The terms vector and vector-borne disease
The subject of the book Vectors and Vector-Borne Pathogens is not only both vectors and pathogens that can be found in them but also the diseases that they can cause in animals or humans.
Vector is an invertebrate animal (most usually an arthropod) that transmits infectious agents to vertebrates. In infectious disease epidemiology, vector is an insect or any living carrier that transports an infectious agent from an infected individual, or its wastes to a susceptible individual or its food or immediate surroundings [1]. In short, it is an organism that transmits a pathogen from one host to another.
Vector-borne disease can be transmitted differently:
1. Mechanical way of pathogen transmission—includes just mechanical transmission of the pathogen by a crawling or flying insects, on their legs, feet or wings, or proboscis, or by passage of the pathogens through their gastrointestinal tract. There is no multiplication or development of the pathogen within the mechanical vector, so no port of the pathogens life cycle occurs in the mechanical vector.
2. Biological way of pathogen transmission—involves part of the pathogens life cycle to occur within the vector: propagation (multiplication), stage development, or some combination of them is needed to occur in the vector, before it can transmit the infective form of the pathogen to the host (an animal or human). The incubation period is therefore needed after the infection so that this process can occur, before the vector becomes infectious and is able to transmit the infection. The pathogen within the vector can also be transmitted vertically to the next generation of the vector (transovarian transmission). Also, a trans-stadial transmission can occur, meaning that the pathogen can be transmitted from one stage of the life cycle to another, like for example, from the nymph to the adult.
When the pathogen is “ready” within the vector, the transmission of the pathogen from vector to host can be done in different ways. The pathogen can be injected from a salivary gland with the fluid during the blood meal of the vector. Or, it can be transmitted by the regurgitation process, or deposition on the skin of feces or other material that can penetrate through a bite wound or an area of traumatized skin from scratching or rubbing [1]. Transmission like this usually occurs by an infected non-vertebrate host and it is not a simple mechanical carriage by a vector. Whichever role the arthropod takes, it is labeled as a vector.In order to transmit the disease, a vector has to be competent for it. Vector competence is the ability of a vector to acquire, maintain, and transmit microbial agents. Not all blood-sucking arthropods are vectors (transmitters) of disease agents [1].
One same vector-borne disease can be seen as a neglected or endemic one, or an emerging or a reemerging one. It all depends on the geographic appearance of the disease (country or a region) and the relation of the countries public health toward that disease.
Neglected diseases are the ones that there is at least an evidence of the pathogen present in the environment, but there is no official acknowledgment of the threat from the disease. On the other hand, once the pathogen is in the environment, with appropriate vectors, hosts, and climatic conditions, the disease can develop to its full capacity causing clinical symptoms in animals and humans and then the disease becomes endemic for a certain region/country. Endemic diseases are maintained in a population without the need of external outputs. Emerging disease is either a newly recognized, clinically distinct disease or a known infectious disease whose reported incidence is increasing in a given place or among a specific population. They are rapidly increasing in incidence or geographic range.
4.