The 1986 dengue and dengue hemorrhagic fever epidemic in Puerto Rico: epidemiologic and clinical observations.

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.

The 1986 dengue and dengue hemorrhagic fever epidemic in Puerto Rico: epidemiologic and clinical observations

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 percent) followed by dengue 1 (DEN-1) with 134 isolates (37 percent) and dengue 2 (DEN-2), 69 isolates (19 percent). Transmission peaked during September, but large numbers of cases occurred through November. Seventy-one (91 percent) 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 percent of all confirmed cases were reported to have developed some type of hemorrhagic manifestation, and 6 percent 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

Dengue shock syndrome in an American traveler with primary dengue 3 infection.

A previously reported case of childhood dengue shock syndrome in an American traveler to India was investigated serologically. The original studies neither indicated the infecting serotype nor proved primary or secondary infection. However, BHK suspension PRNT of 6-year convalescent serum now indicates that the child had primary dengue type 3 infection. Dengue, dengue hemorrhagic fever, and dengue shock syndrome are potential hazards for American travelers and American residents of dengue-receptive areas.

Dengue 3 virus transmission in Africa.

The first known transmission of dengue 3 virus in Africa was documented by virus isolation during an epidemic of dengue-like illness in Pemba, Mozambique, in late 1984 and early 1985. Dengue 3 virus was the only serotype isolated. Most patients appeared to be experiencing secondary flavivirus infections, but whether this was the result of previous dengue, yellow fever, or other flavivirus infection is not known. Two cases of hemorrhagic disease with shock and death were associated with the epidemic.

Dengue in Puerto Rico, 1977: public health response to characterize and control an epidemic of multiple serotypes.

The largest and most extensive documented dengue epidemic in Puerto Rico struck an estimated 355,000 Puerto Rican residents from July-December 1977. The mixed epidemic of dengue types 2 and 3 coincided with a Caribbean pandemic of dengue type 1, first introduced into the western hemisphere in early 1977 and into Puerto Rico in the fall of that year. Health officials assembled a team to assess the epidemic and mounted a campaign to end it. Attempts to monitor the incidence and spread of dengue were confounded by simultaneous co-circulation of influenza virus, underscoring problems in formulating public health strategies dependent on nonspecific clinical and epidemiologic case criteria, and the need for rapid and reliable diagnostic capabilities. Despite co-circulation of multiple dengue serotypes, a risk factor associated with severe and fatal dengue hemorrhagic fever (DHF) in Southeast Asia, hospital and death certificate surveillance disclosed no cases of DHF in Puerto Rico. The epidemic serves as a reminder that when preventive measures are impossible or infeasible, developed countries with high living standards may be susceptible to large scale epidemics of infectious diseases.

Dengue transmission in two Puerto Rican communities in 1982.

Paired serologic, entomologic, and environmental surveys were performed in two Puerto Rican communities, Salinas and Manatí, in summer and fall 1982. Paired samples on 434 persons in Salinas and 324 persons in Manatí showed recent dengue infection rates of 35% and 26%, respectively. Ae. aegypti larval indices were higher in Salinas than in Manatí but were relatively high throughout both communities. Breteau indices in neighborhoods ranged from 43 to 172, and infection rates in the neighborhoods were 22% to 45%. With a multivariate technique, we analyzed possible associations of environmental variables with dengue incidence and prevalence of dengue antibody. Wood-constructed housing and low socioeconomic status were among the variables significantly associated with dengue incidence. Predictors of dengue antibody prevalence included socioeconomic level, tree height, shade, and window and door screens. Recent dengue infections clustered within the sampled members of households (P less than 0.05, binomial test). An estimated 35% of dengue infections were symptomatic, and no serious illnesses were reported. The potential for high dengue infection rates in Puerto Rico will continue unless substantial reductions in vector populations are achieved. Targeting dengue surveillance and vector control activities in areas with demonstrated environmental risk factors may limit transmission during future outbreaks.

Low rates of antigen detection and virus isolation from the peripheral blood leukocytes of dengue fever patients.

We evaluated direct fluorescent antibody (FA) testing of peripheral blood leukocytes (PBL) from patients in Puerto Rico with serologically and/or virologically confirmed dengue fever as a possible rapid diagnostic test and compared rates of dengue virus isolation from PBL with the rates from plasma or serum using the mosquito inoculation technique. Dengue antigen was detected in the PBL of only 1 of 19 patients with confirmed dengue. Virus was isolated from 3 of 19 PBL specimens and from 6 of 19 acute-phase serum or plasma samples. Four viruses were obtained from serum or plasma only and 1 isolate came from PBL only. We conclude that FA testing of PBL from dengue fever patients has little promise as a rapid diagnostic technique. Despite small numbers, our data suggest that virus isolation from PBL is less sensitive than that from serum or plasma. Our results differ considerably from those of previous studies of dengue hemorrhagic fever patients conducted in Thailand.

A case of natural concurrent human infection with two dengue viruses.

The first documented case of concurrent human infection with 2 dengue viruses is reported. Dengue 1 and 4 viruses were isolated from the serum of a 16-year-old male during the 1982 outbreak in Puerto Rico. The illness was mild and does not support the hypothesis that double infection with dengue viruses leads to more severe hemorrhagic disease.

Mosquito cell cultures and specific monoclonal antibodies in surveillance for dengue viruses.

During the fall of 1981, a new method for the routine isolation and identification of dengue viruses in Puerto Rico was implemented utilizing C6/36 cell cultures and serotype specific antidengue monoclonal antibodies. A blind comparison of the monoclonal antibody indirect fluorescent antibody test (IFAT) and the complement fixation (CF) test for identification of 89 newly isolated dengue viruses of all four serotypes from the Caribbean, Asia and Africa showed 100% agreement. Although virus isolation rates were slightly lower than with the mosquito inoculation technique, use of the C6/36 cell culture system was much less time-consuming and allowed the processing of larger numbers of sera. Beginning in November 1981, a new virologic surveillance system was begun in Puerto Rico. Acute sera from persons with suspected dengue were selected for virus isolation attempts on the basis of geographic area of residence on the island, day after onset the blood was taken and clinical signs and symptoms. These sera were processed for virus isolation in C6/36 cell cultures, and virus isolates were identified by the IFAT using the monoclonal antibodies. Using this system, 2,702 sera were tested from November 1981 through August 1982. Dengue virus was isolated from 518, for an isolation rate of 19.2%. Dengue 1 was the predominant virus until December 1981, when dengue 4 became dominant. The changing patterns of dengue 1 and 4 distribution by time and geographic location on Puerto Rico were followed. This system allows the dengue viruses being transmitted in an area to be monitored with a minimal amount of effort and provides the early warning capability necessary to predict epidemic dengue.

Epidemiologic investigations of dengue infection in Mexico, 1980.

A binational investigation was conducted in two Mexican cities in 1980 to study epidemiologic characteristics of dengue. Two study areas were selected in each of the cities (Merida and Tampico); in each area, in February and in September, sanitarians recorded information concerning abundance of Aedes aegypti, and public health nurses obtained blood specimens and clinical information from residents. Ninety-nine individuals (24% of the study population) showed serologic evidence of recent dengue 1 infection by hemagglutination inhibition or complement fixation. Infection rates in the four study areas (9%-51%) increased with age in three of the four areas and were higher in females in all four areas. These differences in rates may be related to exposure to infectious mosquitoes in the home; A. aegypti feed most actively during daylight hours, and both females (p less than 0.001) and older individuals (p less than 0.001) were more likely than males or younger persons to be in the home when the study was conducted. A positive correlation was found between infection rates and the container index (number of potential A. aegypti breeding sites per premise--Pearson correlation coefficient 0.95, p = 0.05), suggesting that this index may be a useful predictor of neighborhoods at high risk of dengue transmission. Pending additional studies, public cleanup campaigns should be targeted to neighborhoods in which container indices are highest when an outbreak of dengue is likely to occur.

Reintroduction of dengue fever into the continental United States. I. Dengue surveillance in Texas, 1980.

Two surveillance systems were initiated in Texas in 1980 to detect cases of dengue fever. Physicians throughout the state were requested to report cases of dengue (passive surveillance), and 27 out-patient facilities serving geographically and ethnically high risk populations were asked to report cases of dengue-like illness weekly (active surveillance). Additionally, two clinics participating in active surveillance submitted acute-phase blood specimens weekly for dengue virus isolation. Sixty-three cases of illness due to dengue type 1 infection (dates of onset 2 August-10 November) were documented by virus isolation or serologic testing; 52 of them (83%) occurred n countries adjacent to the Texas-Mexico border. Fifty-six patients (89%) were Hispanic; 46 (73%) were females. Twenty-seven patients (43%) had not traveled outside the U.S. before becoming ill. Since no clinically apparent outbreak of dengue was ever recognized by public health officials in Texas in 1980, the active surveillance system in other Gulf Coast states should be considered when the risk of introduction of dengue is considered high.

Lack of greater seroconversion of rhesus monkeys after subcutaneous inoculation of dengue type 2 live-virus vaccine combined with infection-enhancing antibodies.

Four groups of six nonimmune male rhesus monkeys were inoculated subcutaneously with formulations of dengue type 2 vaccine virus DEN-2/S-1. Group A received 1.9 x 10(4) plaque-forming units of vaccine in normal human serum albumin diluent. Group B received the same dose combined with a dengue type 2-immune human serum diluted 1:1,600, beyond its neutralization endpoint of 1:300, but having an immune enhancement titer of 250,000. Groups C and D received 10-fold dilutions of these respective formulations. No migration-inhibitory factor was found when peripheral blood mononuclear leukocytes obtained on day 68 post-immunization from monkeys of all experimental groups were tested. No viremia was detected in any of the monkeys when sera taken on postvaccination days 1 through 12 were inoculated into adult Toxorhynchites amboinensis mosquitoes and LLC-MK2 cells. By day 89, four of the six monkeys had seroconverted by the neutralization test in each of groups A, B, and C, and three of five monkeys in group D (one monkey died from cardiac collapse after anesthesia) had seroconverted. Immune enhancement of dengue virus infection is known to occur in humans and monkeys circulating heterologous flavivirus antibodies. In this study, there was no enhancing effect when antibody was mixed with dengue type 2 vaccine virus and injected subcutaneously.

Factors affecting syncytial development in Aedes pseudoscutellaris cells by dengue viruses.

Several factors that were suspected of affecting the development of syncytia in cultured Aedes pseudoscutellaris cells inoculated with dengue viruses were studied. The results indicated that fresh media (less than 1 week old), low cell density at inoculation (2.8 x 10(5) cells/cm2), and low cell passage level (less than 52 passages) favored the development of syncytia. All three types (1, 2, and 3) of dengue viruses tested could be isolated from human sera by Aedes pseudoscutellaris cell culture by using syncytial development as an indicator, but the isolation rate was lower than that obtained by using intrathoracically inoculated Aedes aegypti mosquitoes.

Prevalence of selected zoonotic diseases in vertebrates from Haiti, 1972.

Vertebrate animals collected in Haiti in 1972 were tested for selected zoonotic diseases. No rabies virus or neutralizing (N) antibody was detected in bats (Artibeus jamaicensis). However, N antibody against St. Louis encephalitis, Western equine encephalitis (WEE), and Eastern equine encephalitis were detected in resident species of birds and WEE antibody in bats. No N antibody against Venezuelan equine encephalitis was found. The possible introduction by migratory birds and local transmission of these arboviruses is discussed.

A rapid fluorescent focus-inhibition test for determining dengue neutralizing antibody and for identifying prototype dengue viruses.

Neutralizing antibody to dengue virus in human and animal sera was assayed by the rapid fluorescent focus-inhibition test (RFFIT). Neutralizing-antibody titers could be detected after only 24 h compared to 5--6 days required by the plaque-reduction test. The RFFIT is more definitive than the conventional complement fixation (CF) or hemagglutination-inhibition (HI) test in identifying prototype dengue viruses, is reproducible, and is applicable to the routine detection of neutralizing antibodies to dengue viruses.

Dengue fever with hemorrhagic manifestations: a report of three cases from Puerto Rico.

During the 1975 dengue epidemic in Puerto Rico, we studied three patients who had serologically confirmed dengue with hemorrhagic manifestations. None of the patients went into shock and none died. Only one of the patients had disease that resembled dengue hemorrhagic fever (DHF) as observed in Southeast Asia. This patient was a 14-year-old boy who had epistaxis, a positive tourniquet test, moderate thrombocytopenia, and significant hemoconcentration. The other two patients had hemorrhagic disease which was of clinical importance, but was not typical of DHF. These cases of dengue with hemorrhagic manifestations are the only ones known to have been documented in Puerto Rico.