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Dengue type 2 outbreak in the south of the state of Bahia, Brazil: laboratorial and epidemiological studies.

During March 1994 cases of a exanthematic acute disease were reported in the municipalities of Itagemirim, Eunápolis and Belmonte, state of Bahia. Dengue fever was confirmed by serology (MAC-ELISA) and by dengue virus type 2 isolation, genotype Jamaica. Signs and symptoms of classic dengue fever were observed with a high percentual of rash (73.8%) and pruritus (50.5%). Major haemorrhagic manifestations were unfrequent and only bleeding gum was reported. Dengue virus activity spreaded rapidly to important tourism counties like Porto Seguro, Ilhéus, Santa Cruz de Cabrália, Prado, Alcobaça and others, representing a risk for the spreading of dengue virus into the country and abroad.

Brazil↗

[A dengue epidemic in Ipupiara and Prado, Bahia. A seroepidemiologic survey].

Serologic studies in Brazil have indicated a 25% to 56% prevalence of dengue virus infections. However, these studies were carried out in populations of middle-sized and larger cities. The present study describes two epidemics of classic dengue fever in two small cities in the State of Bahia. The first occurred in 1987, in Ipupiara and was caused by dengue serotype-1 (DEN-1), the second occurred in 1995, in Prado and was caused by dengue serotype-2 (DEN-2). The laboratory diagnosis was made by the hemagglutination-inhibition test. 461 serum samples were collected in 1995 in Ipupiara (district of Chapada Diamantina) out of a population of 3,868 and 228 samples out of a total of 9,126 inhabitants of Prado (in the southernmost coastal region). The seropositivity of the samples was 11.9% (55/461) in Ipupiara and 17.5% (40/228) in Prado. These were no statistically significant differences as to age and sex between seropositive and seronegative individuals of the two cities studied. However, the seropositive cases in Ipupiara indicated a higher percentage (15.9% vs. 9.3%) of residency in or travel to other states of Brazil (p<0.03). Based on these data we estimate the occurrence of 460 and 1,597 cases of infection in Ipupiara and Prado, respectively. In conclusion, dengue virus infections in smaller cities probably have singular characteristics, since they exhibit a lesser prevalence of seropositivity caused by decreased breeding possibilities of Aedes aegypti.

Adult↗

Clinical manifestations of dengue hemorrhagic fever in Puerto Rico, 1990-1991. Puerto Rico Association of Epidemiologists.

The aim of the study reported here was to demonstrate that dengue hemorrhagic fever occurs in Puerto Rico, that it is underreported, and that this underreporting is due partly to underdiagnosis in hospitals. Surveillance for severe dengue identified 986 hospitalizations for suspected dengue in 1990-1991. At the time, on the basis of available clinical and laboratory data, the surveillance system routinely identified 20 DHF cases, including three with dengue shock syndrome (DSS). Our subsequent review of these 986 patients' hospital records identified 102 whose records supported a clinical diagnosis of DHF (88) or DSS (14). Of the 102, there were 57 with positive virologic or serologic results for dengue and that met the World Health Organization criteria for DHF (fever, hemorrhagic manifestations, thrombocytopenia, and excessive capillary permeability). This group of 57 patients had a mean age of 38 years, contained a preponderance of males (34, 59.3%), included eight cases of DSS, and involved two (3.5%) fatalities (in females 16 and 55 years old). Hemorrhagic manifestations were mild; hemoconcentration, hypoalbuminemia, and elevated aspartate and alanine aminotransferase (AST and ALT) levels were frequently encountered. The median duration of hospitalization was five days. The clinical description of these laboratory-positive DHF cases in Puerto Rico is consistent with previous descriptions of DHF in the medical literature; but the patients' age distribution is similar to the pattern typically found in the Americas (where all age groups tend to be affected), as opposed to Southeast Asia (where mostly younger children are affected). The number of DHF cases identified by our study was nearly three times that reported through the established surveillance system. Our findings indicate that recognition and reporting of DHF by local clinicians needs to be improved.

Adolescent↗

[Quality control of the serological diagnosis of dengue in laboratories throughout the Americas, 1996-2001].

OBJECTIVE: To report the results from participating laboratories for four external quality control proficiency tests of dengue serological diagnosis that were carried out in the Region of the Americas in the period of 1996-2001. METHODS: External quality control proficiency tests of dengue serological diagnosis were carried out in 1996-1997, 1998-1999, 1999-2000, and 2000-2001. Panels made up of 20 serum samples (12 of them positive for dengue IgM antibodies) were sent to participating laboratories in the Region. The sera were negative for HIV antibodies, hepatitis C virus antibodies, and hepatitis B surface antigen. The sera were stored at -20 degrees C until they were sent in refrigerated shipments to the participating laboratories. The presence of IgM antibodies was determined through IgM-capture enzyme-linked immunosorbent assay (ELISA), while the IgG antibody titer was determined by hemagglutination inhibition or by IgG ELISA. The results of the IgM antibody testing that differed from those of the reference center were considered discordant. The IgG antibody titer was considered discordant when the results differed by two dilutions or more with respect to the reference center's results. RESULTS: A total of 27 laboratories received a total of 59 serum panels over the 1996-2001 period, and the results from testing 54 of those panels (91.5%) were sent back in. Of the total of 1 080 sera samples from those 54 panels, the results from 95.6% of the IgM antibody tests were concordant with the results from the reference center. With 47 of the 54 panels (87.0%) the participating laboratories' agreement with the reference center's results for the IgM antibody testing was 90.0% or higher. The laboratories sent back results from a total of 27 IgG antibody titer tests, and 22 of them (81.5%) coincided with those from the reference center. Considering the IgM antibody testing results from the four periods, the findings from 22 of the participating laboratories coincided with those from the reference center for at least 90% of the samples, and 13 of the laboratories were in complete concordance with the reference center. CONCLUSIONS: The majority of the participating laboratories showed an excellent level of performance in detecting dengue IgG and IgM antibodies. However, the deficiencies found in some instances confirm the need for continuing to improve laboratory diagnosis of dengue in the Region of the Americas.

Americas↗

Epidemiological significanceof subterranean Aedes aegypti (Diptera: Culicidae) breeding sites to dengue virus infection in Charters Towers, 1993.

The objective of this study wasto determine the epidemiological significance of subterranean mosquito breeding sites to the 1993 outbreak of dengue fever (type 2) in the northern Queensland town of Charters Towers, Australia. In recent studies on subterranean mosquito breeding, containers such as wells and service manholes have been shown to be important breeding sites to Australia's only dengue vector, Aedes aegypti (L.). This study demonstrates a direct epidemiological association between subterranean breeding sites and dengue virus infection. The mean distance between residents seropositive for dengue 2 and the nearest subterranean container (113 m) was significantly less than for a randomly selected control (191 m), (F = 81.9; df = 1, 478; P < 0.001). Residents positive for dengue 2 antibodies was 2.47 (95% confidence interval 1.88-3.24) times higher for those living within 160 m of a well or service manhole, compared with those residing further away. These findings emphasize the importance of incluuding subterranean water containers in Ae. aegypti surveillance and control programs.

Aedes↗

A 65-kDa trypsin-sensible membrane cell protein as a possible receptor for dengue virus in cultured neuroblastoma cells.

Dengue virus infects primary neurons in mouse experimental model and tissue culture cells of the central nervous system (CNS). In the present work, a mouse neuroblastoma cell line (N1E-115) and a human neuroblastoma cell line (SK-N-SH), susceptible to dengue virus infection were used to study the presence of cell membrane receptor for dengue-2. By day 5 postinfection (pi), viral antigen was detected by immunofluorescence in the cytoplasm and surrounding the nucleus of N1E-115 cells, while on day 7 pi, it was also present along neural extensions. Infection of N1E-115 cells was diminished with trypsin treatment but not with neuraminidase or endoglycosidase H. Partially purified cell membrane proteins from neuroblastoma cells were analyzed by the Virus Overlay Protein Blot Assay (VOPBA), and a single band migrating at 65 kDa was detected in mouse and human neuroblastoma cells but not in C6, a non-susceptible rat glial cell line which was included as a negative control. The 65 kDa protein was eliminated only when nitrocellulose membranes were treated with trypsin. Analysis of neuronal cell infection by dengue virus provides a useful tool to understand the nature of cellular receptors and mechanisms involved in the infection of the nervous system by dengue viruses.

Animals↗

Dengue hemorrhagic fever in infants: research opportunities ignored.

The age distribution of cases of dengue hemorrhagic fever and dengue shock syndrome (DHF/DSS) in infants under the age of 1 year are reported from Bangkok, Thailand, and for the first time for Ho Chi Minh City, Vietnam; Yangon, Myanmar; and Surabaya, Indonesia. The four dengue viruses were isolated from Thai infants, all of whom were having a primary dengue infection. Progress studying the immunologically distinct infant DHF/DSS has been limited; most contemporary research has centered on DHF/DSS accompanying secondary dengue infections. In designing research results obtained in studies on a congruent animal model, feline infectious peritonitis virus (FIPV) infections of kittens born to FIPV-immune queens should be considered. Research challenges presented by infant DHF/DSS are discussed.

Age Distribution↗

Dengue fever, Hawaii, 2001-2002.

Autochthonous dengue infections were last reported in Hawaii in 1944. In September 2001, the Hawaii Department of Health was notified of an unusual febrile illness in a resident with no travel history; dengue fever was confirmed. During the investigation, 1,644 persons with locally acquired denguelike illness were evaluated, and 122 (7%) laboratory-positive dengue infections were identified; dengue virus serotype 1 was isolated from 15 patients. No cases of dengue hemorrhagic fever or shock syndrome were reported. In 3 instances autochthonous infections were linked to a person who reported denguelike illness after travel to French Polynesia. Phylogenetic analyses showed the Hawaiian isolates were closely associated with contemporaneous isolates from Tahiti. Aedes albopictus was present in all communities surveyed on Oahu, Maui, Molokai, and Kauai; no Ae. aegypti were found. This outbreak underscores the importance of maintaining surveillance and control of potential disease vectors even in the absence of an imminent disease threat.

Dengue↗

Dengue or Kokobera? A case report from the top end of the Northern Territory.

In early April 1998, the Centre for Disease Control in Darwin was notified of a possible case of dengue which appeared to have been acquired in the Northern Territory. Because dengue is not endemic to the Northern Territory, locally acquired infection has significant public health implications, particularly for vector identification and control to limit the spread of infection. Dengue IgM serology was positive on two occasions, but the illness was eventually presumptively identified as Kokobera infection. This case illustrates the complexity of interpreting flavivirus serology. Determining the cause of infection requires consideration of the clinical illness, the incubation period, the laboratory results and vector presence. Waiting for confirmation of results, before the institution of the public health measures necessary for a true case of dengue, was ultimately justified in this case. This is a valid approach in the Northern Territory, but may not be applicable to areas of Australia with established vectors for dengue.

Adult↗

Dengue outbreaks in Guánica-Ensenada and Villalba, Puerto Rico, 1972-1973.

Epidemics of dengue fever occurring in Puerto Rico in 1963 to 1964 and 1969 were caused by dengue-3 and dengue-2 (DN-2) viruses, respectively, but endemic dengue transmission has never been documented on the Island. Since the 1969 epidemic, a surveillance system has detected DN-2 activity on the Island during each of the years 1970 through 1973, which suggests endemic persistence of the virus. This report describes the investigation of localized outbreaks of DN-2 in Guanica-Ensenada (1972) and Villalba (1973), and presents epidemiological, serological, and virological data from the outbreaks. Analysis of geographic distribution of dengue activity in Puerto Rico in recent years indicates that the DN-2 transmission in 1970 to 1973 may represent a long tail-off of the 1969 epidemic rather than the emergence of a truly endemic situation.

Adolescent↗

Shock syndrome in primary dengue infections.

During 1974, 114 patients with dengue hemorrhagic fever were studied at the Bankok Children's Hospital. Over 40% of the patients had dengue shock syndrome. Five fatal cases were included in the study. Primary dengue infections were identified by absent or low titered antibodies in acute sera and the sequential development of IgM antibodies followed by IgG antibodies during convalescence. Three patients, aged 4,8, and 12 years, had primary dengue infections with shock. Although no convalescent sera could be tested two other patients, aged 7 to 12 years, with fatal disease also appeared to have primary infections. At the time of shock patients with primary infections had subnormal concentrations of complement factor 3. The data show that in older children dengue shock syndrome associated with complement depression can occur during primary as well as secondary infections.

Antibodies, Viral↗

Variation in susceptibility to oral infection with dengue viruses among geographic strains of Aedes aegypti.

The comparative susceptibility of 13 geographic strains of Aedes aegypti to oral infection with dengue viruses was studied by feeding the mosquitoes on a virus-erythrocyte-sugar suspension. Significant variation in susceptibility to four dengue serotypes was observed among the geographic strains tested. Mosquito strains which were more susceptible to one serotype were also more susceptible to the other serotypes, suggesting that the factors controlling susceptibility were the same for all types. The amount of virus required to infect mosquitoes orally varied inversely with the susceptibility of the geographic strain. Thresholds of infection were not the same for dengue types 1, 2, 3 and 4. There was no apparent difference in infectivity between prototype and recently isolated strains of dengue types 1 and 3. Crossing experimentibility as the resistant parent. No difference was observed between resistant and susceptible mosquito strains in the rate or the amount of viral replication after infection by the parenteral route, or in their ability to transmit dengue 2 virus after infection by the oral route.

Aedes↗

Epidemic dengue 3 in central Java, associated with low viremia in man.

An outbreak of dengue type 3 was studied in Central Java, Indonesia, in 1978. In contrast to previous dengue 3 epidemics in Central and East Java, this outbreak was less explosive, associated with mild illness, and low viremia. The dengue virus isolation rate from serologically confirmed patients was only 32% compared to 65% for an epidemic in Bantul a year earlier. Neither dengue hemagglutination-inhibition antibody titers nor day of illness on which specimens were collected accounted for this difference. These data suggest that some naturally occurring strains of dengue virus (endemic strains) are associated with low viremia and generally cause only mild illness in man.

Antibodies, Viral↗

Transovarial transmission of dengue 2 virus by Aedes aegypti in nature.

Dengue 2 virus was recovered from three of 123 pools of naturally infected Aedes aegypti larvae (6,200 insects) collected from water containers in Rangoon. The virus was also isolated from two of 76 pools (7,730 mosquitoes) of male Ae. aegypti, collected as larvae and reared in the laboratory to adults. Minimum field infection rates among these two groups of mosquitoes were 1:2,067 and 1:3,865, respectively. Insect pools were inoculated into Toxorhynchites splendens mosquitoes and dengue viral antigen was subsequently detected in headsquash preparations by direct fluorescent antibody technique. Identification of the dengue serotype was done by complement-fixation test. This is the first report of dengue virus isolation from naturally infected mosquito larvae. These findings suggest that transovarial transmission of dengue virus occurs in nature.

Aedes↗

Etiologic and serologic investigations of the 1980 epidemic of dengue fever on Hainan Island, China.

Virologic and seroepidemiologic studies were carried out during an epidemic of dengue fever on Hainan Island in 1980. Dengue 3 virus was isolated from 46 of 77 acute phase sera and from 1 of 10 pools of adult Aedes aegypti. Dengue 1 virus virus was isolated from a single acute phase serum. Seroepidemiologic investigations showed that 74% of healthy individuals in the epidemic area had antibody to dengue virus compared to 54% in an area where epidemic dengue had occurred in 1978, and less than or equal to 8% in nonepidemic areas. There were no significant differences in antibody prevalence for different sex and age groups.

Aedes↗

Demonstration of yellow fever and dengue antigens in formalin-fixed paraffin-embedded human liver by immunohistochemical analysis.

Two immunohistochemical techniques to determine the presence of yellow fever and dengue antigens in fixed tissue samples were developed for the purpose of making retrospective diagnoses of these viral diseases in humans. A horseradish peroxidase label was used for one technique and an alkaline phosphatase label for the other. In the former technique, acid hematin was removed from the tissues, iron-containing pigments were counterstained with Prussian blue, and the product of the diaminobenzidine reaction was enhanced with a dilute solution of osmium tetroxide that differentiated antigen from lipofuscin. In the latter technique, alkaline phosphatase was used as the enzyme labeling system with a red chromogen that contrasted nicely with the pigments in the tissues, as mentioned above. Thus, pigment removal or differentiation from antigen was not required. Replicate sections were cut and mouse polyclonal antibodies for yellow fever and all dengue types were applied to individual sections. On samples positive for dengue antigen, monoclonal antibodies were applied to additional replicate sections to demonstrate antigen of dengue types 1 and 4. In order to test the assay, samples of formalin-fixed liver tissue from Brazilian and Peruvian individuals who had died from a variety of causes as long as eight years earlier were received in a blinded fashion for immunohistochemical analysis. The techniques appeared to be highly reliable for yellow fever diagnosis; however, not enough cases were observed to adequately evaluate the procedures for dengue diagnosis. Both procedures appeared to have similar sensitivity.

Adolescent↗

Dengue type-2 virus envelope protein made using recombinant baculovirus protects mice against virus challenge.

The gene coding for the envelope (E) glycoprotein of dengue-2 virus was cloned into baculovirus (Autographa californica nuclear polyhedrosis virus). The recombinant virus contained the entire E protein gene, preceded by 38 nucleotides from the end of the prematrix glycoprotein gene and followed by the first 83 nucleotides of nonstructural protein 1. When expressed in Spodoptera frugiperda (Sf9) cells, approximately 1 mg of recombinant E antigen was made per 10(9) cells. This antigen reacted with polyclonal, anti-dengue type-2 antibody and a dengue type-2-specific, neutralizing monoclonal antibody. BALB/c mice immunized with the recombinant antigen produced only non-neutralizing antibody against dengue-2 virus, but were partially protected against morbidity and mortality after intracranial challenge with virulent dengue-2 virus.

Aedes↗

Risk factors for dengue infection during an outbreak in Yanes, Puerto Rico in 1991.

In November 1991, during a five-month dengue outbreak, we performed epidemiologic and serologic surveys linked to an earlier entomologic study in a community of 425 houses in Yanes (Florida), Puerto Rico. We obtained a household response rate of 95% (98 of 103) and blood samples from 84% (345 of 410) of the participants. Dengue incidence, as volunteered by the respondents, was 5% (21 of 410), but serologic diagnosis (immunoglobulin M and IgG-enzyme-linked immunosorbent assays [ELISA]) indicated a recent infection rate of 18% (59 of 331). The presence of anti-dengue antibodies was detected in 277 (84%) of 331 persons tested. In our final sample of 65 households and 112 persons, we analyzed (by univariate and multivariate logistic regression methods) the association of 12 entomologic, environmental, and behavioral variables with the proportion of household members with laboratory-confirmed recent dengue. The number of female Aedes aegypti per person was the only significant (P = 0.02) household risk factor. The results of our study underscore the importance of intradomiciliary mosquito populations in dengue transmission, and may serve as a guide for mosquito control efforts.

Adolescent↗