Chagas disease, or American trypanosomiasis, is a parasitic disease caused by Trypanosoma cruzi and transmitted mainly by the blood-sucking insect known as the “assassin bug” or “kissing bug.” The disease is endemic in 21 countries in Latin America, though cases have also been reported in Europe, the US, and Japan. The World Health Organization (WHO) estimates that there are eight to ten million cases worldwide and that the disease kills at least 10,000 to 12,000 people each year, making it the largest parasitic killer in the Americas.
Dr. Carlos Chagas, a Brazilian physician, first described the condition in 1909, noting the damage it does over time to the victim’s cardiovascular, nervous, and digestive systems and the likelihood that it can be fatal if it is not treated. Unfortunately, despite its prevalence, treatments and diagnostic tests for Chagas are at present inadequate and ill suited for resource-poor settings, a fact that continues to frustrate medical staff caring for people living with the disease. The majority of patients will not develop symptoms for many years after they are first infected. Many patients die suddenly in adulthood without ever knowing they had contracted Chagas disease.
Chagas is most common among poor and vulnerable populations. The bugs that transmit Chagas live in cracks in the walls and roofs of mud and straw housing, which are common in rural areas and urban slums in Latin America. Often unaware of how the disease is caught or what their chances of being cured are, those infected might not even know that they have contracted. Even if they did, most are unlikely to be in a position to fight for their right to be treated, let alone afford the care.
Despite the need, treatment of the disease has been systematically sidelined by national and regional health authorities. At the same time, however, population movements from rural to urban areas in the 1970s and 1980s brought Chagas into cities, and in some instances, it was transmitted through blood transfusions. Blood banks reported infection rates ranging from 1.7 percent in Sao Paulo, Brazil, to 53 percent in Santa Cruz, Bolivia, where Chagas infection rates far exceeded those of HIV and hepatitis.
Transmission and Symptoms
When the parasite-carrying bug bites a person, it deposits feces on the person's skin; when the person rubs their eyes, mouth, or the bite wound, the feces containing the parasite enters the bloodstream. Chagas can also be transmitted through blood transfusions, as mentioned, as well as from mother to child during pregnancy, or less commonly, via organ transplants or contaminated food. There is no vaccine against Chagas, and a person can be reinfected after treatment.
Chagas infection progresses in stages. Though the initial stages do not cause major symptoms or problems—which also makes it harder to diagnose—the final, chronic stage, while lengthy, is often fatal.
During the first, acute stage of the disease, which occurs in the immediate aftermath of infection, an infected person may develop a fever, swollen lymph glands, an enlarged liver and spleen, or an inflamed bite wound. These non-specific symptoms may often be confused with those of other common illnesses and would-be patients carry on unaware. This is particularly true for children, though the immediate impact on them can be more pronounced. Five percent of children with acute Chagas die from the disease, in fact.
The second stage, the chronic stage, is divided into two additional stages. The chronic indeterminate stage begins between eight to ten weeks after the initial infection and may last for many years. In this stage people do not have symptoms and, once again, can carry the parasite for years without knowing it.
About 10 percent to 30 percent of those infected will later—10 to 20 years after first contracting Chagas—enter the chronic symptomatic phase of the disease. By this time, patients will have developed lesions causing irreversible damage to the heart, esophagus, and colon that can eventually lead to death—in some cases, without the deceased or their families knowing that Chagas was the root cause of their ailments.
Several issues complicate and delay Chagas diagnosis, allowing the disease to cause damage long before its detected. Doctors usually need to perform several blood tests to determine whether a patient is infected. In adults, the disease is often not actively diagnosed in early stages because carriers tend to be asymptomatic. Unfortunately, by the time a patient has developed chronic Chagas, treatment with the drugs that are currently available is no longer effective. Because Chagas can be treated while the disease is still asymptomatic, efforts should be made to develop better methods of screening vulnerable populations and diagnosing the acute phase of the disease, when full recovery is still possible. Currently, the best method of finding and diagnosing patients with acute Chagas is testing all members of a population with high rates of the disease.
Specific diagnosis classically relies on two laboratory tests that detect antibodies against the parasite. Unfortunately, these tests are too complex to be widely used at the primary health care level. It is essential that communities living in endemic zones have access to diagnosis through simpler tools and can find out if they have been infected with T. cruzi.
There are currently only two medicines to treat Chagas disease: benznidazole and nifurtimox. Both drugs were developed more than 40 years ago in investigations not specifically aimed to find Chagas treatments. Now, however, benznidazole is the recommended first-line treatment. Nifurtimox remains a second-line treatment option since safety, specifically in adult patients, is a big concern.
Treatment during the acute phase has high rates of success. Treatment for chronic cases, however, is less effective, can have multiple side effects, and has to be undertaken under medical supervision. As the side effects of the treatment are more common in older patients and as there is no practical test of cure, doctors have been reluctant to administer the medicine to this cohort until recently. The experience of MSF and other programs have shown that the adverse effects that adults experience in treatment are manageable with regular medical follow-ups. This means it is both feasible and beneficial to treat patients in the chronic phase, even after the heart is mildly affected (initial clinical forms of the chronic phase).
With the limited resources currently available to treat patients with Chagas disease, however, medical teams have to deal with many shortfalls and at times don’t have any treatment options. The needs are clear, but the will to address them is not.
The long-term availability of the existing medications is not guaranteed, and neither of the two Chagas drugs is ideal. They are of limited effectiveness when the disease is in the chronic phase, the treatment can have severe side effects and must be administered with medical supervision—a challenge, given that the treatment regimen lasts one to three months—and the treatments have not been adapted for children. At present, medical staff must cut adult tablets in pieces in order to achieve the appropriate dosage, and mothers have to mix the crushed pills in juice or breast milk for babies. What’s more, neither treatment can be prescribed to pregnant women who risk passing the disease to newborns.
Beyond all of that, though, there have been recent instances when the medicine supply has simply run out, causing grievous setbacks to treatment programs. In 2011, for example, a major shortage of benznidazole brought treatment regimes and initiatives to a halt. MSF’s program in Paraguay was forced to suspend diagnosis of new patients in a bid to mitigate the effects of the shortage because patients who stop treatment mid-course are more likely to develop resistance.
Some initiatives have been made to increase treatment distribution. Following an agreement negotiated by WHO, a one-time donation of five million tablets of nifurtimox was made available to Latin America's Ministries of Health through the Pan American Health Organization (PAHO) in 2004. Although the donation temporarily released the financial burden for those who needed treatment, treating the disease today is still difficult given ongoing and widespread access, production, and cost issues. Overall there is a clear and urgent need for secured production supplies of benznidazole, new diagnostic tests, better medicines, and an effective test for cure. MSF is among the groups who have recognized that this will not happen if Chagas remains a low priority for research and development initiatives, which is exactly what it’s been for too long. Overall R&D funding on Chagas amounted to only $20 million in 2010.
Prevention programs such as vector control and blood transfusion testing are in place in most Latin American countries, but they are not always implemented or effective. Vector control strategies, which are fundamental to limit the spread of the disease, depend on detecting the vector (the assassin bugs) and spraying houses and peri-domestic areas with insecticides. In some areas, the assassin bugs have been found to be resistant to certain products. To eliminate the insects from houses, spraying must be completed thoroughly and housing conditions must be improved.
It has been argued that treatment should be available to patients regardless of whether or not vector control activities exist or are functioning. While MSF began with this strategy, it has realized that treating Chagas in areas without prevention programs in place can backfire. In Bolivia, for example, where vector control is patchy at best, there is a considerable risk of re-infection.
As a result of its experiences, MSF now only treats patients when the registered infestation rate is below 3 percent. However, this position raises moral and practical dilemmas. Vector control does not always deliver beneficial results and often it is not even possible. Should people living in inaccessible regions such as the Amazon Basin then not be treated at all? What about areas where vector control is possible but is not carried out or completed? Patients’ chances of being cured may vanish while waiting for governments to institute effective control programs.
In addition, greater efforts must be made to ensure the quality of blood banks to avoid contamination from transfusions, to screen mothers for early detection of congenital transmission, and to achieve early diagnosis and treatment of all patients infected.
MSF has used different operational models to provide free diagnosis and treatment for Chagas since 1999 in Honduras, Nicaragua, Guatemala, Colombia, and most recently in Paraguay. MSF also currently runs projects in Bolivia—which has the world's highest prevalence of Chagas—just across the border from Paraguay and Colombia. Between 1999 and September 2011, MSF tested more than 80,000 people for Chagas and treated more than 4,200 patients. In addition to impacting the lives of the people who were treated, this work has shown that Chagas treatment is indeed possible in places with limited resources. It also hints at how much could be done if more resources were directed toward diagnostics, treatment, and prevention efforts.
While there have been efforts to understand Chagas and to control the spread of the vector, too little attention has been paid to treating those who have been infected. Through its programs in Latin America, MSF aims to show that treatment is not only possible, but imperative. MSF's clinical results demonstrate that the existing drugs, though not optimal, can be used more widely than previously understood and with manageable side effects. Meanwhile, governments of endemic countries will have to recognize their responsibility for public health and commit to taking care of their high-risk populations—by integrating Chagas testing and monitoring into primary health care networks, for instance. There is clear momentum for integrated national Chagas programs in Latin America, but significant funding is needed from the international community to support the battle against Chagas.
In its recently released report on NTDs, MSF called for the following in regards to Chagas:
MSF is also calling for increased funding of more needs-driven R&D:
© 2013 Doctors Without Borders/Médecins Sans Frontières (MSF)