thumb|Sir [[Patrick Manson, considered the father of tropical medicine.]]
Tropical medicine is an interdisciplinary branch of medicine that deals with health issues that occur uniquely, are more widespread, or are more difficult to control in tropical and subtropical regions.
Physicians in this field diagnose and treat a variety of diseases and ailments. Most infections they deal with are endemic to the tropics. A few of the most well-known include malaria, HIV/AIDS, and tuberculosis. They must be knowledgeable in the 21 lesser known neglected tropical diseases, which include Chagas disease, rabies, dengue, lymphatic filariasis, onchocerciasis, schistosomiasis, and scabies. Poor living conditions in developing regions of tropical countries have led to a rising number of non-communicable diseases as well as the prevalence of neglected tropical diseases. These diseases include cancer and cardiovascular disease, which, in the past, have been more of a worry in developed countries. Physicians trained in tropical medicine must also be prepared to diagnose and treat these diseases.
Sir Patrick Manson is recognized as the father of tropical medicine. He founded the London School of Hygiene & Tropical Medicine in 1899. He is credited with discovering the vector by which elephantiasis was being passed to humans. He learned it was a microscopic nematode worm called Filaria sanguinis hominis. He continued to study this worm and its life cycle and determined the worms underwent metamorphosis within female Culex fatigans mosquitoes. Thus he discovered mosquitoes as a vector for elephantiasis. After this discovery, he collaborated with Ronald Ross to examine the transmission of malaria via the mosquito vector. His work on vectors as modes of transmission was critical in the founding of tropical medicine and the current understanding of many tropical diseases.
Challenges
HIV
In developing countries alone, 22 million people are living with HIV. Most infections are still in Africa, but Europe, Asia, Latin America, and the Caribbean are now seeing large numbers of infections as well. 95% of expected new infections will occur in the low-income countries in the tropics. The parasite that causes malaria belongs to the genus Plasmodium. Once infected, malaria can take a wide variety of forms and symptoms. The disease is placed into the uncomplicated category or the severe category. If quickly diagnosed and treated, malaria can be cured. However, some of the more serious symptoms, such as acute kidney failure, severe anemia, and acute respiratory distress syndrome can be fatal if not dealt with swiftly and properly. Certain types of Plasmodium can leave dormant parasites in the liver that can reawaken months or years later, causing additional relapses of the disease. In the World Malaria Report of 2016, the World Health Organization reported a malaria infection rate of 212 million, 90% of which occurred in the African region. However, malaria infection rates had fallen 21% since 2010 at the time of the report. The WHO also reported an estimated mortality rate of 429,000 deaths in the year 2015. The malaria mortality rate had fallen 29% globally since 2010. Children under 5 contract the malaria disease more easily than others, and in the year 2015, an estimated 303,000 children under the age of 5 were killed by malaria. Since the year 2010, however, the mortality rate of children under 5 fell by an estimated 35%. TB can either be in its latent or active form. TB can be latent for years, sometimes over a decade. Research has shown that if the subject is infected with HIV, the risk of latent TB becoming active TB is between 12 and 20 times higher. In the Global Burden of Disease Study of 2001, it was discovered that 20% of deaths in sub-Saharan Africa were caused by non-communicable diseases. In 2005, the World Health Organization performed a study that showed 80% of chronic disease deaths occurred in low to middle-income countries.
Neglected tropical diseases' effect can be measured in disability-adjusted life year (DALY). Each DALY corresponds to one lost year of healthy life, whether by death or disability. In the year 2010, it was estimated that 26.6 million DALYs were lost. In addition, it is estimated that NTDs cause a loss of 15–30% of productivity in countries where NTDs are endemic.
Interdisciplinary approach
Tropical medicine requires an interdisciplinary approach, as the infections and diseases tropical medicine faces are both broad and unique. Tropical medicine requires research and assistance from the fields of epidemiology, microbiology, virology, parasitology, and logistics. Physicians of tropical medicine must have effective communication skills, as many of the patients they interact with do not speak English comfortably. They must be proficient in their knowledge of clinical and diagnostic skills, as they are often without high-tech diagnostic tools when in the field. For example, in an attempt to manage the Chagas disease being brought into the almost Chagas-free Brazilian city São Paulo by Bolivian immigrants, an interdisciplinary team was set up. The Bolivian immigrant population in São Paulo had a prevalence of Chagas disease of 4.4%, while Chagas disease transmission in São Paulo has been under control since the 1970s. This influx of cases of Chagas disease led to the formation of an interdisciplinary team. This team tested the feasibility of managing Chagas disease and transmission at the primary healthcare level. The interdisciplinary team consisted of community health agents and clerical healthcare workers to recruit Chagas-infected persons for the study, physicians, nurses, lab workers, and community agents. A pediatrician and cardiologist were also on call. Each was trained in pathology, parasitology, ecoepidemiology, and how to prevent, diagnose, and control Chagas disease. Training from experts in these respective fields was required. They examined reasons for lack of adherence to treatment and used this knowledge to improve the effectiveness of their interventions. This interdisciplinary approach has been used to train many teams across Brazil in the management of Chagas disease.
Tropical medicine also consists of a preventive approach, especially in an educational aspect. For example, from 2009 to 2011, the London School of Hygiene & Tropical Medicine did an interventional study on a cohort of female sex workers (FSW) in Ouagadougou, Burkina Faso, a country in Western Africa. 321 HIV-unaffected FSWs were provided with peer-led HIV/STI education, HIV/STI testing and care, psychological support, general healthcare, and services for reproductive health. The same cohort would continue to follow up, quarterly, for 21 months. At each follow-up, they were tested for HIV and were able to utilize the preventive interventions if needed. Using models based on the same study population, had there been no interventions, the expected prevalence of HIV infections was 1.23 infection per 100 person years. In the actual cohort with access to interventions, no HIV infections were observed in the collective 409 person-years of follow-up.
Tropical research in the military
Throughout history, American military forces have been affected by many tropical diseases. In World War II alone, it was estimated that almost one million soldiers had been infected by a tropical disease while serving. Most affected soldiers served in the Pacific, especially in the Philippines and New Guinea. Malaria was especially widespread in the Pacific, though soldiers in Southern Europe and Northern Africa also contracted tropical diseases.