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More than 60 million Americans leave the country each year, so it's statistically certain that a small percentage of them will fall ill while traveling. If you're a worrier, or just like to keep informed, you should consider getting vaccinated for the majority of the Deadly Dozen of Infectious Diseases if you are planning to travel into areas where they are prevalent. (Some of the 12 have no vaccines, sad to say.)

The International Association for Medical Assistance to Travellers (IAMAT) says 80% of adults in the western world have not maintained their immunizations status since their school years. If you are one of those 80%, IAMAT recommends you have the following vaccinations before leaving the USA or Canada:

Hepatitis A & B, Tetanus-Diphtheria, Polio, Measles (unless born before 1963), Mumps (unless born before 1957), flu (if over 50 or if you have certain chronic illnesses) and pneumonia. Infants and children have a special schedule for many diseases, as do women of child-bearing age (rubella).

So here are the Deadly Dozen, some waiting for you in far-flung places, others available right here at home. Cross your fingers and be prepared. (In the listing below, the more prevalent disease is given first, diseases of lesser incidence later. Note that the Caribbean is included in the Latin America region discussions.)

Africa, Asia & Latin America

1. Malaria

Malaria is endemic everywhere in Africa (except Libya), everywhere in Latin America (except Cuba, Chile and Uruguay) and in all of Asia (except Japan, Russia, Mongolia, Taiwan, Kazakhstan and some parts of China).

The disease is transmitted by mosquitoes. There is no vaccine, but chemical prophylaxis strategies are available.

2. Cholera

Usually acquired from food and drink. Vaccine available.

Location: all developing nations. 95% of reported cases, however, originate in Africa.

3. Dengue Fever

Also transmitted by mosquitoes, and there is no vaccine available.

Infested with disease-transmitting mosquitoes is all of Latin America, with the exception of Chile and Central America. All of central, southern and eastern Africa also infested. In Asia, the infested areas include the portion of the continent between Pakistan on the west to Papua New Guinea on the east, as well as Philippines, Taiwan and Queensland in Australia.

A few cases have been reported in Texas and Hawaii, and the type of mosquito responsible is prevalent in the southeastern USA.

Africa & Latin America

4. Yellow Fever

Mosquitoes cause this and there is a vaccine.

Location: yellow fever is confined to sub-Saharan Africa (a wide strip across the continent from Senegal in the west to Ethiopia in the east) and the tropical parts of South America. In the latter case, it is the Amazon Basin that defines the area of infection, with much of Brazil, all the Guiana's, all of Colombia, and parts of Venezuela, Peru, Ecuador, Bolivia and Paraguay.

Asia

5. Japanese Encephalitis

The risk is low unless you plan to be outdoors a great deal or visit rural areas for a prolonged period. Transmission is by mosquito bite. A vaccine is available.

Location: From Pakistan through Japan, and from China to Indonesia, Papua New Guinea and the northern tip of Queensland in Australia, as well as Philippines, Taiwan and Guam/Saipan.

Anywhere Worldwide, Including the U.S. and Canada

6. Traveler's Diarrhea (TD)

The CDC says that about 80 to 85% of cases are caused by bacteria, about 10% by parasites and about 5% by viruses. This is actually the Number One disease affecting travelers anywhere. Transmission is by ingesting infected food or drink. There is no vaccine available.

Low risk areas: U.S. and Canada, Australia, New Zealand, Japan, northern and western Europe (except Portugal), the dividing line south of Scandinavia running roughly from Szczecin to the Adriatic.

Intermediate risk areas: eastern Europe and Russia, South Africa, Chile, Argentina, some Caribbean islands.

High risk areas: everywhere else, namely, most of Asia, the Middle East, Africa, most of Latin America. On average, 30% to 50% of travelers in these areas will develop TD in a one- or two-week stay.

7. Hepatitis A

Transmitted through human feces, requiring care in food and drink. Vaccine available.

Low risk areas: USA, Canada, Australia, New Zealand, Japan, northern and western Europe, the dividing line running roughly from Szczecin to the Adriatic.

Intermediate risk areas: eastern Europe and Russia, Turkey.

High risk areas: rest of the world, including all of central and South America, Africa, balance of Asia and Mideast, Greenland.

8. Hepatitis B

Passed on through blood or blood-related fluids, sex and tattooing the predominant causes. Vaccine is available.

Low risk areas: USA (except Alaska), most of Mexico, Colombia, Argentina, Paraguay, Uruguay, central and northern Chile, southern Bolivia, Australia, New Zealand, northern and western Europe (excepting Iberia).

Intermediate risk areas: Alaska, Ecuador, Venezuela, the Guianas, non-Amazon Brazil, northern Africa, Iberia, eastern Europe, Russia, Japan, the Middle East (except Saudi Arabia) and India.

High risk areas: rest of the world, including northern Canada, Greenland, the Amazon Basin, central and southern Africa, central and southeast Asia, China, Indonesia, Philippines.

9. Meningococcal Meningitis

Although this can occur anywhere, frequent epidemics occur mostly in the so-called Meningitis Belt across the Africa continent, from Senegal in the west to Ethiopia in the east. Bacteria are the cause. There is a vaccine available.

10. Tetanus

Usually caused by wounds, and can occur anywhere, especially if wounds are not kept properly clean and bandaged. There is a vaccine.

11. Typhoid Fever

This can occur anywhere, but most cases take place in South Asia and developing countries in Africa, Asia and Latin America. The cause is bacteria in food or drink. There is a vaccine available, though you may need it only if you plan to spend much time in rural areas and small towns in those developing areas.

12. HIV/AIDS

Although mostly sexually transmitted, HIV/AIDS can also occur when blood testing or transfusions are required. There is no vaccine.

Though this can occur anywhere, the fastest-growing rate of the disease is in southern and central Africa, and in Russia, Thailand, Myanmar and Papua New Guinea.

Sources

Information and statistics in this article were obtained from two sources:

(1) CDC Health Information for International Travel 2008, published by the Centers for Disease Control & Prevention, and available in printed form for $24.95. Also available on the CDC website, which is www.cdc.gov/travel.

(2) IAMAT, International Association for Medical Assistance to Travellers, a not-for-profit charitable organization based in Canada. Membership (with a worldwide Directory of English-speaking Doctors) is free, though a donation would be appreciated Their website is www.iamat.org.

Note: The author is vice president (pro bono) of the International Association for Medical Assistance to Travellers (IAMAT), a registered not-for-profit charity.

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