Virulence vs Pathogenicity
A plant, animal, or insect becomes diseased when attacked by a pathogen. Pathogen is a microorganism that has the ability to cause a disease. Host and pathogen should come in contact, for disease to occur.
At early times after microbes had been identified, among many microbes, identifying pathogens from a non-pathogen was a challenge . To cause a disease, contacts of three factors are important i.e. pathogen, host, and the environmental factors. If one of the factors is not contacted, disease will not occur.
After an infection, there may be three possible outcomes. The first possibility is, pathogen may be removed from primary defense system of the host. The second possibility is, pathogen can enter to the host and cause disease, and the third outcome may be an equilibrium where pathogen and host will live together and minimize the harm caused by the pathogen .
Pathogenicity is the ability to cause a disease in host organisms . The pathogenicity is a qualitative measurement (Soledad and Fernando, 2008). It is measured by virulence. Disease is an outcome of the relationship between virulence of a pathogen and the resistance of the host. Many factors in a pathogen give reasonable contribution to cause the disease. Those are called virulence factors . Virulent factors include toxins that kill the host cell, enzymes that act on the host cell walls, and substances that alter the normal cell growth .
All these virulent factors do not act on the host simultaneously when diseases occur. As an example, in necrotic diseases, toxins are functioning whereas, in soft rot disease, cell wall digestion enzymes are operating.
The important fact is that all pathogenic species are not equal in virulence i.e. amounts of harmful substances may vary from species to species.
Virulence is the measurement of the ability to cause a disease in host . It describes the quantitative negative effect on host (Soledad and Fernando, 2008). To cause a disease, two factors are important i.e. the nature of the pathogen and the nature of the host. To cause a disease, the genetic makeup of both pathogen and host is important. The defense systems in host such as immunity systems in an animal or phenolic compound in a plant will alter the ability of causing the disease. How-ever, high virulence may result in host mortality, and it affect negatively to host transmission, which leads to the pathogen fitness (Soledad and Fernando, 2008).
Virulence factors are responsible for causing disease. Virulence factors may be protein, which is coded by virulence genes. There may be virulent bacteria and viruses.
What is the difference between Pathogenicity and Virulence?
• Pathogenicity is the ability to cause a disease in host organisms, whereas virulence is the measurement of the ability to cause a disease in the host organism.
• Pathogenicity is a qualitative measure, whereas virulence can be represented by a quantitative measure.
• Pathogenicity is not much suitable to explain the degree of harmfulness of a pathogen, whereas virulence can be used to express the degree of harmfulness of a pathogen.
• Virulence and pathogenicity have different genetic control.
Soledad S. and fernando G. (2008) The evolution of virulence and pathogenicity in plant pathogen populations, Molecular Plant Pathology (3), 369–384