The causes, transmission and global impact of disease

7/27/2019 The causes, transmission and global impact of disease

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Attiya Rehman

The causes, transmission and global impact of disease

Health can be defined as your physical, mental and social wellbeing. If you are in good health you are

free from disease, well fed with a balanced diet and suitably housed with proper sanitation. A

disease is a malfunction of the body or mind which causes symptoms which could be physical,mental or social. There are many different types of disease which can be grouped into different

categories depending on their cause.

A wide range of organisms can cause disease. For example a parasite is an organism that lives on or

in a host. Parasites can cause harm to the host by taking their nutrition from the host and can live all

or part of their life in or on the host. Parasites that live on their host are called external parasites

whilst parasites that live inside their host are called internal parasites. Parasites can cause disease in

humans. They can cause damage that allows other organisms to invade the host and cause

secondary infections. Some parasitic diseases are easily treated and some are not. Pathogens are

also organisms that can cause disease. The human body creates a good habitat for microorganismsto survive. As a result there are many types of microorganisms that live on or in our bodies. They

also live by taking nutrition from their host and also cause damage in the process.

Animal-like protoctista (protozoa) can cause a number of diseases. Amoeboid dysentery and malaria

are 2 examples. These organisms usually cause harm by entering host cells and feeding on the

contents as they grow. The malarial parasite plasmodium has immature forms that feed on the

contents of red blood cells. Malaria is transmitted exclusively through the bites

ofAnopheles mosquitoes which is the vector. The female Anopheles mosquito carries the

plasmodium from an infected person to an uninfected person. The mosquitos feed on the blood and

have mouthparts which are adapted as a fine tube or proboscis which can be used to penetrate ablood vessel and withdraw blood. Malarial parasites live in the red blood cells of the human host and

feed on the haemoglobin. The intensity of transmission depends on factors related to the parasite,

the vector, the human host, and the environment.


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Attiya Rehman

Athletes foot and ring worm are caused by fungi which can cause a variety of different diseases.

There are many different species of fungi that can cause skin diseases e.g. Microsporum,

Trichophyton and Epidermophyton. The fungus lives in the skin and when it sends out reproductive

hypae, these can grow to the surface of the skin to release spores.

Bacteria can also cause disease by damaging cells or by releasing waste products which are toxic to

us. Bacteria are prokaryotic cells, which are smaller than our cells but they can reproduce rapidly. In

the right conditions (provided by the human body) some types of bacteria can reproduce every

20minutes. Once in the human body they can multiply rapidly. Cholera is caused by the bacteria

Vibrio cholerae. Tuberculosis is caused by two different species of bacterium mycobacterium

tuberculosis and mycobacterium bovis. TB is usually found in the lungs and is transmitted by droplet

infection. The bacteria are contained in the tiny droplets that are released when an infected person

coughs, sneezes, laughs or talks. A person can become infected by inhaling those droplets however

its not that easy to contract TB. It takes close contact with an infected person over a long period of

time to contract the disease. Overcrowding, poor ventilation, poor health, poor diet and

homelessness can make contraction and spread of TB more likely.

A lot of well-known diseases including the common cold and influenza are caused by viruses. Viruses

invade cells and take over the genetic machinery and other organelles of the cell. They then cause

the cell to make more copies of the virus. The host cell eventually bursts releasing many more

viruses. HIV/AIDs are also caused by a virus along with the widespread plant disease tobacco mosaic

virus which affects many plants including tomatoes. HIV/AIDS is caused by the human

immunodeficiency virus. HIV can be transmitted by exchange of body fluids such as blood-to-blood

contact, unprotected sexual intercourse, unscrewed blood transfusions, use of unsterilized surgical

equipment, sharing hypodermic needles and from mother to baby during breast feeding.

HIV/AIDS is a worldwide disease and continues to be a major global public health issue having

claimed more than 25 million lives over the past 3 decades. There were approximately 45million

people living with HIV/AIDS by the end of 2005 and 34million people living with HIV in 2011 with

sub-Saharan Africa being the most affected region with 1 in 20 adults living with HIV.


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Attiya Rehman

Every year around 5million people are newly infected with HIV and by 2007 was spreading rapidly in

China, Russia and other Eastern European countries. Predictions show the number of people with

HIV/AIDS in China will soon exceed the number in any other country.

TB is another worldwide disease and is the second biggest killer worldwide due to a single infectious

agent after HIV/AIDS. TB is a leading killer of people living with HIV causing one quarter of all deaths.

Approximately 1% of the world population is newly infected each year and 10-15% of those go on to

develop the disease. The percentage of the worlds population struck by TB peaked in 2004 and held

steady in 2005. In 2005, around 8.8million new cases of TB were recorded and approximately 1.6

million died. Estimates show 30% of the worlds population may be infected by mycobacterium

showing it is still a great threat however the estimated number of people falling ill with tuberculosis

each year is declining, although very slowly, which means that the world is on track to achieve the

Millennium Development Goal to reverse the spread of TB by 2015.

The 22 countries shown on the map below account for 80% of the tuberculosis cases in the world.


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Attiya Rehman

Malaria is a life threatening disease caused by parasites that are transmitted people to people

through the bites of infected mosquitoes, killing about 3million people each year. Around 300million

people are affected by malaria worldwide and the number is increasing.

In 2010, malaria caused an estimated 660 000 deaths mostly among African children, where a childdies every minute from malaria. Of those people with malaria, 90% live in sub-Saharan Africa. This is

because malaria is limited to the areas in which the vector mosquito -Anopheles can survive. This is

shown by the map above. Due to increased global warming, the vector mosquito may be able to

survive further north, even in parts of Europe however, Malaria mortality rates have fallen by more

than 25% globally since 2000.

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The causes, transmission and global impact of disease