The kissing bug, Panstrongylus geniculatus, native to Trinidad, is becoming an increasingly important vector of the debilitating Chagas disease. Chagas is just one of many animal-borne diseases predicted to rise as a result of human activities and climate change.
During his travels to South America in 1835, Charles Darwin wrote in his journal of a vivid nighttime encounter:
“At night I experienced an attack, & it deserves no less a name, of the Benchuca, 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 round & bloated with blood, & in this state they are easily squashed.”
Darwin had been bitten by Triatoma infestans, another kissing bug, and a major vector of Chagas Disease. Infectious disease experts speculate that Darwin’s decades of poor health and eventual death may actually have been as a result of him contracting Chagas from similar encounters during the same trip.
The disease itself is caused by a unicellular pathogen, Trypanosoma cruzi. As with other vector-borne diseases, the pathogen hitches a ride between infected individuals and new hosts on an animal vector, in this case, blood-sucking kissing bugs. The pathogen is actually not transmitted through the bug’s bite itself, but through its droppings, which can become transferred from the surrounding skin to the bite wound when scratched. Once the pathogen is in, the first signs of infection can include skin lesions or a purple swelling on the lids of one eye, fever, pains and difficulty breathing, although often no symptoms are present initially. Over time, the pathogen infects internal organs, particularly the heart and digestive muscles, which can lead to a range of symptoms including cardiac, digestive, neurological disorders. While both the pathogen and bugs are present on some Caribbean islands, here in Trinidad, Chagas is considered to be of low public health concern. But is it time to re-evaluate the risk?
Are we really low risk?
Trinidad is home to six kissing bug species, all potential vectors of Chagas disease. P. geniculatus, shown at the top of this piece is thought to be the most common and potentially significant vector in humans. Research conducted in the 1980s sampling these insects found that almost half of specimens tested positive for T. cruzi, the pathogen responsible for Chagas.
How then, could we be deemed low risk? Well, the high infection rate in vectors does not in itself necessarily indicate high risk to humans. Usually, P. geniculatus resides in forested areas, preying on wild mammal species such as armadillos, opossums and rats. As such the transmission of Chagas disease is usually confined to the wild environment with the only humans at risk of contracting the disease being those who spend extended periods of time in or near to forested areas. Such humans are a “dead-end” for the pathogen as there are no vectors in the urban areas to transmit the disease to other humans. As such, the risk of a large human outbreak remains small, though it is still possible for some individuals to get the disease.
However, if the bugs are able to adapt to and thrive in human settlement, transmission could occur within human areas, leading to an outbreak. How might these bugs make the jump from wild to urban areas? It’s a lot to do with our encroachment into forested areas and the human activities near the boundary between settlement and forest. To survive, P geniculatus need plenty of mammals to feed on and small dark crevices such as woodpiles, poorly maintained buildings or abandoned construction materials to reproduce. In particular, livestock farming in and near forested areas can provide ample feeding opportunities and dwelling places for bugs. Further, the removal of the bugs’ natural hosts and habitats through hunting and forest destruction can lead them to human areas seeking alternative food sources.
In recent years, scientists studying P. geniculatus have documented exactly this kind of worrying trend towards domestication in several countries, including Venezuela, Brazil and Colombia. Here, livestock farms and rural communities near forests, particularly those with adobe and thatch structures, may serve as breeding grounds for the bugs.
Right here in Trinidad, a handful of studies spanning the 1960s to 1990s provide evidence of T. cruzi infection in humans, particularly among cardiac patients (see here for a summary of this work). Yet we have not documented any confirmed cases of Chagas Disease. Most recently, a 2020 study analyzing 53 P. geniculatus collected from various residential sites around Trinidad, found that most bugs sampled were infected with T. cruzi, and that 57% of these individuals had previously fed on humans. Alarmingly, Of the 30 bugs with human blood meals, 26 were from bugs infected with T. cruzi.
Though preliminary, this work suggests hitherto unrecognised levels of human T. cruzi infection in Trinidad.
Researchers, however, did not find any evidence of the bugs breeding in human areas, and suggest that P. geniculatus likely moves between human and animal environments feeding opportunistically on a wide range of species. They speculate that the depletion of natural prey through hunting may partially account for the bugs having to venture into human areas for food.
What can we do about it?
As with all vector-borne diseases, preventing the spread of Chagas in humans comes down to eliminating the vector from human settlement. As such, we actually have a great deal of control over how the situation unfolds. Here’s what we can do to avoid and eliminate kissing bugs:
1. Learn how to identify them
Luckily kissing bugs are distinctive, and so are easy to recognize and remove. The main species of concern, P. geniculatus, is about 3 cm long with a distinctive oval body, black and orange stripes along the sides of the abdomen. The second distinctive feature is the
head, which is relatively long with large eyes bulging on the sides near the base of the head:
Now, there are other insects, such as weevils and other types of bug with similar tapered heads which are harmless. For correct identification, look out for the combination of the oval striped body and the head features which make the kissing bug so distinctive.
2. Report kissing bug sightings
If you think you’ve found a kissing bug report it to Life Science Department, University of the West Indies for advice on what to do and how you can help their research.
3. Eliminate breeding grounds at home
Kissing bugs breed in any dark crevices such as cracks in walls, roof spaces, within
building material. Places with loose materials such as lean-to structures, carat roofs, tapia walls, are most likely to become infested, particularly those near forested areas, and those which house domesticated animals. Houses with smooth walls and few crevices are unlikely to become infested. Clearing up any loose materials and keeping surroundings clean should keep kissing bugs out of your home. Kissing bugs can also be attracted to light sources at night, so if you live near forested areas, look out for them under light sources and consider keeping outdoor lights off at night.
In summary, the best thing you can do is to be aware of the risks posed by kissing bugs, identify and avoid them. Luckily for us in Trinidad, our homes are typically constructed with materials that keep the risk of infestation low in most communities, although far more research is needed to find out the true current and future risks. However, the currently available evidence suggests that infected kissing bugs do leave the forests to opportunistically forage in human areas, so be vigilant and consider keeping bright lights off or windows closed at night, particularly near forested areas.
A bigger trend
Recent years have seen a rise in the frequency of outbreaks of animal-borne diseases, from Zika, Dengue and Swine Flu to Ebola, SARS and Covid-19. This is largely attributed to our increasing interactions with wild and domesticated animals through activities like hunting, livestock farming and our communities encroaching more and more into previously wild areas. Infectious disease experts have warned of these risks for years, and hope that in the wake of the Coronavirus Pandemic, governments will take proactive steps to address these threats. Indeed, China, where the Coronavirus pandemic began has vowed to ban the sale and consumption of wild animals, a major step in reducing the risk of new diseases emerging. What we need here in the Caribbean is support for research into diseases, like Chagas, to determine the true risks now and in the future, and what we can do to prevent the next outbreak before it happens.