Difference Between Vector and Carrier

Main Difference – Vector vs Carrier

Vector and carrier are two types of agents involved in the transmission of diseases between organisms. The main difference between vector and carrier is that a vector does not show any symptoms of the disease whereas a carrier is an infected organism capable of transmitting the disease-causing microorganisms to a healthy individual. Anopheles mosquito that carries malaria parasites between humans is an example of a vector. A human with HIV, who can transmit the virus to another healthy individual is an example of a carrier. Carriers also transmit genetic diseases such as hemophilia, cystic fibrosis, and sickle cell anemia. However, the carriers of the genetic diseases do not show any symptoms of the disease.

Key Areas Covered

1. What is a Vector
– Definition, Facts, Types, Examples
2. What is a Carrier
– Definition, Facts, Types, Examples
3. What are the Similarities Between Vector and Carrier
– Outline of Common Features
4. What is the Difference Between Vector and Carrier
– Comparison of Key Differences

Key Terms: Asymptomatic Carrier, Biological Transmission, Genetic Carrier, Mechanical Transmission, Microorganisms, Symptomatic Carrier, Vector

What is a Vector

Vector refers to an organism that spreads diseases by conveying pathogens from the host to another individual but without causing diseases by itself. Typically, vectors are blood feeding (haematophagous) arthropods such as mosquitoes, sandflies or ticks. Malaria, dengue fever, leishmaniasis, and West Nile virus are some examples of vector-borne diseases. The transmission of Flavivirus genus through a mosquito vector is shown in figure 1.

Figure 1: Transmission of Flavivirus Genus through a Mosquito Vector

The disease can be transmitted through a vector either mechanically or biologically.

Mechanical Transmission

Mechanical transmission takes place when the pathogen does not develop or replicate in or on the vector. Thus, only the transport of the pathogen occurs during the mechanical transmission. Insects such as flies are types of vectors involved in the mechanical transmission of diseases.

Biological Transmission

Biological transmission occurs when the pathogen completes a part of its life cycle inside the vector. Thus, the vector serves as the intermediate host of the pathogen. The vector can be fleas, ticks or mosquitoes that inject the pathogen into or onto another host during their blood meal. The transmission of the disease is characterized by abundance and spatial spread of hosts and the vector, demography, and feeding rate of the vector.

What is a Carrier

Carrier refers to an organism that harbors a specific infectious agent in the absence of discernible clinical disease and serves as a potential source of infection. A carrier can be divided into three categories based on the type of disease they carry and symptoms they display: asymptomatic carrier, genetic carrier, and symptomatic carrier.

Asymptomatic Carrier

Asymptomatic carrier refers to an organism infected with an infectious disease but, displays no symptoms. Typhoid fever, HIV, Epstein-Barr virus (EBV), Clostridium difficile infection, Chlamydia infection, and poliomyelitis are some of the diseases that do not show any symptoms in the carrier.

Genetic Carrier

Genetic carrier refers to an individual who has inherited a mutated genetic trait of a disease but, shows no symptoms. Hemophilia is an example of a genetic disease located on the X-linked recessive gene. It does not show any symptoms in the carrier. Cystic fibrosis and sickle cell anemia are such diseases that do not show symptoms in the carrier. The inheritance of an X-linked recessive defective gene is shown in figure 2.

Figure 2: X-Linked Recessive Inheritance

Symptomatic Carrier

Symptomatic carrier refers to an organism that carries the disease while showing the symptoms of the disease. Hemophilia carriers with gene mutations in the factor VIII or IX are typically known as obligate carriers since they do not show any symptoms of the disease. However, some females who carry hemophilia gene may show problems with bleeding. They are considered as symptomatic carriers.

Similarities Between Vector and Carrier

Vector and carrier are two types of agents that transmit diseases between organisms.
Both vector and carrier transmit disease-causing microorganisms.
Both vector and carrier are involved in the biological mechanical transfer of diseases.
Disease-causing microorganisms may live on or in the body of both vector and carrier.

Definition

Vector: Vector refers to an organism that spreads diseases by conveying pathogens from the host to another individual, but without causing diseases by itself.

Carrier: Carrier refers to an organism that harbors a specific infectious agent in the absence of discernible clinical disease and serves as a potential source of infection.

Symptoms of the Disease

Vector: Vector does not show any symptoms of the disease.

Carrier: Generally, carrier shows the symptoms of the disease as it is also an infected organism.

Genetic Diseases

Vector: Vectors generally do not transmit genetic diseases.

Carrier: Carrier also transmit genetic diseases.

Examples

Vector: Anopheles mosquito that carries malaria parasites between humans is an example of a vector.

Carrier: A human with HIV, who can transmit the virus to another healthy individual is an example of a carrier.

Conclusion

Vector and carrier are two types of agents involved in the transmission of diseases from one individual to another. Generally, a vector does not show the symptoms of the disease. Some disease-causing organisms complete their life cycle within the vector. The main difference between vector and carrier is the appearance of the symptoms of the diseases in each type of transmitting agent.

Reference:

1. “Warwick Infectious Disease Epidemiology Research.” Vector, Available here.
2.“What are Symptomatic Carriers?” The Hemophilia, von Willebrand Disease & Platelet Disorders Handbook, Available here.
3. “Disease carrier.” Wikipedia, Wikimedia Foundation, 26 Jan. 2018, Available here.

Image Courtesy:

1. “Disease Vector” By Kwasnyje – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “X-linked recessive” By XlinkRecessive.jpg: National Institutes of Healthderivative work: Drsrisenthil – XlinkRecessive.jpg, Public Domain) via Commons Wikimedia