Every year, millions of people travel abroad, exposing themselves to various diseases. As many as a third of short-term travelers experience a health problem during an international trip, and many have a febrile illness. Over 90% of infections related to short-term travel present within six months of return.
The most common diseases in travelers to the tropics are travelers’ diarrhea, followed by acute respiratory infections. Pre-travel health assessment and planning can prevent or ameliorate many of these problems (Table 1). Useful information about travel-related infections can be found at the websites of Public health agency of Canada, the World Health Organization, United States Centers for Disease Control and Prevention and the international society for travel medicine.
In the assessment of an ill returning traveler, a detailed travel history is essential. These are important lines of questioning. Details of potential specific exposures are essential.
- Travel departure and return dates
- Countries visited, including stopovers
- Destinations within the countries; rural or urban
- Climatic conditions, season
- Exposure to bites: insect, arachnid, reptile, mammal
- Exposure to ill people
- Type of food and liquids consumed, how and where prepared
- Vaccination history: review certificate and compliance
- Type of travel
- Quality of travel
- Medications (specific for trip and routine)
- Timing and sequence of symptoms
The physician needs to know the incubation periods of potential infections. The possibility of an infection acquired on a flight or on a cruise ship should not be forgotten. Often, distinctive physical findings are not seen in returning travelers. However, there may be findings that point to travel-acquired disease as opposed to common diseases.
The most important causes are malaria, enteric fever (S. typhi), hepatitis, amoebic liver abscess, arbovirus infections, rickettsial infection (e.g. scrub typhus), septicaemia, and meningitis.
Of the four species of plasmodia that infect people, Plasmodium vivax is the most common but Plasmodium falciparum is the most serious and most likely to be fatal. The risk of contracting malaria is highest in Oceania and Africa, followed by Asia and Latin America.
Most cases of falciparum malaria will become apparent within 7 days to 2 months after exposure; P vivax, Plasmodium ovale, and Plasmodium malariae infections are usually obvious 3-6 months after exposure, but P. ovale and P. malariae infections might take a year or longer to appear. Most cases of malaria in travellers are due to lack of or inappropriate chemoprophylaxis, which includes stopping the regimen too soon after returning home.
The typical symptoms of malaria are fever (intermittent or periodic), chills, headache, nausea, vomiting, abdominal pain, and myalgia. Travelers who lack immunity to malaria are most likely to suffer severe disease including cerebral malaria (unrousable coma), renal failure, acidosis, hypoglycaemia, adult respiratory distress syndrome, shock, or repeated generalized convulsions.
Malaria is diagnosed by detecting the parasite in a blood film or by detection of circulating malarial antigen. Initial blood films may be negative, and repeat films should be taken every six to 12 hours for 36–48 hours before malaria can be confidently excluded.
Patients with falciparum malaria require hospital admission until the disease is clearly under control. All should be treated as if they have chloroquine-resistant disease. Uncomplicated disease is treated with oral quinine plus either doxycycline, clindamycin,or pyrimethamine–sulfadoxine. Alternative therapies include mefloquine as a single agent, or the combination of atovaquone and proguanil (Malarone). Severe malaria requires intravenous quinine or quinidine. Malaria caused by the Plasmodium species vivax, ovale and malariae are treated effectively with oral chloroquine followed by primaquine to eradicate the hepatic stages of P. vivax and P. ovale. Patients receiving primaquine should have prior testing for glucose-6-phosphate dehydrogenase deficiency, as the drug may cause severe haemolytic anaemia in people with this common genetic variation.
Caused by Salmonella typhi and Salmonella paratyphi, enteric fever is contracted from contaminated food or water. Common presentations include a slowly increasing fever in a “stepladder” pattern over 1-2 weeks, headache, abdominal pain, and cough. Cultures of blood are most useful in the first week of illness. Afterwards, stool and bone marrow cultures are more helpful in confirming the diagnosis. Generally recommended empirical therapy for enteric fever is ciprofloxacin. However, quinolone-resistant strains of Salmonella typhi are increasingly reported and third-generation cephalosporins (e.g. ceftriaxone or cefotaxime) or azithromycin may be required.
While many viruses can cause fever, Dengue is likely the most common viral cause of fever in North American travelers. It has a wide geographic distribution including much of the Caribbean and is transmitted by Aedes mosquitoes, which tend to be urban and to bite during the day. Most patients have non-specific symptoms such as fever, chills, myalgia, malaise, arthralgia, headache (notably retro-orbital), diaphoresis, and rash. Diagnosis depends on amplification of viral nucleic acid or serological tests (dengue IgM or IgG seroconversion). There is no effective antiviral therapy, and supportive treatment is all that can be offered. Spontaneous resolution is usual.
Rickettsial infections are the third most common vector-borne disease acquired during international travel, and they have a worldwide distribution. Infections include African tick typhus (Rickettsia africae), Mediterranean tick typhus (Rickettsia conorii), and scrub typhus (Orientia tsutsugamushi). Rickettsial infections are transmitted by arthropods. A painless eschar at the site of the arthropod bite or attachment is an important specific finding. Travelers who hike, camp, or travel on safari in grassy or scrubby areas are at high risk for infection.
These related infections are all characterized by fever, headache, and myalgia. Rashes, which vary by type of infection, are common. Regional lymphadenopathy, leukopenia, and thrombocytopenia are also common manifestations. The diagnosis is established by serologic tests.
Doxycycline is an effective treatment for this group of infections. Second-line therapies include chloramphenicol or ciprofloxacin.
Diarrhea is the most common illness to affect travellers. The main causes are bacteria, viruses, parasites, and toxins. However, the cause will remain unknown in a large proportion of cases. Bacteria cause 80% of the cases, with enterotoxigenic E. coli, shigella species, and Campylobacter jejuni being the most common pathogens.
In assessment of the travelers with diarrhea, it is helpful to divide the condition into acute (less than 14 days) or chronic types (more than 14 days) inflammatory and non-inflammatory. The stools are usually watery and not associated with fever when caused by enterotoxigenic E. coli. With invasive pathogens – Shigella spp., Salmonella spp., Campylobacter spp., and Entamoeba histolytica, stools can be bloody and fever may be present. Chronic watery diarrhea may be due to amoebiasis or giardiasis, or, rarely, tropical sprue.
The viral agents that most commonly cause acute traveler’s diarrhea are Hepatitis A, Noroviruses, rotavirus, adenovirus, caliciviruses, and astroviruses.
Protozoa such as Giardia spp., E. histolytica, Cryptosporidium spp., Cyclospora spp., and Isospora spp. commonly cause persistent (chronic) diarrhea. Giardiasis is the most common protozoal infection in returning travellers and typically presents after a 1-2-week incubation period with a wide range of illness, from asymptomatic or vague intestinal discomfort to a severe illness with intermittent soft foul-smelling stools, foul-smelling flatus or eructation, weight loss, malabsorption, lactose intolerance, abdominal distension, and fatigue.
Stool culture is indicated in patients with fever, bloody diarrhea, or persistent diarrhea.
Because traveler’s diarrhea is usually self-limiting fluid replacement and maintaining hydration is the cornerstone of therapy. Anti-motility agents such as loperamide can be used for symptomatic relief in travelers who have no evidence of fever, or bloody/inflammatory diarrhea. Specific antimicrobial therapy (with a fluoroquinolone or azithromycin for 1-3 days) is indicated when disease is moderate-to-severe or symptoms suggest an invasive pathogen.
People going on short trips to resorts in Mexico, Dominican Republic, Cuba etc. are appropriately fearful of even a relatively short bout of diarrhea. Provision of a supply of antibiotic to be self instituted is a reasonable approach. The patient is instructed to start antibiotic after second or third watery bowel movement and to continue for 1 – 2 days after cessation of diarrhea. Loperamide can be taken concomitantly. Ciprofloxacin, norfloxacin, and azithromycin are commonly used for this purpose.
Skin disorders are fairly common, useful in assessment of returned ill travelers and can result from infections, environmental factors, and envenoming. The most common skin disorders are insect bites, myiasis, tungiasis, urticaria, tinea (ringworm), cutaneous larva migrans, and leishmaniasis.
Cutaneous Leishmaniasis, contracted from the bite of sandflies, is an increasing risk worldwide, and presents as painless ulcer.
Cutaneous larva migrans is typically caused by dog and cat hookworm larvae in soil, which penetrate skin. Serpiginous tracks that are intensely pruritic are typically found where larvae usually enter on the feet, buttocks, and thighs.
Cutaneous myiasis, an infestation in skin by fly larvae, in tropical parts of the Americas it is due to Dermatobia hominis (bot fly) eggs deposited by mosquitoes; in tropical Africa to Cordylobia anthropophaga (tumbu fly) laying eggs on clothing, then hatched larvae placed against the skin burrow inwards. As the larvae mature in the skin, they cause furuncle-like lesions that are pruritic and can be painful.
Tungiasis is a painful infestation of the epidermis by the sand flea, Tunga penetrans, and is typically located on the toes and feet.
Many travelers have respiratory symptoms while away or on return. The most common causes are allergy and viral infection of the upper respiratory tract. Decisions regarding investigation or therapy are not generally affected by travel.
Meningococcal meningitis is more common in sub-Saharan Africa. Nearly all cases of meningococcal meningitis are due to five Neisseria meningitidis serotypes with an incubation period of 2-10 days: A, B, C, W-135, and Y. Pre-travel immunization against N. meningitidis does not rule out infection, since the quadrivalent vaccine does not cover the B strain.
Sexually transmitted diseases
Sexually transmitted diseases may or may not have symptoms directly related to genitalia: gonorrhoea, chlamydia, primary syphilis, and herpes simplex are fairly easy to identify; however, hepatitis B, hepatitis C, HIV, and late-stage syphilis infections might be less obvious. Antibiotic resistance of venereal organisms is increasing and can complicate treatment.
Eosinophilia may be an isolated finding or associated with symptoms. Helminth infestations (strongyloidiasis, filariasis, hookworm, schistosomiasis, cutaneous larva migrans and ascariasis) are the main causes of eosinophilia.
Initial investigation of eosinophilia should include three stool examinations for ova, cysts and parasites to detect the more common gastrointestinal helminths, whose eggs may be excreted intermittently. Specific serological testing is available for schistosomiasis, strongyloidiasis, filariasis, echinococcosis, toxocariasis and angio-strongyliasis.
Strongyloidiasis is an infection is acquired by penetration through intact skin of filariform larvae of Strongyloides stercoralis in faecally contaminated soil. Strongyloidiasis may be diagnosed with stool microscopy and serological testing. Effective treatments include ivermectin, albendazole and thiabendazole.
Schistosomiasis results from contact with fresh water. It is widespread throughout the tropics, but is most prevalent in Africa. It can present as pruritic dermatitis, nonspecific illness, and asymptomatic eosinophilia. Eosinophilia is a reliable sign during acute infections, but diagnosis is best confirmed by finding eggs in urine or stool samples, or in biopsy samples of rectum, bladder, or liver. ELISA testing might also be helpful in making the diagnosis. The standard treatment is praziquantel (20 mg/kg orally for two doses, four hours apart).