the following signs/symptoms with or without fever must be evaluated for CNS infection:
meningismus, altered mental status (delirium, lethargy, obtundation, or coma), seizures,
severe headache, photophobia, or focal neurologic findings (80). Common tropical infections
such as malaria (cerebral malaria), typhoid, and TB should remain high on the differential
diagnosis. The diagnostic approach including CNS imaging studies (CT or MRI scans) with
cerebrospinal fluid (CSF) analysis will be similar to the approach used in nontravelers. The
incubation period is particularly important when trying to decide if certain etiologic agents
need be considered. Travelers presenting within two to three weeks post-travel from
developing regions may have acquired regional arboviruses causing meningoencephalitis or
meningococcal disease whereas incubation periods exceeding two to three weeks require
inclusion of TB, African trypanosomiasis, and rabies.
Endemic or sporadic meningococcal disease varies between 1 to 3 and 10 to 25 cases per
100,000 persons in developed and developing regions respectively (81). In addition to this
increased endemic risk for travelers, there is also the potential of epidemic meningococcal
disease (primarily serogroup A) with attack rates as high as 1000/100,000 as seen in the
meningococcal belt of sub-Saharan Africa (81). Rapid diagnosis using CSF analysis
(neutrophilic pleocytosis, elevated protein, low glucose, and gram-negative diplococci) with
prompt institution of antibiotic therapy is critical since treated meningococcal meningitis
carries mortality rates in the range of 5% to 15% (82).
Herpes simplex (HSV-1) encephalitis is the most common cause of sporadic viral
encephalitis seen by clinicians in the United States; however, endemic arboviruses such as
California group bunyaviral encephalitis are also not uncommon (83). Additionally, interna-
tional travel into developing regions with potential mosquito exposure further broadens the
differential diagnosis. Knowledge of the regional arboviral threats, such as Japanese
encephalitis in rural areas of eastern Asia and the Indian subcontinent and Rift Valley fever
in Egypt and central/southern Africa, will allow appropriate inclusion/exclusion of arboviral
threats (84–86). Flavivirus encephalitis occurs in both developed and developing countries
with regional threats such as Japanese encephalitis in South and Southeast Asia, Murray Valley
encephalitis in Australia and New Guinea, West Nile encephalitis across many areas including
Africa, Southwest Asia, Europe, and North America, and St. Louis encephalitis throughout the
Americas (87). These viral encephalitides have much higher rates of asymptomatic infection as
compared to CNS illness and may present with a meningitis syndrome rather than
encephalitis. Human rabies is often transmitted in developing urban areas through contact
with rabid dogs and cats unlike the wild animal reservoir in the United States (88). Patients
presenting with a compatible clinical syndrome for rabies (respiratory and/or GI prodromal
symptoms followed by acute neurologic symptoms, furious or paralytic, leading to coma)
should have a thorough travel history focusing on any animal contact. Diagnostic testing,
virus-specific fluorescent material in skin biopsy, serum or CSF antirabies antibodies, and/or
virus isolation in saliva, should be used in appropriate settings with prompt initiation of
isolation precautions and postexposure immunoprophylaxis (88). Emergent threats such as the
Nipah virus in Malaysia in 1998–1999 further add to the differential diagnosis for returning
travelers with encephalitis (89). An open-label trial reported a 36% reduction in mortality for
acute Nipah virus encephalitis when treated with intravenous ribavirin (90). Eosinophilic
meningoencephalitis (CSF leukocytosis with>10% eosinophils) is a clinical syndrome with
relatively limited etiologies including parasites (Angiostrongylus cantonensis, Gnathostoma
spinigerum,migrating ascarids, and schistosomiasis), coccidiomycosis, and hypersensitivity
reaction (drug-related) (91). The travel and exposure history will greatly assist in the
inclusion/exclusion of parasitic etiologies.
Acute Abdomen
Returning travelers presenting with an acute abdomen are most likely to have common
conditions seen in nontravelers such as appendicitis, cholecystitis, diverticulitis, or peptic ulcer
with perforated viscus (92). Two common diseases in indigenous populations, enteric fever and
amebic liver abscess, occur occasionally in immigrants and less commonly in naive travelers (92–
94). Both of these diseases may present with an acute abdomen secondary to severe abdominal
pain from uncomplicated disease or as a result of complicated disease such as cyst rupture in
Tropical Infections in Critical Care 329