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

Xenodiagnosis

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 8^th Ed. Boston: McGraw Hill, 2009.

Is Your Cat Causing Your PMS? Actually, No

Late January 2017 brings a flurry of online articles about cats and premenstrual syndrome (PMS). Cats, it seems, cause PMS, or severe PMS, or a cat parasite causes PMS, or a cat parasite makes PMS worse, or women infected with the parasite are more likely to have PMS. Once again, cat owners are looking askance at their furry friends and wondering if it’s time to switch to a goldfish.

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All this results from an article published in the Journal of Clinical Medical Research in October 2016 (online August 30, 2016): “Toxoplasma gondii Infection and Premenstrual Dysphoric Disorder: A Cross Sectional Study.” The authors of the study conclude that infection with the parasite might be associated with more severe symptoms of premenstrual dysphoric disorder, and that further research would help confirm or disprove the link. Do they think cats cause PMS? No.

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PMS Is Not the Same Thing as Premenstrual Dysphoric Disorder

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According to the Mayo Clinic, 75% of menstruating women experience PMS to some degree.  It brings both physical and emotional symptoms ranging from fatigue to depression. This is not premenstrual dysphoric disorder, and it isn’t the group that the researchers studied. They report that only 1.3% to 8% of women experience premenstrual dysphoric disorder, a severe form of PMS, which has serious psychological symptoms. Thus, the study had nothing to say about the PMS that the majority of women experience, and did not link PMS to Toxoplasma gondii (or cats!).

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Are Women Infected with Toxoplasma gondii More Likely to Have PMS?

Toxoplasma gondii forms microscopic cysts
 in the tissues of cats, humans, and other hosts

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The study didn't address this question; however, in this study group, the reverse appears to be true for premenstrual dysphoric disorder. The authors report that 10 out of the 151 women subjects tested positive for either antibodies to the parasite, or the parasite itself. That's 6.6%

​The prevalence of infection in humans varies widely from country to country, however in Mexico, where this study was done, 15% to 50% of the general population tests positive, depending on the region. There’s no evidence here that infection causes premenstrual dysphoric disorder.

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Does Toxoplasmosis Make Premenstrual Dysphoric Disorder Worse?

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The researchers looked at 59 distinct signs and symptoms experienced by women suffering from premenstrual dysphoric disorder. Their results suggested that the parasite might make two of them worse: feeling overwhelmed, and feeling out of control.

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These results are preliminary at best. The sample size of 151 women was small, and there was low prevalence of T. gondii infection in the group. It’s inaccurate to draw conclusions about all women with both toxoplasmosis and premenstrual dysphoric disorder based on 10 women. It’s possible the parasite is unfairly maligned here, let alone the cat.

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If You Are Infected With Toxoplasma gondii, Did You Get it From Your Cat?

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Infective oocysts of Toxoplasma gondii
contaminate the environment via cat feces

Cats, and cat litter boxes, can be the direct source of T. gondii in humans, but there are quite a few other ways to catch toxoplasmosis. The most common source of infection varies from place to place, but most of us are more likely to catch it by eating undercooked meat or contaminated food or drinking contaminated water.

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That’s not to say there isn’t a cat involved in the story somewhere because infected cats do cause contamination of food and water, but it’s not really fair to draw a straight line from a house cat to its owner. Feral cats and wild felines play a significant role.

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Things to Remember About Cats and Toxoplasma gondii

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A cat with toxoplasmosis will only pass oocysts in its feces for a couple of weeks when it’s first infected. For the rest of its life, the cat has the parasite but isn’t infectious (unless you eat your cat without cooking it first; I doubt this happens often).

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Cats that don’t go out are less likely to become infected with T. gondii. Cats, too, catch it from eating raw or contaminated food (mice etc.).

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Cats often become infected with
Toxoplasma gondii by eating infected prey

Is T. gondii a cat parasite? Cats are the only animals that host the sexually reproductive stage of the parasite (and pass oocysts). Hundreds of other species of animals host the parasite in tissues, and are infectious if eaten without thorough cooking.

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If T. gondii does turn out to cause worse symptoms in premenstrual dysphoric disorder, should we blame the unfortunate cat, caught between a ubiquitous parasite and people who have spread millions upon millions of feral cats all around the globe? I think that’s misleading, to say the least.

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Further reading

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Alvarado-Esquivel, C., Sanchez-Anguiano, L. F., Hernandez-Tinoco, J., Perez-Alamos, A. R., Rico-Almochantaf, Y. del R., Estrada-Martinez, S., … Guido-Arreola, C. A. (2016). Toxoplasma gondii Infection and Premenstrual Dysphoric Disorder: A Cross-Sectional Study. Journal of Clinical Medicine Research, 8(10), 730–736. http://doi.org/10.14740/jocmr2699w

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Hernandez-Cortazar, I., Acosta-Viana, K. Y., Ortega-Pacheco, A., Guzman-Marin, E. del S., Aguilar-Caballero, A. J., & Jimenez-Coello, M. (2015). Toxoplasmosis in Mexico: Epidemiological Situation in Humans and Animals. Revista Do Instituto de Medicina Tropical de São Paulo, 57(2), 93–103.