It’s winter in the northern hemisphere and many are itching to hit the sun and sand in an exotic location. I, myself, took leave from the cold weather and spent several weeks this January traveling through India. This is the first time I travelled to Asia, and it took slightly more than a few months to get my ducks in a row for this trip. Aside from the slightly cumbersome visa process (don’t get me started), I was also pricked with enough needles to make a grown woman cry (confession: that woman was me). But while I was sitting in the cold examination room, on the crinkly white paper with my t-shirt sleeves rolled up high above my shoulder, I realized that I didn’t know much about the pathogens these vaccines were going to protect me against. So, ladies and gentlemen, I did what any self-proclaimed microbiology nerd would do, and looked ‘em all up.
As my doctor explained, the CDC encourages travelers to India to receive a slew of prophylactic treatments in preparation for the barrage of a new micro-ecosystem. At the very least, everyone in the U.S. who is capable of receiving vaccinations should be vaccinated for Tdap (tetanus, diphtheria and pertussis), MMR (measles, mumps, rubella), chickenpox (varicella), polio and get the annual flu shot.
Travelers to Asia are also encouraged by the CDC to get Hepatitis A and the Typhoid vaccine, regardless of travel duration and plans. Certain travellers may also elect to get Hepatitis B, Japanese encephalitis or Yellow Fever vaccines and a prescription prophylactic for Malaria, depending where they plan to go and what they plan to do there (are you going to catch and study wild bats? Then you probably want to get that rabies vaccine as well.)
This is all well and good, but what are these vaccinations actually for? What do these pathogens do, and how do they affect the host? In a time when vaccination is under fire in the U.S., it may be best to focus not on the act of vaccination itself but rather on the gruesome diseases vaccines protect us from.
BUT FIRST: Routine Vaccinations in the US are a must-have before travel
Most recommended vaccinations sound like random assortments of letters with no particular meaning. MMR? TDAP? In fact these letters represent the very nasty and potentially fatal infections that these vaccines protect us from.
Figure 1. Swollen glands due to the Mumps Virus. Source.
The MMR vaccine protects against the viruses that cause Measles, Mumps and Rubella. Measles is a highly contagious airborne viral infection that causes high fever, inflammation and rash, similar to the Rubella virus (though they are two different viruses). Mumps is another highly contagious viral infection characterized by fever and painful swelling of one or both parotid salivary glands. Although the MMR vaccine is highly effective in preventing all three, recent backlash to vaccination has resulted in recent outbreaks of measles and mumps within communities with poor vaccination records.
TDAP is another blend of three vaccines, this time against the bacteria that cause tetanus, diphtheria and pertussis. Unlike MMR, which only needs to be administered once, TDAP requires a booster shot every 10 years to remain effective. Tetanus, also called lockjaw, is caused by an infection by the Gram-positive Clostridium tetani usually introduced through a scratch or puncture wound. C. tetani produces the toxin tetanospasmin, which causes intense muscle spasms capable of causing respiratory failure and even death. Diphtheria is an infection caused by Corynebacterium diphtheriae, which causes fever and swelling of the lymph nodes. In certain cases, lymph nodes grow so large that they obstruct breathing and a tracheotomy must be performed. Pertussis, or whooping cough, is caused by infection by the bacterium Bordetella pertussis and is a highly contagious cough characterized by a “whoop” sound following a coughing fit as the person tries to inhale air. This disease is particularly dangerous to infants, who are too young to be immunized, and must be hospitalized if infected.
Varicella and Polio
Chickenpox may not seem like a big deal, but once infected, the virus that causes chickenpox, varicella-zoster, lays dormant in the nerves and may wreak havoc on the nervous system decades later in the form of an extremely painful nerve disease called shingles. The only way to prevent both chickenpox and shingles is the varicella vaccine.
Figure 2. Lower extremity deformation caused by poliomyelitis. Source
Polio is another virus that causes devastating nervous system symptoms. A type of enterovirus, poliovirus usually inhabits the intestines and can easily be spread through fecal matter contaminated food and water. However, once the virus becomes present in the blood, it easily can infect the meninges and cause damage to the central nervous system. This causes the characteristic polio paralysis of the legs. Although a global effort to eradicate poliovirus began in 1988, cases of polio remain constant at 1000-2000 cases per year.
Finally on our list of routine vaccinations is the flu. Three letters do no justice to the vast number of influenza strains present year to year, nor does “the flu” quite capture the incredible rate in which these strains mutate. Flu vaccines protect against three or four viruses that research suggests will be most common that coming year. Of course, the predictions cannot always be accurate, and a new or mutated strain may rear its head against the odds as it did in 2014. Regardless, getting the flu shot may lessen the overall course of the flu, even if mutated. And finally, contrary to what some believe, no, the flu shot doesn’t give you the flu.
If you are planning to travel and you’ve received your cluster of vaccinations recommended in the US, you’re ready to move on to the more exotic diseases.
Travel Vaccines for diseases spread through food and person-to-person contact
Excited to see a crowded, hustling, bustling city? Looking forward to the local cuisine? Make sure you get the appropriate vaccines for foodborne and easily communicable diseases.
Vaccines have been formulated for the viruses Hepatitis A and B, but not yet for C due to its great genetic variability (you can read more about why there isn’t a vaccine yet here). All three viruses infect the liver, causing inflammation, which can later lead to cirrhosis or even liver cancer. The Hepatitis A vaccine is highly recommended for those traveling through densely populated areas since the virus is easily passed via person-to-person contact or through contaminated food and water. Hepatitis B, on the other hand, is transmitted via contact with the blood or other body fluids of an infected person. Its prevalence is highest in sub-Saharan Africa and East Asia. There, between 5–10% of the adult population is chronically infected with Hepatitis B compared to less than 1% of the population in Western Europe and the United States. Since the mid 1990s, the Hepatitis B vaccine has been mandated for infants born in the U.S. and often the first of three doses is administered within 24 hours of birth. However, those above 18 years of age may not have received the vaccination and should double check their immunization records before heading to endemic regions.
Typhoid fever is caused by ingesting food or water contaminated with the bacterium Salmonella enterica serovar Typhii, a Gram-negative enteric pathogen that causes a high fever and constipation. There are two types of typhoid vaccine: an inactivated injection and an oral live typhoid. These can prevent about 30% to 70% of cases during the first two years but needs to be boosted regularly to continue protection. If infected, the patient may be treated with antibiotics but antibiotic resistance of S.enterica has been growing, which is making treatment of the disease much more difficult. For this reason, getting vaccinated before heading to a Typhoid endemic region is important.
Travel Vaccines for diseases spread by mosquitos
Mosquitos are a global pest and several species are responsible for transmitting vastly different pathogens. Here are some of them.
Malaria is a tropical disease found across the globe. Unlike most of the diseases on this list, malaria is caused by a eukaryotic parasite for wich a vaccine does not exist. Instead, travelers can request a prophylactic to prevent infection. Four species of the parasite Plasmodium are responsible for causing Malaria, which is transmitted by the bite of infected female Anopheles mosquitoes. Once an individual is infected, the parasite travels via blood to the host’s liver where it thrives and reproduces. The infection causes fever, vomiting, and even seizures, coma, and death. Most deaths are due to P. falciparum, but P. vivax, P. ovale, P. malariae can all cause disease. Rarely, P. knowlesi can cause disease in humans as well, though it mostly infects other primates.
Malaria is endemic in a broad band around the equator, including the Americas, Asia, and most of Africa. Thus, prophylactics against the disease are commonly prescribed before travel. Chloroquine had been classically prescribed for malaria prevention but increasing numbers of Plasmodium species have developed resistance to the drug in certain areas of the world (including India). In those areas three medications can be used to prevent plasmodium infection: mefloquine, doxycycline, or a combination of atovaquone and proguanil hydrochloride. In order to be effective, the medication, in oral form, must be taken up to two weeks ahead of travel and continued throughout exposure to Plasmodium and up to a month after returning.
Interestingly, humans have developed an inheritable mutation in the hemoglobin beta gene — an allele responsible for red blood cell shape and oxygen carrying capacity. Carrying two copies of this allele is dangerous — it causes shrinking of the cell membrane resulting in sickle cell anemia, but carrying one normal and one mutant copy has a protective effect against Plasmodium infection.
The Japanese Encephalitis Virus (JEV) causes fever, headache and potentially lethal swelling of the brain. JEV is closely related to the West Nile virus and transmitted by mosquito bites mainly by the species Culex tritaeniorhynchus. Pigs and wild birds serve as asymptomatic amplifying reservoirs for JEV, while humans, horses and cattle are hosts. While most cases are asymptomatic, 1 in 250 human Japanese Encephalitis cases result in encephalitis, or a serious swelling of the brain, which can lead to seizures, stroke, mental retardation, and death. Though rare, the possibility of these symptoms occurring is enough to get vaccinated, especially if you will be in tropical and mosquito filled areas. There are currently three forms of Japanese Encephalitis vaccine available that confer protection for two to three years, after which a booster is required.
(figure 3) The Yellow Fever virus usually appears as an acute viral infection with fever, headache, chills, loss of appetite and fatigue for about 5 days. However, in 15% percent of cases, a recurring fever is accompanied by liver damage and abdominal pain. Liver damage causes jaundice, which gives the skin a yellowish tinge, aptly naming the infection. The virus is spread by Aedes aegypti mosquitos and is common in tropical areas such as parts of Africa, Asia and South America. Because there is no treatment for Yellow Fever, vaccination is recommended especially for non-natives travelling to infected areas as they tend to suffer more severe illness when infected. Vaccination has a protective effect 10 days after injection and lasts around 10 years.
We are incredibly lucky that so many diseases have safe and effective vaccines that allow us to travel the world with a decreased risk of infection. However, there are still several diseases without vaccinations, such as Hepatitis C, and Zika, which is now endemic in India, as well as South America, Mexico and and parts of the United States. Fortunately, vaccine research is growing and the first 100% effective Ebola vaccine has recently been reported.
This list is not exhaustive and any and all medical decisions should be discussed with your physician. But for now, you have a glimpse into what unpleasant infections vaccines protect us from both at home in the U.S. and while traveling the world abroad.