The Diseases

Numerous exotic diseases await those traveling to developing countries, but some simple precautions and vaccines can minimize the risk.

The most commonly acquired disease is traveler's diarrhea that affects up to 40% of travelers. Hepatitis A, a more serious disease, affects less than 1% of travelers. Typhoid fever, malaria, yellow fever, and meningitis are even rarer. The latter diseases are potentially fatal, and the sensible traveler should take precautions against them. Some of these diseases are transmitted by biting insects, others by eating contaminated food or inhaling organisms.

The following list shows ways certain diseases are spread:

• Diseases spread by contaminated food and water: traveler's diarrhea, hepatitis A, thyroid fever, polio, and cholera
  
  
• Diseases spread by mosquitoes and other insects: malaria, yellow fever, and Japanese encephalitis
  
  
• Diseases spread through coughs and close respiratory contact: meningococcal meningitis, tuberculosis, and influenza
  
  
• Disease spread by animals: rabies
  
  

Traveler's diarrhea: Diarrhea is among the most frequent health problems encountered by travelers. Up to 40% of short-term travelers to developing countries and up to 70% of long-term travelers will experience at least one bout of diarrhea. Because traveler's diarrhea is caused by eating or drinking contaminated food and water, people traveling under primitive conditions are at highest risk.

• The risk of diarrhea varies according to the destination, with the highest risk (30-70%) found in Asia, Africa, and Latin America. Travel to the Caribbean, the Mediterranean, Pacific islands, southern Europe, Israel, and Japan carries a lower risk of diarrhea.
  
  
• Many different types of organisms cause traveler's diarrhea. Symptoms vary, but most affected travelers have four to five stools per day for three to four days. Some people have only a few hours of diarrhea. More unfortunate travelers have profuse and frequent stools. About 30% of affected travelers are confined to their rooms, and 40% have to curtail their scheduled activities. High fever, significant abdominal pain, and bloody stools are hallmarks of a more serious type of diarrhea and should cause the traveler to seek medical attention.
  
  
• Select food and drink with care. In most cases, the traveler should carry along an antibiotic to take in case diarrhea develops. If diarrhea is mild, bismuth subsalicylate (Pepto-Bismol), loperamide (Imodium), or diphenoxylate hydrochloride (Lomotil) may be taken to slow things down while the antibiotic is working. These medicines should not be taken if bloody diarrhea, severe abdominal pain, or high fever is present.
  
  
• It is possible to reduce the risk of diarrhea by taking antibiotics or bismuth subsalicylate daily. However, this approach has its own risks and inconveniences. It should be reserved for the rare traveler for whom even a couple hours of diarrhea would be a serious inconvenience.

Cholera: Although cholera calls up visions of medieval plagues and can be a major cause of anxiety in tourists, it is really very hard to catch. The risk of cholera has been estimated at two cases per million travelers.

• Cholera is a problem in areas where significant amounts of human waste contaminate food or water. The level of contamination must be very high, because a large number of the cholera bacteria must be ingested to cause the disease. This causes the food to smell or taste so bad that few tourists are tempted to eat it. Occasionally, the foul taste is covered with spicy sauces. Raw shellfish have been a source of disease in some areas.
  
  
• For the very rare tourist who gets cholera, the good news is that symptoms are usually limited to a few days of diarrhea. If careful attention is paid to drinking fluids, and in severe cases to replacement of salts and sugars, the symptoms go away and do not return. With severe disease, you may have copious watery diarrhea that may exceed 1 liter per hour.
  
  
• The cholera vaccine is not very effective. Currently, vaccination is not recommended or required for international travel. In fact, it is no longer on the market in the United States.

Hepatitis A: Hepatitis is an inflammation of the liver. Hepatitis A is found throughout the world and is transmitted primarily when tiny amounts of human waste are inadvertently swallowed. The disease is caused by a virus that attacks the liver.

• Infection is common throughout the developing world. In developed countries, including the United States, community outbreaks still occur.
  
  
• Food that is handled by infected workers can transmit the disease to unwary tourists, as can vegetables or fruit grown in human night soil. Risk for infection increases with a longer duration of travel. The risk is higher for those traveling to rural areas and for those who eat and drink in settings with poor sanitation. To decrease this risk, it is important to wash hands frequently and observe food and water precautions.
  
  
• Symptoms don't appear immediately. It takes about a month before the sudden onset of fever, fatigue, nausea, and a yellowing of the skin called jaundice. Full recovery may take weeks. Death is rare but does occur. Unlike some other types of viral hepatitis, hepatitis A goes away completely and does not cause chronic disease.
  
  
• Protection against hepatitis A is recommended for all those traveling to developing countries. The vaccine is especially important for those who will visit rural areas or eat in local restaurants. Three options exist to protect the traveler from hepatitis A:
  
• A single dose of the inactivated vaccine in adults is 94-100% effective in preventing disease and provides protection for at least one year. Frequent travelers or those with prolonged stays should get a booster dose at least six months after the first shot. Estimates suggest that the booster shot may protect against hepatitis A for 20 years. The vaccine is not approved for children younger than 2 years.
  
  
• Immune globulin, also known as gamma globulin, is about 85% effective in preventing hepatitis A. Unfortunately, the protection lasts only two to five months (depending on the dose). Those traveling with children under 2 years of age and those who are allergic to a vaccine component should consider immune globulin.
  
  
• A combined vaccination protecting against both hepatitis A and hepatitis B is available for adults. This vaccination is given in three doses, the same as the regular hepatitis B vaccine schedule.

Hepatitis B: Like hepatitis A, hepatitis B is caused by a virus that attacks the liver. The two diseases have significant differences, however.

• Hepatitis B is transmitted through sexual intercourse, dirty needles used to inject drugs, and contaminated blood transfusions. In addition, the virus can be transmitted when having medical, dental, or cosmetic procedures (including tattooing or body piercing) with needles or contaminated equipment. Hepatitis B is not transmitted through more casual contact such as shaking hands, eating, or drinking.
  
  
• Hepatitis B infection occurs throughout the world. The areas with the highest number of people with chronic infection include Africa, Southeast Asia, the Middle East, Pacific Islands, Amazon regions, and certain parts of the Caribbean.
  
  
• Once the virus enters the body, the virus begins to attack the liver. It takes an average of four months for symptoms to develop. Symptoms include nausea, vomiting, and abdominal pain. The hallmark of the disease is the yellowing of the skin called jaundice. Death is rare, but does occur.
  
  
• Most people can clear their body of the virus after a few weeks, but about 6-10% of adults and 30-90% of infants and children fail to clear the virus and become chronic carriers of the disease. Chronic carriers may develop cirrhosis (irreversible scarring of the liver) or primary cancer of the liver.
  
  
• No treatment is available for the acute illness. Medications are available to treat chronic infection.
  
  
• Effective vaccines are available to prevent hepatitis B. The vaccine is recommended for those traveling to areas with increased levels of transmission, especially travelers contemplating sexual intercourse abroad, those likely to seek medical and dental care in local facilities, and those providing health care. All unvaccinated children and adolescents in the United States should receive the vaccine. The vaccine is safe and is actually recommended as one of the routine childhood vaccines for U.S. children. Complete protection requires three shots over six months, but even one or two shots offer significant protection. In addition, a combined vaccination is available that offers protection against both the hepatitis A and hepatitis B virus.

Japanese encephalitis: Japanese encephalitis is caused by a virus that is transmitted by mosquitoes. This rare disease exists in much of Asia, but it is very unusual for travelers to contract it. Transmission is more marked in rural areas, in flooded rice paddies, and during wet seasons. Even where the disease is common, only 1-3% of mosquitoes are infected. The risk to the average traveler is less than one case per million per year. The risk is increased by prolonged stays in infected areas.

• Symptoms include fever, lethargy, and coma. Up to one in five infected people die, and the remainder often have nerve or brain damage.
  
  
• An effective vaccine is given as a three-shot series over two to four weeks. The vaccine can cause side effects including arm pain, fever, and even serious allergic reactions. Vaccination should be reserved for long-term (usually more than one month in duration) travelers to Asia with significant exposure to infected areas during appropriate seasons (often May through October). The CDC has listed the important areas and seasons for transmission on their Web site.

Malaria: Malaria is a disease transmitted by the bite of an infected female Anopheles mosquito. Transmission occurs mostly in areas of Central and South America, Haiti, the Dominican Republic, Africa, Asia (including the Indian subcontinent, Southeast Asia, and the Middle East), Eastern Europe, and the South Pacific.

• Fever is the major symptom of malaria. The disease must always be suspected when fever occurs during or after travel to an infected area. In addition, flu-like symptoms can occur, including chills, headaches, muscle aches, and fatigue. The disease may also cause seizures, mental confusion, kidney failure, coma, and death.
  
  
• Travelers should observe mosquito precautions that include protective clothing, screened windows, mosquito netting, and insect repellants containing DEET. Currently no vaccine is available, but there are medications that can be taken before, during, and after exposure to prevent the disease. The CDC provides information both via the Internet and through a 24-hour hotline (1-877-FYI-TRIP, 1-877-394-8747) for detailed recommendations on proper medication for the destination and specific prevention tips.
  
  
• Several medications are available. The specific type of medication and length of treatment depends on several factors including the traveler's destination. The medicine does not stop the mosquito from biting or the organism from entering the bloodstream. The goal of taking the medication is to destroy the organisms before they have a chance to take hold. Thus, the medications must be continued after leaving the malaria-prone area.

Meningococcal meningitis: Meningococcal meningitis is a bacterial infection of the lining around the brain and spinal cord. The bacteria are transmitted from person to person through the air.

• The disease occurs sporadically in clusters throughout the world. However, the most significant outbreaks occur in sub-Saharan Africa, known as the "Meningitis Belt," extending from Senegal to Ethiopia and recently extending further south into the Great Lakes regions. Transmission is higher in the dry seasons. Those traveling to the meningitis belt during the dry season should be advised to receive the vaccine.
  
  
• During the Hajj, the annual pilgrimage to Mecca, Saudi Arabia hosts thousands of wayfarers from all over the world. Crowded conditions and arrivals from the infected zone of Africa combine to create the potential for an epidemic. Due to an outbreak associated with the 1987 Hajj, Saudi Arabia requires that Hajj and Umrah visitors have a certificate of vaccination before entering the country.
  
  
• Symptoms of meningitis include sudden onset of fever, intense headache, stiff neck, nausea, and vomiting. Other symptoms may include confusion or coma. This disease is potentially fatal and should be considered a medical emergency.
  
  
• Meningococcal meningitis can be treated with a number of effective antibiotics. Vaccination is not required for entry into any country except Saudi Arabia, for those traveling to Mecca during the annual Hajj and Umrah pilgrimage.
  
  
• The bacteria that cause meningococcal meningitis have developed into five slightly different strains, known as serotypes. Currently two vaccines are available. One has been available since 1981, and the other, thought to provide better and longer lasting protection, was licensed in 2005. The newer vaccine is also thought to be better at preventing the disease from spreading from person to person. Both vaccines can prevent four strains of the disease, including two of the three most common in the United States and one type that causes epidemics in Africa. Travelers should check to see if the vaccine is recommended for their destination and receive the vaccine at least one week before departure.

Plague: Plague is caused by a bacteria called Yersinia pestis and is transmitted when people are bitten by fleas or rodents. It has gained attention in recent years as a potential weapon of bioterrorists. Transmission usually requires close contact with rodents in a rural area. Only a handful of cases have been reported in American travelers in the last century. Due to the very low risk of disease, plague is not a concern for the routine traveler. No vaccine is available. Travelers who will live or work in close contact with rodents, such as field biologists, may consider taking daily doxycycline to reduce the risk of disease.

Polio: Although vaccination has eliminated naturally occurring polio in North and South America, rare cases continue to occur in developing countries of Africa, Asia, the Middle East, and Eastern Europe. The disease is caused by a virus that is spread when human waste is inadvertently swallowed. Symptoms include muscle aches and paralysis. Many infected people never have any symptoms. Travelers to infected areas should be immune to polio. For most adults who have already been vaccinated in the remote past, this means a single vaccine dose of the injectable vaccine before travel.

Rabies: Rabies is spread through contact with infected secretions, often from a bite wound from an infected animal. Infected saliva can spread disease into open cuts. In caves, disease may occur when bat guano is aerosolized and inhaled. Dogs, cats, skunks, raccoons, bats, cattle, and foxes are among animals that can transmit rabies.

• Rabies is caused by a virus that works its way into the brain over days to months. Once there, the virus causes coma and is virtually always fatal. Travelers at high risk include veterinarians, spelunkers (cave explorers), and those who will handle wild animals. Travelers should avoid petting, touching, or playing with animals in developing countries.
  
  
• Travelers to developing countries who will not have access to medical care for prolonged periods should consider vaccination.
  
  
• Bite wounds should be cleaned immediately with soap and water. Unless there is a way of ensuring that the animal is free of rabies, the bitten traveler should be evaluated by experienced medical personnel and will require vaccination to prevent rabies from occurring. Although the vaccine available in the United States is relatively safe, vaccines available in developing countries may cause significant side effects. Further, the cleanliness of needles used for injection may be a concern. In most cases, evacuation to a developed country for vaccination is recommended even if this would delay vaccination by a few days. Sometimes, an injection of rabies antibodies is also needed. Even travelers who have been vaccinated in the past need to be evaluated and often vaccinated after bite wounds.

Smallpox: Smallpox is caused by a virus that is transmitted from person to person. Naturally occurring smallpox was eradicated from the globe in 1980. Smallpox remains a concern only as a potential weapon for bioterrorists. An effective vaccine exists but is not recommended on the basis of travel to a developing country. No country requires vaccination for entry.

Typhoid fever: Typhoid fever is a bacterial infection of the intestinal tract and blood stream. It is spread by contaminated food and water. The bacteria are passed in the feces and urine of those infected. Therefore, infection can occur by eating food handled by someone who has not washed their hands after using the bathroom or by drinking water directly contaminated by sewage containing the bacteria.

• Regions affected include the Indian subcontinent and other developing countries in Asia, Africa, the Caribbean, and Central and South America. There are approximately 22 million cases worldwide. Approximately 400 cases are reported in the United States, mostly among travelers.
  
  
• Fever is the hallmark of the disease. Headache, weakness, stomach pains, diarrhea, and loss of appetite can occur. Some people may develop a rash of flat, rose-colored spots that usually disappears in three or four days. Although most people clear the bacteria from their system, a few may appear to recover but still shed the bacteria in their stool. These carriers feel fine but can inadvertently spread the disease to others.
  
  
• Antibiotic therapy is the only effective treatment for typhoid fever. Supportive measures, including fluids, medications to bring down fevers, and appropriate nutrition are also important.
  
  
• Frequent hand washing is recommended, as are food and water precautions.
  
  
• Two new typhoid vaccines are available. One is a capsule by mouth requiring a booster every five years and the other is an injection with a booster recommended every two years. Both vaccines are safe and effective. Vaccines need to be completed at least one week before travel.

Yellow fever: Yellow fever is a viral infection that is spread by mosquitoes. The disease occurs in sub-Saharan Africa and South America. It has never been documented in Asia. The CDC provides current information about which countries and regions are affected.

• People who are infected get fatigued, become feverish, and their skin turns yellow. A small number die. The diagnosis can be confirmed by blood tests. No specific treatment is available for yellow fever.
  
  
• Those traveling to at-risk areas should take general precautions against exposure to mosquitoes. Wearing long-sleeved shirts and long pants, using insect repellents containing DEET on exposed skin and permethrin-containing repellents on clothing, and staying in screened-in and air-conditioned areas can reduce mosquito bites. However, the vaccination is the most important measure for protection, and therefore it is important to contact a health-care provider at least two weeks before travel to determine if the vaccination is recommended.
  
  
• The yellow fever vaccine is a safe and effective vaccine that can only be given at authorized yellow fever vaccination centers. Protection occurs in 95% of those who receive the vaccine and takes place within one week. After one dose, protection lasts for 10 years. Those traveling to areas at risk should talk to their health-care provider before receiving the vaccine. Vaccination is sometimes required before travelers are permitted to enter selected countries. Some countries require vaccination only if the traveler is coming from an infected area. The United States is not an infected area. An International Certificate of Vaccination, stamped by an official vaccinating center, affords proof of vaccination. In the United States, the CDC is responsible for licensing official vaccination centers. The official vaccination certificate is good for 10 years.

Other immunizations and diseases: A visit to a doctor for travel-related vaccines is a good time to make sure your routine vaccines are up to date.

• In the United States, tetanus boosters are recommended every 10 years.
  
  
• People born after 1956 should make certain that their measles vaccines are up to date. Older people are usually assumed to have had measles as children.
  
  
• Influenza occurs in the winter season in temperate areas and year-round in the tropics. Vaccination should be considered in travelers aged 50 years and older and in persons with chronic medical conditions.
  
  
• Tuberculosis has a worldwide distribution. Long-term travelers may want to consider getting a skin test prior to departure. Travelers with negative skin tests should have a repeat test after returning. The BCG vaccine is of uncertain value and is neither recommended nor available in the United States.