Infectious diseases

Disclaimer: This article gives an overview of infectious diseases, and is not intended to replace professional medical advice.

There are many infectious diseases that can pose a hazard to travellers who may not be familiar with them and their risks, because they are rare or absent in their home countries. This article is a basic introduction to some of these hazards of travel, how to avoid them, and how to deal with one if you contract it. For those unfamiliar with medical jargon, the words infectious and contagious have distinct meanings. An infectious disease is one that is caused by a pathogen, such as a virus, bacterium, fungus or other parasites. A contagious disease is one that is easily transmitted by being in the vicinity of an infected person. All contagious diseases, such as influenza and measles, are infectious diseases, but the reverse is not necessarily true, with various diseases such as AIDS or yellow fever being infectious but not contagious.

Vast improvements in sanitation and healthcare standards, combined with the widespread availability of vaccines, have made many once common diseases largely a thing of the past in developed countries. However, these diseases may continue to persist in less developed parts of the world where people do not have access to proper medical care and sanitation, and vaccine coverage is low. Also, differences in climate often mean that both pathogens and their vectors (carriers which are usually pests, such as mosquitoes) are quite different. Local people have developed immunity to many of the local pathogens, but travellers will be vulnerable. Travellers' diarrhea is the commonest of these infections.

Before travelling

Legal requirements

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.

Health requirements

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.

Information sources

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

Disease by transmission method

Pests are not only a nuisance in and of themselves; they can also spread microbe infections to people.

Arthropod vectors

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.

• Mosquitoes — in particular the "yellow fever mosquito" Aedes aegypti and "asian tiger mosquito" Aedes albopictus are vectors for many tropical diseases.
  • Malaria — a parasitic infection (Plasmodium spp.) transmitted by the Anopheles mosquitoes. There are multiple species of malarial parasites, which can cause a range of severity in illness. It is present in many regions around the world including tropical Africa, South America, southeast Asia, and the Indian subcontinent. Infections require immediate qualified diagnosis and treatment. Preventative medications are available.
  • Yellow fever — a viral infection caused by the yellow fever virus. It is primarily present in the tropics of Africa and the Americas. It can cause asymptomatic infection to severe disease leading to multiple organ failure. Symptoms include fever, headaches, general muscle pains, nausea, and vomiting. A vaccine is available, and even mandatory for entering some tropical countries in Africa and the Americas.
  • Dengue fever — a mosquito-borne febrile virus transmitted by an infective Aedes aegypti or Aedes africanus mosquito. Causes high fever, headache, joint and muscle pain and in some cases leads to a more severe manifestation, dengue haemorrhagic fever (DHF), which can eventually lead to death. Occurs in many tropical countries and is the most important tropical infectious disease after malaria and the world's most serious (human) arbovirus disease. DHF infections require immediate qualified diagnosis and treatment – vaccine is only approved in Mexico and Brazil (as of 2016), but it is only 40 to 60% effective. Five serotypes of the virus exist, so having had dengue before only makes you immune to that one serotype, not the others. In fact, research has shown that the disease is usually more serious for those who have had it before because the immune system is busy producing the wrong antibodies.
  • Chikungunya (CHIKV) — also known as epidemic polyarthritis and rash, and buggy creek virus. A febrile virus transmitted, like dengue, by an infective A. aegypti or A. africanus mosquito. After 3-12 days flu-like symptoms develop including severe headaches, chills, fever, joint pain, nausea and vomiting - no vaccine is available. Historically present in Africa and Asia, since 2005 there have been outbreaks in Indian Ocean islands, Pacific islands, and countries in and around the Caribbean. Management of this disease is supportive care of symptoms.
  • Zika virus - a febrile illness linked with causing birth defects in infected pregnant women. For adults, the illness is usually mild. Spread by Aedes mosquitoes and causes symptoms that include fever, headache, fatigue, and joint and muscle pains lasting about a week. Management of this disease is supportive care of symptoms. It is present in South and Central America, parts of Africa, the Indian subcontinent, Southeast Asia, and some Pacific islands. Pregnant women and people trying to conceive should be cautious about traveling to Zika-affected areas, due to the risk of birth defects, and should consult their doctor. The virus can be found in semen for a couple of months and therefore can affect fetal development if there is conception.
  • Japanese encephalitis - an illness caused by the Japanese encephalitis virus transmitted by the Culex mosquitoes. Majority of people infected are asymptomatic, but in more severe disease can cause fevers, diarrhea, headache, vomiting, paralysis, and inflammation of the brain leading to death. It can have long term lasting damage due to the effects of the brain inflammation. The virus is present throughout most of Asia and areas of the western Pacific. Risk to travelers is low with risk highest in residents of rural agricultural areas. However, there can be outbreaks of this disease increasing risk. A vaccine is available for Japanese encephalitis. Management of infected people is supportive care of their symptoms.
  • Filariasis - a parasitic infection caused by long thread-like worms spread through the bite of a variety of Anopholes, Aedes, and Culex mosquitoes. Causes symptoms including fevers, lymph node inflammation, lung disease, and over the long term, elephantiasis (enlargement and hardening of limbs). Transmission of this parasite can be found in parts of Latin America, Africa, Asia, and the Pacific islands, but short term visitors to these areas have very low risk. Only with extended time living in endemic areas are you likely to be infected. There is treatment for this disease.
  • West Nile virus - a disease transmitted through the Culex mosquitoes where the majority of people infected with this do not present with any symptoms. Some may present with fevers, headache, muscle and joint pain, nausea, abdominal pain, vomiting, and rash. Very rare individuals with develop serious effects such as meningitis. Documented transmission on all continents, but has the potential for outbreaks of more severe disease. Management of patients is supportive care of symptoms.
  • Other arboviruses - there are a variety of other viruses transmitted by mosquitoes that present in similar ways with a febrile illness. These include Ross River fever, Western/Eastern equine encephalitis, Rift Valley fever, St. Louis encephalitis, and many others. They are found in a range of locales around the world. Risk to travelers is low for transmission for these viruses and management of infection is usually supportive care of symptoms.
• Ticks
  • Lyme disease (aka borreliosis) — If you run a fever and experience other flu-like symptoms after hiking in tick-infested areas where deer ticks carry this disease (much of the temperate Northern Hemispere), especially if you've also seen a bull's-eye-shaped rash around the site of a bite (a common but not invariable symptom), see a doctor and get tested as soon as possible! Caused mainly by the bacteria Borrelia burgdorferi in North America_._ Other strains of the bacterium can cause this disease in Europe. In early stages, Lyme disease usually is well treatable with doxycycline or other antibiotics. However, if the disease is misdiagnosed or otherwise not treated early, it can cause chronic arthritis and other serious effects, including impairment of thinking due to infection of the brain.
  • Tick-borne encephalitis (TBE). This is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis, or meningoencephalitis. Can be fatal. Long-lasting or permanent neuro-psychiatric consequences are observed in 10 to 20% of infected patients. Vaccine is available (2 doses: 0 day and 30 day, 1 year; booster dose every 3 years) and recommended for extended stay in the worst areas. If not vaccinated, only symptomatic therapy available which is not very effective. Can be found in Central and Eastern Europe and Northern Asia. The tick-borne encephalitis virus is known to infect a range of hosts including ruminants, birds, rodents, carnivores, horses, and humans. The disease can also be spread from animals to humans, with ruminants and dogs providing the principal source of infection for humans. After any activity in nature, thorough inspection of body for ticks is obligatory.
  • Rickettsial (tick-borne) infections — Broad range of agents that cause a variety of diseases. Symptoms often include fever, headache and malaise as well as a rash. Can lead to serious outcomes involving multiple organs. Antibiotic treatment is available. Rickettsial infections include, but are not limited to:
  • *Rocky Mountain spotted fever - United States (mostly in the southern US), Canada (Western Canada), Argentina, Brazil, Mexico, Colombia, Central America
  • *Mediterranean spotted fever - Africa, India, parts of Europe and Middle East adjacent to the Mediterranean, Black and Caspian Seas.
  • *African tick-bite fever - sub-Saharan Africa including Botswana, South Africa, Zimbabwe, Swaziland
  • *North Asian tick fever - North China, Mongolia, Asiatic Russia
• Mites
  • Scabies — an extremely contagious skin infestation caused by the mite Sarcoptes scabiei. Children and the elderly are at the most risk, especially in crowded living conditions. The mites burrow into the skin to live and deposit eggs, and an allergic reaction of severe itching results. Despite its being contagious, you shouldn't fear shaking hands with others. The mites need minutes – not seconds – to infect. Only humans are susceptible; animals have a slightly different mite, and the infection is called "mange."
  • Scrub typhus - disease characterized by a skin ulcer with eschar formation followed by fevers, headache, rash, and can cause serious respiratory and neurological complications. Caused by the transmission of Orientia tsutsugamushi through bites of the chigger mite. Can be treated with antibiotics such as doxycycline.
• Others
  • (Epidemic) Typhus — a bacterial infection caused by Rickettsia prowazekii transmitted by the human body louse. Presents with a sudden onset of headache, fatigue, fever, and generalized pains. A rash then forms which spreads across the body. Symptoms can also include a cough and confusion. Occurs in unhygienic conditions around the world, but especially focused in regions of Central and South America, Asia, and central and eastern Africa. Doxycycline can be used to treat the disease.
  • Chagas disease — Pronounced with a "SH" sound, and endemic to mainland Latin America and parts of the Caribbean, roughly from Mexico to central Chile and Argentina. (The Mexican border regions with the U.S. are safe, except for Matamoros. Most cases are in the southern half of Mexico.) It is a parasitic disease spread by triatominae (blood sucking bugs) and blood transfusions, and there is no vaccine against it. Unlike mosquitoes, bites are usually along the face. Never scratch these bites, as this is the main mode of infection. Chagas disease starts with little to no symptoms, but for 20-40% of all victims, it slowly develops into a chronic heart disease, and sometimes stomach disease. This can take decades, in some cases. Treatable with benznidazole or nifurtimox if caught early. Sleeping in thatched huts poses the greatest risk. If you stay in standard tourist accommodations, it's very unlikely you would get this disease.
  • Sleeping sickness (African trypanosomiasis), transmitted by the tsetse fly, kills tens of thousands of people every year in East Africa. Drugs can be used to treat this disease, but patients may relapse for two years following that.

Enteric illnesses

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.

• Bacterial:
  • Cholera is a bacterial disease caused by Vibrio cholerae. Transmission is through ingestion of contaminated food or water. It's mostly found in developing countries where sanitation remains poor. Common symptoms include painless massive watery diarrhea and vomiting. The profound water loss leads to severe dehydration, which can lead to death. Re-hydration is absolutely critical for affected patients with either oral re-hydration solution (ORS) or intravenous re-hydration. For severe cases, antibiotics may reduce the severity of symptoms. Severe cholera can kill within hours, so do not delay treatment. Dukoral (brand name) is an oral vaccine that you drink for cholera and travellers' diarrhea caused by enterotoxigenic E. coli (ETEC). It is only partly effective, and not effective against other bacterial illnesses, so still take precautions against contamination. Nevertheless, it does provide a measure of protection from the worst of the diarrhea diseases. Some countries don't require a doctor's prescription, such as the U.S. and most of Canada.
  • E. coli diarrheal diseases is a grouping of diseases caused by a variety of E. coli bacteria. It is a frequent cause of traveller's diarrhea. They can present with fever, abdominal cramping, watery or bloody diarrhea, and vomiting. Severe complications from these infections include rapid kidney failure, especially in infants, toddlers, and the elderly. Severe illnesses can cause death. Prevention of these diseases include good hand washing, avoiding or washing raw fruits and vegetables well, and drinking bottled water in places with non-potable water. Antibiotics can be used to decrease severity and duration, but antibiotic resistance is high – and antibiotics can make the situation worse by lessening competition from non-resistant benign bacteria. Re-hydration is recommended and anti-motility agents (e.g.loperamide) can also help with symptoms. There is an oral vaccine available (Dukoral) for the ETEC strains and cholera (see above).
  • Typhoid fever is a life-threatening infection caused by Salmonella enterica typhi bacteria, and is much more serious than the common Salmonellosis. It can cause prolonged fever, fatigue, headache, nausea, abdominal pain, and constipation or diarrhoea. Some patients may have a rash. Severe cases may lead to serious complications or even death. Typhoid is a general health problem in all less-developed countries. Unusually compared to other enteric illnesses, typhoid fever presents often with constipation rather than diarrhea. Transmission is by contaminated food and water, especially in rural areas. A vaccination is available, but offers no absolute safety. The best options are being careful with what you drink and eat. It can be treated by fluids and antibiotics.
  • Food poisoning or foodborne intoxicants refers to a grouping of illness caused by the toxins produced by bacteria such as Staphylococcus aureus, Clostridium perfringens, and Bacillus cereus. They are caused by contamination of food with this bacteria and improper cooking and handling. These illnesses present in an abrupt onset of severe nausea, vomiting, abdominal pain, and diarrhea usually lasting a day or two. Severe illness requiring hospitalization is rare. Adequate re-hydration is recommended if you come down with food poisoning.
  • Salmonellosis, the most common form of food poisoning, is caused by bacteria in the genus Salmonella, and is spread through eating contaminated under-cooked or raw food. Contamination after cooking is also possible, both by exposure and not thoroughly washing one's hands. Poultry is a common cause, and this can include ingredients such as raw eggs. Be especially careful with ice cream – even if the cream is pasteurized, the raw eggs might not be. Although bacteria can barely multiply while frozen, they do not die either. Thus, contaminated frozen food will remain contaminated indefinitely (unless well cooked, if applicable). Symptoms of Salmonellosis typically include diarrhea, vomiting, fever, and abdominal cramps. No vaccine is available, and the usual treatment for milder presentations of this disease is re-hydration. Severe, complicated salmonellosis should be treated with antibiotics.
  • Listeriosis is very similar to Salmonellosis (above) for the same foods, but is a more serious disease. An infection usually caused by eating food contaminated with the bacterium Listeria monocytogenes. The disease primarily affects pregnant women, newborns, older adults, and people with weakened immune systems.
• Parasites:
  • Cryptosporidiosis, informally called crypto, is a parasitic disease caused by Cryptosporidium. Found worldwide, this disease is an untreated and chlorine-treated water risk. It can even be spread if an infected person bathes in a treated public swimming pool. It causes diarrhea, cramps and fever. Lasts about 10 days, but faeces carry infection for weeks. Prevention by avoiding mouth coming into contact with infected water or faecal matter and maintaining scrupulous toilet and bathing hygiene after being infected, to prevent reinfection of self or others. There is no cure. Prevented by boiling all drinking water, including tap water, in infected areas.
  • Schistosomiasis/Bilharzia is a nasty parasite that can be picked up by swimming in contaminated fresh water. The worm is carried by freshwater snails, and emerges daily into the water, where it is attracted to water turbulence, shadows, and chemicals found on human skin. While unlikely to be fatal, Schistosomiasis is a devastating disease, which should be treated as soon as possible. Symptoms include abdominal pain, diarrhea, coughing, genital sores, itching especially around the feet, but above all serious fatigue. Schistosomiasis, while present throughout much of the world, is primarily a problem in sub-Saharan Africa, and is easily, if unhappily, prevented by not swimming in fresh water.
  • Trichinosis — a roundworm - from eating improperly cooked infected meats, particularly pork.
  • Strongyloidiasis —another roundworm. Risk from going barefoot in areas with poor septic systems and poverty.
  • Cysticercosis — a tissue infection caused by the young form of the pork tapeworm
  • Hydatids — another tapeworm - from eating improperly cooked infected meats, particularly sheep/mutton. Can also be spread by dogs that have been eating infected meat.
• Viral:
  • Hepatitis A. Contracted through food or water contaminated with faeces, often by unwashed hands. The virus can remain active for days. Young children who contract it do not usually show symptoms. In older children and adults, symptoms appear two to six weeks after infection, and usually last less than two months, though may continue for six months. Symptoms include fever, fatigue, nausea, and abdominal pain, which may lead to jaundice. Acute hepatitis A resulted in 11,200 deaths in 2015. The mortality rate for hepatitis A was estimated to be 0.015% for the general population, but ranged up to 1.8-2.1% for those aged 50 and over. The disease gives lifelong immunity. Hepatitis A occurs throughout the world but levels are low in high-income regions (Western Europe, Australia, New Zealand, Canada, United States, Japan, South Korea and Singapore). Travellers from low-income countries often have immunity due to childhood infection. A vaccine is available, and vaccination is the best way to prevent infection. Travellers from high and medium-income countries may consider vaccination before travelling to low-income countries.
  • Norovirus, also known as Norwalk virus, is a very common disease associated with profuse vomiting and diarrhea, abdominal pain, and muscle aches lasting up to three days. Hospitalization is rare unless people become severely dehydrated. It is frequently implicated in outbreaks on cruise ships and restaurants because it is highly transmissible. It is spread both through contaminated food and water and through person-to-person transmission from aerosolization of bodily fluids. Management is through adequate re-hydration.
  • Polio is a viral disease that is spread through contaminated food or water. The vast majority of infections are asymptomatic, but the virus invades the nervous system in some individuals and may cause paralysis to one degree or another. Sometimes, patients can develop permanent respiratory difficulties as a result of damage to nerve tissue controlling the diaphragm, which often results in death. Thanks to widespread vaccination efforts, polio is no longer an issue in most countries, but continues to persist in Afghanistan and Pakistan, where vaccination rates remain relatively low due to the influence of extremist Muslim clerics who claim that polio vaccinations are a conspiracy by the West to make Muslims sterile. If travelling to those areas, make sure you get vaccinated before you go.
• Other:
  • Seafood poisoning is a group of diseases caused by the toxins of algae contaminating seafood or of the seafood itself. It can range from tingling and burning sensation in the mouth (scombroid poisoning) to paralysis from eating shellfish (paralytic shellfish poisoning) contaminated with toxins from algae from red tides. Common symptoms also include nausea, vomiting, abdominal pain, and diarrhea. A rare risk is puffer fish poisoning leading to paralysis and death from eating improperly prepared fugu - a Japanese delicacy.

Sexually transmitted infections/blood-borne diseases

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.
• Cervical cancer. One of the few infectious cancers in humans, caused by the human papillomavirus (HPV). It is primarily spread by sexual contact. 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 girls a few years before their first sexual intercourse.

Respiratory transmission

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, and there is no vaccine anymore.

• 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 for 10–14 days is recommended for travellers coming from some areas; in some cases quarantine is mandatory. The situation is changing rapidly, so stay up to date on official guidance and restrictions. Vaccines have been available since December 2020, though their availability varies widely between countries.
• 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.

Others

• 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 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 25,000 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.<br /> 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.<br /> 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.

After travel

If you feel sick in the weeks after your trip, you should tell your healthcare providers about your travel history. If you were in a malaria zone, allow for one year.

In some outbreaks it may be recommended to self-isolate or monitor yourself for symptoms after travel. Self-isolation is recommended for many travellers amid the COVID-19 pandemic. Aid workers who may have been exposed to Ebola are advised to self-monitor for symptoms.