Immunizations for Adventure Travellers

Dec 29

Wilderness and adventure travellers go to places where there are many different and dangerous diseases. It is essential to receive proper vaccinations when travelling. Vaccination is when a vaccine is administered to a person. Immunization is what happens in the body after a person has the vaccination. The vaccine stimulates the immune system so that it can recognize the disease and protect it from future infection. This chapter talks about some of the most important vaccines for world travel.

General Vaccines for World Travellers

Yellow Fever

Yellow fever is an acute viral infectious disease that is transmitted through the bite of infected mosquitoes, usually the Aedes. Though some cases of yellow fever are mild and self-limiting, yellow fever is often a life-threatening disease, causing haemorrhagic fever and hepatitis (hence the term "yellow" from the jaundice it can cause). This viral disease occurs in tropical areas of Africa and South America and is endemic in these areas. Each year there are an estimated 200,000 cases of yellow fever worldwide, leading to approximately 30,000 deaths.

About 99% of people develop immunity to yellow fever within one month of vaccination. Vaccination appears to be lifelong. Additional doses after the first vaccine are generally not needed. The vaccine can be used to control outbreaks of the disease, and it is given either by injection into a muscle or just under the skin.

Since the yellow fever vaccine is a live virus, it should not be given to those with weak immune function, those undergoing immunosuppressive therapies, or those who have had transplants, as they are on immuno-suppressant drugs. Yellow fever vaccine is generally safe for people, including those with HIV infection (but without symptoms). Patients with a malignant neoplasm have weakened immune systems and should not be given the vaccine.

Live vaccines administered to a pregnant woman pose a theoretical risk to the fetus. Therefore, live and attenuated virus vaccines generally are contraindicated during pregnancy. Benefits of vaccinating pregnant women usually outweigh the potential risks when the likelihood of disease exposure is high, when infection would pose a risk to the mother or fetus, and when the vaccine is unlikely to cause harm. Thus, the yellow fever vaccine may be used for pregnant women if the benefit outweighs the risk.

Typhoid Fever

Typhoid causes high fever, weakness, stomach pains, headaches, and sometimes a rash. If it is not treated, it can kill up to 30% of the people who contract it. About 50% of people who contract typhoid become "carriers" and can spread the disease without knowing they have it.

Typhoid fever is a systemic infection caused by the Gram-negative bacillus Salmonella typhi. Most salmonella types only cause a local infection of the gastrointestinal tract. However, as an invasive organism, typhoid fever can result in acute systemic infection. Intestinal haemorrhage and perforation may be life-threatening, as well as organ failure due to sepsis. Typhoid is spread by the faecal-oral route and is, therefore, associated with poor sanitation and ineffective personal hygiene. Typhoid infects about 21 million people per year around the world and kills about 200,000.

There are two vaccinations available for typhoid fever. The inactivated vaccine is given as a shot at least two weeks prior to travel. For patients receiving the shot, a booster dose is needed every two years for people who remain at risk. The other vaccine type is an attenuated vaccine, which is taken orally every other day for a week, with the last dose given at least one week before travel. For patients receiving the oral vaccine, a booster dose is needed every five years for people who remain at risk. Neither of these vaccines provides lifelong immunity.

The most common reaction to the typhoid vaccine shot (inactivated typhoid vaccine) is redness and swelling at the site of injection. A mild fever and a light headache are also common for this vaccine. For the oral (live typhoid vaccine), the most common reaction is a headache. Gastric symptoms such as stomach pain, nausea, vomiting, and rash are actually very rare. Neither form of vaccine has a high allergic rate. The risk of typhoid vaccine causing serious harm, or death, is extremely small. Typhoid vaccines are not 100% effective and are not a substitute for being careful about what a person eats or drinks.

The Live typhoid vaccine (oral) can be given to children older than age six. The Inactivated typhoid vaccine (shot) can be given to children older than age two. A person should wait at least three days after completing any antibiotic therapy before taking the oral vaccine. Several factors influence the age at which a vaccine is administered, including age-specific risks of the disease and its complications, the ability of children of a given age to develop an adequate immune response to the vaccine, and potential interference with the immune response by passively transferred maternal antibodies.

Japanese Encephalitis

Japanese encephalitis virus is a flavivirus related to dengue, yellow fever, and West Nile viruses and is spread by Culex mosquitoes. These mosquitoes often feed on pigs and wading birds (common to pig farms and rice fields, particularly in the rainy season). It cannot be transmitted by other humans.

Japanese encephalitis is usually a mild illness. In many cases, there are no symptoms. Vaccines are available for adults and children. However, in a small number of cases (about 1 in 250 infected people), the illness is more serious. The case-fatality rate can be as high as 30%. Permanent neurologic or psychiatric sequelae can occur in up to 50% of those infected. The infection may start with fever, tiredness, headache, and vomiting, and can sometimes cause confusion and agitation. This may progress to inflammation-causing encephalitis, which can cause permanent brain damage. Twenty-four countries in South-East Asia and Western Pacific regions have endemic transmission, exposing more than three billion people to the risks of infection.

Japanese encephalitis vaccine is not recommended for short-term travellers of less than one month whose visits will be restricted, primarily to urban areas or short trips outside in low transmission areas. However, a vaccine is recommended for travellers who plan to spend one month or more in endemic areas during the virus transmission season. This includes long-term travellers, recurrent travellers, or expatriates who will be based in urban areas but are likely to visit endemic rural or agricultural areas during a high-risk period of Japanese encephalitis virus transmission. This also includes travellers to endemic areas who are uncertain of specific destinations, activities, or duration of travel.

The Japanese encephalitis vaccine is more than 90% effective. How long this protection will last is not clear, but its effectiveness does appear to decrease over time. For those with HIV/AIDS, or for those who are pregnant, an inactivated vaccine should be used. The vaccines are relatively safe. Pain and redness may occur at the site of injection. There are at least 15 different vaccines available. Some are based on recombinant DNA techniques, others are based on a weakened virus, and others are inactivated viruses. In the United States, it costs between $100 and $200 US dollars for a course of immunizations.

Hepatitis A

Hepatitis A is usually spread by eating or drinking food or water contaminated with infected faeces. It is not spread by blood-to-blood transmission. The first symptoms of hepatitis A usually show up anytime between two and six weeks after exposure to the virus. Globally, there are approximately 1.4 million symptomatic cases that occur each year, and about 102 million infections (symptomatic and asymptomatic).

It is more common in regions of the world with poor sanitation and inadequate safe water. In the developing world, about 90% of children have been infected by age ten and thus are immune by adulthood. Only around 10–15% of people experience a recurrence of symptoms during the six months after the initial infection. Acute liver failure may rarely occur (with this being more common in the elderly).

Hepatitis A often occurs in outbreaks in moderately developed countries where children are not exposed when young, and vaccination is not widespread. The World Health Organization (WHO) estimated that, in 2016, 7,134 people died from hepatitis A worldwide. One of the largest outbreaks was in 1988 in Shanghai, China. The outbreak was related to food and water that affected more than 300,000 individuals.

Hepatitis A can be prevented by vaccination, good hygiene, and sanitation. The two types of vaccines are one containing inactivated hepatitis A virus, and another containing a live but attenuated virus. Both provide active immunity against future infection. The vaccine protects against the hepatitis A virus in more than 95% of cases for longer than 25 years. In the US, the vaccine was first used in 1996 for children in high-risk areas, and in 1999 it was spread to areas with elevated levels of infection.

The vaccine is given by injection. An initial dose provides protection starting two to four weeks after vaccination. The second booster dose, given six to twelve months later, provides protection for over 25 years. After a single infection of hepatitis A, a person is immune for the rest of their life. Hepatitis A is an acute infectious disease of the liver caused by the hepatitis A virus (HAV). Many cases have few or no symptoms, especially in the young. The time between infection and symptoms, in those who develop them is between two and six weeks. When symptoms occur, they typically last eight weeks and may include nausea, vomiting, diarrhoea, jaundice, fever, and abdominal pain.

Travellers who are exposed to hepatitis A and who have not received the hepatitis A vaccine previously should undergo post-exposure prophylaxis. As well, they should be administered a single dose of single-antigen vaccine or immune globulin (IG) as soon as possible, preferably within two weeks.

All travellers for any purpose, frequency, or duration to countries that are mildly endemic with hepatitis A should be vaccinated for it. Considering the complexity of interpreting hepatitis A risk maps and the potential risk of foodborne hepatitis A in countries that are not endemic, many experts advise people who are travelling to consider hepatitis A vaccination regardless of their destination.

Although the Advisory Committee for Immunization Practices recommends hepatitis A vaccination for travellers, published maps may not be the best guide for determining endemicity in developing countries. Prevalence patterns of hepatitis A infection vary among regions within a country and missing, or obsolete data presents a challenge. Countries, where the prevalence of hepatitis A infection is decreasing have growing numbers of susceptible people, and risk for large outbreaks of hepatitis A. In recent years, large outbreaks of hepatitis A were reported in developed countries among people who had been exposed to imported food contaminated with hepatitis A. Recognized exposures to hepatitis A through infection in food handlers have also increased.

For healthy people aged one to forty years, a dose of the monovalent hepatitis A vaccine is recommended. For people older than forty years, IG is preferred, but the vaccine can be used if IG is unavailable. IG is recommended for children less than one-year-old, for people who are immunocompromised, for people who have chronic liver disease, and for people for whom the vaccine is contraindicated.

Information about the relative efficacy of the vaccine compared with IG post-exposure is limited, and data is not available for people aged forty years or older, or those with underlying medical conditions. Therefore, decisions to use the vaccine, or IG, should consider patient characteristics, including older age and chronic liver disease. Of note is that years of experience have demonstrated that IG performs well as post-exposure prophylaxis in all populations and settings.

Babies and toddlers should be vaccinated whenever possible against common travel-related diseases before they travel abroad. Several factors influence the age at which a vaccine is given to a baby or toddler. These include age-specific risks of the disease and its complications, the ability of children to develop an adequate immune response, and potential interference with the immune response by passively transferred maternal antibodies.

Many vaccines, such as typhoid, have strict requirements on age while others do not, such as the hepatitis A vaccine. Babies and children will be exposed to the same travel-related disease as adults. In addition, babies and toddlers need to be up to date on regular vaccines. Although some diseases such as polio, diphtheria, and pertussis are now practically non-existent in developed countries, they still exist in many developing countries. Immunizations are particularly important if a child is likely to have close contact with local children.

Polio

Polio is a disease caused by a virus that affects the nervous system and is mainly spread by person-to-person contact. Polio can also be spread by drinking water, and other drinks, or eating raw or undercooked food that is contaminated with the faeces of an infected person. Most people with polio do not feel sick. Some people have only minor symptoms such as fever, fatigue, nausea, headache, nasal congestion, sore throat, cough, stiffness in the neck and back, and pain in the arms and legs. Most people recover completely. In rare cases, polio infection causes permanent loss of muscle function in the arms or legs (usually the legs). If there is a loss of function in the muscles used for breathing or an infection of the brain, death can occur.

From the late 1940s to the early 1950s, polio crippled millions of people, making it one of the most feared diseases of the 20th century. Only three countries remain where polio has not been stopped: Afghanistan, Nigeria, and Pakistan. The affected areas in these three countries have become smaller. However, polio has been exported to countries that had previously been polio-free, and seven other countries have had cases of wild polio virus and the spread of polio in the last 12 months. Until polio is stopped everywhere, even polio-free countries are at risk for outbreaks.

Travellers going to certain parts of Africa and Asia may be at risk for polio. Everyone should be up to date with their routine polio vaccination series. In addition, a one-time adult polio vaccine booster dose is recommended for travellers to certain countries. A person should see individual country requirements for vaccine recommendation information.

If you are travelling to one of the following countries (that have had active spread of poliovirus in the past 12 months), for more than four weeks, the government of these countries may require you to show proof of polio vaccination when you are exiting that country. They are Afghanistan, Burma (Myanmar), Guinea, Laos, Madagascar, Nigeria, Pakistan, and Ukraine. This list may change frequently.

Rabies

For a human to contract rabies, two things must happen. First, a person must have contact with a rabid animal (not necessarily a bite or a scratch). Second, the contact must allow for the transmission of infected material, which will involve exposure to the saliva of the infected animal, usually through a bite or scratch. Contaminated tissue in the rabid animal includes saliva.

Another potentially infectious tissue is in the brain or nerve tissue. The virus is transmitted only when the virus gets into bite wounds, open cuts on the skin, or mucous membranes (for example, into your eyes or your mouth). The virus then spreads from the site of the exposure to your brain and eventually spreads throughout your body's major organs.

Bites are the most common source of transmission. Scratches by infected animals are far less likely to cause infection but are still considered a potential source of rabies transmission. Rabies has rarely been transmitted by other means. However, documented examples include inhaling a large number of bat secretions in the air of a cave by two cave explorers and inhaling the concentrated virus by laboratory workers who were studying rabies.

When treating rabies, there are several important questions to consider when determining if a patient should receive post-exposure prophylaxis. The behaviour of the animal is important because normal behaviour would imply that an animal does not have rabies. Some animals are more likely to carry rabies, and other animals might be higher transmitters of the disease.

Raccoons are the most common wild animal carriers of rabies in the United States, Canada, and Europe. Bats are the most common animals responsible for the transmission of human rabies in these countries, accounting for more than half of human cases since 1980, and 74% since 1990. Rabid bats have been reported in all these countries. Skunks, foxes, and coyotes can also be infected with rabies. The biggest carrier and transmitter of rabies in the world is the dog. Bats have tiny teeth, so tiny scratches caused by a bat might result in rabies. However, bites or scratches are often not confirmed in cases of human rabies traced to bats. Since 1990, in the 20 cases of human rabies associated with a bat, a definite history of a bat bite could be confirmed in only one case. It is unclear how the virus was transmitted in the other case, perhaps by an undetectable bite or scratch.

Reptiles, fish, or birds are not known to carry the rabies virus. Small rodents like squirrels, hamsters, guinea pigs, gerbils, chipmunks, rats, mice, and lagomorphs, including rabbits and hares, are almost never found to be infected with rabies. As well, these small rodents have not been known to transmit rabies to humans.

In most countries, patients receive one dose of immunoglobulin (HRIG) and four doses of the rabies vaccine over a 14-day period. If anatomically feasible, the full dose of HRIG is infiltrated around and into any wounds. Any remaining volume is injected intramuscularly at a site distant from the vaccine administration. HRIG is not administered in the same syringe or at the same anatomic site as the first vaccine dose. However, subsequent doses (i.e., on days 3, 7, and 14) of the vaccine in the 4-dose vaccine series can be administered in the same anatomic location in which HRIG was administered. The first dose of rabies vaccine should be given as soon as possible after exposure (day 0), with additional doses on days 3, 7, and 14 days after the first vaccination.

Treatment after exposure is highly successful in preventing the disease if administered within six days after infection and completion of a 14-day treatment regimen. It is effective until the patient develops the disease. Thoroughly washing the wound as soon as possible with soap and water is very effective at reducing the number of viral particles. Exposed mucous membranes such as the eyes, nose, or mouth should be flushed very well with water.

Veterinarians, veterinary technicians, animal control officers, wildlife rehabilitators, and zoo employees who have regular contact with potentially rabid animal species should be vaccinated for rabies. International travellers to areas with endemic canine rabies who are likely to encounter dogs or wild animals and where access to medical care and appropriate biologics may be limited should also be vaccinated regardless of if they are close to medical care or not. Pre-exposure vaccines to rabies are effective.

Disclaimer: This information has been developed for educational purposes only. It is not a substitute for professional medical advice. Should you have questions or concerns about any topic described here, please consult your healthcare professional.

Philip Swart https://www.munromedicalsolutions.com/