Avoiding malaria is one of the more controversial issues in travel health, and a lot of specialists have different opinions on the best prevention methods. I'm not a doctor, just a backpacker, so my advice comes from thorough research - as yours should - and plenty of personal experience.
Malaria is common in sub-Saharan Africa; in large areas of the Middle East, South and South East Asia, Oceania, Haiti, Central and South America; and in parts of Mexico, North Africa and the Dominican Republic. Just draw a wide band along the equator and you're more or less in malaria territory.
It's been around since Antiquity, and was thought to come from bad air, or 'mal aria' near swamps.
There are three key things you should know about malaria.
First, there is no vaccine for it.
Second, nothing can protect you 100%.
And finally, it can appear months after you've been bitten so if symptoms resembling flu - high fever accompanied by severe chills and muscle spasms - appear after you've returned home, head for the clinic and tell them you've been in a malaria-risk region. Left untreated, malaria can be fatal.
The first thing you need to do is be aware of the malaria risk where you're going. How bad is it? Is it equally distributed throughout the country? There are a number of precautions you should take to avoid being bitten and here are the most common - and most effective.
The female anopheles mosquito, which carries malaria, tends to bite at night, from dusk to dawn.
Keeping mosquitoes away is only part of your protection and on its own it's not enough. The principal way of avoiding malaria is by taking antimalarial pills. They may not be 100% effective, but more than a million people die each year of the disease and you don't want to be one of them.
The first thing to do is to consult a specialist to find out which drug is best not just for you, but for where you're going. And please do consult a special travel clinic or doctor. Unless you live in the tropics, your kind general practitioner down the road is probably not well-versed in the best malaria drugs, especially since a number of these drugs can cause anywhere from mild to severe side effects. For example, chloroquine can cause nausea, the antibiotic doxycycline may make it easier for you to get sunburned, and mefloquine can provoke severe psychological disturbances (while I never suffered from it I've met people who had such bad episodes they literally had to go off the drug).
The most popular drug was once chloroquine but it is increasingly ineffective as mosquitoes build up resistance to it, although it is still used in places where resistance isn't too strong.
Most of Central America and the Middle East, for example, tends to be suitable for chloroquine, but huge swathes of South America, Africa, South and Southeast Asia are resistant to it. So make sure you tell your doctor exactly where you're going (and for how long, because that also affects which drug you'll take). Come armed with some research if your doctor isn't a tropical medicine specialist.
There seems to be some belief that the drug with the least side effects is the newest one, Malarone. I've taken it for trips to Panama, Senegal and the Congo and haven't felt any side effects at all. Nor did I get malaria, despite being bitten by several mosquitoes.
This doesn't mean it will work for everyone but new drugs are constantly being developed so please, stay abreast of developments if you're headed to an area with a high malaria risk.
Be aware that not all parts of a country are necessarily a malaria risk. Here, experts disagree on the best ways of avoiding malaria. Some say take the pills no matter where you go in the country, while others say do so only if you're going to malarial areas.
It's likely you'll face fewer risks in the cities. For example, you won't have to worry much about malaria in Bangkok, but you will have to in the rural north and south. And Rio doesn't carry the same risks as the Amazon. Altitude also plays a part: malaria tends to occur at lower altitudes and anything above 1500m should be less worrisome.
Even if you're careful you may still get malaria so best to know the symptoms: similar to flu, including fever, chills headache, aching muscles, tiredness, nausea and diarrhea. It usually starts with the shivers, after which you get hotter and hotter until you sweat profusely.
If you develop these symptoms when you're in a malaria risk area, it is essential to get to a doctor, not in a few days, but immediately. Otherwise you may be at risk of developing cerebral malaria, which can be fatal. A blood test, available throughout the developing world, will determine whether you're infected, and treatment is widely available.
Avoiding malaria is one thing, but there's also dengue fever, a painful disease from mosquito bites that can take a long time to subside and makes your bones feel like they're breaking (this from a friend who caught it in Thailand). Like malaria there is no vaccine, and also like malaria, dengue requires avoiding bites by covering up and using repellent. It is found in similar climates, tropical and sub-tropical, with the difference that mosquitoes bite during the day.
The bad news: where malaria and dengue coexist, you'll have to take major precautions both day and night.
For the latest information on avoiding malaria, visit the CDC website before you go.