Kissing bugs and Chagas disease

From the NC State University Plant Disease and Insect Clinic blog

By Matt Bertone, NC State University

News reports out of Texas, and now North Carolina, have been stirring up fears about “deadly” insects and a lesser known, but potentially serious illness: Chagas disease. Most people in the United States have never heard of this malady, yet it affects millions of people every year…in Central and South America.

The vast majority of Chagas disease cases are from rural areas in the New World tropics. Cases in the United States are rare, and most have been diagnosed from people who traveled here from outside the country. In fact there are at present only seven verified cases of natively-infected (termed “autochthonous”) Chagas in the United States since 1955, and none of these was from North Carolina (see Reference 2). To put this in perspective, malaria — a mosquito transmitted protozoan disease often thought of as exotic — has been recorded as autochthonous 63 times since 1957.

Since I am an entomologist and not a medical pathologist I will not be writing about the disease itself, including its forms of transmission, symptoms and treatment. However, there are many great resources that describe the disease including the Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), and Wikipedia. I would, however, like to discuss the biology, identification, methods/risks of bites, and prevention in relation to the bugs themselves.

On that note, let’s start off with a real kissing bug found right here in NC: (go to blog for photo)

Kissing bugs are true bugs (Hemiptera) in the family Reduviidae, most of which are referred to as assassin bugs. With ~7,000 species worldwide, the family Reduviidae is among the largest in the order. Most species in the family are predators, feeding on other insects and arthropods. However, the subfamily Triatominae, and the subject of this post, has largely abandoned the predatory lifestyle for one of blood-feeding. These bugs feed on a wide variety of vertebrate hosts, including reptiles, amphibians, birds, and mammals. In all there are over 130 species of kissing bugs, the majority being found in the Western Hemisphere.

Although most species are tropical, kissing bugs are native to North Carolina and have been for as long as humans have been here. At least two species can be found in the state: Triatoma sanguisuga and T. lecticularia. T. sanguisuga is more common, but even it is not frequently encountered. The reasons why they are so rarely found are two-fold. First, they are nocturnal, preferring to hide during the day. They may be seen at lights at night after dispersing (they have wings and can fly) but otherwise it’s not often that you will see them in your daily lives. Second, they are often associated with small mammal nests, especially species of Neotoma sp. (woodrats); the Eastern woodrat (Neotoma floridana), for example, can be found in North Carolina where it builds nests out of sticks and other debris. These nests are a perfect habitat for kissing bugs to hide before feeding on the inhabitants. Other mammal hosts of particular importance are opossums (Didelphis virginiana), raccoons (Procyon lotor), and armadillos (Dasypus novemcintus), but they will feed on a variety of mammals including livestock, pets, and humans.

As true bugs, kissing bugs undergo incomplete metamorphosis: after the egg, there are eight nymphal stages (instars) before they become an adult. All free-living stages feed on vertebrate blood, although they have been known to take other insects as food. The name “kissing” bug comes from the fact that when the bugs feed on humans at night, they prefer the face, especially the lips and eyes. Kissing bugs swell greatly when engorged, usually taking 20 minutes or so to feed. Their bites do not initially hurt, so as not to wake their victims, but often become itchy, swollen and painful. The bites can last for weeks and in some cases allergic reactions to the saliva can occur, even resulting in anaphylaxis.

The Chagas disease cycle begins when a bug feeds on an infected host, drinking blood containing the parasites. Many mammals that are fed on by kissing bugs (but not typically birds) can harbor the pathogen that causes the disease, but these animals rarely show symptoms. In fact, researchers at Wake Forest University (North Carolina), found that 1 of 12 (8.3%) opossums and 3 of 20 (15%) raccoons they trapped locally had the parasite. The parasite then grows and multiplies in the bug until it is ready to infect another organism. Unlike mosquitoes and many other blood-sucking arthropods, the disease is not transmitted directly through the bite. Instead, the parasites are found in the feces which may be deposited while feeding or somewhere near the bite. Intense itching causes the person to rub the feces into the eyes, mouth or wound where the parasites can enter the new host to complete the cycle. Thus an important factor for getting the disease is not the bite itself, but the likelihood of the feces getting into open wounds or mucous membranes. In this sense our native kissing bugs are rather courteous and discreet with their excreta — they most often wait until they leave the host before defecating. This is thought to be the main reason why the disease is not common in the United States despite the bugs, disease and reservoir animals being present. In fact many kissing bugs that are tested for the disease have it, as do local mammals. But humans are not a preferred host and are not typically exposed to the parasite-riddled feces.

Go to blog for the rest of the story.

Also see Mike Merchant’s Insects in the City blog post on kissing bug identification.

3 Responses

  1. Matt, thanks for your article and beautiful blog images. I agree that the media is making this sound scarier for people than it really is, especially in the big scheme of disease issues in the country. However, according to the Texas Department of State Health Services there were at least 12 locally acquired cases in Texas from 2013-2014, a big jump from the previous estimate of 7 autochthonous cases over 60 years. That, together with blood bank data is causing some public health researchers to think it may be a lot more common than previously thought (though still not a major public health threat). Risks are certainly higher in southern areas like Texas, and the veterinary aspect of chagas infections among dogs is especially concerning here, with almost hundreds of tested dogs from 20 (mostly south Texas) counties testing positive. Bug infection rates and risks for North Carolina dogs and people are undoubtedly much lower.

  2. Not worried yet. There have been less than 10 autochthonous cases of Chagas in the US. The triatomine that we have here is not a suitable vector. That’s not to say that we won’t get that vector–the vectors for many of these diseases come over in commercial shipments, and global warming takes many previous caveats off the table.

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