Bugs That Are Bugging Us: Vector-borne Diseases
“Small bite: big threat."
- World Health Organization slogan, World Health Day 2014
“Bugs never bug my head. They are amazing. It is the activities of humans which actually bug me all the time.”
- Munia Khan, poet and author
Most of us use the word “bug” loosely to describe any very small creature with legs including insects. Whereas all bugs are insects, not all insects are bugs. But some bugs, like some insects, are vectors that transmit pathogens that cause many diseases in humans. In this week’s Germ Gems post, you’ll learn about a bug you don’t need to worry as a vector—bed bugs—and two that you do—fleas and sand flies.
Science class refresher. In your high school biology class, you probably learned a little taxonomy—the science of naming, describing and classifying organisms according to their Domain, Kingdom, Phylum, Class, Order, Family, Genus and Species. (Perhaps you remember the classification system by using what is often cited as a “non-vulgar” mnemonic: “Dear King Philip Came Over For Good Soup.”) Here is a brief refresher about the classes and orders of bugs.
All insects are found under the class Insecta. Creatures belonging to the class Insecta always have three-part bodies, usually two pairs of wings, and three pairs of legs. Bugs are a type of insect and members of the class Insecta but belong to the order Hemiptera. Members of this order are called “true bugs” and share two main traits: forewings and piercing-sucking mouthparts.
Bed bugs. Bed bugs are “true bugs.” They belong to the family Cimicidae of the insect order Hemiptera. As is true for all “true bugs,” bed bugs suck. They have a specialized body part called a proboscis that works like a straw in their mouth to suck juices, mostly from plants but also from the blood of animals they bite like us.
If you’re planning a trip to Paris, you may recently have seen an article like this in Morning Brew on October 13th, “Have bedbugs taken over Paris? The City of Love is really stressing out over the tiny bloodsuckers.” If so, you may have wondered whether bed bugs could transmit dangerous microbes by their bite rather than just “bugging ” (annoying) you.
Bed bugs don’t deposit any pathogens while biting you. They just look disgusting, can cause a rash and/or itching, are difficult to control, and seem to thrive in many cities. (According to the article “Bed bugs are all over New York City, according to a recent study. Here’s how to spot them,” published on January 29, 2023 in silive.com. At the time, Chicago ranked number one in America for bed bug infestations followed closely by New York City.)
Vector-borne pathogens. By definition, “vectors” are living organisms that can transmit infectious pathogens between humans, or from animals to humans. Many of these vectors are bloodsucking insects like mosquitoes or blood sucking arthropods like ticks. (Arthropoda is a separate phylum.)
According to the World Health Organization (WHO), vector-borne diseases account for more than 17% of all infectious diseases and cause more than 700,000 deaths annually. You can find a complete listing of vectors, vector-borne pathogens, and the diseases they cause in the March 2020 WHO article, “Vector-borne diseases.”
Flies and ants are bugs that are infamous for carrying bacteria. They regularly contaminate food with harmful bacteria such as E. coli, Salmonella, and Shigella, that they transfer to food from animal feces.
Murine typhus and leishmaniasis are two vector-borne diseases that, until recently, were rarely seen in the U.S. but are now on the rise. Murine typhus is a flea-borne zoonotic infection caused by the bacterium Rickettsia typhus. Signs and symptoms of flea-borne typhus include fever and chills, nausea and vomiting, loss of appetite, and rash. Three people living in Los Angeles County recently died from the disease.
Cutaneous (skin) leishmaniasis is a parasitic infection transmitted by sand flies. Signs and symptoms of the infection include skin lesions leading to open sores and swollen lymph glands. In the U.S., most reported cases are from southern and southwestern states. Until now, leishmaniasis has been a big problem in many tropical countries but not here. As National Institutes of Health staff scientist Dr. Luiz Oliveira recently stated, “It’s not just a traveler’s disease anymore.”
Why are vector-borne diseases mounting? As a consequence of global warming, the breeding season of many bugs, insects, and arthropods is expanding as is their geographic range. And so are the vector-borne diseases they cause. (See“Climate Change and Vectorborne Diseases,” New England Journal of Medicine, November 2022.)
Fortunately, the WHO and the Centers for Disease Control and Prevention are addressing the challenges of climate change and vector-borne diseases (See, September 2020, “A National Public Health Framework for the Prevention and Control of Vector-Borne Diseases in Humans.”). Let’s hope their efforts are successful. If we can’t stop global warming, we can be sure that the vectors and pathogens they carry will increasingly “bug” humans—possibly to death. (Over one million people worldwide now die from mosquito-borne diseases every year.)