Vector-borne diseases: directions in transmission

Pathogens, including viruses and bacteria, have one primary goal: reproduction. Transmission is the movement of a pathogen from one host to the next. Infectious pathogens that cause disease have evolved to enhance the likelihood of transmission so that they can infect more hosts.

For example, influenza virus and the measles virus are both highly contagious (highly virulent) pathogens because they can infect many hosts by traveling through the air (airborne transmission). Other microbes, like the pathogenic strain of Escherichia coli, are passed from the gut into animal (or human) feces which can contaminate water, soil, and food. When contaminated food is eaten, the E. coli is passed by fecal-oral transmission.

Infectious pathogens have also found a way to transmit through disease vectors. These are typically organisms that act as an intermediate carrier that can pass a virus, bacteria, or parasite onto new hosts. Arthropods make up the most common disease vectors: mosquitoes, ticks, flies, mites, etc. The World Health Organization states that vector-borne diseases make up about 17% of all infectious disease worldwide.

Vector-borne diseases are transmitted when an insect takes a blood meal from a host. For example, when a mosquito feeds on a person infected with dengue virus, the viral particles mix with the mosquito’s saliva. Then during the next blood meal, the infectious agent is passed through the saliva from the insect vector into a new host.

Since arthropods are cold blooded, they thrive well in warmer climates. Therefore, most vector-borne illnesses put a heavy burden on tropical and subtropical geographic regions. Additionally, the economic status of the countries in these regions limit resources to control vector populations, allowing the disease-causing insects to spread. As effects from climate change continue across the globe, rising temperatures in northern countries allow for disease vectors to migrate and survive during the warmer seasons. Amblyomma americanum, commonly known as the Lone Star tick, is a vector for several diseases and can also cause a red meat allergy in hosts. Native to the Southeast United States, it has been identified recently in more Northern states, with related cases of red meat allergies rising.

Researchers have the opportunity to research many different aspects of vector-borne diseases to further understand why certain pathogens are only carried by certain vectors, the mechanism of transmission during a blood meal, transmission control methods, and vaccine strategies. This knowledge will help prevent transmission of potentially harmful diseases and improve quality of life in regions most affected by insect vectors.

Featured image credit: Centers for Disease Control

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