Tuesday, 7 February 2017

Reduviid Bug – The Bug That Transmits American Trypanosomiasis

In his Voyages of the Adventure and Beagle Volume III, Charles Darwin wrote “We slept in the village, which is a small place surrounded by gardens, and forms the most southern part, that is cultivated, of the province of Mendoza [Argentina]; it is five leagues south of the capital. At night I experienced an attack (for it deserves no less a name) of the Benchuca (a species of Reduvius) the great black bug of the Pampas. It is most disgusting to feel soft wingless insects, about an inch long, crawling over one's body. Before sucking they are quite thin, but afterwards become round and bloated with blood, and in this state they are easily crushed.”

Rhodnius prolixus is one of the species of kissing bugs that transmits
Chagas disease. It’s an elegant bug that almost looks carved.
Image by Dr. Erwin Heubner, University of Manitoba

Darwin’s attacker was a kissing bug, an insect of many names, that lives close to people in Central and South America and sucks their blood. It transmits Chagas disease (American trypanosomiasis) in the process.

What Is a Kissing Bug?

I’ve met kissing bugs myself, but I didn’t have to endure them crawling over me or feeding on me. I was fortunate enough to visit the London School of Hygiene & Tropical Medicine when it was feeding time in the kissing bug colony. They were well aware that there were people about and they rushed to the top of their glass enclosure, driving their proboscises up through a membrane in a quest for human blood. They are large, impressive, and not altogether unattractive bugs.

Kissing bugs, classified among the reduviid bugs, are also known by many other names, including triatomid bugs, conenose bugs, the benchuca, and assassin bugs (although the name “assassin bug” more specifically refers to reduviids that do not bite humans). Whatever you choose to call it, however, this bug is a serious pest.

Kissing Bugs and Parasites

The kissing bug is so called because of its habit of biting humans on the lips, usually while the victim is sleeping. When the bug bites, it also defecates on the skin – it is the bug’s feces, rather than its saliva that contain the parasite Trypanosoma cruzi, agent of Chagas disease (American sleeping sickness). Like many insect bites, the bite of the triatomid bug itches, and the victim soon scratches, rubbing bug feces and parasites into the wound.

A map of Central and South America showing areas where
Chagas disease is endemic. Image by Tomatoo356 CC BY-SA 3.0

Where Kissing Bugs Live

Conenose bugs live in or near dwellings, particularly in thatched roofs, dirt floors, and walls with many cracks and crevices. They may also be found in considerable numbers in wood piles and tiled roofs, and increase in number with higher densities of people. In addition to biting humans, triatomid bugs also feed on animals and transmit T. cruzi to them as well. Thus, animals such as cats, dogs, and rats are important reservoirs of the infection in areas where Chagas disease occurs.

Triatomid bugs aren’t confined to Central and South America, though that’s where they’ve caused the most trouble. Both the bug and the parasite are found in the United States; however, relatively few cases of trypanosomiasis originate there. This may be due to differences in bug species and parasite strains, but it likely has as much to do with the standard of living, and a lower level of contact between people and animal reservoirs of the disease.   

Raising public awareness and spraying for kissing
 bugs has helped reduce the number of people
 infected with Trypanosoma cruzi. Image by Palp
 CC BY-SA 3.0


Why would a laboratory keep a colony of kissing bugs? For educational and research purposes, of course, but also sometimes to aid in diagnosis of Chagas disease.

Trypanosoma cruzi parasites may be almost impossible to detect in the blood of an infected person due to low numbers, so the technique of xenodiagnosis is sometimes used. In xenodiagnosis, lab- reared triatomid bugs that are free of the parasite are deliberately allowed to feed on a patient who is thought to be infected. After a suitable time lapse, the feces of the bugs are checked for parasites: the presence of parasites in the bugs confirms infection in the patient.

This is a clever and sensitive way of diagnosing the infection, though most people would rather have a needle or syringe draw their blood than a big bug with a long proboscis!

Further reading about Chagas disease

Charles Darwin. 1839. Voyages of the Adventure and Beagle, Volume III. London: Henry Colburn.  

CDC. American Trypanosomiasis (also known as Chagas Disease). Accessed April 10, 2017; Lat Updated May 24, 2016.

Schmidt, Gerald D. and Larry S. Roberts. Foundations of Parasitology 8th Ed. Boston: McGraw Hill, 2009.