“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,” wrote Charles Darwin, on March 26, 1835, after spending an unpleasant night in an Argentine village. Some believe Darwin’s insect attackers were reduviid bugs, or “kissing bugs”, so called after their penchant for biting near the eyes or mouth. Reduviid bugs carry a single-celled parasite called Trypanosoma cruzi (T. cruzi), which causes Chagas disease, a devastating illness that some have come to call the “HIV/AIDS of the Americas.”
While some investigators have deemed the comparison between Chagas and HIV/AIDS to be unrealistic or even unfair, most would agree that it is vitally important to bring awareness of this disease to the general population. While Chagas disease may not currently pose a major threat in the U.S., it does have the potential to become a serious problem if we continue to keep it under the radar.
Chagas disease was discovered in 1909 by the Brazilian doctor Carlos Chagas. Infection occurs when a reduviid bug takes a blood meal from a human host and simultaneously deposits T. cruzi-containing feces near the bite wound. T. cruzi enters the host through the bite wound and replicates inside cells near the infection site. It then enters the bloodstream, targets various tissues, and replicates further inside the cells making up these tissues.
T. cruzi infection leads to symptoms such as fever, tissue swelling and malaise. About 30 percent of patients also develop more serious, and often fatal, symptoms 10-30 years after the initial onset. During this chronic phase, some patients develop digestive problems due to an enlarged colon or esophagus, but more frequently suffer from a variety of cardiac problems that can ultimately result in death. In fact, Darwin died from heart complications, leading some to speculate that he succumbed to Chagas disease.
According to the Centers for Disease Control and Prevention (CDC), 8-11 million people suffer from Chagas disease. Most cases occur in impoverished rural areas of Mexico, Central America, and South America. But, increased immigration from these regions has led to approximately 300,000 cases in the U.S. Despite the seriousness of this disease, much of the U.S. population remains unaware of its existence.
In a recent editorial Dr. Peter Hotez brings increased awareness to the disease by drawing comparisons between Chagas and HIV/AIDS. Both diseases affect mainly impoverished areas, are stigmatizing, and are chronic conditions requiring prolonged and expensive treatment regimens. They can also be passed on by blood transfusion or from pregnant mother to fetus. No preventative vaccine has yet been developed for either disease.
However, the two diseases are still distinct. HIV/AIDS is fatal without retroviral therapy, whereas 70-80 percent of people afflicted with Chagas disease do not even progress to the deleterious chronic phase. Only two drugs are available for treating Chagas disease, whereas dozens of retrovirals have been developed for treating HIV/AIDS.
So could Chagas disease really become a problem similar in magnitude to the AIDS epidemic of the 1980s? There are a number of different factors at play that may indeed promote the spread and persistence of the disease in the U.S., including climate change, socioeconomic issues and surveillance.
Several species of reduviid bugs carrying T. cruzi already live across the southern U.S. Until recently, scientists believed that reduviid bugs in the U.S. do not feed on humans. However, a recent study has shown that about 4 in 10 reduviid bugs collected in California and Arizona contained DNA remnants of human blood. The investigators hypothesized that reduviid bugs capable of transmitting T. cruzi to humans may be moving further north as a result of global warming.
Substandard housing in poorer areas of the country, like the border regions between the U.S. and Mexico and the Delta region of Louisiana, may also facilitate spread of the disease. Dr. Hotez notes that in South Texas, many poor immigrants live in inadequate housing without plumbing, air conditioning, or window screens. These conditions all promote reduviid bug infestation. It seems unlikely at this point that Chagas disease could become a real threat in urban areas like Chicago due to the infrastructure already in place in such settings. However, if the disease becomes more prevalent in poor rural areas of the country, it may exacerbate the cycle of poverty as more people suffering from the disease become less able to support themselves and their families.
Surveillance of the disease in this country has also been lacking. Widespread screening for T. cruzi antibodies from U.S. blood donors was only implemented in 2007. Even still, many healthcare facilities in impoverished areas lack the resources for proper screening. And despite widespread screening in blood donations, it is currently estimated that 30,000-45,000 cases of undiagnosed cases of Chagas disease still exist in the US today.
Should Chagas disease become prevalent in the U.S., treatment options are limited. First, no preventative vaccine currently exists. Benznidazole and nifurtimox are the only two drugs currently in use for treating the disease, but they are only effective during the acute phase and cause severely adverse side effects. Treatment is also expensive, costing patients approximately $1,000 per year.
Pharmaceutical companies are reluctant to devote resources to drug development for Chagas disease because the potential for making large profits is small. But, this attitude may be changing. For example, the European Union-funded BERENICE research project aims to use nanotechnology for developing a more tolerable and cost-effective form of benznidazole treatment.
Darwin may have been a victim of a disease that no one yet knew about. Today, we are much more aware of how Chagas disease manifests itself and spreads. We also realize that it may become a much bigger problem in this country if we continue to ignore it. In Latin America, where resources are much more scarce, concerted efforts to reduce reduviid bug populations and to ensure mandatory blood bank screening have already significantly reduced disease spread. There is no reason why we cannot also make better efforts at controlling the numbers of reduviid bug species living in the U.S., see to it that screening for T. cruzi is provided in every health facility and blood bank, and devote more resources toward drug and vaccine development. In essence, we need to nip Chagas in the bud before it even has a chance of becoming the next “HIV/AIDS of the Americas.”