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An outbreak of encephalitis occurred in New York City in late August 1999, the first caused by West Nile virus in North America. Histopathologic and immunopathologic examinations performed on human autopsy materials helped guide subsequent laboratory and epidemiologic investigations that led to identification of the etiologic agent.

The genome of a candidate dengue type 2 (DEN-2) vaccine virus, strain PDK-53, differs from its DEN-2 16681 parent by nine nucleotides. Using infectious cDNA clones, we constructed 18 recombinant 16681/PDK-53 viruses to analyze four 16681-to-PDK-53 mutations, including 5' noncoding region (5'NC)-57 C-to-T, premembrane (prM)-29 Asp-to-Val (the only mutation that occurs in the structural proteins), nonstructural protein 1 (NS1)-53 Gly-to-Asp, and NS3-250 Glu-to-Val. The viruses were studied for plaque size, growth rate, and temperature sensitivity in LLC-MK(2) cells, growth rate in C6/36 cells, and neurovirulence in newborn mice. All of the viruses replicated to peak titers of 10(7.3) PFU/ml or greater in LLC-MK(2) cells. The crippled replication of PDK-53 virus in C6/36 cells and its attenuation for mice were determined primarily by the 5'NC-57-T and NS1-53-Asp mutations. The temperature sensitivity of PDK-53 virus was attributed to the NS1-53-Asp and NS3-250-Val mutations. The 5'NC-57, NS1-53, and NS3-250 loci all contributed to the small-plaque phenotype of PDK-53 virus. Reversions at two or three of these loci in PDK-53 virus were required to reconstitute the phenotypic characteristics of the parental 16681 virus. The prM-29 locus had little or no effect on viral phenotype. Sequence analyses showed that PDK-53 virus is genetically identical to PDK-45 virus. Restriction of the three major genetic determinants of attenuation markers to nonstructural genomic regions makes the PDK-53 virus genotype attractive for the development of chimeric DEN virus vaccine candidates.

We constructed chimeric dengue type 2/type 1 (DEN-2/DEN-1) viruses containing the nonstructural genes of DEN-2 16681 virus or its vaccine derivative, strain PDK-53, and the structural genes (encoding capsid protein, premembrane protein, and envelope glycoprotein) of DEN-1 16007 virus or its vaccine derivative, strain PDK-13. We previously reported that attenuation markers of DEN-2 PDK-53 virus were encoded by genetic loci located outside the structural gene region of the PDK-53 virus genome. Chimeric viruses containing the nonstructural genes of DEN-2 PDK-53 virus and the structural genes of the parental DEN-1 16007 virus retained the attenuation markers of small plaque size and temperature sensitivity in LLC-MK(2) cells, less efficient replication in C6/36 cells, and attenuation for mice. These chimeric viruses elicited higher mouse neutralizing antibody titers against DEN-1 virus than did the candidate DEN-1 PDK-13 vaccine virus or chimeric DEN-2/DEN-1 viruses containing the structural genes of the PDK-13 virus. Mutations in the envelope protein of DEN-1 PDK-13 virus affected in vitro phenotype and immunogenicity in mice. The current PDK-13 vaccine is the least efficient of the four Mahidol candidate DEN virus vaccines in human trials. The chimeric DEN-2/DEN-1 virus might be a potential DEN-1 virus vaccine candidate. This study indicated that the infectious clones derived from the candidate DEN-2 PDK-53 vaccine are promising attenuated vectors for development of chimeric flavivirus vaccines.

Four serotypes of dengue viruses produce dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. They are the most important arbovirus infections of humans, in terms of both morbidity and mortality, constituting one of the most rapidly expanding and re-emerging infectious disease problems in Latin America. In less than 20 years, the region has transformed itself from hypoendemic to hyperendemic, while serotype circulation in most countries has gone from none or single to multiple. Changes in endemicity have coincided with the emergence and increasing incidence of the severer forms of dengue infection. This article reviews the clinical presentations of these diseases. Health care providers who see patients in or returning from areas of Latin America, the Caribbean, and other tropical areas must consider dengue in the differential diagnosis of patients presenting with compatible symptoms, and must be knowledgeable in the current management of this important disease.

The epidemic/epizootic of West Nile (WN) encephalitis in the northeastern United States in the summer and fall of 1999 was an unprecedented event, underscoring the ease with which emerging infectious pathogens can be introduced into new geographic areas in today's era of rapid transportation and increased movement of people, animals, and commodities. This epidemic/epizootic and the increased frequency of other exotic pathogens being imported into the United States raises the issue of whether local, state, and national public health agencies are prepared to deal with epidemics/epizootics of vector-borne infectious diseases. The overwintering of WN virus and the epizootic transmission in the summer of 2000 reinforces the need to rebuild the public health infrastructure to deal with vector-borne diseases in this country. This article summarizes guidelines for surveillance, prevention, and control of WN virus that were drafted in December 1999 to help prepare state and local health departments for monitoring WN virus activity in the spring and summer of 2000 and also summarizes the data collected from those surveillance systems through September 2000.

This report describes the clinical, laboratory, and epidemiological findings on 27 cases of Mayaro virus (MV) disease, an emerging mosquito-borne viral illness that is endemic in rural areas of tropical South America. MV disease is a nonfatal, dengue-like illness characterized by fever, chills, headache, eye pain, generalized myalgia, arthralgia, diarrhea, vomiting, and rash of 3-5 days' duration. Severe joint pain is a prominent feature of this illness; the arthralgia sometimes persists for months and can be quite incapacitating. Cases of two visitors from the United States, who developed MV disease during visits to eastern Peru, are reported. MV disease and dengue are difficult to differentiate clinically.

Vector-borne infectious diseases are emerging or resurging as a result of changes in public health policy, insecticide and drug resistance, shift in emphasis from prevention to emergency response, demographic and societal changes, and genetic changes in pathogens. Effective prevention strategies can reverse this trend. Research on vaccines, environmentally safe insecticides, alternative approaches to vector control, and training programs for health-care workers are needed.

Dengue fever, a very old disease, has reemerged in the past 20 years with an expanded geographic distribution of both the viruses and the mosquito vectors, increased epidemic activity, the development of hyperendemicity (the cocirculation of multiple serotypes), and the emergence of dengue hemorrhagic fever in new geographic regions. In 1998 this mosquito-borne disease is the most important tropical infectious disease after malaria, with an estimated 100 million cases of dengue fever, 500,000 cases of dengue hemorrhagic fever, and 25,000 deaths annually. The reasons for this resurgence and emergence of dengue hemorrhagic fever in the waning years of the 20th century are complex and not fully understood, but demographic, societal, and public health infrastructure changes in the past 30 years have contributed greatly. This paper reviews the changing epidemiology of dengue and dengue hemorrhagic fever by geographic region, the natural history and transmission cycles, clinical diagnosis of both dengue fever and dengue hemorrhagic fever, serologic and virologic laboratory diagnoses, pathogenesis, surveillance, prevention, and control. A major challenge for public health officials in all tropical areas of the world is to develop and implement sustainable prevention and control programs that will reverse the trend of emergent dengue hemorrhagic fever.

Dengue/dengue haemorrhagic fever has been one of the most important resurgent tropical diseases in the past 17 years, with expanding geographic distribution of both the viruses and the mosquito vectors, increased frequency of epidemics, the development of hyperendemicity (co-circulation of multiple virus serotypes) and the emergence of dengue haemorrhagic fever in new areas. This paper briefly reviews the changing epidemiology of dengue, discusses some of the factors responsible for the recent resurgence, and reviews the current options for reversing the trend of emergent disease.

Single-strand conformation polymorphism (SSCP) analysis was used to characterize genetic polymorphisms among 12 isolates of dengue-2 virus, which were previously genetically characterized by RNase T1 oligonucleotide mapping and by sequencing the viral envelope (E) gene. Specific cDNA fragments from the dengue-2 isolates were amplified by the reverse transcriptase-polymerase chain reaction. The viral E, premembrane (prM), and nonstructural 5 (NS5) gene cDNAs of 291 basepairs (bp), 291 bp, and 201 bp, respectively, were denatured, rapidly chilled to promote intrastrand reassociation, electrophoretically separated on nondenaturing polyacrylamide gels, and SSCP patterns were observed by silver staining. The SSCP analysis revealed polymorphisms among a number of dengue-2 isolates from the same topotype, and these were markedly different between isolates of different topotype (distinct genetic group). Comparison of nucleotide sequence and SSCP analyses of the 291-bp E cDNA demonstrated that virus isolates that produced identical SSCP patterns contained 0-7 nucleotide substitutions, whereas isolates that showed different SSCP patterns contained 4-25 nucleotide substitutions. Positive predictive value and negative predictive value as measures of certainty for predicting identical and different sequences were 26% and 100%, respectively. The SSCP patterns of the 12 dengue-2 isolates suggested greater genetic variation in the prM gene region than in either the E or NS5 gene regions. The SSCP analyses should allow easy, sensitive, and rapid screening of dengue viruses isolates and the assessment of variation at a number of sites in the virus genome. Additionally, SSCP screening of dengue-2 virus for genetic variability may reveal the introduction of new viral genotypes in a given geographic area. These genetic variants of the virus could serve as markers of the epidemic potential of the virus strain.

An outbreak of a febrile illness characterized by headache, ocular pain, myalgia, and arthralgia occurred during June 1994 among Peruvian army troops in Northern Peru. On June 14-16, 1994, clinical data and blood samples were obtained from eight soldiers with a febrile illness, and from 26 others who had a history of febrile illness during the past three months. A follow-up blood sample was obtained 107 days later from four of the febrile and seven of the afebrile soldiers. Serum samples were tested for dengue (DEN), Oropouche (ORO), and Venezuelan equine encephalitis (VEE) IgM and IgG antibodies by an enzyme-linked immunosorbent assay (ELISA). Virus isolation was performed by inoculation of newborn mice and Vero cell cultures. Viral isolates were identified by immunofluorescence, ELISA, and nucleotide sequencing. A VEE virus infection was confirmed in three of the eight febrile soldiers, two by virus isolation, and one by serology. Antigenic analysis indicated that one of the virus isolates was similar to VEE subtype I, variety ID, viruses previously isolated in Colombia and Venezuela. Nucleotide sequence data showed that both viral isolates were identical to one another and closely related to VEE ID viruses previously isolated in Peru, Colombia, and Venezuela. Serologic results showed that two of 26 afebrile soldiers had IgM antibody to VEE and four had IgG antibody to VEE; two febrile soldiers had IgG antibody in their first serum samples. Oropouche-specific IgM antibody was detected in one of the eight febrile and five of the afebrile soldiers, and 18 of the 34 soldiers had low titers of ORO IgG antibody titers, which did not meet the diagnostic criteria for confirmed cases. All soldiers were negative for DEN IgM antibody, and 10 had flavivirus IgG antibody that reacted with DEN antigens. These data indicated that VEE ID virus was one of the causes of illness among Peruvians soldiers and that this was the first association of this VEE subtype with human disease in Peru.

We identified nine nucleotide differences between the genomes of dengue-2 (DEN-2) 16681 virus and its vaccine derivative, strain PDK-53. These included a C-to-T (16681-to-PDK-53) mutation at nucleotide position 57 of the 5'-untranslated region, three silent mutations, and substitutions prM-29 Asp to Val, NS1-53 Gly to Asp, NS2A-181 Leu to Phe, NS3-250 Glu to Val, and NS4A-75 Gly to Ala. Unpassaged PDK-53 vaccine contained two genetic variants as a result of partial mutation at NS3-250. We constructed infectious cDNA clones for 16681 virus and each of the two PDK-53 variants. DEN-2 16681 clone-derived viruses were identical to the 16681 virus in plaque size and replication in LLC-MK2 cells, replication in C6/36 cells, E and prM epitopes, and neurovirulence for suckling mice. PDK-53 virus and both clone-derived PDK-53 variants were attenuated in mice. However, the variant containing NS3-250-Glu was less temperature sensitive and replicated better in C6/36 cells than did PDK-53 virus. The variant containing NS3-250-Val had smaller, more diffuse plaques, decreased replication, and increased temperature sensitivity in LLC-MK2 cells relative to PDK-53 virus. Both PDK-53 virus and the NS3-250-Val variant replicated poorly in C6/36 cells relative to 16681 virus. Unpassaged PDK-53 vaccine virus and the virus passaged once in LLC-MK2 cells had genomes of identical sequence, including the mixed NS3-250-Glu/Val locus. Although the NS3-250-Val mutation clearly affected virus replication in vitro, it was not a major determinant of attenuation for PDK-53 virus in suckling mice.

In 1986 Puerto Rico experienced its eleventh dengue outbreak of this century, but the first with simultaneous transmission of three dengue virus serotypes, and the first with significant numbers of severe and fatal hemorrhagic disease. Overall, 10,659 cases were reported; 1,257 cases were laboratory confirmed as having current or recent dengue infection. Dengue 4 (DEN-4) was the predominant serotype (160/363 isolates, 44%) followed by dengue 1 (DEN-1) with 134 isolates (37%) and dengue 2 (DEN-2), 69 isolates (19%). Transmission peaked during September, but large numbers of cases occurred through November. Seventy-one (91%) of Puerto Rico's 78 municipalities had laboratory-confirmed cases. Fifty-one percent of all confirmed cases occurred in metropolitan San Juan. Most cases presented clinically as classical dengue fever, but 37% of all confirmed cases were reported to have developed some type of hemorrhagic manifestation, and 6% reported hematemesis. In addition, 29 laboratory confirmed cases met the WHO case definition for dengue hemorrhagic fever, 3 of which were fatal. Among the 29 laboratory-confirmed cases of dengue hemorrhagic fever/ dengue shook syndrome, virus was isolated from 12; one DEN-1, three DEN-2, and eight DEN-4. Among laboratory confirmed cases, infants less than one year of age were at greater risk of developing dengue hemorrhagic fever/ dengue shook syndrome, hematemesis and any reported hemorrhage than were the other age groups evaluated.

From October 1991 to February 1992, an outbreak of acute fever (in which thick blood films were negative for malaria) spread rapidly in the city of Djibouti, Djibouti Republic, affecting all age groups and both nationals and foreigners. The estimated number of cases was 12,000. The clinical features were consistent with a non-haemorrhagic dengue-like illness. Serum samples from 91 patients were analysed serologically for flavivirus infection (dengue 1-4, West Nile, yellow fever, Zika, Banzi, and Uganda-S), and virus isolation was attempted. Twelve strains of dengue 2 virus were isolated. Dengue infection was confirmed by a 4-fold or greater rise in immunoglobulin (Ig) G antibody in paired serum specimens, the presence of IgM antibody, or isolation of the virus. Overall, 46 of the suspected cases (51%) were confirmed virologically or had serological evidence of a recent flavivirus infection. Statistical analysis showed that the presence of a rash was the best predictor of flavivirus seropositivity. In November 1992, Aedes aegypti was widespread and abundant in several districts of Djibouti city. A serological study of serum samples collected from Djiboutian military personnel 5 months before the epidemic showed that only 15/177 (8.5%) had flavivirus antibodies. These findings, together with a negative serosurvey for dengue serotypes 1-4 and yellow fever virus performed in 1987, support the conclusion that dengue 2 virus has only recently been introduced to Djibouti.

In September 1994, in response to a reported epidemic of plague in India, the Centers for Disease Control and Prevention (CDC) enhanced surveillance in the United States for imported pneumonic plague. Plague information materials were rapidly developed and distributed to U.S. public health officials by electronic mail, facsimile, and expedited publication. Information was also provided to medical practitioners and the public by recorded telephone messages and facsimile transmission. Existing quarantine protocols were modified to effect active surveillance for imported plague cases at U.S. airports. Private physicians and state and local health departments were relied on in a passive surveillance system to identify travelers with suspected plague not detected at airports. From September 27 to October 27, the surveillance system identified 13 persons with suspected plague; no case was confirmed. This coordinated response to an international health emergency may serve as a model for detecting other emerging diseases and preventing their importation.

Vascular endothelium regulates multiple aspects of platelet function through secretion of a variety of substances, including von Willebrand factor, nitric oxide, and prostacyclin (PGI2). The objective of this study was to determine whether procoagulant albumin (P-A1), a modified form of albumin present in normal human plasma could modulate endothelial cell secretion of these substances. P-A1 did not affect constitutive secretion of von Willebrand factor or nitric oxide, but did increase PGI2 secretion in a time- and concentration-dependent manner. Pre-treatment of endothelial cells with aspirin, or use of suramin, a broad-specificity inhibitor, prevented the response to P-A1. Prostaglandin H synthase-2 contributed to the P-A1-induced PGI2 secretion. These results indicate that in addition to inducing tissue factor activity and reducing protein C activation and fibrinolysis, P-A1 also modulates vascular endothelial cell PGI2 secretion, and potentially, platelet function.

During studies of arboviral epidemiology in Vietnam, five virus isolates were recovered from Culex tritaeniorhynchus mosquitoes. Three of the five isolates were identified as strains of Japanese encephalitis virus, but the others, collected at Me Tri village, Hanoi, were shown to represent an alphavirus, for which we propose the name Me Tri virus. This newly recognized virus is most closely related to Semliki Forest virus. The two isolates appear to be antigenic subtypes of a single virus, and each was associated with central nervous system illnesses in children. Serologic surveys indicate widespread distribution of these viruses in both humans and livestock in Vietnam. We suggest that Me Tri virus is an etiologic agent of human disease in southeast Asia.

A dengue type 1 epidemic occurred in Fiji between July 1989 and July 1990. Virus isolation in C6/36 cell cultures and Toxorhynchites mosquitos yielded 36 strains. Of the 3686 cases recorded by the Ministry of Health, 60% involved indigenous Fijians and 37%, Indians. A house-to-house survey revealed that a large majority of patients had classical dengue symptoms and 8% reported haemorrhagic manifestations. Among the children and adults hospitalized for dengue, 43% had haemorrhagic manifestations, including epistaxis, gingival bleeding, haematemesis, melaena and haematuria. A total of 15 patients with haemorrhagic manifestations and/or shock died, 10 of whom were aged 0-15 years; the diagnoses were confirmed in four cases by virus isolation or serology.

The global geographic expansion and increased incidence of dengue/dengue hemorrhagic fever in the past 15 years has made dengue one of the most important emergent diseases of tropical urban centers worldwide. This paper discusses the urgent need to develop more effective prevention and control strategies, and for public health officials to coordinate these efforts with urban planning and environmental health specialists.

Problem/condition: Dengue is an acute, mosquito-transmitted viral disease characterized by fever, headache, arthralgia, myalgia, rash, nausea, and vomiting. The worldwide incidence of dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) increased from the mid-1970s through 1992. Although dengue is not endemic to the 50 United States, it presents a risk to U.S. residents who visit dengue-endemic areas., Reporting Period Covered: 1986-1992., Description of System: Dengue surveillance in the 50 United States and the U.S. Virgin Islands relies on provider-initiated reports to state health departments. State health departments then submit clinical information and serum samples to CDC for diagnostic confirmation of disease among U.S. residents who become ill during or after travel to dengue-endemic areas and among residents of the U.S. Virgin Islands. In Puerto Rico, an active, laboratory-based surveillance program receives serum specimens from ambulatory and hospitalized patients throughout the island, clinical reports on hospitalized cases, and copies of death certificates that list dengue as a cause of death. Laboratory diagnosis relies on virus isolation or serologic diagnosis of disease (i.e., IgM or IgG antibodies against dengue viruses)., Results: In 1986, the first indigenous transmission of dengue in the United States in 6 years occurred in Texas; from the time of that incident through 1992, however, no further endemic transmission was reported. During 1986-1992, CDC processed serum samples from 788 residents of 47 states and the District of Columbia. Among these 788 residents, 157 (20%) cases of dengue were diagnosed serologically or virologically. Of the 157 patients, 71 (45%) had visited Latin America or the Caribbean; 63 (40%), Asia and the Pacific; seven (4%), Africa; and nine (6%), several continents. All four dengue virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4) were isolated from travelers to Asia and the Pacific; however, travelers to the Americas acquired infections with only DEN-1, DEN-2, or DEN-4. Even though the number of laboratory-diagnosed dengue infections among travelers was small, severe and fatal disease was documented. In the U.S. Virgin Islands and Puerto Rico, three serotypes (DEN-1, DEN-2, and DEN-4) circulated during 1986-1992. In Puerto Rico, disease transmission was characterized by a cyclical pattern, with peaks in incidence occurring during months with higher temperatures and humidity (usually from September through November). The highest incidence of laboratory-diagnosed disease (1.2 cases per 1,000 population) occurred among persons < 30 years of age; rates were similar for males and females.(ABSTRACT TRUNCATED AT 400 WORDS)

We constructed a battery-powered backpack aspirator to collect adult Aedes aegypti mosquitoes. This simple, easily constructed aspirator facilitates the indoor collection of this important vector species. The collections made with the aspirator provide useful information about the biology and behavior of Ae. aegypti that can be used in education and vector control programs and in the evaluation of ultra-low volume insecticide spray programs directed against this species. The cost for construction is ca. $150.

Dengue viruses are maintained in endemic transmission cycles in tropical urban areas where epidemics periodically occur. Until about 30 years ago, there were long intervals (10-40 years) between epidemics but they are now occurring in many areas at 3-5-year intervals. These epidemics are most likely caused by virus strains with different epidemic potential. Accompanying this increased frequency in epidemic activity has been a change in the disease pattern with cases of the severe form of dengue (dengue hemorrhagic fever) becoming much more common. The occurrence of these factors and the expanding geographic distribution of dengue hemorrhagic fever in the past 15 years have made it necessary to re-evaluate currently recommended methods for prevention and control. The result has been increasing emphasis on the development of effective sustainable Aedes aegypti control programs based on source reduction using community participation. A brief overview of global programs using this approach is presented with emphasis on the Puerto Rican program, one of the earliest developed.

The incidence of dengue and dengue hemorrhagic fever has increased dramatically in the past 15 years in most urban centers of the tropics. Coincident with this increase has been the emergence of epidemic dengue hemorrhagic fever in the American region. The current changing disease pattern in the Americas is very similar to that which occurred in southeast Asia 30 years ago. The similarities in the evolution of severe disease in the two regions and the possible reasons for the changing disease pattern are discussed.

Elevated blood levels of homocysteine represent an independent risk factor for premature arterial vascular disease and thrombosis. We investigated whether homocysteine could induce tissue factor (TF) procoagulant activity in cultured human endothelial cells. Homocysteine increased cellular TF activity in a time- and concentration-dependent manner. Low concentrations of homocysteine (0.1 to 0.6 mmol/L), similar to those found in the blood of patients with homocystinuria, enhanced TF activity by 25% to 100%. Other sulfur-containing amino acids (cystine, homocystine, cysteine, and methionine) induced less TF activity than did homocysteine; however, beta-mercaptoethanol and dithiothreitol were more effective than homocysteine in increasing TF activity. Preincubation of homocysteine with a sulfhydryl inhibitor such as N-ethylmaleimide prevented homocysteine induction of TF activity. A quantitative polymerase chain reaction method indicated that homocysteine increased TF mRNA in endothelial cells. These results indicate that an atherogenic amino acid, homocysteine, can initiate coagulation by the TF pathway through a mechanism involving the free thiol group of the amino acid and by TF gene transcription. These data support the hypothesis that perturbation of vascular coagulant mechanisms may contribute to the thrombotic tendency seen in patients with homocystinuria.

An outbreak of dengue 4 occurred in the Yucatán, México in 1984. During the course of the outbreak, 538 of 5486 reported cases of dengue-like illness were studied; 200 were confirmed as dengue serologically and/or virologically. Dengue 4 virus was isolated from 34 patients and dengue 1 from one. Severe haemorrhagic symptoms were observed in 9 laboratory confirmed patients, including four deaths. Thus, the outbreak in Yucatán is the second dengue epidemic in the Americas after the Cuban epidemic in 1981 in which a number of patients suffered from haemorrhagic complications. It was notable that 5 of 9 hospitalized, severe cases were young adults and that only one met the WHO criteria of DHF, in contrast to primary pediatric nature of DHF in Southeast Asia. In this paper we describe clinical, serologic, and virologic studies conducted during the outbreak.

During 1990 and 1991, adult mosquitoes were collected along the Ob River and its tributaries in western Siberia from approximately 51 degrees 18'N to 66 degrees 4'N. Fifteen virus strains were isolated from 74,196 mosquitoes tested in 1,874 pools. These included Tahyna virus from Aedes cataphylla-punctor subgroup (one) and Ae. excrucians (one), and Inkoo (INK) virus from Ae. communis (one), Ae. communis subgroup (one), Ae. hexodontus (two), Ae. punctor subgroup (two), Ae. punctor complex (one), and unidentified Aedes species (three). In addition, a single Ae. euedes yielded a strain of snowshoe hare (SSH) virus and a strain of Getah, an alphavirus. A Bunyamwera serogroup virus was isolated from Ae. excrucians. With the exception of the two isolates from a single mosquito, minimum infection rates among mosquito taxa ranged from 0.4 to 16.7 per 1,000. The INK virus isolates were widely distributed geographically; however, seven of the 10 isolates were from two sites north of the Arctic Circle. During 1991, sera from two mouse species, five vole species, and four shrew species were collected along the upper Ob River for serologic tests. The prevalence of neutralizing antibody to SSH virus in these sera was 80%. Prevalence rates in the four most abundant species were Apodemus agrarius, 73%; Clethrionomys rutilus, 71%; Microtus arvalis, 80%; and Sorex araneus, 91%. This is the first attempt to clarify the vector and vertebrate host relationships of California serogroup viruses in western Siberia.

We demonstrate that Borrelia burgdorferi infection in the rhesus monkey mimics the early and early disseminated phases of human Lyme disease. Clinical, bacteriological, immunological, and pathological signs of infection were investigated during 13 weeks after inoculation of the spirochete. Three animals were given B. burgdorferi (strain JD1) by needle inoculations, six animals were exposed to the bite of B. burgdorferi-infected Ixodes dammini ticks, and three animals were uninfected controls. B. burgdorferi could be recovered from all animals that were given the spirochete. Bacteria were detectable until week 6 postinoculation (p.i.) in blood, until week 8 p.i. in skin biopsies, and at 10 weeks p.i. in the conjunctiva of one of two animals which developed conjunctivitis. Erythema migrans (EM) appeared in one of the three animals infected by needle inoculation and in five of the six animals infected by ticks. Deep dermal perivascular lymphocytic infiltrations (characteristic of human EM) were observed in all animals showing EM clinically. Both EM and conjunctivitis were documented concomitantly with the presence of the spirochete. Lethargy, splenomegaly, and cerebrospinal fluid pleocytosis were also noted in some animals, but the direct connection of these signs with the infection was not shown. The appearance rate of immunoglobulin M and immunoglobulin G antibodies to B. burgdorferi, as well as the antigen spectra recognized, were remarkably similar to those seen in humans. Serum antibodies from infected animals were able to kill B. burgdorferi in vitro in the presence of rhesus complement. The rhesus monkey model appears to be useful for the investigation of the immunology and pathogenesis of Lyme disease and for the development of immunoprophylactic, diagnostic, and chemotherapeutic protocols.

Determination of serotypes of dengue viruses involved in sequential infections is important since, according to a theory of the pathogenesis of dengue haemorrhagic fever, a particular serotype may be a risk factor. It has been reported in Asia that at least the serotypes involved in the first infections could be serologically identified by the plaque reduction neutralization test (PRNT) because the highest PRNT titres after the second infections corresponded to the serotypes in the first infections. We re-examined the application of this theory of 'original antigenic sin' in Puerto Rico to evaluate its utility in serodiagnosis. Our results showed that it could not be applied reliably because of discrepant results.

Three etiologically proven outbreaks of dengue fever and one etiologically confirmed epidemic of dengue haemorrhagic fever have occurred in south China since 1978. The first of these, an epidemic of dengue due to virus type 4 took place in Shiwan town, Foshan city, Guangdong Province, in 1978; the epidemic began in May and ended in November. The clinical manifestations of 583 hospitalized patients were observed from August to October. The majority (81.3%) of patients were aged 21-50 years (male:female = 1.2:1). The course of illness was about 1 week in most cases; three patients (0.5%) died. A local outbreak of dengue due to virus type 1 occurred in Shiqi town, Zhongshan County, Guangdong Province, from September to November 1979. The majority of patients were older children and adolescents. There was no marked difference between males and females in terms of the course of the illness, and there were no complications or deaths. A large epidemic of dengue due to virus type 3 occurred on Hainan Island in 1980. The clinical manifestations of 510 hospitalized patients (mostly adolescents and adults) were observed from April to September. Some patients developed rare complications, such as loss of hair, acute intravascular haemolysis, and multiple peripheral paralysis; there were four deaths (0.78%). The first known epidemic of dengue haemorrhagic fever in China occurred among 10-29-year-olds on Hainan Island in 1985 and 1986. There were no essential differences between males and females. Some cases had rare complications such as acute intravascular haemolysis, while others had diffuse intravascular coagulation and altered mental status; 10 patients (6.5%) died.

Hundreds of thousands of dengue cases are reported worldwide each year. Given the difficulty in obtaining full reporting, the actual number of human infections is probably much higher than the number reported. Dengue is usually a nonspecific febrile illness that resolves with supportive therapy but the clinical spectrum ranges from asymptomatic infection through severe hemorrhage and sudden fatal shock. The pathophysiology of the severe forms of dengue may be related to sequential infection with different serotypes, variations in virus virulence, interaction of the virus with environmental and host factors or a combination of these factors. Control of dengue at the present time is dependent on control of the principal vector mosquito, A. aegypti. Efforts to achieve such control are now focusing on community education and action towards eliminating this mosquito's breeding sites near human dwellings. Vaccine development continues, but at present the only way to avoid dengue in an area where it is endemic or epidemic is to use repellents and mosquito barriers. The movement of people to and from tropical areas makes dengue an important differential diagnosis in any patient with an acute illness and history of recent travel to tropical areas. Because of continued infestation of the southeastern United States with A. aegypti, indigenous transmission in the continental United States remains a public health concern.

In many countries, measles surveillance relies heavily on the use of a standard clinical case definition; however, the clinical signs and symptoms of measles are similar to those of dengue. For example, during 1985, in Puerto Rico, 22 (23%) of 94 cases of illnesses with rashes that met the measles clinical case definition were serologically confirmed as measles, but 32 (34%) others were serologically confirmed as dengue. Retrospective analysis at the San Juan Laboratories of the Centers for Disease Control showed also that at least 28% of all laboratory-confirmed cases of dengue in Puerto Rico in 1985 met the measles clinical case definition. If the true measles vaccine efficacy (VE) is assumed to be 90%, the occurrence of laboratory-confirmed dengue cases that meet the measles clinical case definition results in a reduction of the apparent measles VE to only 64% (a 29% relative reduction from the true VE). The results of the study demonstrate the importance of a laboratory-based surveillance system in measles control or elimination efforts in dengue-endemic areas.

Although the hemagglutination-inhibition (HI) test has been the standard test used by the World Health Organization (WHO) for the classification of serologic response in dengue infections, it is slow, requiring paired specimens. Furthermore, not all investigators have accepted the classification. Thus, there is an urgent need to develop a rapid test which employs a single specimen. We developed an enzyme-linked immunosorbent assay (ELISA) for rapid classification of serologic responses in dengue infections based on the ratio of IgM and IgG in a single specimen. Using the criteria established by the WHO (1986) for comparison, concordant results were obtained in 81% and 95% of primary and secondary infections, respectively, when serum specimens were tested as pairs. When tested as single specimens, the diagnoses by ELISA and HI agreed in 41% and 52% of acute specimens of primary and secondary infections, respectively. The lower rate of concordance in acute-phase samples was due to the absence of detectable IgM in acute specimens collected at outpatient clinics. On the other hand, diagnoses by ELISA and HI agreed in 79% and 95% of primary and secondary infections when single convalescent specimens were used. Analysis of the discordant results between the two tests revealed that the interpretation by the IgM-IgG ratio agreed better with HI classifications practised by some investigators than it did with the WHO.

The ongoing resurgence of Aedes aegypti in the Americas--abetted by poor mosquito control, urbanization, and increased air travel--has led to dengue hyperendemicity, more frequent dengue epidemics, and the emergence of dengue hemorrhagic fever (DHF). This article describes a program developed to cope with this situation that emphasizes disease prevention rather than general mosquito control measures.

Dengue 4 (DEN-4) virus strain 341750 Carib was modified by serial passage in primary canine kidney (PCK) cell cultures. By the 15th PCK passage, this virus was less infectious for monkeys and resulted in a significantly reduced viremia as compared to the parent DEN-4 virus. The 30th PCK passage of DEN-4 341750 Carib was non-infectious for monkeys. A vaccine prepared at the 20th PCK passage in DBS-FRhL-2 cells stimulated the production of both neutralizing and hemagglutination inhibition antibodies in monkeys; these animals were also protected against challenge with the homologous strain as well as a heterologous strain of DEN-4. An ID50 titration in monkeys resulted in a titer of greater than 10(4) plaque-forming units (PFU) for the vaccine virus and 0.5 PFU for the parent virus. Reduced monkey infectivity of this magnitude has been correlated with human attenuation in previous dengue vaccine candidates. The DEN-4 strain 341750 Carib PCK-20/FRhL-4 vaccine has been characterized and sufficiently tested to be considered for safety and immunogenicity trials in humans.

Laboratory studies were carried out with two geographic strains of Aedes polynesiensis and one strain of Aedes aegypti to determine whether they could transmit Ross River virus (RRV). Both species were shown to be good vectors of RRV, but Ae. polynesiensis was the most susceptible. Ae. polynesiensis represents a new vector for this virus and the epidemiologic implications of RRV spread by both mosquito species are discussed.

Dengue and dengue hemorrhagic fever are emerging as major public health problems in most tropical countries. Effective prevention and control programs will depend on improved surveillance designed to provide early warning of dengue epidemics. This article outlines a reasonable approach to dengue surveillance of this kind. Virologic surveillance should be considered the most important element in any such early warning system. Dengue virus transmission should be monitored to determine which serotypes are present, their distribution, and the type of illnesses associated with each. Other key components of an active surveillance system should include monitoring of fever activity and clinical surveillance for cases of severe and fatal disease associated with viral syndromes. Collectively, these three surveillance components can provide an early warning capability permitting emergency mosquito control measures to be implemented and major epidemics to be averted.

Serum specimens from Puerto Rican residents were tested for antibodies to human T lymphotropic virus type I (HTLV-I) using an enzyme immunoassay, Western immunoblot, and radioimmunoprecipitation assays. Of 1,279 specimens obtained during a dengue virus surveillance program in 1986 and 1987, 3 (0.2%) tested positive; an additional 11 were indeterminate. Of 602 specimens obtained from blood donors in Ponce in 1987, 1 (0.2%) was positive; an additional specimen was indeterminate. Of 21 persons hospitalized for problems related to intravenous drug use in 1986 and 1987, 1 (5%) tested positive for HTLV-I antibodies.

An epidemic of Ross River virus infection occurred in the Cook Islands early in 1980 and affected the majority of the inhabitants of Rarotonga, the most populated island in the group. This represents the easternmost extension of the virus which, until 1979, was believed limited to Australia, New Guinea, and the Solomon Islands. The clinical manifestations of Ross River disease, predominantly polyarthritis, did not differ significantly from those observed previously in Australia. However, unlike the experience in Australia, where Ross River virus has never been isolated from a patient with polyarthritis, the agent was recovered from the serum of one-half of approximately 100 such patients with serologically proven infections. It is not known if this latter observation is the result of a change in the virus, the different virus isolation technique employed, or other factors. It was found that the incubation period of the disease could be as short as 3 days--much less than previously suspected. Ross River virus was isolated from six pools of Aedes polynesiensis mosquitoes collected in nature and it appeared that this species was the most probable vector on Rarotonga. In view of the widespread distribution of Ae. polynesiensis on islands, in the eastern Pacific it would not be surprising if Ross River virus occurs in other previously unaffected areas in the future.