Many governments require visitors entering, or residents leaving, their countries to be vaccinated for a range of diseases. These requirements may often depend on what countries a traveller has visited or intends to visit. For example, if you have recently visited tropical countries in Africa or Latin America, then other countries may require evidence of yellow fever vaccination before letting you in (if they are also susceptible).

If you are bringing prescription medicine with you, carry a copy of the prescription, or at least have it in the original container with a pharmacy/chemist label showing both your and the doctor's name, name of the drug, and dosage instructions.

For much travel, especially to tropical or developing countries, additional vaccinations or other precautions such as anti-malarial medication may be necessary.

Before starting your travels you should consult a doctor with experience in the field of travel medicine. You should do this at least 8 weeks before you plan to leave, to give time for vaccinations.

There are many sources of additional information for travellers:

• The US government's Centers for Disease Control and Prevention, who also maintain a Health map showing current outbreaks of many of the diseases listed below.
• The International Society for Travel Medicine has an index of travel medicine clinics
• The World Health Organization has a downloadable book written for doctors

Diseases in these categories are typically spread by being bitten by arthropods; a group of small animals including insects such as mosquitos, fleas and flies, as well as others such as mites, ticks and lice. The risk from such diseases can be reduced by appropriate clothing, mosquito nets, insect repellents and permethrin-treated fabrics, especially when travelling to rural areas.

For more information on prevention and treatment of diarrhea, see the Travellers' diarrhea article.

For more information on water contamination and filtering, see the Water article.

Diseases in this category are typically transmitted by ingesting contaminated food or water. The best precautions are to do proper boiling or filtering of water before you drink it. This includes ice made from tap water, as freezing does nothing to kill germs. Also, ensure that any food you eat is well cooked. Fruits and vegetables that can be peeled are much safer than those that cannot. Be sure any knives used for cutting are clean.

If the main symptoms of an illness are an initial fever and vomiting with persistent diarrhea, it was most likely caused by something you ate. Most fevers are low grade, though a high fever may indicate a serious, possibly life-threatening illness.

Diseases in this category (also known as sexually transmitted diseases, STDs) are typically spread by having unprotected sex with infected persons. However, many of them can also be transmitted by sharing needles, or through contaminated blood transfusions. The best forms of protection against such diseases are monogamy, abstinence, or safe sex practices. Sharing of needles should be avoided, and should you need to receive an injection, ensure that all needles used on you are properly sterilized. Some travellers bring their own sterile disposable needles.

While these diseases are not spread by casual contact, the reverse is not true — all contagious diseases can be transmitted through sexual activity. In addition, some vector-borne diseases, such as Zika, can infect via sexual transmission.

• Hepatitis B and C. Can be spread by entry of blood or bodily fluids from an infected person into the body, such as through sexual contact, sharing of hypodermic needles, or blood transfusion. "Hepatitis B is not spread through food or water, unlike hepatitis A (US CDC FAQ); nor by sharing eating utensils, breastfeeding, hugging, kissing, coughing, sneezing or casual contact." Symptoms of acute hepatitis A or B include abdominal pain, vomiting, and jaundice; either can sometimes kill. Acute hepatitis C is rare. Over many years, any of the hepatitis infections can cause liver scarring and liver cancer.

There are effective vaccines for hepatitis A and B, often combined into a single shot. These are recommended for many travellers; check with your doctor. As of mid-2021, there is no vaccine for hepatitis C yet.

It is controversial whether type C is even sexually transmitted at all. However, this matters little to the average person, who must take precautions against the myriad of other STIs. Hepatitis B infection can be suppressed with antiviral medications similar to HIV. Hepatitis C can be completely cured in most cases, but the price of the medication used varies hugely; see medical tourism for details.

• HIV (AIDS). Human immunodeficiency virus (HIV) is spread in the same way as hepatitis B. If left untreated over several years, the virus will cause a person's immune system to fail and lead to acquired immune deficiency syndrome (AIDS). Chastity or safer sex practices such as always correctly using high-quality condoms – and an absolute ban on needle-sharing – are wise precautions in any country of the world. No vaccine is available and there is no cure. Antiretroviral medication can keep an HIV infection from progressing to AIDS for decades and is used prophylactically for those who have been exposed or at high risk of being exposed to the virus (e.g. after a needlestick injury).
• Herpes. A viral disease spread primarily by sexual contact, but also through kissing. Primarily has two forms - oral herpes and genital herpes. Symptoms of the disease are typically cold sores. The virus is able to stay latent in the human body, and reactivate later in life. While medical treatment can reduce the recurrence of a relapse, there is no cure or vaccine.
• Gonorrhea. A bacterial disease primarily spread through unprotected sex. Symptoms include a burning sensation when urinating, as well as pus being discharged from the penis in men. Particularly dangerous for pregnant women, as it can spread to the baby during childbirth. No vaccine is available, but it can be treated with antibiotics.
• Syphilis. A bacterial disease primarily spread through sexual contact. Early symptoms include chancres on the genitals. In later stages, papules and nodules can start to form all over the body. Severe cases cause infections of the brain. If not treated, it can cause architectural distortion of all parts of the body called gummatous syphilis. Particularly dangerous for pregnant women as it can spread to unborn babies and cause deformities, a condition known as congenital syphilis. No vaccine is available, though it can be treated with antibiotics such as penicillin.
• Chlamydia. A bacterial disease that is one of the most common sexually transmitted diseases in the world. Symptoms include pus discharge from the penis in men. Infection in women is usually asymptomatic, but sometimes causes inflammation of the cervix. If left untreated, it can spread to the eye and cause blindness. No vaccine is available, but antibiotics such as azithromycin are available to treat the disease.
• HPV. The human papillomavirus (HPV) is a sexually transmitted virus linked to several forms of cancer, including cervical and anal cancer. A vaccine for some strains of HPV is available, and while it does not prevent all cases, it greatly reduces the risk of contracting the disease. However, the vaccine is most effective when administered to people a few years before their first sexual intercourse.
• Mpox. Commonly known as monkeypox, Mpox is usually spread through sexual contact with an infected person, although it can also be spread via nonsexual contact or by eating an infected animal. This disease is almost exclusively found in the Democratic Republic of the Congo, but the disease spread around the world during the 2022-2023 outbreak and as of August 2024 is present in several African countries as part of the ongoing epidemic.

Diseases in this category can be extremely contagious. They are spread through respiratory droplets of infected individuals. Some can be contracted simply by sharing the same airspace with an infected individual (e.g. measles, chicken pox, and tuberculosis). There is realistically nothing much you can do to avoid them completely, but you can mitigate the risks. Hand washing with soap and water, or use of alcohol-based hand sanitizer, and the use of personal protective equipment such as masks can decrease risk of transmission for some of these diseases. Surgical masks are a popular measure but their effectiveness is unclear. Ensure you have all the relevant vaccinations (e.g. measles-mumps-rubella, diphtheria, pertussis, chicken pox, influenza) where available. Avoid traveling to areas where there are epidemics of such diseases if you are not adequately immunized, especially for highly contagious diseases such as measles. Note: Smallpox was eradicated in 1977.

• COVID-19 or Coronavirus Disease 2019. A pandemic of this illness, caused by the SARS-CoV-2 virus, began in Wuhan, China, in late 2019. As of January 2022 the pandemic had caused hundreds of millions of cases and millions of deaths around the world. Its fatality rate is highest for older people and those with underlying health conditions. Infected people who do not have symptoms can transmit the virus to others. Mask wearing, frequent handwashing, physical distancing, and avoiding travel to affected areas are the recommended preventative measures. Self-quarantine after infection may be recommended, and in some cases it is mandatory. Stay up to date on official guidance and restrictions. Vaccines have been available since December 2020.
• Avian influenza. A viral infection normally affecting birds but the Avian Influenza A virus has also been found, albeit extremely rarely, in some human infections. Current outbreaks among animals occurred in South-East Asia (Cambodia, China, Indonesia, Laos, Malaysia, Thailand, and Vietnam). The disease is transmitted to humans by contact with infected birds (especially poultry) and their excrement and may cause serious disease. Precautions include avoiding contact with wild birds and their excrement. Avian influenza infection appears frequently in the news because it could be a source for new influenza strains to which no-one has immunity and which have the potential to evolve to cause deadly epidemics. However, from the traveller's perspective the personal risk from avian influenza is extremely low. Travellers should obey recommendations on contact with poultry as a matter of civic duty, to prevent spreading the avian disease to birds in other countries. There is no vaccination available.
• Influenza or the flu. Outbreaks of the flu occur every year in the colder half of the year. The disease kills an estimated 36,000 Americans each year, and results in 200,000 hospitalizations a year (CDC flu page). It is generally a miserable but not otherwise dangerous disease for the vast majority of people, and most deaths from influenza are of people who have other underlying health issues, with few deaths being reported in otherwise healthy individuals. As a general precaution an annual vaccination is often recommended for the latest strains prevalent in the countries you are visiting. The flu comes in many strains, with new ones being discovered every year, and vaccination will only protect you against certain strains, and not the others. There is no substitute for maintaining a healthy lifestyle, which will reduce the risk of complications from the disease.
• Chicken pox. An extremely contagious viral disease. Symptoms include vesicular skin rash, fever and oral ulcers. It is generally a mild disease in children, who usually recover after a week or so. However, it tends to be more severe in adults, who are at a greater risk of developing complications such as pneumonia, encephalitis, and rarely, hepatitis (inflammatory, not contagious to others), all of which could eventually lead to death. Chicken pox is easily preventable by vaccination. If you've had chicken pox in the past, and are roughly over the age of 50 or 60, a shingles vaccination is available to avoid a nasty rash and possible eye damage. Persons with shingles are contagious to those with no immunity to chicken pox, though shingles itself is not contagious.
• Measles. An extremely contagious viral disease. Symptoms include rash, fever, running nose, cough and sore, red eyes. A mild though extremely unpleasant disease in most people, who usually recover after a few days' rest, it has nevertheless been the cause of many deaths, for example from the complication of encephalitis. The virus causes epidemics in populations with poor immunization coverage due to its high transmissibility. Every one infectious case is estimated to be able to infect 12 to 18 non-immune individuals. Easily preventable by vaccination.
• SARS - Severe Acute Respiratory Syndrome (SARS-CoV). Caused by a coronavirus that is believed to have originated in bats, and spread to humans via civets and was highly infectious. Its control is an example of how unidentified (new) diseases can be controlled by simple but burdensome public health measures. As of early 2020, there is no evidence that this virus is present in humans.
• MERS - Middle East Respiratory Syndrome (MERS-CoV). Another illness caused by a coronavirus thought to have originated in bats, and spread to humans via camels. First discovered in 2012 in Saudi Arabia, it can cause a range of illnesses from mild flu-like symptoms to severe respiratory symptoms resulting in death. Sporadic cases continue to occur in the Middle East with some outbreaks linked with circulation within hospitals. There is no vaccine and treatment consists of management of symptoms.
• Tuberculosis (TB). An illness caused by Mycobacterium tuberculosis and formerly known as consumption. Considered a third world disease due to its link with poverty and poor health care. About a quarter of the world's population is infected with the bacteria. Ninety percent of people infected are asymptomatic (latent TB), but it can reactivate causing pulmonary tuberculosis with symptoms of chronic, sometimes bloody, cough, fatigue, and weight loss. TB can also affect other organs (extrapulmonary TB) including bones, the brain, and the skin. TB is endemic in many parts of the world with the greatest burden in India. It can occur in developed countries where the health care system makes treatment expensive or in marginalized groups such as the homeless. Starting a new job after moving internationally or taking an extended international trip sometimes requires a TB test (a chest X-ray, skin test, or blood test). TB is curable with antibiotics, but mis/incomplete treatment in some countries means antibiotic resistant strains are also a problem. A vaccine is available, although there is questionable efficacy in adults and it is usually not recommended for adult travelers. Discuss with your health care provider about the appropriateness.
• Diphtheria. A contagious bacterial disease that is spread by coming into contact with infected people. Symptoms include a fever, and sore throat, as well as a swollen neck in more severe cases, which often results in death. If suspected, it is important to get immediate medical attention, as delaying treatment will usually result in the treatment being less effective. Preventable by vaccination.
• Pertussis. Also known as whooping cough, an extremely contagious bacterial disease. The main symptom is usually severe coughing fits characterized by a whooping sound. Vomiting can also occur due to the severity of the cough. While rarely fatal in otherwise healthy adults, it is extremely dangerous in young children and babies, often resulting in death. Preventable by vaccination.
• Meningococcal disease. A disease caused by the bacterium Neisseria meningitidis that is spread primarily through saliva and can be aerosolized by sneezing and coughing. Usually it colonizes the nose without causing any symptoms. However, rarely it can cause infection of the blood and the membrane covering the brain (meningitis) leading to severe disease that may result in death. Blood stream infections are characterized by rapidly spreading bruise like rashes while meningitis is characterized by confusion, severe headaches, and neck stiffness. It's a particular problem in the meningitis belt of Africa and in Saudi Arabia. There are vaccinations that protect against the strains that cause meningococcal disease. Infections of this disease require hospitalization and treatment with intravenous antibiotics.
• Mumps. A contagious viral disease. Symptoms include fever, headache, loss of appetite, and painful swelling of the salivary glands. The disease is rarely fatal, though it is more commonly known to cause inflammation of the testes and sometimes, sterility in adult men. It is also known to cause miscarriages in infected pregnant women. Preventable by vaccination.
• Rubella. Also known as German measles, a contagious viral disease similar to but distinct from measles, hence the alternative name. Symptoms are similar, but tend to be milder than those for measles. Although it is a mild disease for most people, it is particularly dangerous for pregnant women, as the disease often causes deformities to develop in unborn babies, a condition known as congenital rubella syndrome. Preventable by vaccination.

• Ebola. Found largely in Sub-Saharan Africa after contact with infected animals (especially bats, humans and other primates), this disease is usually fatal if not treated aggressively and early and has a 70–90% fatality rate overall. Call a hospital immediately upon experiencing symptoms. In 2014, a major ebola outbreak in West Africa caused over 4,000 deaths, including visitors from the United States and Spain. Since late 2019, vaccines have become available.
• Lassa fever. An acute viral illness that occurs in West Africa. In areas of Africa where the disease is endemic (that is, constantly present), Lassa fever is a significant cause of morbidity and mortality. While Lassa fever is mild or has no observable symptoms in about 80% of people infected with the virus, the remaining 20% have a severe multi-system disease. Lassa fever is also associated with occasional epidemics, during which the case-fatality rate can reach 50%.
• Leptospirosis. A bacterial disease carried mostly by rodents, but all animals are susceptible. It is often transmitted by animal urine or by water or soil containing animal urine coming into contact with breaks in the skin, eyes, mouth, or nose. Fortunately, most cases are mild, but kidney failure, severe pulmonary hemorrhage syndrome, and meningitis do occasionally occur. Seek immediate treatment, as it can be deadly.
• Q fever. A bacterial disease caused by Coxiella burnetti due to contact with soil and dust contaminated with infected carcasses from goat, sheep, and cattle and also through contaminated unpasteurized milk.

  

  

• Rabies. A horrific disease which is almost invariably fatal once symptoms develop. All warm-blooded creatures are capable of infecting you with rabies, but dogs and bats are the main source of human rabies deaths, contributing up to 99% of all rabies transmissions to humans. Human deaths following exposure to foxes, raccoons, skunks, jackals, mongooses and other wild carnivore host species are very rare, and bites from rodents are not known to transmit rabies. Almost all of the estimated 55,000 annual human deaths are in Asia and Africa. Human-to-human transmission through bites or saliva is theoretically possible but has never been confirmed. The same applies for transmission to humans via consumption of raw meat or milk of infected animals.
  If you have any suspicion that you have been bitten or infected, thoroughly wash the wound as soon as possible with soap and water for a minimum of 15 minutes and use a virus killing antiseptic such as iodine tincture. Alcohol is also good – the stronger the better, though it must contain some water (min. about 10%) to be effective. Also, flush your mouth, nose and eyes well with water in case drops of saliva have hit them. Seek proper medical care as a matter of extreme urgency. Slow transport or a lack of medical facilities may mean victims cannot be quickly treated after being infected. Treatment must begin before symptoms appear, as once symptoms have started to appear, medical treatments are useless and death is virtually certain. There have been several million cases of symptomatic rabies over the last century, and only around 14 documented case where the patient survived.
  There is a pre-exposure vaccine recommended to animal workers, outdoor travellers, and people living in remote high-risk areas with limited local access to rabies biologics. However, you must still seek treatment as soon as possible. The prophylactic vaccine only buys you some more time, and less painful and complicated treatment. Rabies immunoglobulin (RIG) and rabies vaccine are both required as post-exposure measures (PEP), but are difficult to access in many countries. As much of RIG as is anatomically feasible should be injected at the wound site. Because rabies virus can persist in tissue for a long time before invading a peripheral nerve, a traveler who has sustained a bite that is suspicious for rabies should receive full PEP, including RIG, even if a considerable length of time has passed since the initial exposure. If completed in time, rabies treatment after infection is completely effective and will save your life. More info on WHO website.
• Cat-scratch disease. Caused by the bacterium Bartonella henselae transmitted by the bite, scratch, or lick of a cat or kitten (young cats pose a greater risk than older cats). Symptoms include fever and inflamed lymph nodes and typically begin within 3–14 days following infection. The primary treatment is supportive. Antibiotics speed healing and are recommended in those with severe disease or immune problems. Recovery typically occurs within 4 months but can require a year.
• Sepsis. Formerly described as "blood poisoning", it has been discovered that this life-threatening disease is caused by the body's overreaction to a serious infection. Sepsis can even continue after the infection is gone, and causes millions of deaths globally each year. Although sepsis isn't contagious, the initial infection certainly could be. If one person in your group develops sepsis, anyone else with the same infection should be closely monitored – especially blood relatives. Symptoms typically include those related to the infection, but are often accompanied by high fever, hot and flushed skin, elevated heart rate, hyperventilation, altered mental status, swelling, and low blood pressure. The disease is both more likely and more deadly in the very young and old; these victims may also have a dangerously low body temperature (hypothermia). Gangrene is a common complication of untreated sepsis, and doctors may have no other choice than to amputate affected limbs. Regardless of age, seek medical treatment immediately.
• Tetanus. Also known as lockjaw, it is a bacterial disease which is usually contracted by coming into contact with contaminated soil through an open wound. The disease generally causes painful muscle spasms throughout the body for up to four weeks, and in some cases causes problems with muscles involved in breathing, which leads to respiratory problems. Without treatment, it usually results in death. Unlike many other diseases, having suffered from tetanus does not result in immunity. However, a vaccine for tetanus is available, and vaccination usually prevents or at least reduces the severity of the disease. Virtually everyone should get this vaccine every ten years, regardless of travel. However, a booster vaccine is recommended if it's been over five years, and you have an open wound, or are traveling somewhere with limited medical access.