Tropical Fevers
Tropical fevers refer to a broad spectrum of infectious diseases that are endemic to tropical and subtropical regions of the world, particularly South Asia, Southeast Asia, Africa, and parts of Central and South America.
Dengue
Dengue fever is a viral infection caused by one of four closely related dengue virus serotypes, all transmitted primarily by the Aedes aegypti mosquito, which thrives in tropical and subtropical climates. The disease is highly endemic in regions of Asia, Latin America, and Africa, with outbreaks often coinciding with the rainy season due to increased mosquito breeding in stagnant water. Dengue presents a significant global health challenge, affecting millions annually and causing a spectrum of illness ranging from mild febrile illness to severe and life-threatening conditions. The initial phase of dengue is characterized by sudden high fever, severe headache, pain behind the eyes, muscle and joint pains (earning the disease the nickname “breakbone fever”), rash, and mild bleeding manifestations such as nose or gum bleeding. The nonspecific early symptoms frequently lead to misdiagnosis, complicating early detection and management.
Severe dengue, which occurs in a subset of patients, represents a critical complication due to plasma leakage, hemorrhagic manifestations, and organ impairment. The critical phase usually appears between days 3 to 7 after fever onset and is marked by increased vascular permeability leading to fluid accumulation in the chest or abdominal cavity and hypovolemic shock. Thrombocytopenia and coagulopathy exacerbate the bleeding risks, which can be life-threatening without prompt intervention.
Management of dengue remains primarily supportive because no specific antiviral therapies exist. Careful fluid management is critical to prevent shock and organ damage, while avoiding fluid overload is equally important to reduce complications from fluid accumulation. Antipyretics such as paracetamol are used to control fever and pain, while nonsteroidal anti-inflammatory drugs (NSAIDs) are avoided due to increased bleeding risk. Public health efforts focus on vector control through insecticide spraying, eliminating mosquito breeding sites, and community awareness programs to reduce transmission. Research is ongoing into vaccines and antiviral agents, but currently, prevention relies heavily on personal protective measures and environmental management.
Malaria
Malaria is a parasitic infection caused by protozoa of the genus Plasmodium and transmitted to humans through the bite of infected female Anopheles mosquitoes. It remains a leading cause of morbidity and mortality in tropical and subtropical regions, particularly sub-Saharan Africa and parts of South Asia. The disease manifests with a characteristic cyclical pattern of fever, chills, sweating, and malaise that corresponds to the lifecycle of the parasite within red blood cells. There are five primary species that infect humans: Plasmodium falciparum, vivax, ovale, malariae, and the zoonotic knowlesi, each varying in severity and geographical distribution. Plasmodium falciparum is the most virulent and associated with severe complications including cerebral malaria, severe anemia, respiratory distress, and multi-organ failure, all of which demand urgent medical attention.
The pathophysiology of malaria involves the invasion and destruction of red blood cells by the parasite, triggering inflammatory responses and microvascular obstruction due to sequestration of infected erythrocytes. This leads to tissue hypoxia, metabolic derangements, and, in severe cases, cerebral involvement with seizures, coma, and death if untreated. Diagnosis relies on microscopic examination of blood smears to identify parasites, supplemented by rapid diagnostic tests detecting parasite antigens.
Treatment of malaria depends on the species involved and local drug resistance patterns. Artemisinin-based combination therapies (ACTs) are now the mainstay of treatment for P. falciparum infections due to their rapid action and efficacy. Severe malaria requires intravenous artesunate or quinine, intensive monitoring, and management of complications like seizures, hypoglycemia, and renal failure. Preventive strategies include insecticide-treated bed nets, indoor residual spraying, chemoprophylaxis for travelers, and vaccine development efforts such as the RTS,S vaccine.
Scrub Typhus
Scrub typhus is a rickettsial infection caused by the intracellular bacterium Orientia tsutsugamushi, transmitted to humans through the bite of infected larval mites known as chiggers. It is endemic to a region known as the “tsutsugamushi triangle,” which includes parts of South and Southeast Asia, northern Australia, and the Pacific islands. The disease often presents as an acute febrile illness with nonspecific symptoms such as high fever, headache, myalgia, and malaise. A pathognomonic feature in many patients is the presence of an eschar, a necrotic lesion at the site of the mite bite, although it can be easily missed depending on its location and skin pigmentation. Scrub typhus can cause multisystem involvement, including pneumonitis, meningoencephalitis, myocarditis, and acute kidney injury, making it a significant cause of morbidity and mortality if untreated.
The pathogenesis involves bacterial invasion and multiplication within endothelial cells lining blood vessels, leading to vasculitis and increased vascular permeability. This results in widespread inflammation, tissue damage, and organ dysfunction. Diagnosis is often clinical but supported by serological tests such as IgM ELISA and indirect immunofluorescence assay, while molecular techniques like PCR offer definitive identification. In resource-limited settings, the Weil-Felix test, though less sensitive, is still used. Due to its nonspecific presentation and overlapping symptoms with other tropical febrile illnesses, scrub typhus is often underdiagnosed, delaying appropriate treatment and increasing the risk of severe complications.
Leptospirosis
Leptospirosis is a zoonotic bacterial infection caused by pathogenic species of the genus Leptospira. The bacteria are shed in the urine of infected animals, primarily rodents, and humans become infected through direct contact with contaminated water, soil, or food. This disease is common in tropical and subtropical regions, especially in areas prone to flooding, poor sanitation, and overcrowding. It often affects agricultural workers, sewer workers, and people exposed to contaminated water during recreational activities. The clinical manifestations of leptospirosis vary widely, ranging from a mild, self-limiting febrile illness to severe and potentially fatal forms characterized by jaundice, renal failure, hemorrhage, and pulmonary complications known as Weil’s disease.
Treatment requires early initiation of appropriate antibiotics, with doxycycline or penicillin being the drugs of choice for mild to moderate disease, and intravenous penicillin or third-generation cephalosporins reserved for severe cases. Supportive care in intensive care units, including dialysis for renal failure and mechanical ventilation for respiratory distress, significantly improves outcomes. Preventive measures emphasize rodent control, proper sanitation, protective clothing for at-risk workers, and public education on avoiding exposure to contaminated water. Given the increasing incidence of leptospirosis worldwide, improved surveillance, rapid diagnostic tools, and better awareness are vital to reduce the global burden of this potentially deadly disease.