Diseases

Health is the state of mental, physical and social wellbeing, not just absence of disease.

Disease is a departure from good health caused by a malfunction of the mind or body.

Parasites are organisms that live on or in another living thing, causing them harm.

Pathogens are organisms that cause diseases.

Bacteria can cause diseases by damaging cells or releasing waste products that are toxic. Fungi can cause diseases by sending out reproductive hyphae. Viruses can cause diseases by invading cells and taking over the genetic material, causing the cell to make more copies of the virus. The host cell then bursts, releasing the viruses. Protoctista usually cause harm by entering host cells and feeding on the contents as they grow.

Malaria is caused by a eukaryotic organism with the genus Plasmodium. The most common species is Plasmodium falciparum.

Malaria is spread by a vector. The vector is the female Anopheles mosquito. The malaria cycle goes like this:

• The mosquite bites an infected person sucking in the gametes of Plasmodium.
• The gametes fuse and form zygotes in the stomach of the mosquito. This then migrates to the salivary glands.
• The mosquito bites an uninfected person, releasing saliva as it does so. The saliva contains the infective stages of Plasmodium.
• This migrates to the liver where it multiplies before passing into the blood again.
• In the blood they feed on haemoglobin and produce gametes.

Malaria is limited to the areas in which the vector mosquito, Anopheles, can survive.

HIV is human immunodeficiency virus. Once inside the body it attacks T helper cells in the immune system and destroys them. This makes the body less able to defend itself and resist infections. The person is more likely to contract opportunistic infections which eventually kills the person.

HIV can be transmitted through the exchange of bodily fluids through unprotected sexual intercourse, across the placenta, during breast feeding, use of unsterilised equipment and through blood-to-blood contact.

It is a worldwide disease and spreading in pandemic proportions.

This disease is caused by a bacterium with two species: Mycobacterium tuberculosis and Mycobacterium bovis. The disease is spread through droplet infection.

Conditions that make a person more likely to contract the disease are

• Overcrowding
• Poor ventilation
• Poor health and diet
• Through milk or meat of cattle. This is mostly in less developed countries.

Tuberculosis is a worldwide disease. There is an increasing threat from new strains of Mycobacterium which are resistant to the drugs available to treat it.

The World Health Organisation is a part of the UN. it is the specialised agency for health. The objective is to attain the highest possible level of health by all people.

They use epidemiology to study the spread of the disease and factors affecting the spread. Through this we can:

• identify risk factors associated with disease
• determine the incidence of a disease (number of new cases)
• determine the prevalence of a disease (number of people at a given time)
• determine the mortality (number of deaths per year)
• determine the morbidity (the number as a proportion of a population)
• identify as an endemic (always present), epidemic (spreading rapidly) or a pandemic (worldwide epidemic)