Vectors

 

Vectors

Definition of Vector

A vector is an organism that transmits pathogens or parasites from one host to another. Vectors play a crucial role in the spread of infectious diseases, often carrying viruses, bacteria, protozoa, or helminthes. Most vectors are arthropods, such as mosquitoes, ticks, and flies, which either mechanically or biologically transfer pathogens.

Types of Vectors

Vectors are broadly classified into two main types based on the mode of pathogen transmission:

1. Mechanical Vectors

• Carry pathogens passively without any biological development or multiplication of the pathogen inside their body.
• Pathogens are transported on the vector’s body surface or through contaminated mouthparts.
• These vectors do not serve as hosts but act as a mode of transmission.

Examples:

• Houseflies (Musca domestica) – Transmit bacteria like Salmonella and E. coli by contaminating food.
• Cockroaches (Periplaneta americana) – Carry intestinal pathogens on their legs and body surface.

2. Biological Vectors

• In these vectors, the pathogen undergoes development, multiplication, or both before being transmitted to the host.
• The vector serves as an intermediate or definitive host for the pathogen.
• Transmission can occur through bites, feces, or bodily fluids.

Types of Biological Transmission:

1. Propagative Transmission: The pathogen multiplies within the vector but does not change in form.
• Example: Plague bacteria (Yersinia pestis) multiply in flea guts.
2. Cyclopropagative Transmission: The pathogen multiplies and undergoes developmental changes within the vector.
• Example: Malaria parasite (Plasmodium spp.) in Anopheles mosquitoes.
3. Cyclodevelopmental Transmission: The pathogen undergoes developmental changes but does not multiply inside the vector.
• Example: Filarial worms (Wuchereria bancrofti) in Culex mosquitoes.

Transmission of Vectors

Vectors transmit diseases through different mechanisms:

1. Direct Transmission

• The vector directly introduces the pathogen into the host’s body.
• Example: Mosquito bites introduce Plasmodium into the human bloodstream, causing malaria.

2. Indirect Transmission

• The pathogen is deposited on food, water, or surfaces and later ingested or contacted by the host.
• Example: Flies carrying Salmonella deposit bacteria on food, leading to food poisoning.

3. Transovarial Transmission

• The pathogen is passed from the mother vector to its offspring through eggs.
• Example: Ticks transmit Rickettsia bacteria causing Rocky Mountain spotted fever.

4. Transstadial Transmission

• The pathogen remains within the vector through different life stages.
• Example: Lyme disease bacteria (Borrelia burgdorferi) persist in ticks from larvae to adults.

Vectors play a vital role in disease transmission, influencing public health and epidemiology. Understanding their types and transmission mechanisms helps in designing effective disease control strategies, such as vector management and vaccination programs.