declared the world free of smallpox.

Diphtheria: In 1923, a vaccine was released however it took until the 1940s and 1950s for

the spread of the disease to shift from cyclical epidemics to occasional outbreaks of low intensity.

The vaccine injected is usually called DTP because it immunizes against diseases such as diphtheria, tetanus and pertussis (whooping cough). In 1990, the WHO stated that 80% of children were vaccinated against this disease.

Polio: Until 1955 when a vaccine was introduced, thousands of children in

industrialised countries became crippled with the disease. By the 1960s, an oral form of the vaccine was introduced and polio was

brought under control. It has now largely been eradicated from most part of the world except parts of Asia and Africa. In 2005, there were 2033 cases reported to WHO worldwide across 188 countries and a 95% vaccination rate across 184 countries.

The suppression of the immune response in organ transplant patients: When an organ is transplanted, it is recognised by the immune system as

non-self. The body then attacks the new organ as if it was an invading pathogen. T cells are the main cell type responsible for the rejection of transplanted tissue.

To overcome this problem, transplant patients are given powerful drugs to suppress their natural defences. This can lead to susceptibility to infection for the patient, so antibiotics are also given to the transplant patient.

Epidemiological studies involve the collection and careful statistical analysis of large quantities of data. Such studies assist the causal identification of non-infectious diseasesThe main features of epidemiology:

Epidemiology is the study of epidemics, especially by looking for common factors in populations affected by the disease. Their work can support vaccination programs for controlling infectious diseases, but commonly it relates to risk factors for non-infectious diseases.

Epidemiology studies may be descriptive or analytical. There are three types of these studies: a case study, a cohort study and a randomized study.

Factors of a good epidemiological study include:o Statistical association between the factor and diseaseo Consistency across the studyo The related material used in the study confirms the result

Lung cancer as an example: In the past, there were some epidemiological studies that found a protective effect associated with beta-carotene. However, when investigators undertook a double blind randomized controlled trial, they found that beta-carotene increased the risk of mortality for patients who were at risk of developing lung cancer.

The relationship between smoking and lung cancer: Doll and Hill in England and Hammond and Horn in the US established that

cigarette smoking markedly increased the chances that a person would develop lung cancer.

Other evidence comes from comparisons of trends in smoking rates across sexes and trends in lung cancer. More males smoked and more males had lung cancer. Male smoking rates declined before the rate declined in females.

The NSW Cancer Council reports the following research:o Smoking is a major cause of lung cancero Workers exposed to industrial substances such as asbestos either

have a significantly higher risk of developing lung cancero There is a link between passive smoking and lung cancero In 2012, 59% males and 41% females were diagnosed with lung

cancer. Lung cancer is up 200% in women. o It is projected that one in 30 Australians will develop lung cancer by

the age of 75

o There has been a research link between smoking and lung cancer however manufacturers are unable to accept that it is a direct cause and effect relationship and that smoking causes lung cancer.

The causes of non-infectious diseases: Inherited diseases are caused by genetic factors. An example is Down

syndrome, which is an inherited disease that is caused by the non-disjunction of chromosome 21, resulting in three chromosomes and not the usual two. Those with Down syndrome have characteristic appearances.

Nutritional deficiencies can lead to obesity and malnutrition diseases. An example is anorexia nervosa, the under-nutrition of a person, resulting in rapid weight loss and nutritional deficiencies.

Environmental diseases are sometimes associated with factors in the environment that include high stress levels, noise, overcrowding, drugs and pollution. An example is mesothelioma, which is caused by the exposure to asbestos and patients don’t get any symptoms until 20 or 30 years after exposure. There is no cure and treatment can only slow down the progression of the disease.

Non-infectious disease HaemophiliaOccurrence and cause Sex-linked genetic disease.

The gene that controls manufacture of blood clotting proteins occurs on the sex chromosomes. Males with this disease don’t have the genetic information for blood clotting.

Symptoms Bleeding (haemorrhage) from minor injuries or bleed for no apparent reason. They bleed into joints causing severe pain; excessive blood loss causes deformed joints and can cause death.

Treatment/management The blood factor missing is injected into the haemophiliac in concentrated form; genetic counselling informs people of the chances of having a haemophiliac child; genetic engineering has made it possible to clone sheep whose blood contains a substance that can be used to treat patients with haemophilia B.

Increased understanding has led to the development of a wide range of strategies to prevent and control disease

The role of quarantine in preventing the spread of disease, plants and animals in Australia:

Seeks to prevent the entry of harmful disease in Australia to stop the spread of diseases within Australia.

Quarantine regulations have prevented the entry of foot and mouth disease, which has the potential to devastate the livestock industry. Within Australia, some areas are free from certain diseases such as the bunchy top virus in bananas.

Quarantine laws to prevent the spread of the disease have restricted movement of plant materials, such as plant and fruit stock, across regions of Australia. As a further quarantine method, fruit-fly zones have been declared, meaning there is no chance of fruit flies in any of Australian produce.

Pathogens and insect pests: Plants diseases include plant rust, black spots (mould), bugs (mites, aphids)

and damping off, caused by fungus. Symptoms include discolouration, holes in leaves and powdery mildew.

Aim: to observe plant shoots and leaves and detect evidence of pathogens and insect pests.

Method: collect a range of garden plants and observe them using a binocular microscope.

Results: many older varieties of lilly-pilly have obvious lumps on the leaves called pimple gall and also deformed new growth. This is the effect of psyllids. Black inky marks on the leaves of kangaroo paw plants are evidence of a fungus that occurs particularly in moist conditions.

Conclusion: discolouration of leaves, deformation of leaves, irregular shaped leaves and furry white growth on the base of shoots are evidence of insects and pathogens.

The effectiveness of quarantine: Strict quarantine controlling entry of plants and fruits into Australia has

prevented the entering and impact of the bacterial disease fire blight on the Australian pome fruit industry.

Quarantine however, was actually blamed for the rapid spread of equine influenza through horses in NSW and QLD in 2007. Despite the fact that all horses were retained and tested, the disease rapidly spread into police horses and racehorses. It is positive that quarantine originally detected the virus and placed restrictions on horse movement, but the failure to prevent the spread is very disappointing and costly.

Strategies for controlling and/or preventing disease (pesticides): The use of pesticides helps control insect-borne diseases. Insects like

mosquitoes are vectors of diseases such as malaria, dengue fever and West Nile Virus.

Initially, the pesticide DDT was used, but there is now an increased awareness of the risk of chemical pesticide use and there are strict guidelines governing the pesticide used and the manner of its use.

Some pesticides target the mosquito larvae. They can be either biological (such as toxin from specific bacteria that is lethal to mosquito larvae but not to other organisms) or chemical products such as insect growth regulators, surface films or organophosphates.

They are applied directly to water sources that hold mosquito eggs and larvae. Adult mosquitoes can be killed by pesticides in hand-held sprayers, in truck-mounted sprayers or by using aerial spraying.

The shift from treatment and control to management or prevention: Genetic epidemiology will contribute to the discovery of new drug

treatments that could be tailored to an individual’s genetic make-up as well as the prediction of an individual’s future likelihood of getting a particular disease. This will continue to change the emphasis of health care from treatment to prevention.

One example of the changes in methods has been the response to the avian influenza (bird flu). We have become increasingly conscious of the ability of viruses to change and to transmit across species. Bird mobility has a major impact on the effectiveness of quarantine to prevent the spread if this disease, at least among bird populations.

Eventhough the deadly H5N1 avian influenza is extremely rare in humans; between 2004 and 2005 there were 69 confirmed cases and 46 deaths from the virus reported to the WHO. By 2005, the first vaccine was being trialled amongst humans to prevent a further spread of a disease.

The WHO has a website specifically to give updated information to the public ad health professionals called ‘EPR – Epidemic and Pandemic Alert and Response’. International health regulations were revised in 2005 to approach to the prevention, detection and timely response to any public health emergency of international concern.