What are infectious diseases?

What are infectious diseases?


Infectious diseases are caused by microorganisms such as viruses, bacteria, fungi or parasites and can spread between individuals.


What is an infectious disease?

  • Infectious diseases are caused by microorganisms such as viruses?bacteria?, fungi or parasites?.
  • Microorganisms that cause disease are collectively called pathogens.
  • Pathogens cause disease either by disrupting the bodies normal processes and/or stimulating the immune system to produce a defensive response, resulting in high fever, inflammation? and other symptoms.
  • Infectious diseases can be spread from one person to another, for example through contact with bodily fluids, by aerosols (through coughing and sneezing), or via a vector, for example a mosquito.








  • Infectious diseases are one of the leading causes of death worldwide.
  • Many diseases become difficult to control if the infectious agents evolve resistance to commonly used drugs:
    • For example, bacteria can accumulate mutations in their DNA or acquire new genes that allow them to survive contact with antibiotic drugs that would normally kill them.
  • Scientists are currently searching for new approaches to treat infectious disease, focusing on exactly how the pathogens change and drug resistance evolves.

What causes an infectious disease?



  • Viruses are tiny infectious agents that replicate only in the living cells of other organisms.
  • They have a very simple structure consisting of genetic material in the form of DNA or RNA within a protein capsule.
  • They can infect all types of life forms, from animals to plants and bacteria to amoebae.
  • Viruses can be spread in many ways including:
    •  From plant to plant by insects that feed on plant sap. For example, Potato virus Y which is spread by aphids.
    • From animal to animal by blood-sucking insects. For example, Dengue virus which is spread by mosquitos.
    • Spread by aerosols (through coughing and sneezing). For example, influenza virus.
    • Spread by not washing hands after going to the toilet. For example, norovirus or rotavirus.
    • Spread by sexual contact. For example, HIV and Human Papillomavirus (HPV).
    • Spread by exposure to infected blood. For example, Hepatitis B.
  • Viruses can often be prevented through vaccines.




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  • Bacteria are single-celled microorganisms.
  • They come in many shapes including ball-, rod- and spiral-shaped.
  • Most bacteria are not harmful and some are actually beneficial. Less than one per cent of bacteria will actually make you ill.
  • Infectious bacteria can grow, divide and spread in the body, leading to infectious disease.
  • Some infectious bacteria give off toxins which can make some diseases more severe.
  • Bacteria are spread in many ways including:
    • Spread by aerosols (through coughing and sneezing). For example, Streptococcus.
    • Spread by surface and skin contact. For example, Staphylococcus aureus, including MRSA.
    • Spread through body fluids, such as blood and saliva. For example, meningococcal disease (meningitis).
  • Antibiotics are usually given to treat severe bacterial infections.
  • Antibiotic resistance in bacteria is a significant problem.





About The Author

Osigweh Lilian Oluchi is a graduate of the University of Lagos where she obtained a B.A (Hons) in English, Masters in Public and International affairs (MPIA). Currently works with 1stnews as a Database Manager / Writer. [email protected]

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