Tropical Infection

Introduction
Tropical infections are infections there are “acquired” in the tropics which is in the approximate latitude 23 degrees on both sides of the equator.(between the tropic of Cancer and the tropic of Capricorn) These infections thrive in the warm humid environment of this region. With increased travel and global warming, these infections are expanding both northward and southward.

Epidemiology
Tropical infections are endemic in the tropics. Disease morbidity/ mortality reporting varies from country to country, with patchy coverage in the underdeveloped regions and better reporting in more developed countries like Singapore. Western travellers to the tropics are most at risk as they have no immunity to most of these infections. Sometimes, the travellers manifest with symptoms only when they return to their home country. When they bring home “tropical diseases” , doctors in their home country may not be familiar with the clinical presentation, and find difficulty diagnosing and treating these diseases. The notable examples are malaria, Dengue fever and tropical diarrhoeal diseases. The specific diseases are covered under “Types of Infections” on this website.

Clinical Presentation
The common tropical infections that we see can be classified as follows :

  1. Foodborne diseases : Infective diarrhoea due to bacteria, viruses and parasites. Many of these infections are not confined to the tropics but the climate in the tropics predisposes to spoilage of stored food and bacteria contamination. For most travellers, typhoid, paratyphoid, bacillary dysentery and amoebic dysentery are well reported from developing countries
  2. Insect borne diseases : Dengue, Zika, Chikungunya, malaria are mosquito borne diseases which are endemic in the tropics. Other mosquito borne disease include Yellow Fever, Japanese B Encephalitis, Filariasis , etc . Other disease like scrub typhus and endemic typhus are related to shiga mites ( scrub )and rat fleas (murine or endemic ). In certain countries, leishmaniasis is borne by sandflies ( Africa, India, Spain, Italy ) and African Sleeping Illness ( Trypanosomiasis )is borne by tsetse flies.
  3. Water borne diseases : Leptospirosis can be acquired from brackish water contaminated by rat urine and is a serious systemic disease that can result in multi-organ failure and death. Bilharziasis is acquired from swimming in contaminated freshwater lakes ( Lake Malawi is endemic ) , the condition predisposes to bladder cancer. Drinking contaminated water can cause infection as in Cryptosporidiosis and Giardiasis, amoebiasis, etc. Hepatitis A is also a water borne disease but more people know it as a foodborne disease because the virus is concentrated in filter feeders like oysters and shellfish in contaminated waters
  4. Airborne diseases that are more common in the tropics include meningococcal meningitis ( in the meningitis belt in Africa & Saudi Arabia during pilgrimage ) as well as tuberculosis from contact in crowded areas
  5. Parasitic diseases can be acquired from ingestion of contaminated water, food or due to poor hygiene. Avoid eating uncooked food or salads in developing countries and drink only bottled water or boiled water. In extremely rural environments, one may even have to brush teeth with bottled water.

Diagnosis
The types of tests done depends on the suspected pathogens. For fever cases, normally we have to do a blood culture and blood film for malaria parasites. Other tests that are commonly done include :

  • Stool examination and PCR multiplex tests for detection of stool pathogens
  • Urine and stool tests for parasites
  • Serology tests for viral pathogens, typhus and parasites
  • CT scans abdomen eg to look for liver abscess
  • Brain scan for meningitis and lumbar puncture for cerebrospinal fluid examination

Treatment
Treatment depends on the diagnosis. Most viral illness cannot be treated and will run a self limiting course. Bacterial infections are treated with antibiotics based on the type and site of infections. Parasitic infections will require use of specific anti-parasitic agents.

Prevention
In general, attention to healthy eating and personal hygiene will help to prevent most tropical infections. There are vaccinations available to prevent diseases like Hepatitis A, B, Japanese B encephalitis, yellow fever, typhoid, cholera, meningitis, influenza, etc

Drugs to prevent malaria are available if the travel brings you to malarious areas.

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