What is the Difference Between Pathogenicity and Virulence

The main difference between pathogenicity and virulence is that pathogenicity is the ability of a pathogen to cause disease, whereas virulence is the ability of a pathogen or microbe to infect or damage a host. Furthermore, pathogenicity is determined by virulence factors.  

Pathogenicity and virulence are two types of host-pathogen interactions found in a type of symbiotic relationship called parasitism. Generally, a pathogen is an infectious agent or simply, a germ that can produce disease. 

Key Areas Covered 

1. What is Pathogenicity
     – Definition, Features, Importance
2. What is Virulence
     – Definition, Features, Importance
3. What are the Similarities Between Pathogenicity and Virulence
     – Outline of Common Features
4. What is the Difference Between Pathogenicity and Virulence
     – Comparison of Key Differences

Key Terms 

Disease, Pathogen, Pathogenicity, Virulence, Virulence Factors

What is Pathogenicity 

Pathogenicity is the potential of a pathogen to cause disease. Generally, a pathogen is a disease-causing agent. Here, they can be either microorganism such as protozoans, fungi, bacteria, virus, viroid or prion. Or, pathogens can be small animals such as worms and larval insects. However, commensals or opportunistic pathogens are unable to cause diseases.

Figure 1: Adhesion

On the other hand, there are two related concepts of pathogenicity. They are transmission and virulence. Basically, the transmission is the entering of the pathogen through different routes such as airborne, direct, indirect, and sexual contact, through the blood, body fluids, and breast milk, and through the faecal-oral route. Also, there are two types of transmission; vertical transmission and horizontal transmission. Normally, vertical transmission tends to evolve symbiosis while horizontal transmission occurs between hosts of the same species. Meanwhile, virulence is the tendency of a pathogen to cause damage to the host’s fitness is related to pathogenicity. Typically, it occurs when the pathogen spread in the host. 

What is Virulence 

Virulence is the ability of the pathogen to infect or damage a host. Especially, in animals, it can be identified as the degree of damage caused by a microbe to its host. As described above, virulence occurs while spreading pathogens in their hosts. Especially, virulence is related to the pathogenicity as virulence factors are the major determinants of pathogenicity. In bacteria, virulence factors include proteins and other molecules.

Figure 2: Colonization

Moreover, the virulence bacteria cause diseases in a mechanism, which composes of five steps. They are adhesion, colonization, invasion, immune response inhibitors, and toxins. Significantly, adhesion is the first step in causing diseases. During adhesion, bacteria bind to the surface of the host cell. Then, they undergo multiplication in order to form colonies.

Figure 3: Invasion

After that, these virulence bacteria invade host cells by disrupting host cell membranes. In the meanwhile, most of the bacteria produce immune response inhibitors, which inhibit the defense mechanisms of the host immune system. Also, the proteins made by these bacteria serve as toxins, which cause tissue damages. For instance, both immune response inhibitors and toxins are virulence factors. 

Similarities Between Pathogenicity and Virulence  

• Pathogenicity and virulence are two types of interactions, which occur between host and pathogens.  
• Generally,  pathogens are infectious agents that can infect and produce diseases in the host. 

Difference Between Pathogenicity and Virulence 

Definition 

Pathogenicity refers to the absolute ability of an infectious agent to cause disease in a host, while virulence refers to the ability of the pathogen to infect or damage the host. 

Correspondence 

Pathogenicity follows virulence, while virulence is in the initial stage of host-pathogen interactions. 

Significance

Virulence factors determine pathogenicity, while virulence factors are proteins or other molecules. 

Properties 

Pathogenicity is a qualitative term, while virulence is a quantitative term. 

Conclusion 

Pathogenicity is the ability of a pathogen to cause disease. Also, it is determined by the virulence factors of the pathogen. Thereby, commensals or opportunistic pathogens do not show pathogenicity. In comparison, virulence is the ability of a microbe to infect or damage to the host. However, these infected pathogens should have virulence factors in order to become pathogenic. Therefore, virulence is the initial stage of pathogenicity of pathogenic organisms. Hence, the main difference between pathogenicity and virulence is their features and correspondence.  

References:

1. “Pathogenicity vs. Virulence.” Tulance.edu, Available Here.

Image Courtesy:

1. “Adhesion virulence bacteria” By Christopherjackson1053 – Own work (CC BY-SA 4.0) via Commons Wikimedia   
2. “Colonization virulence bacteria” By Christopherjackson1053 – Own work (CC BY-SA 4.0) via Commons Wikimedia   
3. “Invasion virulence bacteria” By Christopherjackson1053 – Own work (CC BY-SA 4.0) via Commons Wikimedia