Communicable Diseases

• There are 4 types of communicable disease: viral, bacterial, fungal and protist.
• An example of a viral disease is HIV or TMV.
• An example of a bacterial disease is gonorrhoea or salmonella.
• An example of a fungal disease is rose black spot or athlete's foot.
• An example of a protist disease is malaria.
• Communicable diseases can be transferred by direct contact, air, water, unhygienic food preparations, or vectors.
• Direct contact

  • Could be sexual contact.
  • Non-sexual, like shaking hands.
• Water

  • Dirty water transmits disease.
  • E.g. Cholera.
• Air

  • An infected person can spray thousands of droplets containing disease particles that can infect others.
  • E.g. Common colds.
• Unhygienic Food Prep

  • Undercooked or reheated food can cause disease.
  • E.g. E.Coli
• Vector

  • Any organism that causes disease is a vector.
  • E.g. Tuberculosis in cows can be spread by badgers.
• Viruses are not alive - they do not complete all 7 life processes:

  • Movement
  • Respiration
  • Sensitivity
  • Nutrition
  • Excretion
  • Reproduction
  • Growth
• Viruses are made of a relatively short length of genetic material DNA which is surrounded by a protein coat.
• Viruses can often survive outside a host for long periods of time.
• When viruses have infected a suitable host cell(s), they replicate themselves within the cell thousands of times. They do not divide and reproduce, but replicate their DNA and protein coats
• The host cell or cells then burst and other nearby cells can be infected with the virus. 
• Viral diseases cannot be treated with antibiotics.
• Tobacco Mosaic Virus

  • It is transmitted by contact between plants, either naturally or through the hands of farmers.
  • It infects the chloroplasts of plant leaves and changes their colour from green to yellow or white in a mosaic pattern.
  • It can also make leaves crinkle or curl up.
  • This reduces the plant's ability to photosynthesise and grow properly.
• Tobacco Mosaic Virus

  • Infects tobacco or other similar species like tomatoes and peppers.
  • It reduces farmers' crop yield.
  • No cure - farmers try to reduce the infection to their crops or attempt to reduce the spread of the virus.
• HIV

  • HIV stands for human immunodeficiency virus.
  • Transmitted by body fluids - unprotected sex, cuts or injecting drugs using shared needles.
  • Immediately after infection, people often suffer mild flu-like symptoms.
  • These pass and for a period of time infected people might not know they are infected.
• HIV

  • AIDS stands for acquired immune deficiency syndrome.
  • Months or years after the infection of the virus, it becomes active and starts to attack the patient's immune system.
  • HIV at this point has become AIDS.
  • No cure for either, although many scientists are trying to find one.
  • Infected people are given antiviral drugs, which can slow the development of AIDS.
• Measles

  • Highly infectious viral disease.
  • Often caught by young children.
  • Transmitted through air in tiny droplets after an infected person sneezes.
  • Causes fever and skin rash.
• Measles

  • Many children in developed countries are given vaccines.
  • Unfortunately, not all countries have it.
  • Infection can cause more serious effects like infertility in adults who did not catch the disease as children.
• Bacteria are larger than viruses, but can still only be seen with a microscope.
• All bacteria are prokaryotic.
• Gonorrhoea

  • Gonorrhoea is a sexually transmitted disease caused by bacteria.
  • Common amongst people aged 15-24.
• Gonorrhoea

  • Causes burning pain when urinating.
  • Forms a yellow or green discharge from an infected person's penis or vagina.
• Gonorrhoea

  • If untreated it can result in infertility.
  • To prevent infection, refrain from anal, oral or vaginal sex.
  • Use barrier contraception - e.g. condom.
• Gonorrhoea

  • Gonorrhoea is treated by antibiotics.
  • Many of the antibiotics which were effective against bacterial diseases like gonorrhoea are not as effective as they used to be.
  • This is because bacteria are evolving to become resistant to existing antibiotics.
  • Scientists are constantly trying to find new antibiotics to treat these diseases.
• Salmonella

  • A bacteria that causes food poisoning.
  • Causes abdominal cramps, vomiting and diarrhoea.
  • It is often found in unhygienic kitchens, undercooked foods such as meat, eggs and poultry, or the same foods that have not been reheated properly.
  • To prevent the spread of salmonella in the UK, all poultry are vaccinated against it.
  • Cooking food thoroughly, after preparing it in hygienic conditions, is the best way to avoid illness.
• All protists are eukaryotic.
• Malaria

  • Malaria is spread by mosquitos which carry the Plasmodium protist.
  • These are often found in areas with higher temperatures like Africa, Asia, and South and Central America, but not the UK.
  • Mosquitos suck blood containing the protists from an infected person.
  • They pass the protist, to other people they suck blood from.
  • The mosquitos do not become ill and are called 'vectors' because they transmit the disease.
• Malaria

  • Causes fever, sweats, chills, headaches, vomiting and diarrhoea.
  • Of the 200 million people infected each year, up to half die from this disease.
  • There is no vaccination for malaria.
  • Only prevented by stopping individuals from being bitten.
  • People sleep under mosquito nets and wear insect repellent to avoid bites.
  • Antimalarial drugs are also taken, which treat the symptoms and can prevent infection.
• Fungal cells are eukaryotic.
• Athlete's Foot

  • A rash caused by a fungus that is usually found between people's toes.
  • Causes dry, red, flaky, white, wet, cracked skin.
  • Often found in communal areas like swimming pool changing rooms or gyms.
  • Transmitted by touching infected skin or surfaces that have been previous contaminated.
  • Treated by antifungal medication.
• Rose Black Spot

  • Caused by a fungus which infects roses.
  • Infects leaves and causes black or purple spots on the leaves.
  • The rest of the leaves often turn yellow and can drop off the plant.
  • This reduces that plant's ability to photosynthesise and reduces growth.
  • Transmitted in air, water, or direct contact by gardeners.
  • It is treatable using fungicides and by removing and destroying infected leaves.
• Preventing Disease

  • Using chemicals or UV light to destroy pathogens in dirty water.
  • Cooking foods thoroughly and preparing them in hygienic conditions kills pathogens.
  • Washing surfaces with disinfectants kills pathogens.
  • Treating existing cases of infection kills pathogens.
  • Vaccinations introduce a small amount of dead or inactive pathogen into your body, and the immune system learns how to defend itself.
  • Using barrier contraception, e.g. condoms, stops the transfer of bodily fluids and sexually transmitted diseases.
• The human body has non-specific defence systems as it is constantly defending from pathogens.
• Skin

  • The skin covers almost all parts of your body to prevent infection from pathogens.
  • If it is cut or grazed it immediately begins to heal itself, often by forming a scab, which prevents infection as the skin acts as a physical barrier.
• Nose

  • The nose has internal hairs, which act as a physical barrier to infection.
  • Cells in the nose produce mucus.
  • This traps pathogens before they can enter the lungs.
  • When the nose is blown, mucus is removed and any pathogens are trapped within it.