Diseases

• Transmissible disease


  A disease that is caused by a pathogen that can be transmitted from 1 person to another
• Pathogen


  A disease-causing organism
• Transmission of transmissible diseases

  1. Direct contact with skin or blood of infected person

  2. Indirectly through inhaling contaminated droplets released by infected person into air during sneezing or coughing
• Method of transmission

  • Inhaling droplets released by infected person into air during sneezing or coughing
  • Consuming contaminated food or water
  • Through vectors such as insects
  • Through sexual intercourse with infected person
  • Through direct skin contact
  • Through touching contaminated surfaces and then touching the eyes or mouth
• Diseases transmitted through inhaling droplets

  • Influenza, tuberculosis, COVID-19
• Diseases transmitted through consuming contaminated food or water

  • Cholera, typhoid
• Diseases transmitted through vectors such as insects

  • Malaria
• Diseases transmitted through sexual intercourse

  • AIDS, syphilis, gonorrhea
• Diseases transmitted through direct skin contact

  • Small pox
• Diseases transmitted through touching contaminated surfaces

  • COVID-19
• Non-transmissible disease


  A disease which is not caused by a pathogen & cannot be transmitted directly from 1 person to another
• Body barriers to pathogens

  • Skin
  • Hairs in nose
  • Mucus
  • Hydrochloric acid
• Skin


  • Serves as primary physical barrier to microbial entry into the body
  • If there is a damage or cut in the skin, clotting of blood occurs & a scab is formed to prevent pathogens from getting into the body
  • Sebum produced by sebaceous glands in the skin contains chemicals that kill bacteria on the skin
• Hairs in nose


  • Act as physical barrier to infection
  • They filter air containing microbes, dust and pollutants, preventing them from entering lungs
• Mucus


  • A fluid produced by cells lining the air passage & contains a sticky substance called mucin
  • It traps bacteria, dust & other foreign particles in inhaled air
  • Contains bacteria-killing enzymes to help fight infections
  • The mucus containing trapped particles can be coughed out or blown out of nose
  • Its removal is aided by beating action of tiny hair-like projections called cilia that line the air passage
  • Cilia sweeps the mucus up the airways from lungs
• Hydrochloric acid


  • Kills bacteria found in ingested food or water in stomach
  • Prevents them from multiplying
• Malaria


  A disease caused by the parasite Plasmodium, transmitted to humans by the bite of female Anopheles mosquitoes
• Transmission of malaria

  1. Female Anopheles mosquitoes feed on human blood to obtain proteins they need to develop their eggs

  2. When they bite a person suffering from malaria, they suck blood that contains gametes of the parasite

  3. These fuse and develop in the mosquitoes' gut to form adult Plasmodium which migrates to the salivary glands of the mosquitoes

  4. When the mosquito bites another person, it first injects saliva to prevent blood from clotting & blocks its needle-like mouthparts

  5. At the same time the Plasmodium in the saliva enters the blood stream of the person and is carried to the liver cells and red blood cells inside which it multiplies
• Control of malaria

  1. Reduce number of mosquitoes by spraying insecticides, draining areas where water accumulates, spraying oil over fresh water

  2. Avoid being bitten by mosquitoes by sleeping under mosquito net, applying mosquito coil or anti-mosquito cream, wearing clothes that cover most of the skin

  3. Use drugs against parasites to treat infected people
• Life cycle of Anopheles mosquito

  1. Mosquitoes lay their eggs in water bodies

  2. Larvae hangs suspended to water surface in order to breathe

  3. Mosquitoes larvae are less mobile & feed on aquatic microorganism

  4. Pupa also come to surface oftenly to breathe

  5. The control of adult mosquitoes population with insecticides treated bed nets & indoor residual sprays remains cornerstone of malaria reduction and elimination
• Reasons for worldwide concern over spread of malaria

  • Plasmodium parasites are becoming resistant to drugs commonly used to control them
  • Mosquitoes are becoming resistant to insecticides hence it is becoming more difficult to kill them
  • Increase in number of epidemics because of climate change favouring the spread of mosquitoes
  • Migration of people who often carry parasites to other places
• HIV-AIDS


  A disease caused by the virus Human Immune-Deficiency Virus (HIV) which destroys the lymphocytes, gradually weakening the body's immune system against infection
• Transmission of HIV-AIDS


  1. During sexual intercourse with an infected person

  2. During sharing of needles (among drug addicts)

  3. During blood transfusion of an infected person

  4. During pregnancy, the virus can cross the placenta to infect the foetus

  5. During breast feeding, the virus can pass in mother's milk to baby
• Treatment of HIV-AIDS


  No vaccine till date<|>Drug therapy can slow down the onset of AIDS preventing replication f the virus
• Prevention & control of HIV-AIDS

  1. Use of condoms during sexual intercourse

  2. Avoid having multiple sex partners

  3. Avoid sexual intercourse with infected or highly-risk partners

  4. Avoid drug abuse & sharing of needles

  5. Screening of blood used for blood transfusion

  6. Educate public making them aware of methods of transmission & prevention of HIV
• Cholera


  A disease caused by the bacterium Vibrio cholera, occurring in parts of the world where people do not have access to proper sanitation, clean water or uncontaminated food and sewage treatment
• Transmission of cholera

  1. Infected people pass out a large number of bacteria in their faeces

  2. If we eat food or drink water contaminated with faeces from an infected person, we become infected also

  3. On consuming the contaminated food/water, the bacteria release a toxin in the intestine which disrupts the functions of the epithelium so that salts & water leave blood
• Treatment of cholera

  Drink solution of salts & glucose to rehydrate the body
• Prevention and control of cholera

  1. Provision of clean, chlorinated water, piped-water to avoid contamination with bacteria

  2. Organization of health campaigns to promote the adoption of good hygiene practices such as hand-washing with soap and storage of food

  3. Set up sewage treatment plans to prevent contamination of water supply
• Alcohol


  A small molecule which is soluble in both water & fat, can easily pass across the lipid bilayer of cell surface membranes, rapidly absorbed into blood by stomach & small intestine
• Effects of alcohol


  Reduces anxiety & tension<|>Dilates small arterioles in skin giving it a feeling of warmth
• Drinking during pregnancy cause foetal abnormalities & reduced physical and mental developments in infants. Can lead to miscarriage and low birth weight
• Social consequences of alcohol

  • Aggressive & violent behavior
  • Increase risk of road accidents during driving
  • Family violence
  • Involved in criminal activities
  • Loss of jobs & rejection by society
• Tobacco smoke


  Smoking causes chronic obstructive lung disease, coronary heart disease and increased risks of several different types of cancer, including lung cancer
• Chemicals in cigarettes


  • Tar (a carcinogen)
  • Nicotine (a stimulant, addictive)
  • Carbon monoxide
• Tar


  • A carcinogen linked to increased chances of cancerous cells developing in the lungs
  • Contributes to COPD by stimulating goblet cells and mucus glands to enlarge, producing more mucus
  • Destroys cilia, inhibiting the cleaning of the airways, and mucus (containing dirt, bacteria and viruses) builds up blocking the smallest bronchioles
  • A smoker's cough is an attempt to move the mucus but it damages the epithelia resulting in scar tissue
• Emphysema

  • Develops as a result of frequent infection, meaning phagocytes are attracted to the lungs where they release elastase - an enzyme that breaks down the elastin in the alveoli walls
  • Without adequate elastin, the alveoli cannot stretch, so they recoil and many burst
  • The breakdown of alveoli results in the appearance of large air spaces, reducing the surface area for gas exchange and making sufferers breathe more rapidly
• Carbon monoxide


  • Binds irreversibly to haemoglobin, reducing the capacity of blood to carry oxygen
  • Puts more strain on the breathing system as breathing frequency and depth need to increase in order to get the same amount of oxygen into the blood
  • Puts more strain on the circulatory system to pump the blood faster around the body and increases the risk of coronary heart disease and strokes
  • Also cause damage to lining of blood vessels increasing fatty deposits on their inner wall and the tendency for blood clot formation increases
• Nicotine


  • Narrows blood vessels so puts more strain on the circulatory system and increases blood pressure
  • Narrow blood vessels are more likely to become clogged with fat, including cholesterol - if this happens in the coronary artery, this causes coronary heart disease
  • Reduces the supply of oxygen and important food molecules to the fetus during pregnancy, resulting in low birth weight
• Smoking during pregnancy can cause nicotine to constrict blood vessels in the placenta therefore reducing blood supply to foetus, and carbon monoxide to combine irreversibly with haemoglobin to form carboxy-haemoglobin thus decreasing oxygen supply to foetus, reducing development of foetus and resulting in lower weight of baby at birth