Tropical diseases – illnesses that are prevalent in tropical or subtropical regions – are most commonly spread by insect vectors that carry infectious parasites, bacteria or viruses. The majority of tropical diseases affect the poorest people living in remote areas, and these poverty-promoting chronic infectious diseases have been termed “neglected tropical diseases” (NTDs). It is thought that the incidence of NTDs has increased in recent years due to the exploration of rainforests and increased tourism in tropical areas. Experts are becoming increasingly concerned about the global spread of dengue, a febrile NTD spread by mosquitoes, with the recent emergence of the virus in several parts of the US. This week, warnings have also been issued about the increased risk of contracting dengue during the football World Cup in Brazil next summer, and researchers in the field are investigating the reasons behind rising infection rates, together with effective control measures.
Dengue fever was one of many tropical diseases discussed at the recent American Society of Tropical Medicine and Hygiene (ASTMH) 62nd annual meeting, where experts across all areas of tropical medicine came together in Washington, D.C. to share their knowledge in this fascinating area of medicine. Donald Shepard from Brandeis University discussed the reasons why dengue infections have increased across the globe in recent years, including urbanization, poor sanitation and population increases. Shepard explained that the disease is a self-limiting fever in most infected people, with slow recovery over time. However, shock and organ involvement can occur as severe complications of dengue infection in a small number of patients, and Bridget Wills from Oxford University emphasized the importance of identifying those likely to develop a more severe course of illness as early as possible. While there is currently no vaccine licensed to prevent dengue, Scott Halstead from the Dengue Vaccine Initiative described several vaccines under clinical development, and indicated that a dengue vaccine is expected to be approved soon.
Vaccination is a vitally important strategy to prevent the spread of many tropical diseases, especially in remote communities with inadequate sanitation and restricted access to healthcare. David Sack from Johns Hopkins University described how the oral cholera vaccine (OCV), licensed by the World Health Organization (WHO) in 2010, shows promise in reducing the spread of cholera in Asia and Africa, but emphasized that in order to have an impact, the vaccine must be targeted to the right groups at the right time. Sack explained that OCV should be utilized together with interventions to improve sanitation and hygiene, such as the UNICEF WASH initiative, in a multidisciplinary approach to reduce the spread of cholera in endemic areas. Vaccination could also be an effective approach to tackle helminth infections, which are one of the most common types of infection affecting the world’s poorest communities. Alex Loukas from James Cook University explained that although there is currently no vaccine available for hookworm infections, there are a number of agents currently in clinical trials, and we remain optimistic that a vaccine will be developed in the near future.
In a significant development in the global fight against malaria, the updated malaria vaccine technology roadmap was released at ASTMH 2013, outlined by Vassel Moorthy from the WHO. The new roadmap includes goals to develop vaccines for malaria elimination in multiple settings, as well as vaccines that decrease transmission of the parasite. This is a considerable step forward; malaria causes an estimated 660,000 deaths worldwide every year, with resistance to widely-used antimalarial drugs increasing, and there is currently no licensed vaccine. In an opinion article published recently in BMC Medicine as part of our Medicine for Global Health collection, Freya Fowkes and colleagues from the Burnet Institute explored the implications of malaria vaccine licensing for the future; more information can be seen in our previous blog. We look forward to seeing further progress in malaria vaccine development, and hope that vaccination will soon be able to reduce the death toll caused by this devastating disease.
Taking another approach to reducing the global burden of malaria, Marcus Lacerda from University of the State of Amazonas described optimistic phase 2 clinical trial results showing that tafenoquine is superior to chloroquine for the treatment of malaria caused by the parasite Plasmodium vivax. Lacerda explained that phase 3 trials of this agent are ongoing, and it could prove to be an important treatment strategy for P. vivax malaria.
Overall, discussions at the ASTMH 2013 meeting highlighted tremendous progress in reducing the global death toll from tropical infectious diseases, both in terms of reducing infection transmission and treating existing disease. We hope to see further developments in licensing and appropriate delivery of vaccines for malaria, cholera and helminth infections in the near future. Given the global importance of these diseases, we are keen to publish research across all areas of tropical medicine, and if you have any potential submissions you would like us to consider, please get in touch at firstname.lastname@example.org.