Tropical Medicine 2: Introduction
Global health encompasses a wide range of considerations, including topics such as healthcare delivery systems, nutrition, water and sanitation, animal health, and infectious diseases. The treatment of tropical infectious disease is referred to as tropical medicine.
Tropical infectious diseases were once the purview of a small
group of experts. Given our modern complexities of rapid travel,
extensive immigration, international tourism and volunteerism, and
military service abroad, a familiarity with tropical infectious disease
is vital to American physicians. Diseases not endemic to the United
States are now regularly encountered, even in rural areas. These
infectious diseases are the focus of this section of the diagnostic and
treatment portals.
Classification of Tropical Infectious Agents
- Viruses
- Prokaryotic organisms (bacteria)
- Eukaryotic organisms
- Protozoan—Single-celled organism
- Lumen-dwelling, eg, Entamoeba, Giardia
- Tissue-dwelling, eg, Plasmodium, Trypanosoma
- Metazoan—Multicellular organisms
- Nematodes—Round worms
- Geohelminths, eg, Ascaris, Trichuris, hookworms
- Filariae, eg, Wuchereria, Onchocerca
- Other tissue-dwelling nematodes, eg, Trichinella, Toxocara
- Cestodes—Flatworms (tapeworms)
- Lumen-dwelling stage, eg, Taenia, Diphyllobothrium
- Tissue-dwelling stage, eg, cysticercosis, hydatid cysts, sparganosis
- Trematodes—Flukes
- Liver or biliary tract, eg, Fasciola, clonorchis
- Mesentery or bladder, eg, Schistosoma
- Lung, eg, Paragonimus
- Nematodes—Round worms
- Protozoan—Single-celled organism
Considerations
Tropical infectious diseases caused by bacteria and viruses tend to progress rapidly. While some may be relatively benign, others can be life-threatening and require prompt diagnosis and treatment.
Parasitic infections, especially the lumen-dwelling ones, tend to have more indolent and chronic courses. Some parasites, however, may be acutely life-threatening, so every effort must be made to reach an accurate diagnosis.
A working knowledge of parasitology is essential for practicing emergency physicians. Worldwide, one billion people are infected with Ascaris, Enterobius, and hookworm.1,2 Malaria affects 250 million people, and causes more than 1.5 million deaths per year in Sub-Saharan Africa alone.1,2 Two hundred million people suffer from schistosomiasis.1,2 While many of these diseases are not endemic to the United States, they are seen increasingly, even in rural areas, due to immigration, international tourism and volunteer work, and the ability to travel around the world in 24 hours. In addition, some parasitic diseases are endemic in the United States (amebiasis, giardiasis) and are seen in susceptible hosts, including institutionalized and immunocompromised patients.
The epidemiology of parasite infestation differ somewhat from the microbes with which American are most familiar, so a brief overview may be helpful.
Risk Factors for Parasitic Disease Include:
- Domicile/traveler in endemic zones
- Consumption of raw or incompletely cooked food (eg, fish – Diphyllobothrium, anisakiasis; pork – Taenia solium [T solium], Trichinella; beef – Taenia saginata [T saginata], Toxoplasma; vegetables [watercress] – Fasciola)
- Barefoot exposure to soil (eg, Toxocara [larva migrans], hookworm)
- Exposure to fresh water (eg, Naegleria, schistosomiasis)
- Blood transfusions, IV drug use, and other blood-to-blood exposures (eg, Plasmodium, Trypanosoma, Babesia)
- Homosexuality (Giardia, Entamoeba)
- Immunocompromised (Toxoplasma, Cryptosporidium, Pneumocystis, Strongyloides, Microsporidium)
Many parasites are transmitted via the fecal-oral route, from either another person or an intermediate (non-human) host. Some parasites are transmitted by consuming the intermediate host. Others are transmitted via vectors, ie, organisms in which an obligate portion of their lifecycle must be completed prior to becoming infectious to humans.
Vectors and Intermediate Hosts—Interesting and Varied
- Mosquitoes—malaria, filariasis
- Flies (eg, sandfly—leishmaniasis; tse tse fly—trypanosomiasis; black fly— onchocerciasis)
- Snail—schistosomiasis
- Kissing bugs—Chagas disease
- Fish—Diphyllobothrium latum
- Large animals—Echinococcus, Taenia, Toxocara, and Giardia
Presentation of the Topics
The series of portals making up the Tropical Medicine section is organized by presenting complaint. Proper evaluation of individuals at risk for tropical infectious disease includes non-tropical etiologies for the presenting complaint. Common things are common, even in the tropics. The Tropical Medicine section focuses on causes of disease that are more unique to the tropics and thus may appear to be more exotic causes of symptoms, assuming that CALS participants already have the knowledge to identify and address non-tropical conditions that may cause the presenting complaints. The following are clinical manifestation of tropical diseases.
References
- Gill GV, Beeching NJ. Lecture notes in tropical medicine, 5th ed. Malden, MA: Blackwell Science, 2004.
- Jamison DT, Breman JG, Measham AR, et al. Disease control priorities in developing countries, 2nd ed. Washington, DC: World Bank and New York, NY: Oxford University Press, 2006 (co-publication).