Amanda J. Panella

Zika virus outbreak on Yap Island, Federated States of Micronesia.

BACKGROUND In 2007, physicians on Yap Island reported an outbreak of illness characterized by rash, conjunctivitis, and arthralgia. Although serum from some patients had IgM antibody against dengue virus, the illness seemed clinically distinct from previously detected dengue. Subsequent testing with the use of consensus primers detected Zika virus RNA in the serum of the patients but no dengue virus or other arboviral RNA. No previous outbreaks and only 14 cases of Zika virus disease have been previously documented. METHODS We obtained serum samples from patients and interviewed patients for information on clinical signs and symptoms. Zika virus disease was confirmed by a finding of Zika virus RNA or a specific neutralizing antibody response to Zika virus in the serum. Patients with IgM antibody against Zika virus who had a potentially cross-reactive neutralizing-antibody response were classified as having probable Zika virus disease. We conducted a household survey to estimate the proportion of Yap residents with IgM antibody against Zika virus and to identify possible mosquito vectors of Zika virus. RESULTS We identified 49 confirmed and 59 probable cases of Zika virus disease. The patients resided in 9 of the 10 municipalities on Yap. Rash, fever, arthralgia, and conjunctivitis were common symptoms. No hospitalizations, hemorrhagic manifestations, or deaths due to Zika virus were reported. We estimated that 73% (95% confidence interval, 68 to 77) of Yap residents 3 years of age or older had been recently infected with Zika virus. Aedes hensilli was the predominant mosquito species identified. CONCLUSIONS This outbreak of Zika virus illness in Micronesia represents transmission of Zika virus outside Africa and Asia. Although most patients had mild illness, clinicians and public health officials should be aware of the risk of further expansion of Zika virus transmission.

Chikungunya Virus in US Travelers Returning from India, 2006

Chikungunya virus (CHIKV), a mosquitoborne alphavirus; is endemic in Africa and Asia. In 2005–2006, CHIKV epidemics were reported in islands in the Indian Ocean and in southern India. We present data on laboratory-confirmed CHIKV infections among travelers returning from India to the United States during 2006.

Evaluation of Commercially Available Serologic Diagnostic Tests for Chikungunya Virus

Chikungunya virus (CHIKV) is present or emerging in dengue virus–endemic areas. Infections caused by these viruses share some common signs/symptoms, but prognosis, patient care, and persistent symptoms differ. Thus, accurate diagnostic methods are essential for differentiating the infections. We evaluated 4 CHIKV serologic diagnostic tests, 2 of which showed poor sensitivity and specificity.

Japanese encephalitis virus remains an important cause of encephalitis in Thailand

BACKGROUND Japanese encephalitis virus (JEV) is endemic in Thailand and prevention strategies include vaccination, vector control, and health education. METHODS Between July 2003 and August 2005, we conducted hospital-based surveillance for encephalitis at seven hospitals in Bangkok and Hat Yai. Serum and cerebrospinal (CSF) specimens were tested for evidence of recent JEV infection by immunoglobulin M (IgM) enzyme-linked immunosorbent assay (ELISA) and a plaque reduction neutralization test (PRNT). RESULTS Of the 147 patients enrolled and tested, 24 (16%) had evidence of acute flavivirus infection: 22 (15%) with JEV and two (1%) with dengue virus. Of the 22 Japanese encephalitis (JE) cases, 10 (46%) were aged ≤ 15 years. The median length of hospital stay was 13 days; one 13-year-old child died. Ten percent of encephalitis patients enrolled in Bangkok hospitals were found to have JEV infection compared to 28% of patients enrolled in hospitals in southern Thailand (p < 0.01). Four (40%) of the 10 children with JE were reported as being vaccinated. CONCLUSIONS JEV remains an important cause of encephalitis among hospitalized patients in Thailand. The high proportion of JE among encephalitis cases is concerning and additional public health prevention efforts or expanded vaccination may be needed.

Hospital-Based Surveillance for Japanese Encephalitis at Four Sites in Bangladesh, 2003–2005

We investigated the epidemiology and etiology of encephalitis at four tertiary hospitals in Bangladesh during 2003-2005. Patients who met a clinical case definition for acute encephalitis and had cerebrospinal fluid (CSF) pleocytosis were eligible for enrollment; a standardized sampling pattern was used to enroll eligible patients. Recent Japanese encephalitis virus (JEV) infection was defined by presence of IgM antibodies against JEV in CSF or serum. Twenty (4%) of 492 cases had laboratory evidence of recent JEV infection; two died. All JE cases occurred during May-December, and cases were identified among all age groups. All cases resided in rural areas. Fifteen patients were re-assessed 4-6 weeks after hospitalization; 5 (33%) patients had physical disabilities and 7 (47%) reported cognitive difficulties. Infection with JEV is clearly an etiology of encephalitis in Bangladesh. Population-based studies to quantify burden of disease could assess options for targeted immunization programs.

Zika Virus Disease in Travelers Returning to the United States, 2010–2014

Zika virus is an emerging mosquito-borne flavivirus that typically causes a mild febrile illness with rash, arthralgia, or conjunctivitis. Zika virus has recently caused large outbreaks of disease in southeast Asia, Pacific Ocean Islands, and the Americas. We identified all positive Zika virus test results performed at U.S. Centers for Disease Control and Prevention from 2010 to 2014. For persons with test results indicating a recent infection with Zika virus, we collected information on demographics, travel history, and clinical features. Eleven Zika virus disease cases were identified among travelers returning to the United States. The median age of cases was 50 years (range: 29-74 years) and six (55%) were male. Nine (82%) cases had their illness onset from January to April. All cases reported a travel history to islands in the Pacific Ocean during the days preceding illness onset, and all cases were potentially viremic while in the United States. Public health prevention messages about decreasing mosquito exposure, preventing sexual exposure, and preventing infection in pregnant women should be targeted to individuals traveling to or living in areas with Zika virus activity. Health-care providers and public health officials should be educated about the recognition, diagnosis, and prevention of Zika virus disease.

Household-Based Sero-Epidemiologic Survey after a Yellow Fever Epidemic, Sudan, 2005

From September through early December 2005, an outbreak of yellow fever (YF) occurred in South Kordofan, Sudan, resulting in a mass YF vaccination campaign. In late December 2005, we conducted a serosurvey to assess YF vaccine coverage and to better define the epidemiology of the outbreak in an index village. Of 552 persons enrolled, 95% reported recent YF vaccination, and 25% reported febrile illness during the outbreak period: 13% reported YF-like illness, 4% reported severe YF-like illness, and 12% reported chikungunya-like illness. Of 87 persons who provided blood samples, all had positive YF serologic results, including three who had never been vaccinated. There was also serologic evidence of recent or prior chikungunya virus, dengue virus, West Nile virus, and Sindbis virus infections. These results indicate that YF virus and chikungunya virus contributed to the outbreak. The high prevalence of YF antibody among vaccinees indicates that vaccination was effectively implemented in this remotely located population.

Multiplex Microsphere Immunoassays for the Detection of IgM and IgG to Arboviral Diseases

Serodiagnosis of arthropod-borne viruses (arboviruses) at the Division of Vector-Borne Diseases, CDC, employs a combination of individual enzyme-linked immunosorbent assays and microsphere immunoassays (MIAs) to test for IgM and IgG, followed by confirmatory plaque-reduction neutralization tests. Based upon the geographic origin of a sample, it may be tested concurrently for multiple arboviruses, which can be a cumbersome task. The advent of multiplexing represents an opportunity to streamline these types of assays; however, because serologic cross-reactivity of the arboviral antigens often confounds results, it is of interest to employ data analysis methods that address this issue. Here, we constructed 13-virus multiplexed IgM and IgG MIAs that included internal and external controls, based upon the Luminex platform. Results from samples tested using these methods were analyzed using 8 different statistical schemes to identify the best way to classify the data. Geographic batteries were also devised to serve as a more practical diagnostic format, and further samples were tested using the abbreviated multiplexes. Comparative error rates for the classification schemes identified a specific boosting method based on logistic regression “Logitboost” as the classification method of choice. When the data from all samples tested were combined into one set, error rates from the multiplex IgM and IgG MIAs were <5% for all geographic batteries. This work represents both the most comprehensive, validated multiplexing method for arboviruses to date, and also the most systematic attempt to determine the most useful classification method for use with these types of serologic tests.

Detection of Anti-Yellow Fever Virus Immunoglobulin M Antibodies at 3–4 Years Following Yellow Fever Vaccination

The duration of anti-yellow fever (YF) virus immunoglobulin M (IgM) antibodies following YF vaccination is unknown, making it difficult to interpret positive IgM antibody results in previously vaccinated travelers. We evaluated the frequency and predictors of YF IgM antibody positivity 3-4 years following YF vaccination. Twenty-nine (73%) of 40 participants had YF IgM antibodies 3-4 years postvaccination. No demographic or exposure variables were predictive of YF IgM positivity. However, persons who were YF IgM positive at 3-4 years postvaccination had earlier onset viremia and higher neutralizing antibody geometric mean titers at 1 month and 3-4 years postvaccination compared with persons who were YF IgM negative. Detection of YF IgM antibodies several years postvaccination might reflect remote YF vaccination rather than recent YF vaccination or YF virus infection.

Development and validation of an ELISA kit (YF MAC-HD) to detect IgM to yellow fever virus

Yellow fever virus (YFV) is endemic in tropical and sub-tropical regions of the world, with around 180,000 human infections a year occurring in Africa. Serologic testing is the chief laboratory diagnostic means of identifying an outbreak and to inform the decision to commence a vaccination campaign. The World Health Organization disseminates the reagents for YFV testing to African reference laboratories, and the US Centers for Disease Control and Prevention (CDC) is charged with producing and providing these reagents. The CDC M-antibody capture ELISA is a 2-day test, requiring titration of reagents when new lots are received, which leads to inconsistency in testing and wastage of material. Here we describe the development of a kit-based assay (YF MAC-HD) based upon the CDC method, that is completed in approximately 3.5h, with equivocal samples being reflexed to an overnight protocol. The kit exhibits >90% accuracy when compared to the 2-day test. The kits were designed for use with a minimum of equipment and are stored at 4°C, removing the need for freezing capacity. This kit is capable of tolerating temporary sub-optimal storage conditions which will ease shipping or power outage concerns, and a shelf life of >6 months was demonstrated with no deterioration in accuracy. All reagents necessary to run the YF MAC-HD are included in the kit and are single-use, with 8 or 24 sample options per kit. Field trials are envisioned for the near future, which will enable refinement of the method. The use of the YF MAC-HD is anticipated to reduce materials wastage, and improve the quality and consistency of YFV serologic testing in endemic areas.