12 Travel Diseases You Need to Know
In 2020, the impact of coronavirus disease 2019 (COVID-19) has brought tremendous change to the global economy—including global travel. Although many borders remain closed to travel, the presence of travel-related illnesses, including COVID-19, is still a pressing issue. Concurrently, on June 1, 2020, the Democratic Republic of Congo (DRC) declared its 11th outbreak of Ebola virus disease (Ebola) since 1976.[1]
The events of the global COVID-19 pandemic have heightened awareness of travel-associated illnesses unlike anything in the past century. However, travel occurs, and with it an increased exposure to, and spread of, severe and life-threatening diseases. These are unprecedented times that require increased inquiry regarding not only travel history and exposures during travel (foreign or domestic) but also the social, environmental, and medical circumstances that impact the risk of acquiring and spreading disease.[2]
This slideshow provides essential information on the transmission, diagnosis, prevention, and treatment considerations of 12 key travel-related illnesses.
12 Travel Diseases You Need to Know
COVID-19
In late December 2019, a previously unidentified coronavirus, now named severe acute respiratory syndrome (SARS) coronavirus (CoV) (SARS-CoV-2), emerged from Wuhan, China.[3] As of August 12, 2020, COVID-19, the disease caused by this novel betacoronavirus (the same type previously seen in the first known outbreaks of SARS [2003] and Middle East respiratory syndrome [MERS][2012 to present][4]) has reached global pandemic status—with over 20 million cases and more than 740,000 deaths worldwide (shown).[5] However, these data account for only officially reported figures; the actual numbers of cases and fatalities are estimated to be much higher.[6,7]
Coronavirus is an enveloped, positive single-stranded RNA virus that has characteristic "crownlike" spikes on its surface (top center).[8] SARS-CoV, MERS-CoV, and SARS-CoV-2 all produce disease in humans, but each subgroup has different biologic characteristics and virulence.[8]
12 Travel Diseases You Need to Know
The axial chest computed tomography (CT) scan shows bilateral patchy consolidations (arrows), some with peripheral ground-glass opacity. These findings are in the peripheral and subpleural distribution, and often noted in patients with COVID-19.
The spectrum of signs/symptoms (s/s) for COVID-19 is quite broad. Symptomatic individuals may demonstrate nonspecific features that include fever, dry cough, and fatigue.[9] Multiple systems may be involved, including cardiopulmonary (cough, dyspnea, sore throat, rhinorrhea, hemoptysis, and chest discomfort), gastrointestinal (GI) (nausea, vomiting, and diarrhea), musculoskeletal (myalgias), and neurologic (headache or confusion). Although many people who test positive are without symptoms, fever, cough, and shortness of breath are common.[9]
After illness onset, initial symptoms are often mild, and viral shedding may occur prior to the onset of symptoms.[9] The time to hospital admission from symptomatic onset varies (4-8 days).[10] Disease progression for those most critically ill includes increasing shortness of breath, hypoxia, acute respiratory distress syndrome (ARDS), need for respiratory support (including mechanical ventilation), and multiorgan system failure.[9-11] Mortality data also vary among and within countries, regions, and territories[6,7,9,12]; current statistics estimate about a 2%-3% case fatality in the United States.[9,12]
12 Travel Diseases You Need to Know
SARS-CoV-2 spreads primarily through droplets of saliva or nasal or oral discharge when an infected person coughs, sneezes, talks, or sings in close proximity to another person.[13] This person-to-person transmission occurs when the droplets contact the mucous membranes—often inadvertently—by touching of the eyes, nose, or mouth with contaminated hands. Awareness and prevention is essential.[13] Everyone should protect themselves and others from infection by frequent handwashing or using an at least 60% alcohol-based hand sanitizer, wearing a face mask, and not touching the face.[13,14]
Traveling is a high-risk exposure for COVID-19 as it generally results in close contact for a prolonged period. Proximity and duration of time next to others denotes increasing risk. Transmission from more indirect contact (eg, passing someone on the street, handling previously touched items) is not well established. Following current personal protective guidelines (eg, mask, glasses/goggles, good hand hygiene, face avoidance) will help reduce travel-associated risk.
12 Travel Diseases You Need to Know
Treatment for COVID-19 remains symptomatic and supportive. Although therapy with hydroxychloroquine and azithromycin have been advocated, results from trials to date remain mixed.[15,16] In May 2020, the antiviral drug remdesivir was granted US Food and Drug Administration (FDA) emergency use authorization for severe COVID-19.[17] Two months later, the US National Institutes of Health (NIH) recommended the corticosteroid dexamethasone for those requiring supplemental oxygenation or mechanical ventilation.[18] The use of convalescent plasma, utilizing antibodies from those who have recovered from COVID-19, is currently being studied.[19]
Researchers around the world are developing more than 165 vaccines for COVID-19, with 31 currently in human trials.[20-23] There are several in phase III trials, with the goal of producing a safe and effective vaccine by early 2021.
12 Travel Diseases You Need to Know
Ebola Virus Disease
Ebola virus disease (formerly, Ebola hemorrhagic fever), a severe and often fatal condition, is caused by a virus of the family Filoviridae, genus Ebolavirus.[23,24] To date, four of the six identified ebolavirus subspecies are known to cause human disease: Zaire, Sudan, Tai Forest (formerly, Ivory Coast), and Bundibugyo ebolavirus.[23,24] (The remaining two ebolaviruses are Reston and Bombali ebolavirus.)
Fruit bats (family Pteropodidae) may be the natural viral host,[23,24] although an insectivorous bat has also been suggested as the culprit.[25] Wild animals transmit the virus to humans; it then spreads among humans through direct contact with or exposure to the blood, organs, or secretions of an infected person or to objects that have been contaminated with such secretions (shown).[23,24,26]
12 Travel Diseases You Need to Know
Ebola outbreaks have occurred mainly in remote villages in Central and West Africa, near tropical rain forests. In March 2014, West Africa experienced the largest outbreak of Ebola in history (>28,000 cases, >15,000 laboratory-confirmed cases, and >11,000 deaths), with widespread transmission in Liberia, Sierra Leone, and Guinea.[23,27] Many countries were affected, including the United States, the United Kingdom, Italy, and Spain, but there are currently no active cases of Ebola in these regions.[23]
The 2020 outbreak in the DRC appears to have started in May and represents a new viral introduction, likely from an animal vector. It is unrelated to the 2018 outbreaks in Eastern DRC and Equateur Province.[28]
Major public health efforts aimed at finding effective eradication, control, and vaccination strategies for this disease continue.[23,29,30]
12 Travel Diseases You Need to Know
During the incubation period (2-21 days; average of 8-10 days), Ebola s/s include arthritis, low back pain, fever/chills, fatigue/malaise, headache, nausea/vomiting, diarrhea, and sore throat.[23,31] Late symptoms include bleeding from the eyes, ears, nose, mouth, and rectum; conjunctivitis; genital swelling; increased pain in the skin; and hemorrhagic rash over the entire body. Disseminated intravascular coagulation (DIC), shock, and/or coma may occur.
Hematologic testing is available for virologic (eg, reverse transcription polymerase chain reaction [RT-PCR], antigen detection, virus isolation) and immunologic (immunoglobulin [Ig] M, IgG) evidence of infection.[23] Ebola virus disease is a diagnosis of exclusion; malaria, typhoid fever, shigellosis, cholera, leptospirosis, plague, rickettsiosis, relapsing fever, meningitis, hepatitis, and other viral hemorrhagic fevers must be concurrently ruled out.[32]
12 Travel Diseases You Need to Know
Consider all patient samples as extreme biohazard risks; conduct all laboratory testing for Ebola under maximum biologic containment conditions. To reduce the Ebola transmission risk, avoid areas with epidemics, wear protective barriers (eg, gown, gloves, masks) around sick patients, isolate infected patients from contact with unprotected persons, and practice other infection-control measures.[33] The CDC provides personal protective equipment (PPE) guidance.
Infected patients are usually hospitalized, and most require intensive supportive care to manage shock and/or infections (eg, intravenous [IV] fluids and drugs).[23] Transfusions of platelets or fresh blood may be needed for bleeding. Up to 90% of patients die of the disease (average fatality: 50%).[23] Several investigational monoclonal antibody treatments remain in clinical trials, with promising results to date.[34] None have received FDA approval yet.
The FDA approved the first Ebola vaccine rVSV-ZEBOV (Ervebo) on December 19, 2019.[35] This single-dose vaccine is protective against the Zaire ebolavirus species.[35] A second vaccine against the Zaire subtype leverages two different components and requires two doses; it remains investigational and has not received FDA approval.[30] In those who recover from Ebola, antibodies have been detected in the blood up to 10 years later—perhaps providing some protective immunity to the subtype that sickened them.[36]
12 Travel Diseases You Need to Know
Malaria
Malaria is caused by the parasite Plasmodium, transmitted via the bite of infected female Anopheles mosquitoes.[37,38]A gambiae is the principal vector in Africa.[39] Infection may also occur through blood transfusions, organ transplantation, needle sharing, and congenital transmission.[39]
In 2018, there were an estimated 228 million cases of malaria in 87 countries, representing a 9% global decrease since 2010.[40] Mortality also fell by 31% in the same period. However, the African region continues to bear a disproportionately high share of the global burden (93% of malaria cases; 94% of malaria deaths).[40]
12 Travel Diseases You Need to Know
Plasmodium parasites multiply in the human liver and then infect red blood cells.[41] Malaria s/s include fever/chills, headache, vomiting, myalgia, and anemia; the incubation period ranges from 7 to 30 days after the mosquito bite.[42] However, s/s may be delayed up to months after exposure.[38]
Clinicians should suspect malaria in anyone with fever who recently traveled to the tropics, particularly malaria-endemic areas, or who received a blood transfusion while in an endemic area or who has s/s consistent with malaria.[38] In many parts of the world, the parasites have developed resistance to several antimalarial agents.[38]
12 Travel Diseases You Need to Know
These images are from a patient with severe Plasmodium vivax malaria. Left (x-ray): Interstitial bilateral infiltrates compatible with acute lung injury. Center (CT scan): Infiltrates in the right midzone. Right (CT scan): Normal image 2 months after the acute episode.
Traditional microscopy remains the gold standard for diagnosing malaria, although other rapid diagnostic tests are increasingly available.[38] Based on risk assessment, travelers should use specific malaria prevention measures (eg, protective clothing, insect repellents, insecticide-treated bed nets, antimalarial agents).[38] The type of antimalarial agent used depends on the region, and the treatment depends on the disease severity.
Chloroquine has been the historic drug of choice, but owing to widespread resistance to this agent, other therapeutic medications are indicated—with artemisinin-based combination therapy (ACT) a top consideration.[37] Medical care, including IV fluids and respiratory support, may be needed for some infected patients. In most cases, the outcome is expected to be good with early treatment.[38] However, severe malaria (especially P falciparum disease) is a medical emergency that requires urgent intervention; malaria disrupts the blood supply to vital organs and can result in seizures, mental confusion, kidney failure, acute respiratory distress syndrome, coma, and death.[38,42]
To date, RTS,S (Mosquirix) is the first and only vaccine to show significant reduction in malaria and severe malaria; it acts against P falciparum.[44] In children who received four doses in large-scale clinical trials, the vaccine prevented about 4 in 10 cases of malaria over a 4-year period.[44]
12 Travel Diseases You Need to Know
Dengue
Dengue is a febrile illness transmitted by Aedes mosquitoes—the same species that transmits Zika, yellow fever, and chikungunya (CHIKV) viruses.[45] There are four serotypes, meaning it is possible to be infected four times.[45,46]
Before 1970, dengue was endemic in 9 countries[45]; over the past 50 years it has spread to involve over 100 countries, with 40% of the world's population (approximately 3 billion people) living in areas with risk of dengue.[46] Approximately 400 million cases of dengue occur annually, of which about 100 million have clinical manifestations and around 22,000 are fatal.[46]
12 Travel Diseases You Need to Know
The top image reveals subconjunctival hemorrhages in a dengue patient with acute liver failure. The bottom images show a confluent maculopapular rash with islands of sparing in the lower extremities of a different dengue patient.
Although most dengue patients are asymptomatic, those with s/s commonly present with high fever, and/or headache, nausea, vomiting, rash, and muscle/joint pain.[45] S/s typically develop within 2 weeks of exposure (incubation: 4-10 days) and last up to 7 days.[45] Rarely, severe dengue may be associated with dengue hemorrhagic fever—with bleeding from the gums and other mucosa, severe abdominal pain, persistent vomiting, and respiratory difficulty—or dengue shock syndrome, both of which may be fatal.[47]
CYD-TDV (Dengvaxia), the first dengue vaccine, was licensed in 2015 and approved by regulatory authorities in about 20 countries by 2017.[45] It received FDA approval in May 2019.[48] The World Health Organization (WHO) recommends vaccination for persons living in areas where dengue is highly endemic who have a confirmed prior dengue infection.[45,48] Treatment remains supportive. Employing routine mosquito avoidance behaviors remains essential.[45,48]
12 Travel Diseases You Need to Know
Cholera
Cholera is caused by the bacterium Vibrio cholerae; it is rare in the United States and other industrialized nations.[49] Globally, there are an estimated 1.3 to 4.0 million cases per year and up to 143,000 cholera-related deaths.[50] The bacterium releases a toxin that increases the release of water from intestinal cells, resulting in severe diarrhea. The main reservoirs for V cholerae are humans and aquatic/marine sources (eg, brackish water, estuaries).[51] Infection occurs through ingestion of food or water contaminated directly or indirectly by feces of infected individuals.[50,51]
Cholera is common in regions with inadequate sewage and drinking water management and can spread rapidly in these settings (eg, areas suffering from war, famine, and crowding).[50,51] Casual contact with an infected person is not a risk factor for becoming ill.[51] Early detection, good hygiene and sanitation, and the establishment of clean water and food supplies are essential to minimizing the spread of cholera during epidemics.[50,51]
12 Travel Diseases You Need to Know
The image depicts interactions between V cholerae with other organisms and the environment.
Cholera infection is often asymptomatic or mild (acute watery diarrhea only), but a small percentage produces severe disease characterized by sudden, profuse watery diarrhea ("rice-water stools") and vomiting that can lead to profound hypotension, dehydration, and shock; muscle cramps; and tachycardia.[50,51] Left untreated, death can occur within hours.[50,51]
The gold standard of diagnostic testing is isolation and identification of V cholerae serogroup O1 or O139 by stool culture.[52] In resource-austere areas, the Crystal VC dipstick rapid test can provide an early warning to public health officials of an impending outbreak.[52] Without testing stool samples, it is almost impossible to distinguish cholera from other conditions that cause acute watery diarrhea.[52] Travelers should always take basic safety and hygiene precautions with food and drinking water,[50,51] even if they have been vaccinated.
12 Travel Diseases You Need to Know
The image is a model for the role of biofilm in V cholerae intestinal colonization. CT = cholera toxin.
Severe cholera can cause acute renal failure, severe electrolyte imbalances, coma, and death; thus, it is essential to promptly restore lost fluids and salts through rehydration therapy (eg, WHO-recommended oral solution).[50,51] Antibiotics (eg, tetracycline, doxycycline) to reduce fluid requirements and the duration of illness are generally reserved for severe cases.[53] Zinc supplementation helps to improve cholera s/s in children (<5 y).[50]
In the United States, one single-dose oral cholera vaccine is available (Vaxchora)[51]; three 2-dose vaccines are available internationally (Dukoral, Shanchol, Euvichol-Plus/Euvichol).[50,51] Vaccines offer incomplete protection and require up to 2 weeks, so vaccination should not replace standard prevention and control measures. The CDC does not recommend routine cholera vaccination for US travelers visiting areas that do not have active cholera transmission.[51] Ongoing surveillance of and vigilance in monitoring diarrheal outbreaks are crucial for minimizing cholera epidemics.[50,51]
12 Travel Diseases You Need to Know
Tuberculosis
Tuberculosis (TB) is a global disease caused by Mycobacterium tuberculosis (Mtb), a slow-growing, rod-shaped aerobic bacterium.[54] Although the incidence has been decreasing by around 2% annually, about 25% of the world's population is infected, with 10 million new cases and 1.5 million associated deaths reported in 2018.[55] TB is among the top 10 causes of death worldwide and is a leading killer of people with human immunodeficiency virus (HIV) infection.[55] The WHO regions of Southeast Asia (44%), Africa (24%), and the Western Pacific (18%) account for most new cases. Eight countries (India, China, Indonesia, the Philippines, Pakistan, Nigeria, Bangladesh, and South Africa) comprise two thirds of the global total of new cases.[55] There remains a significant gap between incidence and notification in these countries.
TB mainly affects the lungs (70%-80%)—in active disease, the upper lobes are most often involved[56]—but it can also affect the kidney, brain, spine, and other organs.[54] TB is primarily an airborne disease; transmission occurs when an actively infected person coughs, sneezes, or spits, propelling Mtb into the air.[55] Common s/s of active lung TB are cough with sputum/blood, chest pain, weakness, weight loss, fever/chills, and night sweats.[54,55] Latent TB is typically asymptomatic and noninfectious[54,55]; active disease may develop years later when the person's immune system becomes compromised.[55]
12 Travel Diseases You Need to Know
Diagnostic tests for TB include the tuberculin skin test (TST), TB blood tests, imaging studies (eg, chest x-ray [CXR] [shown]), and sputum examination/cultures.[54] The WHO recommends the Xpert MTB/RIF rapid molecular assay as the initial diagnostic test in all individuals who present with TB s/s due to this test's ability to quickly (≤2 hours) and simultaneously detect TB and rifampicin resistance (RR).[55] Travelers should avoid close contact with, or prolonged exposure to, known TB patients in crowded, enclosed environments; if avoidance is not possible, travelers should undergo a TST or interferon-gamma release assay (IGRA) test before leaving the United States.[54] If the test result is negative, the TST/IGRA test should be repeated 8-10 weeks after the travelers return.[54]
TB is most often treatable and curable; however, it can be fatal if left untreated, and inadequately treated disease has resulted in growing rates of drug-resistant disease.[55] Active drug-sensitive TB disease requires a multidrug treatment regimen given in a 2-month intensive phase and then a 4- or 7-month continuation phase.[54] The global success rate for multidrug-resistant or rifampicin-resistant TB (MDR/RR-TB) is 56%.[55]
In areas with endemic TB, the bacille Calmette-Guérin (BCG) vaccine is often given to infants and children, but it has variable efficacy in preventing adult disease, and BCG can interfere with TST results in those with latent disease.[54] Clinical evaluation and CXR are most helpful in people who previously received the BCG vaccine.
12 Travel Diseases You Need to Know
Zika Virus
Zika virus is spread to people primarily through the bite of an infected Aedes species mosquito, the same mosquito that transmits dengue and chikungunya.[57,58] Identified in Uganda in 1947, Zika virus is now present in many equatorial countries[57]—a total of 86 countries have reported evidence of mosquito-transmitted Zika infection.[58] Regionally, Zika virus infection has markedly increased in the Americas since May 2015.[57,58] In 2015-2016, large Zika virus outbreaks occurred in the Americas, including limited local transmission in Florida and Texas through 2016-2017.[57,59] No local mosquito-borne Zika virus transmission has been reported in the continental United States between 2018 and August 2020.[59,60]
The most common s/s of Zika virus infection are fever, rash, joint pain, and conjunctivitis.[57,58] They typically begin within days after an individual has been bitten by an infected mosquito, are usually mild, and last 2 days to 1 week. Cases are most commonly managed without hospitalization and with supportive care.[57,58]
12 Travel Diseases You Need to Know
The left image is a transmission electron microscope image of negative-stained, Fortaleza-strain Zika virus (red), isolated from a patient with microcephaly in Brazil. The right image demonstrates a Zika virus–associated rash on a patient's hand. According to the WHO, Zika virus is a cause of microcephaly and congenital and neurologic disorders, including Guillain-Barré syndrome (GBS).[57,58]
Because Zika infection during pregnancy can cause severe birth defects,[57,58] pregnant women should consider postponing travel to any area where the Zika virus is active.[57]
12 Travel Diseases You Need to Know
Measles
Measles, or rubeola, is caused by a single-stranded, enveloped RNA virus (family Paramyxoviridae, genus Morbillivirus).[61] Humans are the only natural hosts for measles virus,[61,62] and the disease is spread via aerosolized droplets.[61]
Measles remains a common, highly contagious disease in many parts of the world, including areas of Europe, the Middle East, Asia, the Americas, and Africa.[62,63] An increasing number of outbreaks have occurred in developed countries—including the United States, which in 2019 had the highest number of cases since 1992—as a result of underimmunized children coming into contact with infected people.[64] Most US measles cases result from travelers who become infected in endemic areas and then bring the disease back home and infect the unvaccinated.[64]
Measles remains a leading cause of death among young children despite the fact that a safe and cost-effective vaccine is available.[61,62] Between 2000 and 2018, vaccination prevented an estimated 23.2 million measles deaths, a 73% reduction (from 536,000 to 142,000).[62]
12 Travel Diseases You Need to Know
Initial s/s of measles, which appear 10-12 days after infection, are high fever, coryza, conjunctivitis, cough, and Koplik spots (left image).[61,62] About 14 days afterward, a rash appears (first on the face/upper neck, gradually spreading downward [right image]).[61,62] The diagnosis is usually made based on the classic clinical picture, but laboratory identification and confirmation by serologic testing for measles-specific IgM/IgG titers, viral isolation from oropharyngeal/nasopharyngeal swabs, or detection of measles RNA by RT-PCR assay are necessary for public health and outbreak control.[61]
Measles can be a serious illness even in previously healthy children, and inpatient care may be required. Complications that tend to affect children younger than 5 years and adults older than 20-30 years, particularly those who are malnourished and/or immunocompromised, include middle ear infections (7%-9%), severe diarrhea (8%)/dehydration, pneumonia (1%-6%), blindness, and encephalitis.[61,62]
12 Travel Diseases You Need to Know
No specific antiviral measles therapy exists, but supportive care to prevent complications includes good nutrition, adequate fluid intake, and rehydration with a WHO-recommended oral solution for fluid losses.[62] Those with uncomplicated measles infection generally recover well; antibiotics are recommended for treating pneumonia and eye/ear infections.[62] The WHO also recommends two doses of vitamin A supplements 24 hours apart for all children with measles to reduce the risk of complications.[61,62]
Routine pediatric measles vaccination (highly effective for prevention) and mass immunization campaigns in countries with high case/death rates are key public health strategies for reducing global measles deaths. The measles vaccine is safe, effective, and inexpensive and has been in use for nearly 60 years.[61,62] Postexposure prophylaxis to reduce the risk of developing measles or ameliorate its s/s includes receiving the vaccine within 72 hours of, or taking serum Ig within 6 days after, viral exposure.[61]
12 Travel Diseases You Need to Know
Chikungunya Virus Disease
CHIKV, an RNA alphavirus (family Togaviridae), spreads in humans via the bite of infected female Aedes aegypti/A albopictus mosquitoes.[65,66] Outbreaks have occurred in Africa, Asia, Europe, and islands in the Indian and Pacific Oceans (shown).[65,66] In 2013, CHIKV disease was found for the first time in the Americas, in the Caribbean, with a peak in cases in 2014 (>1.1 million)[65,66]; in 2015, CHIKV became a nationally notifiable condition in the United States.[67] As of August 6, 2020, a total of 11 travel-associated CHIKV cases in the continental United States have been reported to have occurred during 2020.[67]
Fever and arthralgia are the main s/s of CHIKV; headache, myalgia, and rash may also be present.[65,66] Most s/s resolve quickly, but arthralgia may persist for months. Serious complications are uncommon.[65,66] Those at risk for more severe disease include perinatally infected newborns, older adults (≥65 y), and people with comorbidities (eg, diabetes, heart disease).[65]
12 Travel Diseases You Need to Know
The image shows a rash on the foot of a patient with CHIKV infection in the Philippines.
Serologic studies (eg, enzyme-linked immunosorbent assays [ELISA]) may confirm the presence of IgM and IgG anti-CHIKV antibodies.[66] Use serologic and virologic testing (eg, RT-PCR assay) for samples collected during week 1 after s/s onset.[66] Differentiating CHIKV from dengue can be a clinical challenge due to s/s overlap.[65,66] However, therapy remains supportive for both diseases (eg, rest, adequate hydration, antipyretics/analgesics).[65,66]
The day/night activity of the mosquito vectors and the proximity of their breeding sites to human habitation are significant risk factors for CHIKV infection.[66] Key elements of prevention and infection control are eliminating mosquito breeding grounds (including both natural habitats and plastic containers) and avoiding Aedes mosquito bites (eg, wearing permethrin-treated clothing; using insect repellents that contain N,N-diethyl-meta-toluamide [DEET], picaridin, oil of lemon eucalyptus/p-menthane 3,8-diol [PMD]; using window/door screens and bed nets).[66]
12 Travel Diseases You Need to Know
Polio
Polio (poliomyelitis) is caused by poliovirus types 1, 2, and 3.[68] Poliovirus is an enterovirus, and like other species in this genus, it is transmitted by the fecal-oral or oral-oral route. Acute infection involves the oropharynx, GI tract, and, occasionally, the central nervous system (CNS).[68]
The incubation period for polio is 3-6 days for nonparalytic polio; for paralytic polio, the incubation period for the onset of paralysis is 7-21 days.[70] The three basic patterns of infection are subclinical, nonparalytic, and paralytic. Most polio cases are subclinical; patients may be asymptomatic (72%) or have minor s/s (24%) (eg, low-grade fever, pharyngitis, headache, neck/back stiffness, limb pain).[69,70] Fewer than 1% of polio cases result in permanent limb paralysis (usually the legs) (shown).[69] About 2%-5% of children and up to 15%-30% of adults with paralytic polio die[71]; overall, 5%-10% die from respiratory failure.[69] Postpolio syndrome (weakening of previously unaffected/affected muscles) may develop in 25%-40% patients 15-40 years after the initial infection.[70]
12 Travel Diseases You Need to Know
Diagnostic tests for polio include viral isolation by cultures of throat washings, stool samples, or cerebrospinal fluid (CSF); spinal tap and CSF examination; and serologic measurement of antibodies to the polio virus.[71]
There is no cure for polio, only preventive measures.[69] Polio immunization is over 90% effective.[69] Polio primarily affects children younger than 5 years[69]; most adults are immune as a result of childhood vaccination.[71] Consider vaccination for (1) travelers to polio-endemic or high-risk regions, (2) laboratory workers who may be exposed to polioviruses, and (3) clinicians with exposure to infected people or their close contacts.[71]
As a result of a massive global vaccination campaign since the late 1980s, wild-type cases have decreased by 99%.[69] As of August 12, 2020, polio is endemic only in Afghanistan and Pakistan, with 29 and 147 wild poliovirus cases, respectively, in 2019, and 29 and 56, respectively, in 2020.[72] However, despite the progress in eradicating polio globally, outbreaks still occur, usually in groups of unvaccinated people and those who have traveled to endemic regions.[68]
12 Travel Diseases You Need to Know
Yellow Fever
Yellow fever, named for the jaundice that affects some patients,[73] results from a single-stranded RNA arbovirus[74] (genus Flavivirus) that is transmitted to humans via the bite of infected Aedes or Haemagogus mosquitoes.[73,74] The vectors acquire the virus by feeding on infected primates and then transmit it to other primates. Yellow fever has three transmission cycles (sylvatic [jungle], intermediate [savannah], urban)[73,74] and three disease stages (infection, remission, intoxication).[73-75]
The disease is endemic in tropical areas of Africa and Central/South America (shown).[73,74] Most infected persons are asymptomatic or have only a mild illness (incubation, 3-6 days) that improves 3-4 days after the initial onset. Early s/s include sudden fever/chills, severe headache, back pain, myalgias, nausea/vomiting, and fatigue/weakness.[73,74] After a brief remission of hours to a day, about 12% of patients develop a more severe form of the disease that is characterized by high fever, jaundice, bleeding, and, eventually, shock and multisystem organ failure. Up to 50%-60% of these patients die within 7-10 days.[73,74]
12 Travel Diseases You Need to Know
Micrograph: Yellow fever virus particles. Inset: An A aegypti mosquito feeding.
Yellow fever is difficult to diagnose during the early stages; it can be confused with severe malaria, dengue or other hemorrhagic fevers, leptospirosis, viral hepatitis, and other conditions, as well as poisoning.[73] Diagnostic tests include serology and viral isolation or nucleic acid amplification.[73,74] There is no specific treatment for yellow fever, but supportive and life-saving therapy is used to manage dehydration, respiratory failure, and fever[73,74]; antibiotics should be used to treat bacterial infections.[73]
Precautions to take when traveling to endemic areas include sleeping in screened housing, using mosquito repellents (eg, insect repellents containing DEET, picaridin, IR3535, or oil of lemon eucalyptus), and wearing clothing that fully covers the body.[76] In addition to the ongoing Eliminate Yellow Fever Epidemics (EYE) strategy (to protect at-risk groups, prevent international spread, and quickly contain outbreaks), there is a very effective live-attenuated vaccine against yellow fever, with 99% of persons vaccinated achieving effective immunity within 30 days.[73] The vaccine should be administered at least 10 days before travel to endemic areas.[76]
12 Travel Diseases You Need to Know
Typhoid Fever
Typhoid fever, a life-threatening condition, most often results from infection with the bacterium Salmonella enterica serotype Typhi (ie, S typhi).[77,78] The disease is transmitted through contaminated food or water, moving from the intestines into the bloodstream and then to other parts of the body, including the lymph nodes, gallbladder, liver, and spleen.[79] The intraoperative specimen above shows multiple typhoid ileal perforations.
Typhoid fever is common in developing nations, as in South-East Asia, Africa, the Americas, and the Western Pacific.[78] Globally, up to 21 million cases occur annually, with approximately 200,000 related deaths.[80] An estimated 350 cases of culture-confirmed typhoid fever occur each year in the United States, with most acquired during international travel.[80]
Typhoid fever manifests 1-2 weeks after the bacterium has been ingested (incubation: 6-30 days) and is characterized initially by fever and abdominal pain.[77] As the disease progresses, the fever rises higher (to 102°F-104°F [38°C–40°C]), and severe diarrhea develops. Small red spots may appear on the chest and abdomen of some patients.[77]
12 Travel Diseases You Need to Know
Blood cultures are the mainstay for diagnosis of typhoid fever; the sensitivity increases with multiple blood cultures, whereas only about half of single blood cultures are positive.[77] The diagnostic yield of bone marrow cultures increases to about 80% of cases. Blood cultures are best obtained during week 1 of a patient's illness; stool cultures are usually not positive until later in the disease course.[77] In low-resource areas, the diagnosis is often made clinically based on the history of infection risk and a gradually increasing severity of fever over days.[77]
Treatment includes antibiotics, although resistance has been rising with certain agents (eg, fluoroquinolones, azithromycin); in such cases, third-generation cephalosporins are used.[77,78] Patients with s/s of typhoid fever within 60 days of returning from an endemic area or who have consumed food prepared by a known S typhi carrier should receive empiric broad-spectrum antibiotics before confirmation of the diagnosis, followed by more specific antibiotics once typhoid fever is verified. IV fluid and electrolytes may also be given.[81] Vaccines include oral Ty21a (Vivotif) (live attenuated) and injectable Vi capsular polysaccharide (ViCPS) (Typhim Vi).[77] Note that typhoid vaccines are not 100% effective, therefore safe eating and drinking habits are recommended.[77]
In 2015, an MDR strain of S typhi, H58, emerged from South Asia and spread globally.[82,83] In 2016, H58 mutated, becoming an extensively drug-resistant (XDR) strain identified during an outbreak in Pakistan. These were confirmed in US travelers returning from Pakistan.[83,84] Carbapenems should be used for patients with suspected severe or complicated typhoid fever who have traveled to Pakistan.[84]
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