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Image from the Centers for Disease Control and Prevention (CDC)/ James Gathany.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Economic globalization and rising global travel have increased exposure to, and spread of, severe and life-threatening diseases. In addition to travel history and exposures during travel, where a person lives and their daily exposures greatly impact the risk of acquiring disease.

The ongoing outbreak of Ebola in the Democratic Republic of Congo (DRC) is the 10th outbreak of the disease that the World Health Organization (WHO) has announced in the DRC since 1976. Additional WHO announcements include measles (Brazil, Japan), Rift Valley Fever (Gambia, Kenya), cholera (United Republic of Tanzania, Mozambique, Kinshasa, DRC, Somalia, Cameroon), and Middle East Respiratory Syndrome coronavirus (MERS-CoV) (United Arab Emirates), just to name a few.[1]

This slideshow provides essential information on the transmission, diagnosis, prevention, and treatment of 13 key travel-related illnesses. The image shows a female Aedes mosquito; this species is the vector for dengue, Zika, and Chikungunya virus disease and yellow fever.

Image from the CDC.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Ebola Virus Disease

Ebola virus disease (formerly, Ebola hemorrhagic fever), an extremely severe and often fatal condition, is caused by a virus of the family Filoviridae, genus Ebolavirus.[2,3] Four of the five identified ebolavirus subspecies are known to cause human disease: Zaire, Sudan, Tai Forest (formerly, Ivory Coast), and Bundibugyo ebolavirus.[2,3]

Fruit bats (family Pteropodidae) may be the natural viral host,[2,3] although an insectivorous bat has also been suggested as the culprit.[4] 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).[2,3,5]

Image from the WHO.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

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. 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.[1] The current outbreak in the DRC, which started in 2018 (with patients identified in neighboring Uganda), is the first since the WHO declared the 2014 Ebola outbreak as no longer a public health emergency of international concern on March 29, 2016.[1,6,7]

Major public health efforts aimed at finding effective eradication, control, and vaccination strategies for this disease continue.[2,3,6]

Image from Wikimedia Commons / Mikael Häggström.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

During the incubation period (=1 week; rarely, =2 weeks postinfection), Ebola signs/symptoms (s/s) include arthritis, low back pain, fever/chills, fatigue/malaise, headache, nausea/vomiting, diarrhea, and sore throat.[2,3]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 (reverse transcription polymerase chain reaction [RT-PCR], antigen detection, virus isolation) and immunologic (immunoglobulin [Ig] M, IgG) evidence of infection.[2] 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.[2]

Adapted image from the CDC.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Consider all patient samples as extreme biohazard risks; conduct all laboratory testing for Ebola under maximum biologic containment conditions (shown).[8] 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.[2,9] Infected patients are usually hospitalized, and most require intensive supportive care to manage shock and/or infections (eg, intravenous [IV] fluids and drugs).[2] Transfusions of platelets or fresh blood may be needed for bleeding. Up to 90% of patients die of the disease (average fatality: 50%).[2]

Due to the results of the Sierra Leone Trial to Introduce a Vaccine against Ebola (STRIVE) study, the yet-to-be-licensed rVSV-ZEBOV vaccine has been approved for "compassionate use" in outbreaks.[10] It is currently deployed in the DRC, being applied in people "rings" around confirmed cases and in healthcare workers in the outbreak areas.[10]

Image from the CDC.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Malaria

Malaria is caused by the parasite Plasmodium, transmitted via the bite of infected female Anopheles mosquitoes.[11]A gambiae is the principal vector in Africa.[14] Infection may also occur through blood transfusions, organ transplantation, needle sharing, and congenital transmission.[12] In 2017, there were an estimated 219 million cases of malaria in 87 countries.[11] Mortality rates decreased by 45-51% between 2000 and 2018. However, the African region continues to bear a disproportionately high share of the global burden.[11,13,14]

Plasmodium parasites multiply in the human liver and then infect red blood cells.[15] Malaria s/s include fever/chills, headache, vomiting, myalgia, and anemia; they usually appear 10-15 days after the mosquito bite.[11] However, s/s may be delayed up to months after exposure.[12] Clinicians should suspect malaria in anyone with fever who recently traveled to the tropics, particularly malaria-endemic areas,[12] or who received a blood transfusion while in an endemic area or who has s/s consistent with malaria.[11] In many parts of the world, the parasites have developed resistance to several antimalarial agents.

Images from Fernandez-Becerra C, Pinazo MJ, Gonzalez A, Alonso PL, del Portillo HA, Gascon J. Malar J. 2009;8:55. [Open access.] PMID: 19341456, PMCID: PMC2682795.

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Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

These images are from a patient with severe Plasmodium vivax malaria. Left (x-ray): Interstitial bilateral infiltrates compatible with acute lung injury. Center (computed tomography [CT] scan): Infiltrates in the right midzone. Right (CT scan): Normal image 2 months after the acute episode.

Blood smears are the gold standard to confirm the diagnosis of malaria[12]; other tests include antigen detection, PCR assay, and serology.[12] Based on risk assessment, travelers should use specific malaria prevention measures (eg, protective clothing, insect repellents, insecticide-treated bed nets, antimalarial agents).[11,12] 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 should be considered.[11,12] 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.[11,12] 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.[16]

Images from Lee C, Jang EJ, Kwon D, Choi H, Park JW, Bae GR. Ann Occup Environ Med. 2016;28:16. [Open access.] PMID: 27057314, PMCID: PMC4823875.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Dengue

Dengue is a febrile illness transmitted by Aedes mosquitoes—the same species that transmits the Zika and Chikungunya (CHIKV) viruses.[17-22] Before 1970, dengue was endemic in 9 countries; over the past 50 years it has spread to involve over 100 countries, with half of the world's population now at risk. Approximately 400 million cases of dengue occur annually, of which about 100 million have clinical manifestations, and about 22,000 are fatal.[17]

The images show a confluent maculopapular rash with islands of sparing in the lower extremities of a dengue patient.

Images from (1) Kularatne SA, Imbulpitiya IV, Abeysekera RA, Waduge RN, Rajapakse RP, Weerakoon KG. BMC Infect Dis. 2014;14:141. [Open access.] PMID: 24628767, PMCID: PMC4008311 (main image); and (2) Giri S, Agarwal MP, Sharma V, Singh A. Cases J. 2008;1(1):204 [Open access.] PMID: 18831758, PMCID: PMC2566568 (top right inset).

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Main image: Subcapsular hemorrhage of the liver in a dengue patient with fatal hepatic hemorrhagic necrosis. Top right inset: Subconjunctival hemorrhages in a different dengue patient with acute liver failure.

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.[17,18] S/s typically develop within 2 weeks of exposure (incubation: 4-10 days) and last up to 7 days.[17,18] 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.[17,18]

The WHO recommends vaccination in areas where dengue is highly endemic; the vaccine is not available in the United States. Treatment remains supportive.[17,18] Avoiding mosquito bites is essential.

Images from (1) Lutz C, Erken M, Noorian P, S un S, McDougald D. Front Microbiol. 2013;4:375. [Open access.] PMID: 24379807, PMCID: PMC3863721 (map); (2) the CDC / Janice Haney Carr (top left inset); and (3) the CDC (top right inset).

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Cholera

Cholera is a human-only intestinal illness caused by Vibrio cholera serogroups O1 and O139,[23] accounting for about 1.3-4.0 million cases per year.[24] 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).[25] Infection occurs through ingestion of food or water contaminated directly or indirectly by feces or vomit of infected individuals.[24,25]

Cholera is common and can spread rapidly in regions with inadequate treatment of sewage and drinking water (eg, areas suffering from war, famine, and crowding).[24,25]Casual contact with an infected person is not a risk factor for becoming ill. 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.[24,25]

The map shows the global distribution of V cholerae. Triangles = V cholerae detected by molecular and/or culture-based methods. Red = subgroup O1/O139 detection; light blue = non-O1/non-O139 detection; dark blue = unspecified. Top left inset: Scanning electron microscopic image of V cholerae, serogroup 01 (magnification × 22371). Top right inset:V cholerae grown on thiosulfate-citrate-bile-sucrose (TCBS) agar plate.

Image from Lutz C, Erken M, Noorian P, Sun S, McDougald D. Front Microbiol. 2013;4:375. [Open access.] PMID: 24379807, PMCID: PMC3863721

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Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

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 produce 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.[24,25] Left untreated, death can occur within hours.[24,25]

The gold standard of diagnostic testing is isolation and identification of V cholerae serogroup O1 or O139 by stool culture.[24,25] In resource-austere areas, the Crystal VC dipstick rapid test can provide an early warning to public health officials that an outbreak of cholera is occurring.[26] Without testing stool samples, it is almost impossible to distinguish cholera from other conditions that cause acute watery diarrhea. Travelers should always take basic safety and hygiene precautions with food and drinking water, even if they have been vaccinated.[24,25]

Image from Silva AJ, Benitez JA. PLoS Negl Trop Dis. 2016;10(2):e0004330. [Open access.] PMID: 26845681, PMCID: PMC4741415.

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Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

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).[24,25] Antibiotics (eg, tetracycline, doxycycline) to reduce fluid requirements and the duration of illness are generally reserved for severe cases.[24,25] Zinc supplementation helps to improve cholera s/s in children (<5 y).[24,25]

In the United States, two single-dose oral cholera vaccines are available (Vaxchora, PaxVax)[25]; three 2-dose vaccines are available internationally (Dukoral, Shanchol, Euvichol-Plus/Euvichol).[24] 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.[25] Ongoing surveillance of and vigilance in monitoring diarrheal outbreaks are crucial for minimizing cholera epidemics.[24,25]

Image from the CDC / WHO.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Tuberculosis

Tuberculosis (TB) is a global disease caused by Mycobacterium tuberculosis (Mtb), a slow-growing, rod-shaped aerobic bacterium.[27,28] Although the incidence rate has been decreasing by 2% annually, about 25% of the world's population is infected, with 10.4 million new cases and 1.6 million associated deaths reported in 2017.[27,29] TB is among the top 10 causes of death worldwide and is a leading killer of people with HIV infection.[27] About 87% of new TB cases occur in high TB-burden countries, with 64% from eight countries alone: India, Indonesia, Pakistan, China, the Philippines, Nigeria, Bangladesh, and South Africa.[27]

TB mainly affects the lungs (70%-80%)—in active disease, the upper lobes are most often involved[30]—but it can also affect the kidney, brain, spine, and other organs.[28] TB is primarily an airborne disease; transmission occurs when an actively infected person coughs, sneezes, or spits, propelling Mtb into the air.[27] Common s/s of active lung TB are cough with sputum/blood, chest pain, weakness, weight loss, fever/chills, and night sweats.[27,28] Latent TB is typically asymptomatic and noninfectious; active disease may develop years later when the person's immune system becomes compromised.[27,28]

Image from the CDC via Wikimedia Commons.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

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.[27,28] 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.[28] If the test result is negative, the TST/IGRA test should be repeated 8-10 weeks after the travelers return.[31]

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.[27] Active drug-sensitive TB disease requires a multi-drug treatment regimen given in a 2-month intensive phase and then a 4- or 7-month continuation phase.[27] 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.[28] Clinical evaluation and CXR are most helpful in people who previously received the BCG vaccine.

Image from the CDC.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Middle East Respiratory Syndrome

MERS is a viral respiratory illness caused by the coronavirus MERS-CoV (genus Betacoronavirus), which is closely related to bat coronaviruses.[32]Dromedary camels are a likely reservoir for infection transmission in humans.[32,33] Limited human-to-human spread has usually occurred in settings with close personal contact, primarily involving travelers to, or residents in and around, the Arabian Peninsula (shown), particularly Saudi Arabia.[32,33]

Since the first reported cases in 2012, sporadic or index human MERS cases have occurred in Jordan, Kuwait, Oman, Qatar, Saudi Arabia, the United Arab Emirates, Lebanon, Iran, and Yemen; cases from individuals with recent travel from endemic areas have been reported in 18 additional countries globally.[32,33] Therefore, obtaining a thorough and detailed travel history from patients is paramount.

Image from the CDC / Jennifer L Harcourt.

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Some MERS-CoV–infected individuals may be asymptomatic or have mild symptoms, but most patients have a severe acute respiratory illness with s/s of fever, cough, and shortness of breath within 14 days of exposure.[32,33] Severe complications include pneumonia, kidney failure, and death.[32,33]

Obtain RT-PCR assays on respiratory samples and serologic testing on blood samples (shown) to confirm MERS-CoV infection.[32] No vaccine or specific treatment is available; therapy consists of supportive treatment of vital organ functions (eg, cardiorespiratory support), with overall therapy tailored to the patient's clinical condition.[32,33] Common illness preventive measures include frequent hand-washing, avoiding touching the face, avoiding close personal contact with sick people, and frequent cleaning/disinfection of often-touched surfaces.[32,33]

Image from the CDC.

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Zika

Zika virus is spread to people primarily through the bite of an infected Aedes species mosquito, the same mosquito that transmits dengue and chikungunya. Identified in Uganda in 1947, Zika virus is now present in many equatorial countries; Zika virus infection has markedly increased in the Americas since May 2015.[21] In 2019, as of June 5 there have been 2 reported US cases of Zika, in travelers returning from affected areas, and 18 cases reported in US territories, all presumed to be mosquito-borne acquired.[34] No local mosquito-borne Zika virus transmission has been reported in the continental United States in 2018 or 2019.[34]

The most common s/s of Zika virus infection are fever, rash, joint pain, and conjunctivitis.[21,22] 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.[21-22]

This 2018 map shows an equatorial distribution of areas with risk of Zika infection.

Image courtesy of Carolina O Barbosa, MD, and Antonio C Bandeira, MD, Salvador, Brazil.

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The image demonstrates a Zika virus–associated rash on a patient's hand. According to the WHO, scientific consensus states that the Zika virus is a cause of microcephaly and congenital and neurologic disorders, including Guillain-Barré syndrome (GBS).[35]

Because Zika infection during pregnancy can cause severe birth defects, pregnant women should consider postponing travel to any area where the Zika virus is active.[21]

Image from the CDC.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Measles

Measles, or rubeola, is caused by a single-stranded, enveloped RNA virus (family Paramyxoviridae, genus Morbillivirus).[36] Humans are the only natural hosts for measles virus,[36,37] and the disease is spread via aerosolized droplets.[36]

Measles remains a common, highly contagious disease in many parts of the world, including areas of Europe, the Pacific, Asia, and Africa.[37,38] An increasing number of outbreaks have occurred in developed countries—including the US, which in 2019 has had the highest number of cases since 1992—as a result of underimmunized children coming into contact with infected people.[38] In the United States, most measles cases result from travelers who become infected in endemic areas and then bring the disease back home and infect the unvaccinated.[38]

Measles remains a leading cause of death among young children despite the fact that a safe and cost-effective vaccine is available.[37] Measles deaths worldwide fell below 100,000 annually for the first time in 2016, but then rose to over 110,000 in 2017.[37]

Images from the CDC.

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Initial s/s of measles, which appear 10-12 days after infection, are high fever, coryza, conjunctivitis, cough, and Koplik spots (left image).[36,37] About 14 days afterward, a rash appears (first on the face/upper neck, gradually spreading downward [right image]).[36,37] 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.[36]

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 ear infections (7%-9%), severe diarrhea (8%)/dehydration, pneumonia (1%-6%), blindness, and encephalitis.[36,37]

Image courtesy of Olivia Wong, DO. Data from the CDC.[38]

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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.[37] Those with uncomplicated measles infection generally recover well; antibiotics are recommended for treating pneumonia and eye/ear infections.[37] The WHO also recommends two doses of vitamin A supplements 24 hours apart for all children with measles to reduce the risk of complications.[36,37] 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 over 50 years.[36,37] 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.[36]

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Chikungunya Virus Disease

CHIKV, an RNA alphavirus (family Togaviridae), spreads in humans via the bite of infected female Aedes aegypti/A albopictus mosquitoes.[19,20] Outbreaks have occurred in Africa, Asia, Europe, and islands in the Indian and Pacific Oceans (shown).[19,20] 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); in 2015, CHIKV became a nationally notifiable condition in the US.[19] As of June 6, 2019, a total of 28 travel-associated CHIKV cases in 14 US states and two locally transmitted cases from US territories (Puerto Rico) have been reported to have occurred during 2019.[39]

Fever and arthralgia are the main s/s of CHIKV; headache, myalgia, and rash may also be present.[19,20] Most s/s resolve quickly, but arthralgia may persist for months. Serious complications are uncommon. Those at risk for more severe disease include perinatally infected newborns, older adults (=65 y), and people with comorbidities (eg, diabetes, heart disease).[19,20]

Image from Wikimedia Commons / Nsaa.

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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.[19,20]Use serologic and virologic testing (eg, RT-PCR assay) for samples collected during week 1 after s/s onset. Differentiating CHIKV from dengue can be a clinical challenge due to s/s overlap. However, therapy remains supportive for both diseases (eg, rest, adequate hydration, antipyretics/analgesics).[19,20]

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. 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).[19,20]

Image from the CDC.

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Polio

Polio (poliomyelitis) is caused by poliovirus types 1, 2, and 3.[40] Poliovirus is an enterovirus, and like other species in this genus, it is transmitted by the fecal-oral route or oral-oral route. Acute infection involves the oropharynx, gastrointestinal (GI) tract, and, occasionally, the central nervous system (CNS).[40]

The incubation period for polio is 3-21 days.[40] 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).[40] Fewer than 1% of polio cases result in permanent limb paralysis (usually the legs) (shown). About 2%-5% of children and up to 15%-30% of adults with paralytic polio die[40]; overall, 5%-10% die from respiratory failure.[41] Postpolio syndrome (weakening of previously unaffected/affected muscles) may develop in 25%-40% patients 15-40 years after the initial infection.[40]

Image from Greene SA, Ahmed J, Datta SD, et al. MMWR Morb Mortal Wkly Rep. 2019 May 24;68(20):458-462. PMID: 31120868 PMCID: PMC6532951

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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.[40] There is no cure for polio, only preventive measures. Polio immunization is over 90% effective.[40]Polio primarily affects children younger than 5 years[41]; most adults are immune as a result of childhood vaccination.[40] 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.[40]

As a result of a massive global vaccination campaign since the late 1980s, cases have decreased by 99%.[40,41] As of March 1, 2019, polio is endemic in only 2 countries (Afghanistan and Pakistan), with 33 wild poliovirus cases in 2018 and 29 so far in 2019.[42] 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.[40]

Image from the CDC.

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Avian Flu

Avian flu, or bird flu, is caused by the highly pathogenic avian influenza (AI) type A H5N1 virus subtype.[43,44] Although AI type A viruses usually do not infect humans, rare cases have been reported, with most occurring after direct or close contact with infected poultry or after eating raw or undercooked meat, eggs, or blood from infected birds.[43,44] Highly pathogenic AI type A(H5N1) is an unusually aggressive virus that first infected humans in 1997 during a poultry outbreak in Hong Kong, China.[44]

Other AI viruses have also resulted in limited human infections, including A(H7N7) and A(H9N2)[44]; on February 14, 2018, the first human case of A(H7N4) infection was reported in China.[45]

Image from Wu ZQ, Zhang Y, Zhao N, et al. Int J Environ Res Public Health. 2017;14(3). [Open access.] PMID: 28273867, PMCID: PMC5369099.

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The map shows the geographic distribution of the total number of highly pathogenic AI type A (H5N1 and H5N6) and low pathogenic A (H7N9 and H9N2) virus cases and deaths until November of 2016.

Strongly consider the diagnosis of AI in travelers from regions endemic for Asian highly pathogenic AI H5N1 (Bangladesh, China, Egypt, India, Indonesia, and Vietnam).[43,46] The incubation period for A(H5N1) is 2-5 days (possibly =17 days); for A(H7N9), it is 1-10 days (average, 5 days).[44]

Clinical features depend on which AI virus caused the infection. Highly pathogenic AI infection s/s range from mild illness to severe respiratory illness and multiorgan disease, sometimes accompanied by nausea/vomiting, diarrhea, abdominal pain, and neurologic changes.[43] Complications of A(H5N1) and A(H7N9) infection include hypoxemia, multiorgan dysfunction, secondary bacterial and fungal infections and death.[44] The diagnosis requires high levels of biosafety laboratory testing (molecular, culture, or both) on nasopharyngeal swabs collected from affected patients during the first few days of illness.[43]

Image from US Fish and Wildlife Service / Don Becker, United States Geological Survey Center for Earth Resources Observation and Science (USGS EROS).

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The image shows a scientist cleaning an AI transportation container at the Bird Lab, Anchorage Science Center.

Although episodic resistance has been reported, the CDC and WHO recommend the neuraminidase inhibitor oseltamivir, peramivir, or zanamivir for treatment and prevention of human infection with AI A viruses.[43,44] The prognosis depends on the type of virus and the disease severity.

The best way to prevent infection with AI A viruses is to avoid sources of exposure, including not traveling to nations affected by A(H5N1) or avoiding contact with areas associated with poultry in those regions.[43,44]Wear protective clothing and special breathing masks when working with birds, and avoid undercooked or uncooked meat.[44] Clinicians treating infected patients should use appropriate personal protective barriers and follow recommended infection control measures.[47]

Note that seasonal influenza vaccination will not prevent infection with AI A viruses, but it can reduce the risk of coinfection with human and AI A viruses.[43] The US maintains a stockpile of vaccinations against A(H5N1).[43]

Adapted images from the CDC.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Yellow Fever

Yellow fever, named for the jaundice that affects some patients,[48] results from a single-stranded RNA arbovirus[49] (genus Flavivirus) that is transmitted to humans via the bite of infected Aedes or Haemagogus mosquitoes.[48,49] 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)[48,49] and three disease stages (infection, remission, intoxication).[48,49]

The disease is endemic in tropical areas of Africa and Central/South America (shown).[48,49] 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. [48,49] After a brief remission of hours to a day, about 15% 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% of these patients die within 10-14 days.[48,49]

Images from the CDC (micrograph) and the CDC / James Gathany (inset).

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Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

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.[48]Diagnostic tests include serology and viral isolation or nucleic acid amplification.[48,49] There is no specific treatment for yellow fever, but supportive and life-saving therapy is used to manage dehydration, respiratory failure, and fever; antibiotics should be used to treat bacterial infections.[48,49]

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.[50] In addition to the ongoing Eliminate Yellow Fever (EYE) strategy, there is a very effective live-attenuated vaccine against yellow fever, with 99% of persons vaccinated achieving effective immunity within 30 days.[48] It should be taken at least 10 days before travel to endemic areas.[50]

Image from Caronna R, Boukari AK, Zaongo D, et al. BMC Gastroenterol. 2013;13:102. [Open access.] PMID: 23782915, PMCID: PMC3691877.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

Typhoid Fever

Typhoid fever, a life-threatening condition, most often results from infection with the bacterium Salmonella enterica serotype Typhi (ie, S typhi).[51,52] 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.[53] 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.[51,52] Globally, an estimated 20 million cases occur annually, with approximately 150,000 related deaths.[52] An estimated 300 cases of culture-confirmed typhoid fever occur each year in the United States, with up to 85% acquired during international travel.[53]

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.[53] As the disease progresses, the fever rises higher (to 102°-104°F [38°C–40°C]), and severe diarrhea develops. Small red spots may appear on the chest and abdomen of some patients (see the next slide).[52,53]

Images from the CDC.

13 Travel Diseases You Need to Know

Bret A Nicks, MD, MHA, FACEP | July 16, 2019 | Contributor Information

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.[51] 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.[51] 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.[51]

Treatment includes antibiotics, although resistance has been rising with certain agents (eg, fluoroquinolones, azithromycin); in such cases, third-generation cephalosporins are used.[51,52] 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.[52] Vaccines include oral Ty21a (Vivotif) (live attenuated) and injectable Vi capsular polysaccharide (ViCPS) (Typhim Vi).[51,52] In December 2017, the first conjugate vaccine, which has longer-lasting immunity and fewer doses, was prequalified for typhoid.[52]

In 2015, a multidrug-resistant strain of S typhi, H58, emerged from South Asia and spread globally.[54,55] More recently, H58 has mutated and become an extensively drug-resistant (XDR) strain involved in an ongoing outbreak in Pakistan (November 2016 to beyond May 2019), with cases arising in the United States (5) from travelers returning from Pakistan.[56,57]

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References