Biology- communicable diseases

Vectors

Carry pathogens from one organism to another e.g. water and insects

Pathogens

Microorganisms which cause disease

Tuberculosis

• Bacterial disease

• Spread airborne

• Persistent cough, chest pain

• Treated by long course of antibiotics

• Bacteria infect the lungs (alveoli)

  • Macrophages engulf them but some survive, causing lung damage

Bacterial meningitis

Bacterial disease which infects the meninges, the membrane which surrounds the brain and spinal cord. Membranes become swollen and may cause damage to brain and nerves

Ring rot (potatoes)

• Bacterial disease

• Causes the decay (brown ring) in the vascular tissue of a potato tuber, leaf wilting, rotting

• Caused by Gram positive bacterium

• No cure

• Transmitted by contaminated tools, infected plant material

• Prevented by disinfecting equipment and removing infected plants

• Bacteria infect the xylem and vascular tissue

  • Blocking water transport

HIV / AIDS

• Viral disease

• Transmitted by unprotected sex and sharing needles

• Early flu-like symptoms, HIV may develop into AIDS

• HIV infects T helper cells

• No cure, anti-retroviral drugs slow viral replication

  • Uses reverse transcriptase to make DNA from RNA

  • Integrates into host DNA and destroys T helper cells

  • Weakens the immune system

Influenza (flu)

• Viral disease

• Airborne droplets

• Causes fever, sore throat, headache

• No cure

• Prevented by annual vaccinations, hand washing

  • Vaccines must be updated each year due to antigenic variation (mutation)

• Virus infects the respiratory epithelial cells

  • Replicates inside them

  • Destroys cells

  • Rapid mutation changes surface antigens

TMV

• Viral disease

• Damage to leaves, stunted growth, discolouration, reduced photosynthesis and yield

• Resistant crop strains available, disinfect tools, maintain good field hygiene, but there is no cure

• Caused by contact with infected plants, contaminated tools, handling infected plants

• Virus infects plant cells and damages chloroplasts

  • Reduces chlorophyll production and photosynthesis

Black sigatoka (bananas)

• Fungal disease

• Hyphae penetrate and digest the cells turning the leaves black

• Fungicide treatment can control the spread of the disease but there is no cure

• Fungus infects leaves

  • Reduces the area available for photosynthesis

  • Lowers the glucose production

  • Decreases banana yield

Athlete’s foot

• Fungal disease

• Spread by contact with infected skin, towels shoes

• Itchy, cracked, peeling skin between toes

• Treated with antifungal creams or sprays

• Keep feet clean and dry to prevent

• Fungus grows on the outer layers of skin in warm, damp conditions

Malaria

• Protoctist

• Spread by bite from infected female

• Causes fever, chills, sweating

• Treated by antimalarial drugs

• Prevented with insecticide-treated mosquito nets, insecticide

• Parasite in mosquito enters the bloodstream

  • Reproduces in the liver then red blood cells

  • Red blood cells burst, releasing more parasites

  • Anaemia caused due to red blood cell destruction

Potato blight/Tomato late blight

• Caused by fungus-like protoctists

• The hyphae penetrate host cells, destroying leaves, tubers and fruit

• Fruit/tubers rot, white fungal-like growth underneath leaves

• No cure, resistant strains available, fungicides can slow spread

• Spread by wind dispersed spores, rain splash, infected plant material