Human Communicable Diseases

Section 1 of 8Four diseases compared

Disease	Pathogen	Spread	Main effects	Control
Salmonella food poisoning	Bacterium	Eating contaminated food or food prepared in unhygienic conditions	Fever, stomach cramps, vomiting and diarrhoea	Hygienic food handling, thorough cooking, vaccinating poultry
Gonorrhoea	Bacterium	Unprotected sexual contact	Thick yellow or green discharge and pain on urinating	Antibiotics (though resistance is growing); barrier contraception
Measles	Virus	Droplets from coughs and sneezes	Fever and a red skin rash; can lead to serious complications	Vaccination (MMR)
HIV	Virus	Exchange of body fluids: unprotected sex, sharing needles, mother to baby	Attacks the immune system and can lead to AIDS	Antiretroviral drugs slow the virus; condoms, not sharing needles

Section 2 of 8Routes of infection

Food and water

• Food and water Bacteria such as salmonella are swallowed in contaminated food and multiply in the gut.

Airborne droplets

• Airborne droplets Viruses like measles leave an infected person in tiny droplets and are breathed in by others.

Body fluids and contact

• Body fluids and contact HIV and gonorrhoea pass between people through sexual contact or blood.

Section 3 of 8HIV progression

1Infection

• Infection The virus enters the body and infects white blood cells.

2Immune system weakened

• Immune system weakened Numbers of lymphocytes slowly fall.

3AIDS develops

• AIDS develops The body can no longer fight off other infections.

4Serious illness

• Serious illness Opportunistic diseases take hold and may prove fatal if untreated.

Section 4 of 8Stopping the spread

Preventing infection

Hygiene

• Hygiene Washing hands and preparing food safely stops bacteria reaching people.

Vaccination

• Vaccination Protects against viral diseases such as measles.

Barrier methods

• Barrier methods Condoms reduce transmission of gonorrhoea and HIV.

Treatment

• Treatment Antibiotics treat bacterial infections; they have no effect on viruses.

Section 5 of 8Why viruses and bacteria need different treatments

Bacteria

• Bacteria Bacteria are living cells that reproduce on their own, so antibiotics such as penicillin can kill them or stop them growing.

Viruses

• Viruses Viruses reproduce inside host cells,
  • which makes them hard to attack without damaging the host; antibiotics do not work,
  • so vaccination and antiviral drugs are used.

Resistance

• Resistance Overuse of antibiotics lets resistant bacteria survive and multiply, so gonorrhoea is becoming harder to treat.

Section 6 of 8Applications and exam context

Question wording	What to include
Explain how a disease spreads	Name the pathogen, the route (food, droplets or body fluids) and who is at risk
Suggest how to reduce spread	Match the control to the route: hygiene for food, vaccination for droplets, condoms for body fluids
Explain why a vaccine works	Antigens trigger lymphocytes to make antibodies and memory cells, giving a fast response next time
Explain why HIV leads to other illnesses	It damages lymphocytes, so the immune system cannot fight other pathogens

Section 7 of 8Key terms

Term	Meaning
Communicable disease	A disease caused by a pathogen that can be passed from one organism to another.
Pathogen	A microorganism that causes disease.
Sexually transmitted infection	An infection passed on through sexual contact.
AIDS	The late stage of HIV infection when the immune system is badly weakened.
Vaccination	Giving a harmless form of a pathogen to make the body immune to it.

Section 8 of 8Exam technique

1

Saying antibiotics can cure measles or HIV. These are viruses, so antibiotics do not work.

2

Stating that HIV and AIDS are the same thing. HIV is the virus; AIDS is the condition it can cause.

3

Forgetting that salmonella is a bacterium spread by food rather than by airborne droplets.

4

Giving 'good hygiene' as the only prevention for all four diseases. Choose the method that fits each route of infection.

5

Naming a disease and its pathogen but not stating how it is transmitted when asked to explain spread.