Pathogens are disease-causing agents; they can be bacteria, viruses, or protozoa, among other things. In order for a pathogen to survive and reproduce, it needs two things: a vector and a host.
“Vector” is a noun that refers to any organism that carries a pathogen and is capable of transmitting it to other organisms. That’s pretty simple. However, “vector” is also used as a verb, meaning “to transmit.” So the dual uses of the term might be a little confusing at times.
Arthropods including mosquitoes, biting flies, lice, fleas, ticks, and mites are common pathogen vectors. In animal systems, vectors are often hematophagous, meaning that they feed on blood. The organism contributing the blood is called a host.
Here’s a simple description of what happens when a blood-feeding insect acquires a microscopic pathogen and vectors it to a host:
The vector, we’ll say mosquito in this case, is initially pathogen-free. But then it bites a host, let’s say a horse, which is carrying a virus in its bloodstream. When the mosquito feeds, the blood entering the mosquito’s digestive system contains some virus particles. Assuming that the virus can survive the mosquito’s internal environment, it may replicate itself over and over to the point where virus particles circulate throughout the mosquito’s body, including its salivary glands.
Now, let’s assume that the process we just described has already happened. When the newly infected mosquito bites a pathogen-free host, we’ll say another horse, the mosquito injects saliva into the bite wound as part of the feeding process. Virus particles are likely to be present in the saliva, and if any of them enter the bloodstream and survive the horse’s internal environment, they may reproduce and cause the horse to fall ill.
(In case you’re wondering, mosquitoes do not seem to benefit from vectoring pathogens, and they behave the same way regardless of whether they are carrying pathogens or not.)
Diseases that are transmitted in this way are called vector-borne diseases. Vector-borne diseases make up more than 17% of all infectious diseases and cause more than 1 million deaths every year. Examples include malaria, schistosomiasis, Chagas disease, yellow fever and dengue. Factors such as globalization, increased travel and climate change can impact disease transmission and cause diseases to appear in places they’ve never been reported before.
To help combat vector-borne diseases, the Florida Medical Entomological Laboratory (FMEL) in Vero Beach is dedicated to conducting research on organisms that vector diseases, such as the Asian Tiger Mosquito (Aedes albopictus), an invasive species, which has spread rapidly in Florida since its initial appearance in the 1980s. FMEL scientists also work hard to spread knowledge and awareness of these diseases to people and communities so that they know how to protect themselves from mosquitoes, ticks, flies, and other vectors. For more information about mosquito research at UF/IFAS, check out the Mosquito Information Website at http://mosquito.ifas.ufl.edu/.
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UF/IFAS Photo by Jim Newman