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Mancao, Mary Y. MD*; Imran, Hamayun MD*; Chandra, Sharat MD*; Estrada, Benjamin MD*; Figarola, Maria MD; Sosnowski, Jeffrey MD; Vidal, Rosa MD*

The Pediatric Infectious Disease Journal: June 2009 - Volume 28 - Issue 6 - p 543-545
doi: 10.1097/INF.0b013e3181950e99
Brief Reports

Eastern equine encephalitis virus infection is a rare sporadic central nervous system infection transmitted by a mosquito vector. Hemophagocytic lymphohistiocytosis (HLH) is a rare life-threatening disease associated with the inability of an overactive immune system to effectively respond to infections. Many viruses are known to trigger primary, as well as secondary, HLH. We report a pediatric case of eastern equine encephalitis virus-associated HLH which caused severe neurologic injury and death.


From the Departments of *Pediatrics, †Radiology, and ‡Pathology, University of South Alabama College of Medicine, Mobile, AL.

Accepted for publication November 13, 2008.

Address for Correspondence: Mary Y. Mancao, MD, Division of Infectious Diseases, Department of Pediatrics, University of South Alabama, 1504 Springhill Avenue, Room 5224 Mobile, AL 36604. E-mail:

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (

Infection-associated or secondary hemophagocytic lymphohistiocytosis (HLH) has been reported with Epstein Barr virus and varicella virus infections; secondary HLH develops as a response to intense immunologic activation of the immune system by severe infection.1 Secondary HLH is a difficult diagnosis to establish because it can develop in association with malignancies, can be mistaken for sepsis and child abuse, and also can present as fever of unknown origin.2–5 Eastern equine encephalitis virus (EEEV) infection is an uncommon cause of encephalitis that can lead to considerable neurologic sequelae and death.

We describe a 5-month old infant male diagnosed with fatal EEEV-associated HLH. To the authors’ knowledge, this is the first reported case of EEEV-associated HLH in an infant.

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A previously healthy 5-month old, Hispanic male presented to a local emergency room with 4 days of fever of 103°F associated with right-sided focal seizures, lethargy, and decreased appetite. On examination, he was febrile and irritable with a bulging anterior fontanel. He also had several old mosquito bites on his upper and lower extremities. He had neither hepatosplenomegaly nor any focal neurologic deficits on initial presentation. Lumbar puncture was performed at the referring hospital and cerebrospinal fluid (CSF) analysis revealed 160 white blood cells (WBC)/μL (CSF sample was inadequate for other studies). The patient was transferred to the pediatric intensive care unit of the university hospital for further care and he was given intravenous ceftriaxone, vancomycin, and acyclovir for suspected meningitis. Additional laboratory work-up included peripheral WBC of 10,000/mm3 with 36% segmented neutrophils, 35% band-forms, 27% lymphocytes, and 2% monocytes, hemoglobin of 9.4 g/dL, platelet count of 114,000/mm3, serum aspartate and alanine transaminase of 34 u/L each, serum sodium of 139 mmol/L, and C-reactive protein of 9.8 mg/dL.

By the second hospital day, the patient’s neurologic status deteriorated with intractable seizure activity; he required intubation and mechanical ventilation. On the 10th hospital day, he had persistent fever, hepatosplenomegaly, and progressive pancytopenia (absolute neutrophil count of 340/uL, hemoglobin of 8.7 g/dL, and platelet count of 79,000/mm3). Repeat lumbar puncture was performed and CSF studies revealed 46 nucleated cells/uL, protein 385 mg/dL, glucose 32 mg/dL and rare erythrophagocytic cells in the CSF. An investigation for HLH was made. Further laboratory evaluation revealed elevated values of the following: serum aspartate transaminase 300 U/L, serum alanine transferase 71 U/L, serum triglycerides 226 mg/dL, serum ferritin 3595 μg/L, and serum soluble interleukin-2 receptor 11,000 U/mL. There was absent serum natural killer cell activity (Table 1, Supplemental Digital Content 1, Bone marrow aspirate and biopsy was performed and showed normocellular bone marrow for age, moderate megakaryocytic hyperplasia, granulomatous inflammation, and rare hemophagocytosis.

Serologic studies on the patient’s second CSF were negative for West Nile virus, California encephalitis, and herpes simplex virus. Serum and CSF IgG enzyme-linked immunosorbent assay (ELISA) and IgM capture ELISA were positive for Eastern EEEV. Mutations in perforin, Munc 13-4, and syntaxin-11 genes were not detected ruling out familial HLH (FHL).

Based on the preceding clinical findings and laboratory information, the diagnosis of EEEV-associated HLH was made; chemotherapy was then started per HLH-2004 protocol (which included etoposide, dexamethasone, cyclosporine, with intrathecal methotrexate and prednisolone).1 By the sixth hospital week, chemotherapy led to the resolution of patient’s findings of pancytopenia, normalization of CSF, and reduction of serum ferritin, triglycerides, and interleukin-2 receptor values. The patient continued to be ventilator dependent with no purposeful voluntary movement. Magnetic resonance imaging (MRI) of the brain was obtained and revealed extensive cystic type changes involving gray matter (spongiform appearance). Due to the patient’s persistent neurologic deterioration, brain biopsy was performed. The brain biopsy showed extensive necrosis and chronic inflammation consistent with chronic encephalitis and also revealed sheets of CD68 immunoreactive foamy macrophages identified in the gray and white matter; no other studies were performed on brain tissue. Ventilatory support was withdrawn per the family’s request and the patient expired 2 days after withdrawal of support; autopsy was not performed.

Antibody titers performed on specimen obtained 3 weeks after onset of illness still revealed elevated CSF (1:4) and serum (1:256) IgG and CSF (1:8) and serum (1:1024) IgM titers to EEEV (normal CSF and serum ranges: CSF titers <1:1 and serum titers <1:16). HIV DNA was not detected by polymerase chain reaction (PCR).

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There is an average of 8.2 human cases of EEEV in the United States reported to the CDC each year (Florida and Michigan are states that report at least 1 EEE case per year).6 In the eastern United States, the mosquito Culiseta melanura transmits EEEV to birds; whereas bridge mosquito vectors, such as (Coquillettidia perturbans, Aedes vexans, or Aedes sollicitans) transmit EEEV to humans (who are dead end hosts).7

The CDC case definition of EEEV disease involves meningitis or encephalitis with the following serologic findings: (1) Anti-EEEV IgM antibody in the CSF or (2) elevated anti-EEEV IgM antibody by IgM antibody capture ELISA and neutralizing antibodies by plaque-reduction neutralization test in the serum.6 There is low prevalence of EEEV antibody in the general population in the United States, so that the probability of the diagnosis is high when specific EEEV antibody is found in any acute specimen.7 Newer and more rapid techniques for diagnosis (crucial in surveillance studies of alpha viruses in nonhuman hosts such as mosquitoes and horses), such as the reverse transcription-PCR with an ELISA and the nucleic acid amplification assays, have been developed for the early detection and differentiation of alpha virus infection in both human and veterinary samples.8,9

Prognostic variables in EEEV infection have included laboratory and radiologic tests.10 Deresiewicz et al described 10 of 13 patients with CSF WBC of at least 500 cells/mm3 and 12 of 14 patients whose lowest serum sodium concentration was <130 mmol/L, both groups had significantly unfavorable outcomes.10 Radiologic examination (MRI of the brain) in EEEV infection was also found to be crucial. The diagnosis of EEEV infection was questioned in comatose patients with normal findings on MRI, because MRI was thought to be extremely sensitive to the central nervous manifestations of EEEV infection.10 Results of every MRI obtained from a comatose patient with EEEV infection or patient who was subsequently comatose were abnormal. The most notable MRI findings of EEEV infection included focal lesions in the basal ganglia, thalami, and brain stem compared with herpes simplex encephalitis (clinically resembles EEEV infection), which usually produces lesions in the frontal and temporal lobes.10

Patients infected with EEEV develop febrile illness that may lead to meningitis and encephalitis with rapid progression to coma and death.7 Therefore, there is a high case fatality rate with EEEV infections with estimates ranging from 24% to 75% and permanent neurologic sequelae can lead to lifetime disease-related expenses of approximately $3 million per patient.7,10,11 There is no known treatment for EEEV infection and unfortunately since this is a rare infection, there has not been an impetus to develop pharmacotherapy against human EEEV infection.12 However, prevention, surveillance, and control programs are of paramount importance and require private and public health sector collaboration.

HLH, also known as hemophagocytic syndrome (HPS), is a rare disorder of immune regulation and inflammatory response that can rapidly be fatal. HLH diagnostic criteria have been formulated by the International Histiocyte Society in 1991 and revised in 2004.1 The division of HLH into categories (primary and secondary) has been thought to be confusing; therefore, it is difficult to establish one from the other in the clinical setting, despite the availability of molecular diagnostic techniques.1 The same genetic mutations can also be present in both primary and secondary HLH and there is no specific test that can explicitly define these 2 categories.13

The primary autosomal recessive form of HLH is FHL; it is a fatal disease if left untreated and usually diagnosed in infancy or early childhood.14–16 FHL has an estimated incidence of around 1:50,000 live-born children; it can be associated with consanguinity.14–18 Infections such as varicella and Epstein Barr virus infections can serve as triggers for FHL.14,16 There is no laboratory test or clinical presentation that can differentiate familial or sporadic cases.13 The specific genes linked to FHL include: FHL2–perforin, FHL3–Munc 13-4, FHL4–Syntaxin 11.15,17,18 The second form of HLH known as secondary HLH, is often associated with bacterial, fungal, and viral infections, rheumatologic disorders (primarily macrophage activation syndrome secondary to systemic juvenile rheumatoid arthritis), primary immune deficiencies, and malignancies.1,2,14 Secondary HLH can develop in immunocompromised hosts after being triggered by a viral infection.14

Therapy for HLH involves controlling macrophage activation and modulation of the immune system with chemotherapy (HLH-2004 protocol involves the administration of cyclosporine, etoposide, and dexamethasone).1 Those with FHL and those with relapsing symptoms after chemotherapy most likely will benefit from hematopoietic stem cell transplantation.19

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The authors thank Jacek Polski, MD (Pathology); Anthony Martino, MD (Neurosurgery); Todd Stanley, MD (Radiology); Richard Wesenberg, MD (Radiology); laboratory staff of the Division of Vector-Borne Infectious Diseases; National Center for Infectious Diseases; CDC Fort Collins; Colorado and Alexandra Filipovich, MD (Division of Hematology/Oncology); and laboratory staff of the Immunology, Laboratory at Children’s Hospital Medical Center, Cincinnati, OH in their assistance of the care of this patient.

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hemophagocytic lymphohistiocytosis; eastern equine encephalitis; hemophagocytic syndrome

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