Difference Between Virulence and Pathogenicity

The key difference between virulence and pathogenicity is that virulence refers to the degree of pathogenicity of an organism to cause disease while pathogenicity refers to the ability of an organism to cause disease.

A pathogen is a microorganism that has the ability to cause disease. Hence, pathogens cause diseases to plants, animals and insects, etc. Host and pathogen should come in contact in order for a disease to contract. Three factors are important in disease contraction: pathogen, host, and environmental factors. However, in the absence of even one of these factors, the disease will not occur. Moreover, after an infection, there may be three possible outcomes. The first possibility is that the pathogen may be removed from the primary defense system of the host. The second possibility is the pathogen entering the host and causing disease, while the third outcome may be an equilibrium where pathogen and host will live together and minimize the harm caused by the pathogen. Virulence and pathogenicity are two terms related to the ability to cause diseases and the degree to cause diseases.

CONTENTS

1. Overview and Key Difference
2. What is Virulence 
3. What is Pathogenicity
4. Similarities Between Virulence and Pathogenicity
5. Side by Side Comparison – Virulence vs Pathogenicity in Tabular Form
6. Summary

What is Virulence?

Virulence is the measurement of the ability to cause diseases in the host. It describes the quantitative negative effect on the host. To cause disease, two factors are important: the nature of the pathogen and the nature of the host. Moreover, the genetic makeup of both pathogen and host is important for a disease to occur. The defense systems in hosts (e.g. immunity systems in an animal or phenolic compound in a plant) will alter the ability to contract a disease. However, high virulence may result in host mortality, and it affects negatively to host transmission, which leads to pathogen fitness.

Virulence factors are responsible for causing disease. Virulence factors can be proteins coded by virulent genes. There may also be virulent bacteria and viruses.

What is Pathogenicity?

Pathogenicity is the ability to cause diseases in the host organism. The pathogenicity is a qualitative measurement. Moreover, it is measured by virulence. A disease is an outcome of the relationship between the virulence of a pathogen and the resistance of the host. Furthermore, many factors in a pathogen give a 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. The amounts of harmful substances may vary from species to species.

What are the Similarities Between Virulence and Pathogenicity?

• Virulence and pathogenicity are two terms we use interchangeably.
• Both terms explain the ability of the pathogen to cause diseases.
• However, pathogenicity depends on virulence
• Moreover, virulence and pathogenicity have different genetic control.

What is the Difference Between Virulence and Pathogenicity?

Virulence refers to the severity of an infection. But, pathogenicity refers to the ability of an organism to cause diseases. So, this is the key difference between virulence and pathogenicity. Furthermore, virulence can be a quantitative and qualitative measurement while pathogenicity is a qualitative measurement. Therefore, this is also a significant difference between virulence and pathogenicity.

Moreover, virulence can be used to express the degree of harmfulness of a pathogen. Whereas, pathogenicity is not much suitable to explain the degree of harmfulness of a pathogen. Hence, we can consider this too as a difference between virulence and pathogenicity.

Summary – Virulence vs Pathogenicity

Virulence and pathogenicity are two similar terms. Sometimes, both these terms are used interchangeably. Virulence refers mainly to the disease-producing power of a pathogen while pathogenicity is the ability of an organism to cause diseases. Overall both terms explain the potential ability to cause diseases. Moreover, pathogenicity depends on virulence factors such as enzymes, toxins, pili, fimbriae, flagella, etc. Thus, this is a summary of the difference between virulence and pathogenicity.

Reference:

1. “Virulence.” Wikipedia, Wikimedia Foundation, 11 Mar. 2019, Available here.
2. “Pathogenicity. ” ScienceDirect, Available here.

Image Courtesy:

1. “H pylori virulence factors en” By user:Y_tambe – Y_tambe’s file (CC BY-SA 3.0) via Commons Wikimedia
2. “yersinia pestis, pathogenic, bacteria” (CC0) via Pixino