Although the eradication of life-threatening diseases is a common goal for humanity, strategies to achieve this aspiration are often speculative and uncertain. But by modeling the effects of an international plan for the prevention of Chagas disease, Yale and Johns Hopkins researchers have attempted to limit this unpredictability.
Chagas is a disease that affects as many as eight million people worldwide and is common in Latin America. It is caused by a parasite and most often transmitted by triatomine bugs, also known as kissing bugs, that become vectors by biting hosts as they sleep. Chagas may initially have minimal consequences on someone’s health, but it has the potential to cause cardiac and intestinal complications over many years.
In 2012, the World Health Organization collaborated with influential international organizations to develop the London Declaration on Neglected Tropical Diseases. The document contained a plan to prevent the spread of high-prevalence infectious diseases. In the case of Chagas, the plan called for the full prevention of the three major forms of transmission, triatomine bugs, blood transfusions and pregnant mothers to their children, in all affected countries. The WHO aims to accomplish the task by 2020, according to the Declaration.
“Achieving the 2020 goals will reduce the number of Chagas cases significantly but alone will not eliminate Chagas,” said Bruce Lee, a professor at the Johns Hopkins Bloomberg School of Public Health and the lead author of the study. “This highlights the need to implement other control measures simultaneously, as well as developing new technologies such as vaccine.”
Overseen by School of Public Health professor Alison Galvani, a team of researchers used a computer-generated simulation to estimate the impact of meeting the WHO’s Chagas-control aspirations. The group found that the London Declaration’s Chagas protocols had successful long-term effects.
Assuming the full success of the Declaration guidelines, the model predicted a drastic short-term reduction in new cases. After five years of the London Declaration’s new implements, it estimated a 90 percent reduction in new incidences. The study stated that existing cases would remain in the population for decades, but, after 50 years, the disease prevalence would fall by 67 percent.
Lee’s group chose to factor in the environment of Yucatan, Mexico for its model. He said he believed using Yucatan in the experiment was appropriate because “while there may some differences in the specific numbers, the general conclusions and principles should apply.”
Although the Declaration did not consider potential medical advances, the study said that there are multiple Chagas vaccines in development. It predicted that any drug or vaccine that met the WHO’s minimum standards of efficacy and availability would greatly contribute toward a reduction in the global prevalence of Chagas. But according to Lee, the best way to combat the disease is through a combined effort of the London Declaration’s instructions and a new vaccine.
“While a vaccine would significantly change the situation, there would still be a need for appropriate vector control,” Lee said. “Rarely does a single technology or intervention solve a disease problem. There typically needs to be a combination of different policies and interventions that address different parts of the system causing the spread of the disease.”
In addition to testing the complete elimination of the three major transmission modes, the paper also varied degrees of reduction. It tested the effects of 50, 70 and 90 percent prevention success. The data showed that as levels of transmission control increased, the theoretical prevalence of Chagas decreased.
Heidi Dong ’20, a student in the Global Health Scholars Program, said she was optimistic about the preliminary results of the study.
“While it is disappointing to see that even meeting the goals of transmission interruption would not be enough to control the disease, it is encouraging to hear about the potential benefits of cost-effective vaccines, some of which are already under development,” said Dong. “It seems to me that because there are so many organisms that can serve as reservoirs, it would be quite difficult to completely control the disease, which again makes the development of vaccines so promising.”
Armstrong Noonan ’20 thought the model’s predictions were helpful for further prevention of infectious diseases, adding that he is interested in seeing how the researchers’ model stacks up against observable data.
The research paper is currently an uncorrected proof and is set for publication in PLOS Neglected Tropical Diseases.
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