What are common vector-borne diseases, and how do they commonly spread among vertebrate hosts?

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Let’s begin with a definition of “vectors.”  Vectors carry pathogens from one host to another.  Vectors are frequently invertebrate animals, typically arthropods.  (Arthropods have an exoskeleton, segmented bodies, and jointed appendages).  It should be noted, however, that vertebrates can also act as vectors. Common vertebrate vectors include foxes, raccoons, and skunks. These mammals can transmit rabies, but the majority of disease-causing organisms are arthropods (85%).  Arthropods spread their diseases primarily via stings and bites, and also by infestation of tissues, and through indirect disease transmission.  Mosquitos and ticks, blood-feeding arthropods, are the main culprits here; mosquitos can be vectors of malaria, and ticks can be vectors of lyme disease. Other vectors spread disease by literally carrying pathogens on their bodies from place to place.

Human acquisition of vector-borne diseases go through a three stages:  the presence of the pathologic agent which attaches itself to the arthropod vector, which then finds a human host.

Vertebrate hosts are the way in which most vector-borne diseases promulgate in nature; these hosts are called “zoonoses.”  (Humans, however, are the major hosts for diseases like dengue fever and malaria).  Animal hosts are often intermediaries; the animals serve as a reservoir until the vector can transfer to susceptible humans. How long a pathogen survives is completely dependent on the availability and suitability of hosts, whether that host is intermediary or attaches directly to the human host.  Environmental factors, especially temperature and humidity, also affect how successful a pathogen can become.  The human host’s own immune system, its strength or weakness, also plays a role in a pathogen’s success or failure.

Because of the pathogen’s dependency on temperature and humidity, vector-borne diseases are most common in the tropic and subtropics.  However, some colder climates are...

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Vector borne diseases are illnesses caused by an infectious microbe that is transmitted to vertebrates by another animal, usually an arthropod. This second animal is called a vector for the disease. There are a large number of viral, bacterial and parasitic diseases that can be transmitted by insect vectors. The most common vectors are blood sucking insects such as mosquitoes, fleas, lice, biting flies, bugs, lice, helminthes and ticks.

Most common vector borne diseases affecting people and their vectors are: malaria -anopheles mosquitoes, dengue and chikungunya- aedis mosquitoes, Leishmaniasis - sandflies, trypanosomiasis - flies and bugs, West Nile disease – mosquitoes, filariasis - mosquitoes, encephalitis - mosquitoes and ticks, yellow fever - mosquito, plague - flies, lyme disease - ticks etc.

Vector borne diseases often cause serious illnesses to other vertebrates like livestock. Lyme and bluetongue  (spread by mosquitoes and ticks) are examples of devastating vector borne diseases that create havoc among the livestock population worldwide.

"Vectors typically become infected by a disease agent while feeding on infected vertebrates (like birds, rodents, other larger animals, or humans)." The disease agent usually completes a part of their lifecycle (and multiply) inside the host, and then get transmitted to a susceptible person or other animal through the salivary glands of the vector when it bites another vertebrate.

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