A Guide to Tropical Diseases

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Tropical Diseases, are illnesses that either occur uniquely in tropical and subtropical regions (which is rare), or are either more widespread there or more difficult to prevent or control—mainly for reasons of climate, poverty, and primitive sanitation conditions. Insects such as mosquitoes and flies are by far the most common disease carrier or "vector".

Today I shall cover some common and prevalent tropical diseases. These diseases have substantial impacts on the developing world; in terms of both number of deaths and the ability to maintain a normal life. For further information regarding any of the topics discussed here, please examine the additional resources.

Tuberculosis (TB) is a chronic, communicable infection due to the bacteria Mycobacterium tuberculosis. Tuberculosis most commonly affects the lungs, but can spread to almost any part of the body.

Burden of Disease
  • billions of dollars reduction in income in the poorest countries
Epidemiological Trends
  • Increasing HIV-related trend in Africa and Eastern Europe
  • Increase in multi-drug resistance
Principal Control Strategy
  • Case finding and directly observed multi-drug treatment.

Dengue fever is a mild viral illness transmitted by mosquitoes. It is characterized by fever, rash, and muscle and joint pains.

Burden of Disease
  • Cost of DF/DHF epidemic outbreaks
  • Burden of DF (DALYs only reflect DHF)
Epidemiological Trends
  • Fourfold increase in incidence since 1970
  • Regular epidemics; 1.3 million cases of DF/DHF in 1998
Principal Control Strategy
  • Active surveillance and case management, selective vector control

Malaria is an infection affecting red blood cells, liver, and potentially brain and kidneys. Malaria is caused by the Plasmodium parasite that is transmitted from one human to another by the bite of infected Anopheles mosquitoes vector. There are four species of Plasmodium - the parasite causing malaria. Malarial infection with each of the four species causes on large similar symptoms and signs, although the malaria severity of the symptoms may be different.

Burden of Disease
  • 1.3% reduction in annual economic growth rate in Africa
  • Disability owing to severe disease
Epidemiological Trends
  • Increase in mortality and drug-resistant malaria
  • Increase in epidemic malaria and P. vivax
Principal Control Strategy
  • Early diagnosis and prompt treatment
  • Prevention: ITMs, other vector control, intermittent treatment in pregnancy
  • Early detection/prevention epidemics

Leprosy is an infectious disease caused by the organism Mycobacterium leprae. It is characterized by disfiguring skin sores, nerve damage, and progressive debilitation.

Burden of Disease
  • Psycho-social impact of disability
Epidemiological Trends
  • Major decline in registered cases
  • Impact of MDT on transmission not clear
Principal Control Strategy
  • Case finding and multi-drug treatment

Lymphatic filariasis is a parasitic disease caused by microscopic, thread-like worms. The adult worms only live in the human lymph system. The lymph system maintains the body's fluid balance and fights infections.

Burden of Disease
  • Psycho-social impact of disability filariasis
  • Economic impact: loss of billions annually in India alone
Epidemiological Trends
  • Major decline in past decades in Pacific and China
  • Impact of global elimination campaign not yet known
Principal Control Strategy
  • Interruption of transmission through periodic mass treatment
  • Disability alleviation by local hygiene

Onchocerciasis (river blindness) is infection with the roundworm Onchocerca volvulus. It causes itching, a rash, sometimes with scarring, as well as eye symptoms that may lead to blindness.

Burden of Disease
  • Psycho-social impact of skin lesions
  • Fertile land abandoned for fear of onchocercal blindness
Epidemiological Trends
  • Eliminated as public health problem in OCP area
  • Declining disease burden in treated populations elsewhere
Principal Control Strategy
  • Periodic mass treatment to eliminate the disease as a public health problem

Schistosomiasis is an infection caused by one of the five species of the parasite Schistosoma. Schistosoma infections are contracted through contact with contaminated water. Can damage the liver, bladder, and intestines.

Burden of Disease
  • Significant indirect morbidity and mortality
  • Growth stunting, nutritional and cognitive impairment
Epidemiological Trends
  • Decline in Asia, Middle East and Americas.
  • 85% of DALYs now in Africa
Principal Control Strategy
  • Morbidity control through periodic treatment in high-risk populations

Leishmaniasis is a parasitic disease spread by the bite of infected sand flies. There are several different forms of leishmaniasis. The most common are cutaneous and visceral. The cutaneous type causes skin sores. The visceral type affects internal organs such as the spleen, liver and bone marrow. People with this form usually have fever, weight loss and an enlarged spleen and liver.

Burden of Disease
  • Psycho-social impact of disability
  • Impact of epidemics on development projects
Epidemiological Trends
  • Increase in number of cases in many parts of the world
  • Emerging Leishmania/HIV co-infections
Principal Control Strategy
  • Case finding and treatment, selective vector/animal reservoir control

Trypanosomiasis African: Sleeping sickness is an infectious disease caused by certain flies, which results in swelling of the brain. Sleeping sickness is caused by two organisms, T. brucei rhodesiense and T. brucei gambiense.

Burden of Disease
  • Economic impact of epidemics
  • Physical and intellectual impairment in children
  • Depopulation of fertile lands
Epidemiological Trends
  • Fourfold increase in reported number of new cases since 1990 (48 000 in 1999), actual incidence is much higher.
  • Epidemics especially in conflict zones
Principal Control Strategy
  • Active surveillance, case finding and treatment, selective vector control

Chagas’ disease (American): Chagas disease is caused by a parasite. Infected blood-sucking bugs, sometimes called kissing bugs, spread it.  Symptoms, they might include; Fever, flu-like symptoms, a rash and a swollen eyelid.

Burden of Disease
  • Forced retirement of seropositive employees
  • High cost of palliative treatment in chronic disease
Epidemiological Trends
  • Towards elimination in Southern Cone countries
  • No change in Andean and Central American countries
Principal Control Strategy
  • Interruption of transmission through vector control and improved blood transfusion

Mycoses (fungal infections)
(Image: John L. Bezzant,M.D via UoUtah)
Finally, it is important to consider Mycoses aka Fungal Infections. There are about 1 million fungal species; only about 20 associated with systemic infections and about 12 with superficial infections in humans. Fungal infections however, can be very difficult to treat without harming the host.

A basic resource for an introduction to fungal infections is DrFungus.

Opportunistic Fungal Infections.

Useful Resources
Online
Articles
  • Tuberculosis: Campbell & Bah-Saw: Br Med J 2006; 332:1194-7
  • Leprosy: Naafs: Trop Med Int Health 2006; 11:268-78
  • Filariasis: Tisch et al: Lancet Infectious Diseases 2005; 5:514-523
  • Onchocerciasis: Molyneux: Trends in Parasitology 2005; 21:526-529
  • Schistosomiasis: Southgate et al: J Helminthology 2005; 79:181-185
  • Other Helminths: Bethony et al: Lancet 2006; 367:1521-1532
  • Leishmaniasis/trypanosomiasis: Croft et al: Trends in Parasitology 2005; 21:508-512
  • Tropical protozoan infections: Liñares et al: Current Medicinal Chemistry 2006; 13:335-360.

1 comment:

  1. Thanks for sharing this great article, I really enjoyed the insign you bring to the topic, awesome stuff!


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