Anw hoofdstuk 1 Infectious diseases now
Infectious diseases are still widespread all over the world and affect not only humans but also
animals and plants. They range from minor inconveniences such as a cold or the flu through
devastating diseases such as malaria and aids. Microbes can causes damage as they reproduce
themselves, or they excrete a toxin that causes the damage.
The microbes that cause diseased are single celled bacteria, fungi and viruses. Bacteria can only be
seen with a microscope. Viruses are not really independent organisms. They are packages of DNA
along with some enzymes in an outer case of proteins. Once inside a host cell the virus takes over
the chemistry and uses it to produce new copies of itself [fig. 2.5] The host cell eventually bursts and
viral particles are released.
Preventing spread of disease
- living creatures can transmit disease from one person to another. (Malaria mosquitos)
- Materials such as clothing and bedding can contain microbes.
- direct skin contact
- whenever someone coughs, sneezes or talks, millions of droplets containing microbes are expelled
from the respiratory tract, to be inhaled by someone else.
- Many of the microbes which cause gut diseases are transmitted by food, water, or hands.
- Microbes can enter through cut wounds.
Preventing the body by immunization
When microbes enter the body detects them as foreign. Some white blood cells attack the microbes
immediately. There are also white blood cells which produce antibodies that bind to the invading
microbes. These white blood cells ‘remember’ how to create the antibody. This way the body can
respond quickly when the disease strikes again.
Vaccination
There is no such thing as a perfect vaccination which protects everyone who receives it and is
entirely safe. There are three questions which a parent might ask before allowing a vaccinating.
- Is the vaccine really effective?
-
What are the possible side effects?
What will the authorities do if the child suffers from lasting damage cause by the
vaccination?
The discovery of penicillin.
One summers day in 1928 Alexander Fleming was examining some petri dishes in which were
growing bacteria. Some of the dishes contained a mould. He saw that the bacteria surrounded by the
mould were killed. He realized the mould produced a substance which killed the bacteria. Fleming
injected the substance in mice to see if it would harm them. It didn’t. By chance he had found the
antibiotic. Ernst Chain and Howard Florey took up the investigation. The trials they held proves
penicillin was very effective. During the 2nd world war a large amount of penicillin was needed, and
production was shifted to the USA where large scale manufacturing processes were developed.
Biochemists have now discovered how it works. The drug weakens the cell walls of the bacterial cell
so that they burst and die. Human cells do not have cell walls so they are not affected.
Tuberculosis
Tuberculosis has always been a very common human infection. Infectious people can spread the
disease by coughing, sneezing and spitting. TB can affect many areas of the body including the lungs
and the bones, but the most common forms of TB affect the respiratory system. Symptoms are fever,
night sweats, inability to eat and loss of weight. There is no fully effective vaccine yet. The vaccine
that is used is made from a weakened form of a bacterium closely to the hman TB. However there
are antibiotics that can cure the disease. People with HIV are very likely to get TB, since their immune
system is weakened. TB is a common disease in third-world countries, but the amount of number of
deaths has decreased.
Influenza
Hundreds of millions of people suffer from an influenza infection very year. Influenza, known as flu, is
a common respiratory disease caused by the influenza virus. Influenza infects the cells lining the
tubes leading to the lungs. The people most likely to die are the elderly and people who already
suffer from a lung disease like asthma. Each year the various strains of the influenza virus are subtly
different. But every so and often there is a major change in the virus. The previous vaccination now
doesn’t work anymore, and a new one has to be produced. If a new influenza virus appears for
which the human population has no immunity, there is a risk of simultaneous epidemics of the
disease all over the world. This is a pandemic. Three massive pandemics happened in the 20th
century. The biggest was the Spanish flu, at least 20 million people died.