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Synopsis: There are several different causes of encephalitis among children in Thailand. Most cases, however, are preventable. Parents need not carry unnecessary fears of exotic encephalitis occurring in their children during travel to Thailand.
Source: Chokephaibulkit K, et al. Viral etiologies of encephalitis in Thai children. Pediatr Infect Dis J. 2001;20:216-218.
From 1996 through 1998, a prospective evaluation of childhood encephalitis was undertaken at the Siriraj Hospital of Bangkok’s Mahidol University. Over 30 months, 61 children were identified with clinical findings initially suggestive of encephalitis; 40 of these did have encephalitis, and 21 had other final diagnoses (epilepsy, febrile convulsion, bacterial meningitis, and tuberculosis, for instance). These 40 children with encephalitis were aged 1 month to 13 years (mean, 6.6 years). Antigen and antibody tests were done on blood and spinal fluid samples, and all patients were followed for at least 6 months.
Viral causes of encephalitis were identified in 26 (65%) of the 40 children with encephalitis, and most had abnormal cerebrospinal fluid (CSF) findings. Twenty-seven of the 40 children had CSF pleiocytosis, and polymorphonuclear cells predominated in 15% of these. Specific viruses that were identified included: dengue (8), Japanese encephalitis (6), Herpes simplex (4), HHV-6 (3), mumps (2), enterovirus (1), varicella/zoster (1), and rabies (1).
Children were hospitalized for 4-155 (mean 26) days. Seventy percent of children recovered completely, 13% recovered with persistent neurologic sequellae, and 17% died as a result of the illness.
Comment by Philip R. Fischer, MD, DTM&H
The thought of any child acquiring an exotic "brain infection" can surely stimulate fear among traveling parents. These new data from Thailand are useful in characterizing the sorts of endemic viral encephalitis seen among the pediatric population of a large Asian city. Clearly, not all such infections are exotic.
Mahidol University is renowned for excellence in research and in patient care ("the best in the country," according to the driver who recently transported me between many of Bangkok’s temples and museums). This new report continues to build the institution’s reputation as it provides us with a clear descriptive look at an important pediatric problem. In addition, this information reminds travel medicine practitioners of diagnostic considerations, preventive interventions, and cultural aspects that are important in caring for children in or from other countries.
The children who presented with encephalitis at the beginning of what turned out to be courses of dengue hemorrhagic fever had infections split evenly between serotypes 1, 2, and 3. Most had serologic evidence that this was not their primary dengue infection. While only one of these children had an abnormal CSF analysis with evidence of dengue virus in the CSF, one could argue that most of the dengue-infected patients really had encephalopathy rather than encephalitis. Nonetheless, dengue should be a diagnostic consideration when caring for a child in or from an endemic area who presents with clinical findings of encephalitis.
Japanese encephalitis virus (JEV) immunization is routine in 34 of 76 Thai provinces, but Bangkok is not generally considered within an infected endemic area. Though residence and travel history information is not provided in the Thai report, Chokephaibulkit and collegues do suggest the possibility of future consideration of JEV immunization in Bangkok. There is some interstrain efficacy using current JEV vaccines.1
As was evident in Thailand, disease risks simply do not follow political borders. Travelers should be cognizant of the specific preventive measures effective against locally endemic childhood encephalitis whether they are going to New York (insect avoidance to prevent increasingly endemic West Nile Virus encephalitis2), to Malaysia (avoiding areas of pig farming to prevent Nipah virus encephalitis3), or to Thailand.
Though behavioral and medical interventions are not always 100% effective, more than half of the cases of encephalitis reported in the study from Mahidol could have been prevented by proactive intervention. Dengue is at least partially preventable by insect avoidance efforts, and it follows a seasonal epidemiology with most cases occurring during rainy seasons in Asia. Japanese encephalitis occurs year-round in Thailand; the vaccine is currently recommended for travelers spending more than 4 weeks in rural areas of endemic provinces. Herpes simplex virus and HHV-6, like enterovirus, are less amenable to direct preventive measures. Routine mumps and varicella vaccination should be completed for travelers older than 12 months of age. Rabies vaccination (whether pre- or postexposure) can be effective; travelers, especially those going to Asian cities where stray dogs often carry rabies, should be aware of strategies to prevent this fatal illness. (A recent jog through the streets of Bangkok served to remind me of the prevalence of unrestrained dogs on the streets and around children.)
Fortunately, most of the subjects of the Thai study did well. Since not all encephalitis is avoidable, families traveling with children should know where to seek safe and competent urgent medical care in case the need arises.
Most of us consider altered mental status and convulsive disorders to be extremely negative. That interpretation, however, is not universal. Anne Fadiman’s The Spirit Catches You and You Fall Down documents the fascinating story of a Hmong child’s parents as they battled one American medical system in caring for their daughter with a seizure disorder.4 Caring for immigrants and returned travelers, practitioners of travel medicine have the privilege of bridging belief systems and cultural considerations in caring for children with central nervous system diseases.
1. Kurane I, Takasaki T. Immunogenicity and protective efficacy of the current inactivated Japanese encephalitis vaccine against different Japanese encephalitis virus strains. Vaccine. 2000;18(Suppl 2):33-35.
2. Rappole JH, Derrickson SR, Hubalek Z. Migratory birds and spread of West Nile virus in the Western Hemisphere. Emerg Infect Dis. 2000;6:319-328.
3. Amal NM, et al. Southeast Asian J Trop Med Public Health. 2000;31:301-306.
4. Fadiman A. The Spirit Catches You and You Fall Down. New York, NY: Farrar, Straus, & Giroux; 1998.