The work of preventing and treating tropical diseases has high stakes. Infectious diseases account for approximately half of all deaths in tropical areas of the world, according to the American Society of Tropical Medicine and Hygiene. The vast majority of those deaths occur in children under the age of 5.
As tragic as those statistics are, they only describe part of the impact of tropical diseases, which affect individuals all over the world with wide-ranging health impacts.
Infectious diseases that are more prevalent in –– or unique to –– tropical and subtropical regions are commonly referred to as tropical diseases. Their concentration in tropical and subtropical areas is largely a factor of climate; tropical diseases tend to thrive in hot, humid conditions, and the lack of a cold season allows populations of insects (a major disease vector) to grow unchecked.
However, socioeconomic factors also contribute to the definition of tropical disease. Regions that are less developed economically tend to have characteristics that make them prone to infectious disease spread:
- Limited access to clean water and sanitation
- High population density in urban areas
- Poor nutrition
- Inadequate healthcare infrastructure
Tropical diseases can be transmitted through physical contact, by airborne routes, or through sexual contact. Many are spread via contaminated food and water sources. Some disease agents are spread by an intermediate carrier such as an insect; such intermediate carriers are called vectors. Vector-borne diseases account for more than 17 percent of all infectious diseases and cause more than 700,000 deaths annually, according to the World Health Organization (WHO).
Tropical diseases can be caused by a variety of pathogens:
- Bacteria. Examples of bacterial tropical diseases include cholera and tuberculosis.
- Parasites. Examples of parasitic tropical diseases include Chagas disease and malaria.
- Viruses. Examples of viral tropical diseases include chikungunya, rabies, rotavirus, West Nile, yellow fever, and Zika.
Tropical diseases affect more than a billion people annually, causing substantial numbers of illnesses and deaths. Even preventable, curable diseases have devastating effects:
- Malaria is caused by parasites that are transmitted by mosquito bites. In 2018, 228 million people were infected with malaria and 405,000 people died from malaria, according to the WHO.
- Rotavirus, a highly contagious virus that is the most common cause of diarrhea in infants and children worldwide, leads to more than 215,000 deaths annually, according to the Mayo Clinic.
- Tuberculosis (TB) is caused by bacteria that is spread from person to person through the air. Approximately 10 million people fell ill with TB and 1.5 million people died from it in 2018, according to the WHO.
Malaria, rotavirus, and tuberculosis have relatively high levels of funding dedicated to their mitigation compared to many other tropical diseases. A category of tropical diseases known as “neglected tropical diseases” receive far less attention.
The term “neglected tropical disease” does not have a precise definition, but it generally denotes tropical diseases that primarily affect poor and marginalized populations in low-resource areas. They are particularly prevalent in developing regions of Africa, Asia, Central America, and the northern regions of South America. Because NTDs occur in less developed regions, they often receive inadequate funding for research, mitigation, and treatment.
The WHO maintains a list of approximately 20 neglected tropical diseases. A closer look at three of these diseases highlights the danger they pose:
A viral infection carried by mosquitoes, dengue is concentrated in urban and semi-urban environments. Symptoms of dengue can be very mild but generally resemble a flu-like illness. Dengue is highly treatable, but untreated cases can result in death. Nearly 400 million people are infected with dengue annually. The WHO estimates that about half of the world’s population is at risk for dengue infection.
Also known as elephantiasis, lymphatic filariasis infections occur when filarial parasites (thread-like worms) are transmitted to humans by mosquitoes. Damage done to the lymphatic system by filarial parasites causes abnormal enlargement of body parts. Infected individuals suffer from pain and severe disability, as well as social stigmatization. Preventive chemotherapy stops the spread of lymphatic filariasis, and people infected with the disease can be treated with medications and surgery. Approximately 120 million people are affected by lymphatic filariasis, with one-third disfigured and incapacitated by the diseases. More than 890 million people in 49 countries are threatened by lymphatic filariasis, according to the WHO.
Trachoma occurs when individuals’ eyes are infected by the bacterium Chlamydia trachomatis. Infections are spread through personal contact and by flies. Trachoma is the leading infectious cause of blindness in the world. Blindness from trachoma is irreversible, but infections can be treated with surgery and antibiotics. Trachoma is responsible for the blindness or visual impairment of almost 2 million people in more than 40 countries. The WHO estimates that 137 million people live in areas that put them at risk of trachoma blindness.
Tropical medicine is an interdisciplinary field. The fight to mitigate and eradicate tropical diseases requires professionals across a broad spectrum of health care, including public health. Epidemiologists, community health practitioners, and public health educators work with physicians, microbiologists, and other healthcare experts to prevent the spread of tropical diseases and reduce their impact on a local and global level.
Epidemiologists investigate disease outbreaks, identify causes and risk factors, and recommend prevention and control measures. Public health workers provide critical education services, informing the public about the risk of infectious diseases and providing guidance to communities and government officials about disease control measures.
The educational programs, health services, public policy, and research provided by public health experts have never been more advanced, but the threat posed by tropical diseases continues to evolve. Factors including climate change, urbanization, and international travel and trade bring new challenges to the work of mitigating disease spread.
For professionals interested in combating public health threats, Tulane’s School of Public Health and Tropical Medicine provides a unique opportunity. The school’s Online Master of Public Health (MPH) program provides a foundation in core areas of public health, including epidemiology, environmental health, behavioral science, biostatistics, and management. Designed for early- to mid-career professionals, the online MPH degree prepares students to assess and address health risks and promote social justice and meaningful change.