Running head: MICROBIOLOGY 100 MODULE 4 Microbiology 100 Module 4 July 28, 2009 Microbiology 100 Module 4 Three most important characteristics of infectious disease agents The characteristics of infectious diseases agents play an important role in identification of the modes of disease transmission. Therefore, understanding characteristics of pathogenic organisms is crucial to effective prevention of diseases introduction, controlling and eradicating these infectious agents once they are introduced (MacMahon & Trichopoulos, 1996).
There are three characteristic of infectious disease agents that can be considered of significant importance when identifying the diseases which would place the persons in a community at a greater risk, namely, infectivity, virulence, and toxigenicity. Infectivity is the ability of infectious diseases agent to cause infection by entering the host and multiplying to an infectious dose. Infectivity relates to a minimum number of infectious particles that are required to cause the disease. For example, polio and measles have very high infectivity rates. Virulence refers to the ability of infectious diseases agent to cause mortality. It is measured by proportion of clinical cases developing severe disease or by case fatality rate. Virulence can change with time with the development of new interventions (for example, antibiotics).
Toxigenicity is the ability of the agent to produce toxic substances disrupting normal functions of the cells in the organism. Toxins are very destructive to human cells and tissues (for example, such as botulism and shellfish poisoning) (Gordis, 2008).
The Essay on What Is the Infectious Agent
For example the name of the bacteria, virus, or parasite. Giardia is protozoan and also flagellated. Flagellated means using appendages in a whip-like movement to propel. Giardia attaches to the host through the lining of the upper intestines. Once it attaches itself, it begins to feed and reproduce causing the giardiasis to commence. Giardia reproduces by dividing itself, which defines it as a ...
Although all characteristics are important, infectivity, virulence, and toxigenicity are of the most significance when speaking about the diseases placing individuals in community at a higher risk. For example, in person-to-person transmission, the higher the infectivity of pathogenic organism is, the more secondary infections occur. In person-to-person transmission secondary attack rate is considered a measure of infectivity. The higher the level of infectivity is, the more threat poses a disease to a person in community. For example, while the infectivity of tuberculosis is relatively low, the infectivity of smallpox is very high, thus constituting significant threat to community (Rothman, Epidemiology: An Introduction, 2002).
As far as virulence is the ability of the agent to cause mortality, this characteristic is also very important. Finally, toxigenicity is also a significant characteristic, because the resulting disease is caused not by the microorganism itself but by the toxins produced by this pathogenic microorganism.
Three remaining characteristics are pathogenicity, resistance and antigenicity. Pathogenicity is the ability of the pathogenic microorganism to harm the host and cause the disease. Pathogenicity is a genetic component of pathogen (Aschengrau & Seage, 2007).
Opportunistic pathogens and commensals do not have the inevitable ability to cause disease (Rothman, Greenland, & Lash, Modern Epidemiology, 2008).
The disease is not an inevitable result of the interaction of the host with pathogen; also, pathogens can exhibit a wide range of virulence. For example, measles has very high pathogenicity rate. Resistance is the ability of infectious agent to survive under adverse environmental condition. If the resistance level is low, the agent is more fragile.
For example, hepatitis agents usually have a very high level of resistance, while influenza infectious agents are very fragile. Finally, antigenicity is the ability of infectious agent to induce antibody production in the host. The microorganisms with high antigenicity level typically have very low reinfection rate. At the same time, the infectious agents with low antigenicity rate have higher reinfection rate. For example, the occurrence of reinfection with measles virus is very rare (Szklo, 2006).
The Term Paper on Causal Agent Leaves Disease Plants
Bacterial Spot (bacterial - Xanthomonas campestris pv. vesicatoria) Infected leaves show small, brown, water soaked, circular spots about one-eighth inch in diameter. The spots may have a yellow halo. This is because the centers dry out and frequently tear. on older plants the leaflet infection is mostly on older leaves and may cause serious defoliation. The most striking symptoms are on the green ...
References Aschengrau, A., & Seage, G.
(2007).
Essentials of Epidemiology in Public Health. Jones & Bartlett Publishers. Gordis, L. (2008).
Epidemiology: with STUDENT CONSULT Online Access. Saunders.
MacMahon, B., & Trichopoulos, D. (1996).
Epidemiology: Principles and Methods. Lippincott Williams & Wilkins. Rothman, K. (2002).
Epidemiology: An Introduction. Oxford University Press. Rothman, K., Greenland, S., & Lash, T. (2008).
Modern Epidemiology. Lippincott Williams & Wilkins. Szklo, M. (2006).
Epidemiology: Beyond the Basics. Jones and Bartlett Publishers..
