2. Malaria
Malaria, a parasite acquired through the bite of the female Anopheles mosquito, is a potentially fatal illness in many areas, especially sub-Saharan Africa and South Asia. In fact, it’s responsible for close to a million deaths annually. The classic symptoms include fever that cycles every day or two, muscle aches, chills and fatigue — and these can occur up to a year after your return home. Although a vaccine might be on the horizon, current measures to prevent malaria include taking a course of medication before, during and after your trip, using mosquito repellants with 30 percent DEET, wearing long-sleeved shirts and pants on hikes (rather than T-shirts and shorts) and using mosquito netting when sleeping.

3. Dengue
Dengue is caused by the bite of the Aedes mosquito and has emerged as a significant illness over the last 50 years. It’s found in tropical and subtropical destinations around the world; most instances involving Americans have been on trips to the Caribbean, the Pacific islands (Guam and Samoa), Asia and Central and South America. Thankfully, most cases are mild; more serious cases can cause severe flu-like symptoms and possibly lead to shock and death. As with other mosquito-carried infectious diseases, prevention measures include insect repellant, mosquito netting and proper attire on hikes. Unfortunately, there’s no preventive medicine or vaccine, but early detection can make the difference between mild and severe illness.

4: Hepatitis
There are various forms of Hepatitis. Hepatitis A, a virus that infects the liver, is one of the most common vaccine-preventable travel diseases. You can pick it up in many popular travel destinations — in cities and at resorts — by ingesting contaminated food and water. Although most cases are mild, especially in young children, older children and adults might experience abdominal pain, flu-like symptoms and jaundice. And symptoms can last several months. Thankfully, there’s a safe, effective vaccination; you should strongly consider getting it before trips to developing nations. There’s also a vaccine for Hepatitis B, a potentially chronic and fatal form of the illness that affects the liver. Although the primary mode of transmission is sexual contact, in some places there’s a risk of becoming infected via tainted blood supplies and surgical instruments should you undergo emergency medical care (Hepatitis C is also a risk here in the United States). If you receive the full series of vaccines to treat both forms, you’re considered immune for life. But there currently is no vaccine for Hepatitis C, the most serious of the strains.

5. Typhoid
Typhoid is caused by a bacterium that you can pick up via contaminated food and water. It’s particularly a concern when visiting countries where sanitation and sewage systems aren’t well developed. It can lead to serious illness or even death. Symptoms include fever (and potentially delirium), headache, malaise, a rash and intestinal perforation. The vaccine provides about two years of protection.

6. Polio
Another infectious disease picked up via contaminated food and water, polio was once common in the United States. Though improvements in hygiene practices and immunization campaigns have eradicated it from the U.S., it’s still a concern in central and south Asia and sub-Saharan Africa. Most cases are mild; less than 1 percent of infections lead to the most feared complications of paralysis and death. If you received childhood polio vaccines, you only need one additional vaccine to be protected for life.

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