A Brief Discussion concerning Insect Vectors

Disease vectors are organisms capable of transmitting pathogens, be they viruses, bacteria, or parasites, from one host to another; for the purposes at hand, from animals to humans.1 The most common sort of vector in the world are hematophagous insects, many of which are Dipterans in the Culicidae family. However, there are plenty of other hematophagous Dipterans, including members of the families Simuliidae, Psychodidae, Glossinidae. This is not to speak of other insect groups who habitually take blood meals, which notably includes lice (Order Psocodea), fleas (Order Siphonaptera), and certain individuals within the Hemipteran family Reduviidae. Of these groups, the Culicids are generally the greatest threat, not the least due to the fact that some subspecies have developed a particular taste for human blood in particular. Every year, these vectorially-transmitted pathogens afflict hundreds of millions of humans, and wind up killing close to one million. Consequently, knowledge of insect vectors is considered to be of crucial importance for the sake of human health, with the study primarily concerning itself not just with what these insects do, but what preventative measures can be taken to keep people safer.  

Starting off with the Reduviids, the primary disease vectors within belong to the subfamily Triatominae, a group that seems to have largely developed a taste for blood as opposed to the meals typical of its family.2 They are primarily restricted to the tropics of the Americas, Asia, Africa, and Australia. Like most hematophagous insects, these “kissing bugs” (so called due to their habit of feeding on the face of their human victims) make use of blood meals for nutrition, both for themselves, and, in the case of mating adults, their offspring. However, when this is done, many wind up being responsible for the transmission of the parasite Trypanosoma cruzi, the cause of Chagas disease.

https://www.verywellhealth.com/chagas-disease-overview-4109239

 

This is often acquired by the nymphs or adults during their contact with various animals, which the parasite circulates among during the first few stages of its life. Siphonapterans, the fleas, scarcely need an introduction as vectors given their historical responsibility for spreading the Bubonic Plague. The “Plague,” as it is often known, is caused by a parasite known as Yersinia pestis, which primarily dwells among rodents. Humans generally receive the parasite from these infected rodents rather than the fleas themselves, who primarily function to spread it to and among the rodents, and cases to this day have a sixty-percent chance of proving fatal. Of more immediate concern to people are the Psocodeans, the lice, specifically those specially adapted for living off humans. These lice are capable of spreading the bacteria Rickettsia prowazeki, which is responsible for typhus. Because R. prowaseki is a human-dependent bacteria, lice acquire it from already infected humans before transmitting it to others.  

Of course, the Dipterans are the by far the most significant vectors of disease. The Glossinids, known as tsetse flies, transmit the parasite Trypanosoma, which is responsible for “sleeping sickness.” Black flies, members of the family Simuliidae, may pick up the parasite Onchocerca volvulus from infected humans, which gestate for almost two weeks before getting passed to the fly’s next victim. The parasite causes filariasis, which can in turn result in nonfatal blinding of the victims. Pyschodids, sometimes known as sandflies (although the name also applies to numerous other Dipterans), are vectors of the Leishmania parasite, as well as over two dozen viruses that are responsible for “sandfly fevers.” Nonetheless, the Dipterans that pose the greatest threat to humans are members of the family Culicidae, the mosquitoes. There are three specific genera of mosquitoes that are considered particular threats to humans: Aedes, Anopheles, and Culex. For the most part, mosquitoes serve as the vectors of various parasites and viruses, the latter of which are referred to as “arboviruses” (arthropod-borne-viruses). Famous examples of these arboviruses include Yellow Fever (responsible for 30,000 deaths per year), the dengue virus (which kills about 12,500 people yearly) and West Nile Virus, although there are countless others. All three of the threatening mosquito genera are capable of spreading the parasite Wuchereria bancrofti, which causes Lymphatic Filariasis. It is one of the most common arthropod-borne diseases in the world, infecting over one hundred million people yearly. Of course, the deadliest – and consequently, most well-known – mosquito-borne disease is Malaria, which is caused by the parasite Plasmodium.

https://en.wikipedia.org/wiki/Plasmodium_falciparum

The parasite is transmitted exclusively by the genus Anopheles, which, like most vectors, acquires the parasite through taking blood meals from infected hosts. There are over two hundred million cases of malaria every year, which historically kills close to one million people per year, although that number has been declining over the past two decades.3 Despite its declining numbers, malaria still contributes about 57% of all deaths caused by arthropod-borne diseases. 

Bibliography: 

1. WHO. (2020, March 2). Vector-borne diseases. Who.int; World Health Organization: WHO. https://www.who.int/news-room/fact-sheets/detail/vector-borne-diseases  

2. Manguin, Sylvie & Mouchet, Jean & Carnevale, Pierre. (2011). Main Topics in Entomology: Insects as Disease Vectors. RSC Green Chemistry. https://www.researchgate.net/publication/280638351_Main_Topics_in_Entomology_Insects_as_Disease_Vectors  

3. https://cdn.who.int/media/docs/default-source/malaria/world-malaria-reports/world-malaria-report-2020-briefing-kit-eng.pdf?sfvrsn=eda98467_18&download=true