Chapter 10: Infectious diseases

Infectious diseases are disorders caused by organisms — such as bacteria, viruses, fungi or parasites. Many organisms live in and on our bodies. They’re normally harmless or even helpful. But under certain conditions, some organisms may cause disease. Some infectious diseases can be passed from person to person. Infectious diseases are caused by pathogens and are transmissible. Bacteria and Viruses are the min disease causing pathogens in human.

Common disease and their Pathogens:


  • The disease is water-borne (the bacterium lives in water) and food-borne
  • Cholera can be transmitted when people; bath or wash in contaminated water, drink contaminated water, or eat food exposed to contaminated water

Symptom: Severe diarrhea, dehydration.


  • Prevention of cholera can occur through:
    • Providing adequate sewage treatment infrastructure
    • The provision of clean, piped water that has been chlorinated to kill bacteria (as this occurs in developed countries, cholera is very rare among them)
    • vaccination programmers in areas where cholera is endemic


  • Malaria is caused by one of four species of the protoctist Plasmodium
  • These protoctist are transmitted to humans by an insect vector:
    • Female Anopheles mosquitoes feed on human blood to obtain the protein they need to develop their eggs
    • If the person they bite is infected with Plasmodium, the mosquito will take up some of the pathogen with the blood meal
    • When feeding on the next human, Plasmodium pass from the mosquito to the new human’s blood
  • Malaria may also be transmitted during blood transfusion and when unsterile needles are re-used


  1. Apply mosquito repellent with DEET (diethyltoluamide) to exposed skin.
  2. Drape mosquito netting over beds.
  3. Put screens on windows and doors.
  4. Treat clothing, mosquito nets, tents, sleeping bags and other fabrics with an insect repellent called permethrin.

Tuberculosis (TB)

Tuberculosis (TB) is a potentially serious infectious disease that mainly affects the lungs. The bacteria that cause tuberculosis are spread from person to person through tiny droplets released into the air via coughs and sneezes.

  • When infected people with the active form of the disease cough or sneeze, the Mycobacterium tuberculosis bacteria enter the air in tiny droplets of liquid
  • TB is transmitted when uninfected people then inhale these droplets


  1. Good ventilation: as TB can remain suspended in the air for several hours with no ventilation.
  2. Natural light: UV light kills off TB bacteria.
  3. Good hygiene: covering the mouth and nose when coughing or sneezing reduces the spread of TB bacteria.


  • Human Immunodeficiency Virus is a retrovirus
  • The HIV virus is not transmitted by a vector (unlike in malaria)

HIV can be transmitted in the following ways:

  • sexual intercourse
  • blood donation
  • sharing of needles used by intravenous drug users
  • from mother to child across the placenta
  • mixing of blood between mother and child during birth
  • from mother to child through breast milk

If HIV is not treated, it can lead to AIDS (acquired immunodeficiency syndrome). Learning the basics about HIV can keep you healthy and prevent HIV transmission.


  • Night sweats.
  • Muscle aches.
  • Sore throat.
  • Swollen lymph nodes.


  • To prevent the transmission of HIV the following measures can occur:
    1. Blood donations can be screened for HIV and heat-treated to kill any viruses
    2. HIV-positive mothers and their babies can be treated with drugs (as HIV can be transmitted across the placenta, during birth and through breast milk
    3. Condoms, femidoms and dental dams can be used to decrease the infection risk during sexual intercourse and oral sex by forming a physical barrier between body and fluids
    4. Education programs about how the virus is transmitted can be released into the community to encourage people to change their behaviors in order to protect themselves and others
    5. Intravenous drug users encouraged not to share needles


Antibiotics are drugs that are used to treat infections caused by pathogenic bacteria. They are compounds that are made by microorganisms and modified chemically to increase their effectiveness. Antibiotics work by interfering with the growth or metabolism of the target bacterium

Penicillin prevents the production of new cell walls in bacteria and so does no affect viruses or human cells, neither of which have cell walls. Penicillin is only effective against bacteria that are still growing. Not all antibiotics are effective against all bacteria.

Antibiotic Resistance

Antibiotic resistance happens when germs like bacteria and fungi develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. In summary, the 6 main causes of antibiotic resistance have been linked to:

  • Over-prescription of antibiotics.
  • Patients not finishing the entire antibiotic course.
  • Overuse of antibiotics in livestock and fish farming.
  • Poor infection control in health care settings.
  • Poor hygiene and sanitation.