3 1 communicable diseases

A communicable disease is an illness caused by pathogens that can be spread between individuals within a population.

Pathogens are microorganisms that cause disease.

False. Plants and animals can be affected by pathogens.

Types of pathogen include:

Bacteria cause damage to the body by reproducing rapidly and producing toxins which damage tissues.

Pathogens are transmitted through:

True. Cooking food thoroughly is a method to prevent the spread of pathogens as pathogens are (usually) killed by high temperatures.

Viruses live and reproduce inside living cells of a host organism.

Measles is a viral infectious disease with symptoms including a fever and a rash. It spreads easily and can be fatal if complications arise.

False. Young children are usually vaccinated against measles.

The measles virus is spread by inhalation of droplets (from sneezes and coughs) that contain the virus.

HIV can damage the immune system, eventually leading to acquired immune deficiency syndrome (AIDS).

The initial symptoms of HIV infection are flu-like symptoms (runny nose, sore throat, achy limbs/joints).

HIV is spread by exchange of body fluids, e.g. during sexual contact or when sharing needles. It can also pass across the placenta during pregnancy.

The ‘mosaic’ pattern caused by the virus discolours the leaves; this affects the growth of the plant due to lack of photosynthesis.

Salmonella is a bacterial pathogen **that causes food poisoning; symptoms include:

*Salmonella *enters the human body through ingestion of contaminated food.

True. ** Salmonella bacteria can be found in food prepared in unhygienic conditions. Proper food hygiene can therefore help to prevent **Salmonella infection.

Gonorrhoea is a sexually transmitted disease (STD) caused by a bacterial pathogen. Symptoms include discharge from the sex organs and pain on urinating.

Gonorrhoea is transmitted through sexual contact.

Gonorrhoea transmission can be prevented by:

Rose black spot is a fungal disease of plants where purple or black spots develop on leaves, which often turn yellow and drop early.

Rose black spot affects the growth of the plant as photosynthesis is reduced.

Rose black spot is spread in the environment by water or wind.

Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves.

The pathogens that cause malaria are protists.

A vector is an organism that transfers pathogens from one host to the next.

Malarial protists infect humans when infected mosquitoes bite. The protists pass from the mosquito saliva into the human blood.

Malaria causes recurrent episodes of fever and can be fatal.

The spread of malaria is controlled by controlling the mosquito vectors, e.g. by:

The role of the trachea and bronchi are to trap pathogens, dirt and dust using ciliated epithelial cells and mucus.

False. Stomach acid destroys many pathogens so is a non-specific defence mechanism.

Phagocytes engulf and digest pathogens through phagocytosis.

False. The body's response to infection involves antibodies recognising antigens.

Antibodies attach to antigens on pathogens, binding the pathogens together. This can prevent them from infecting cells, and make it easier for phagocytes to engulf them.

Antitoxins neutralise toxins released by pathogens, preventing them from causing harm to the body.

The difference between antigen, antibody, and antitoxin is as follows:

False. Phagocytes carry out phagocytosis to engulf pathogens; they do not produce antibodies.

Vaccination introduces dead or inactive pathogens into the body in order to induce immunity.

White blood cells recognise the antigens in a vaccine and produce specific antibodies.

Vaccination leads to long term immunity because when someone is infected again by the same pathogen, white blood cells quickly produce the correct antibodies and the symptoms of infection do not arise.

False. Vaccinating a large proportion of a population reduces the likelihood that a pathogen will spread; this is because most people in the population will be immune.

Antibiotics are medicinal drugs that kill pathogenic bacteria.

False. Antibiotics do not destroy viruses, so can only be used to treat bacterial infection.

Antibiotic resistance occurs when bacteria survive exposure to antibiotics that would normally kill them or inhibit their growth.

Painkillers are used to treat the symptoms of disease but do not treat the source of any infection, e.g. ibuprofen can reduce pain and inflammation but does not kill pathogens.

It is difficult to treat diseases caused by viruses because viruses infect body cells. This means that destroying viruses without damaging body tissue is challenging.

Drugs were traditionally extracted from plants and microorganisms, e.g.

Most new drugs are synthesised by chemists in the pharmaceutical industry, although the starting point may still be a chemical extracted from a plant.

Preclinical drug testing is done in a laboratory using cells, tissues, and live animals.

Clinical drug trials are conducted to test the safety, efficacy, and optimal dosage of new drugs.

In a double-blind trial some patients are given a placebo, and neither the doctor nor the patient knows whether each patient is receiving the placebo or the active drug.

A placebo is an inert substance given to some participants in clinical trials instead of a true drug. Its role is to eliminate the effects of the brain and expectations on any results.

The purpose of testing new drugs on animals is to see the effect of medicines on a whole organism.

Clinical trials are conducted as follows: