Infection and immunity

Part 1: Report

• Describe the contribution of Semmelweiss and Koch to the Germ Theory of disease and the early development of epidemiology by Snow.

 

Koch experimentation with anthrax led him to the discovery that specific germs were responsible for certain diseases and this contributed to the great revolution in the field of medicine referred to as the germ theory. His experiment involved examining blood from cows that had died from anthrax. He later conducted an experiment where he exposed mice to the blood obtained from cows stricken by anthrax (Thiel, 2017). The presence of similar rod shaped bacteria in the dead cows’ blood and the mice infected helped Koch to draw the conclusion that specific germs were responsible for the occurrence of diseases and that the diseases could be spread.

Semmelweis contribution to the germ theory of diseases resulted from his studies to explain the occurrence and spread of cholera. From his observations, Semmelweis discovered that maternity wards attended to by students had higher infection rates than those attended to by midwives (NRC, 2004). The realization that infections and death rates were relatively low in summer led to the discovery that the medical students directly contributed to the number of infections. Semmelweis’ research revealed that infections could be spread by human contact as the high infection rates were attributed to poor hand washing hygiene from the medical students (Thiel, 2017).  The high rate of infections was attributed to the students’ failure to wash their hands before attending to patients in the wards especially because they also worked in the autopsy department. Semmelweis’ contribution helped to identify how diseases are spread and also preventive measures that can be taken to reduce the spread of infections. 

Snow’s contribution spearheaded epidemiology as his research involved analyzing data of infected people to determine the cause and origin of the infection. When Snow was conducting research, people believed that cholera was spread through human contact or by Miasmas (Johnston, 2008). After examining the bodies of the victims however, Snow noted that the symptoms displayed affected the gastrointestinal tract and this disapproved the notion that the disease was spread by air since patients did not display any pulmonary symptoms. This led to the discovery that cholera may have been caused by ingesting contaminated water and Snow identified a tap that acted as the source for contamination (Johnston, 2008). Statistics on the number of people infected in specific locations enabled Snow to focus his research to the first boy who had been infected and how his excrements had been disposed off in a cesspool adjacent to the water pump discovered to have been the cause of the infection.

 

• Explain the history of the development of vaccination, including the contributions of Jenner (smallpox) and Pasteur (attenuated vaccines).

 

The history of vaccines can be traced back to hundreds of years when Buddhist monks drake snake venom to raise their immunity to snake bites and Variolation, a Chinese practice that made them immune to small pox. The greatest contribution was however made by Edward Jenner in 1796 when he inoculated a boy with cowpox disease, making him immune to smallpox (Feemster, 2017). Jenner used pus obtained from lesions on a milkmaid’s hand resulting from cowpox. Six weeks after the boy had been inoculated with the pus; Jenner exposed the boy to smallpox and proved is experiment had worked and the same results were recorded from the rest of the tests conducted on other people. The discovery led to the development of a smallpox vaccine, spearheading the start of immunization.

            Louis Pasteur’s contribution encouraged the use of vaccines on other diseases as vaccines were interpreted to mean the use of cowpox to immunize against smallpox. Pasteur was responsible for developing a rabies vaccine that operated as a post-infection antidote due to the long incubation period for germs that cause rabies (Plotkin, 2011). His research motivated research that sought to create vaccines for other diseases other than smallpox and is greatly responsible for how people define vaccines today.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part 2: Structured questions

 

A.C 2.1
Q1.      (a) Describe the range of non-specific responses to infection, including fever.

 

Animals rely on specific and non specific responses for protection against foreign invaders. Specific immune responses are able to differentiate types of invaders and act accordingly but are not present in all animals. Non-specific defences are present in all animals and offer the same type of protection regardless of the nature of invasion. Some of the non-specific responses include barriers and Fever.

            Barriers offer protection by establishing boundaries that separate the organism from elements in the environment that could cause harm (Baron & Dianzami, 2016). Barriers like mucous membranes and the skin control what enters the body and therefore reduces the number of pathogens that enter the body. The barriers also release secretions like saliva and mucus that are acidic and prevent bacterial growth.

            A fever is another form of non-specific protection that triggers the hypothalamus to raise the body temperature once an invader or pathogen is discovered (Baron & Dianzami, 2016). Fevers also speed up the repair process, increase body metabolism and can also slow down bacterial reproduction to allow other cells enough time to get rid of the pathogen.

 

 

 

 

 

1. b) If a person suffers an injury such as cut or graze, the area often becomes inflamed for a few days afterwards. Describe how the inflammatory process protects the person from infection

 

The inflammatory response occurs whenever tissues are damaged by pathogens, trauma, toxins and other causes. The swelling occurs as a result of chemicals like histamine, prostaglandins and bradykinin released by the damaged cells which in turn cause blood vessels to lea fluids into the tissue causing the swelling (Chen et al, 2017).  The process prevents infection as it stops the foreign entity from coming into contact with more body tissue while the toxins attract white blood cells referred to as phagocytes which consume the foreign substance and any dead or damaged cells. The phagocytes eventually die out and the remaining dead tissue and bacteria collects to form pus.

            The ability for antibodies and phagocytic cells to fight pathogens and eradicate them from the body is made possible by the complement system. It comprises of a number of tiny proteins that are located in the blood and synthesized by the liver (Chen et al, 2017). The process is part of the acute phase reaction that occurs during systemic inflammation. When the complement system is stimulated by a trigger it initiates a process where proteases that are in the system start cutting specific proteins in order to release cytokines responsible for activating the cell killing membranes that get rid of the pathogens.

 

 

 

 

 

A.C 2.2

Q2.      (a) Describe how bacteria are destroyed by phagocytes.

 

Phagocytes destroy bacteria through the process of phagocytosis which is initiated when the white blood cells known as phagocytes identify some form of pathogen invading the body. The phagocyte moves closer t the bacterium and uses its cell membrane to fuse with the bacterium and engulf it with a cellular compartment known as the phagosome (Iwasa, 2020). The phagosome in turn fuses with a lysosome containing toxic chemicals and acidic enzymes that create a phagolysosome. The phagolysosome uses the chemicals to break down the bacterium before digesting it and in so doing, destroys the bacteria.

 

 

 

 

 

 

 

 

 

 

 

Q3       Complete the table: 

 

	Where does this cell originate from?	Where does this cell complete its maturation process?	How does this cell remove / destroy pathogens?
Neutrophil	Bone marrow	Liver	Engulf pathogens and neutralize them until they are destroyed
Macrophage	Hematopoietic stem cells	Lymphoid tissue	Engulf pathogens they come into contact with and destroy them with a acid.
T Lymphocyte (T cell)	Bone marrow	thymus	Release perforin and cytotoxins which enters the cells and kills any pathogens inside.
B Lymphocyte (B cell)	Bone marrow	Bone marrow	Produce y shaped proteins that lock on to pathogens and mark I for destruction by other immune cells.

 

 

 

Q4. ( AC2.3)

 

Use the diagram provided to explain why a person infected with chicken pox normally only gets the disease once. You must specifically refer to the importance of memory cells in this process.

People who have already been sick with chickenpox only get the disease once because human beings posses circulating memory cells that are programmed to identify the virus destroy it before the individual gets sick. The memory cells remain in the body after the patient recovers from chicken pox to identify and destroy any pathogens that could cause chickenpox before it develops (Baxter et al, 2016). Once a pathogen is identified, the memory cells facilitate the commencement of secondary adaptive immune responses, producing B cells and T cells that attack and destroy the chickenpox pathogens.

            The secondary adaptive immune response offers protection that prevents the body from developing symptoms associated with chickenpox and the individual may not even be aware that the chickenpox causing pathogens entered the body (Baxter et al, 2016). The memory cells however become more efficient in preventing the reoccurrence of chicken pox as the number of cells that can identify chicken pox are left circulating in the body making the patient more immune.

References

BARON, S. (2016). Medical microbiology. Menlo Park, Calif, Addison-Wesley, Health   Sciences Division.

Chen, L., Deng, H., Cui, H., Fang, J., Zuo, Z., Deng, J., Li, Y., Wang, X., & Zhao, L. (2017).             Inflammatory responses and inflammation-associated diseases in   organs. Oncotarget, 9(6), 7204–7218.  https://doi.org/10.18632/oncotarget.23208

Feemster, K. A. (2017). Vaccines: what everyone needs to know.  New York, NY : Oxford           University Press

Ghebrehewet, S., Stewart, A. G., Baxter, D., In Shears, P., Conrad, D., & Kliner, M.         (2016). Health protection: Principles and practice. Oxford, United Kingdom : Oxford      University Press,

IWASA, J. (2020). Karp's Cell and Molecular Biology: concepts and experiments. John   Wiley

Johnson, S. (2008). The ghost map: The story of London's most terrifying epidemic--and how       it changed science, cities, and the modern world. London: Penguin,

National Research Council, (2004) “A theory of germs” Washington DC: National Academies     Press, retrieved from, vhttps://www.ncbi.nlm.nih.gov/books/NBK24649/

Plotkin, S. A. (2011). History of Vaccine Development. New York, NY, Springer Science+Business Media, LLC. https://doi.org/10.1007/978-1-4419-1339-5.

Thiel, K. (2017). The Germ Theory of Disease. New York, NY, Cavendish Square