Chagas: Main Challenges
• One hundred years of neglected patients
2009 marks the centenary of the discovery by the Brazilian doctor Carlos Chagas of the disease which bears his name. In 1909, Dr. Chagas announced to the world the existence of a new infectious disease. The previous year, he had discovered the parasite which causes it and the vector by which it is transmitted. His triple discovery is considered unique in the history of medicine.
One hundred years later, there is still a lack of innovative treatments and the treatment which does exist is not available to the majority of sufferers. One hundred years later, many of those infected with Chagas disease are still unaware that they are sick. They are dying without knowing why and doing so in silence. Their voices do not reach the governments which should be responding to this public health problem, or the pharmaceutical companies which could be researching and developing new medicines. For one hundred years, Chagas disease has been a silent illness. The time has come to break the silence.
What is Chagas disease?
Chagas disease, or American human trypanosomiasis, is an infectious disease caused by the Trypanosoma cruzi parasite. Endemic in several Latin American countries, cases are found in rural areas, indigenous communities and the poorest suburbs from Mexico to Argentina, including the Caribbean. The disease causes 14,000 deaths each year. It is estimated that 10-15 million people suffer from the disease and 100 million more, 25 per cent of the population of Latin America, are at risk of contracting it. As a result of the increase in global migration and mobility, an increasing number of cases are being reported in the United States, Europe, Australia and Japan.
Estimated global population infected by Tripanosoma cruzi, 2009
How is it transmitted?
Certain insects of the Triatominae species, known as ‘assassin bugs’ or ‘kissing bugs’ depending on the geographical zone, transmit the parasite to humans. They live in cracks in the walls and ceilings of houses made from adobe bricks, sticks, straw, etc., and come out at night to feed on blood. When an assassin bug carrying the parasite bites a person, it deposits faeces on the skin. If the person scratches or rubs their eyes or mouth after touching the bite, the parasites can then pass into the blood stream. If an infected person is bitten by another assassin bug, the parasite infects the insect and the cycle goes on.
In many Latin American countries, prevention programmes are being developed with the aim of reducing the presence of the vector (the transmitting insect), but not all of them are as effective as they should be and they are never enough to eliminate the disease.
Chagas disease can also be transmitted through blood transfusions, from mothers to their children during pregnancy and, less frequently, through organ transplants or the ingestion of contaminated food. It is not transmitted through direct contact with infected individuals.
Diagnosis
The majority of people infected with Trypanosoma cruzi, the parasite which causes Chagas disease, show some sign or symptom at the time of infection. In a small number of cases acute Chagas disease causes death. For the majority, the symptoms go unnoticed and for years those infected have no further problems. It is estimated that approximately 70 per cent of these people live with the parasite without their health being affected. Nevertheless, in the chronic phase of the disease, 30 per cent will develop problems in their heart, gastrointestinal tract and brain which cause irreversible damage. Since it is impossible to predict who will develop the disease, treatment should be offered to all sufferers, with assessment of their clinical status and age.
As the disease often does not present symptoms, active detection of cases should be a priority in programmes to combat Chagas. Diagnosis currently requires confirmation through laboratory tests. In many cases, the endemic countries do not have the necessary facilities or staff available to carry out these tests. It is essential that communities living in endemic zones have access to diagnosis and can find out if they have been infected with T. cruzi. If not, thousands of people will die each year without knowing the cause.
Treatment
There are currently only two medicines to combat Chagas disease: benznidazole and nifurtimox. Both were developed over 35 years ago and in investigations not specifically aimed at Chagas disease. Nowadays, neither of these drugs is adapted for paediatric use and nor can they be used by pregnant women. The success rate reaches almost 100 per cent in newborns and infants. However, in older children, adolescents and adults treatment is only around 60 or 70 per cent effective and can have multiple side effects, and therefore has to be taken under medical supervision. This means having a weekly check-up with a trained healthcare worker.
Until a few years ago it was thought that the treatment was only effective in very young children and not in adults. However, recent studies demonstrate that it is possible to treat adults, even after the heart or the gastrointestinal tract are mildly affected (initial clinical forms of the chronic phase). As the side effects of the treatment are more common in older patients, doctors have been reluctant to administer the medicine out of fear of the consequences. We now know that the adverse effects are manageable.
Before starting treatment for Chagas disease, it is necessary to check that the parasite has not seriously affected the heart or other vital organs. In some very advanced cases, there is no evidence as yet that the treatment is beneficial because T. cruzi has already caused serious vital organ damage. On the other hand, adults aged 50 and above - probably infected by the parasite in their childhood or adolescence - who have not developed any pathology are most likely to fall within the 70 per cent who will not suffer organ damage. In such cases, and bearing in mind the toxicity of the treatment, the risks and the benefits for each individual have to be assessed before starting treatment.
Barriers to access
Millions of sufferers, especially in rural areas, have neither the opportunity to find out that they are infected nor the possibility of being treated. This is due to the numerous obstacles which could be avoided with greater political will and greater investment in research and development:
• Confirming diagnosis of Chagas disease requires laboratory tests, which means that the patient cannot get the result on the first visit to a health centre.
• As evidence regarding the effectiveness of treatment in adults is very recent, some doctors remain unconvinced as to the viability of treating adults and patients in the chronic phase with existing medicines.
• The possible undesirable effects are also an obstacle. Many doctors and nurses are reticent about beginning treatment for fear of causing unpleasant side effects.
• Vector control is not integrated with treatment of patients. Combined with ineffective efforts to combat the assassin bugs, this has caused the insect and the disease to reappear and patients to become re-infected.
• With the methods currently available, confirming the cure of adolescents and adults can take years, making the research and development of new medicines difficult, and dissuading many sufferers from starting treatment.
