An enormous number of people died as a result of the 2004 tsunami in the Indian Ocean — some drowned, some were swept away by the wave, and some were killed by collapsing buildings. In addition to the deaths caused by the tsunami itself, this type of natural disaster disrupts the normal balance of nature and creates many health problems.

For example, many people are left without a place to live after their homes are destroyed. Without shelter, people are exposed to insects and natural elements like extreme heat. To make matters worse, many of the animals that normally feed on insects are killed during a natural disaster, and so even more insects are left to carry diseases. Also, food and water supplies can become contaminated by parasites and bacteria when essential systems like those for water and sewage are destroyed. This can also contribute to outbreaks of serious diseases. These problems often become even more serious because it can be difficult to get medical care to the people who need it when there is so much destruction.

Getting clean drinking water, food, shelter and medical care to survivors as quickly as possible is important to avoid even more illness and death. Medical and public health personnel — like those at the CDC — travel to disaster sites to bring in medical supplies, monitor and survey for infections, and help rebuild water systems and housing. Helping people cope with stress and grief is also important.

After the Asian tsunami, there was a lot of worry about infectious disease outbreaks, particularly those spread though contaminated food and water, or through animals and mosquitoes.

Information on these diseases, and their symptoms and treatments are below.

Diseases like cholera, hepatitis A and E, and typhoid can all be caused by infected food and water. Most often, they occur when drinking water is contaminated by sewage, or when food is prepared by someone who has the virus or bacteria on their hands. Symptoms can range from vomiting and diarrhea for cholera, to abdominal pain and yellow eyes and skin (known as jaundice) for hepatitis, and high fever with typhoid. Most people are fine if they get treatment, but in disaster zones it can be difficult to get the right care. People with cholera and typhoid can die if they don’t get the treatment they need. And, when there aren’t clean water or bathroom facilities, these diseases can spread and infect many people quickly, making it even harder to care for people who are infected.

After a natural disaster like the tsunami, people are also at greater risk of catching diseases from infected animals and mosquitoes. Diseases like leptospirosis, plague and rabies most often occur when a person handles or is bitten by an infected animal, while diseases like malaria, Japanese encephalitis and Dengue fever are caused when a person is bitten by an infected mosquito. A person with leptospirosis who goes untreated could develop kidney damage, meningitis, liver failure or respiratory problems, while untreated cases of rabies, plague, and malaria can kill people.

Most people are okay if they get treated right away. Antibiotics are now available that can treat leptospirosis and plague. There is a vaccine that helps prevent people from catching rabies, and there are prescription drugs to treat diseases like malaria.