Serious adverse events associated with yellow fever 17DD vaccine in Brazil: a report of two cases.

BACKGROUND: The yellow fever vaccine is regarded as one of the safest attenuated virus vaccines, with few side-effects or adverse events. We report the occurrence of two fatal cases of haemorrhagic fever associated with yellow fever 17DD substrain vaccine in Brazil. METHODS: We obtained epidemiological, serological, virological, pathological, immunocytochemical, and molecular biological data on the two cases to determine the cause of the illnesses. FINDINGS: The first case, in a 5-year-old white girl, was characterised by sudden onset of fever accompanied by headache, malaise, and vomiting 3 days after receiving yellow fever and measles-mumps-rubella vaccines. Afterwards she decompensated with icterus and haemorrhagic signs and died after a 5-day illness. The second patient-a 22-year-old black woman-developed a sore throat and fever accompanied by headache, myalgia, nausea, and vomiting 4 days after yellow fever vaccination. She then developed icterus, renal failure, and haemorrhagic diathesis, and died after 6 days of illness. Yellow fever virus was recovered in suckling mice and C6/36 cells from blood in both cases, as well as from fragments of liver, spleen, skin, and heart from the first case and from these and other viscera fragments in case 2. RNA of yellow fever virus was identical to that previously described for 17D genomic sequences. IgM ELISA tests for yellow fever virus were negative in case 1 and positive in case 2; similar tests for dengue, hantaviruses, arenaviruses, Leptospira, and hepatitis viruses A-D were negative. Tissue injuries from both patients were typical of wild-type yellow fever. INTERPRETATION: These serious and hitherto unknown complications of yellow fever vaccination are extremely rare, but the safety of yellow fever 17DD vaccine needs to be reviewed. Host factors, probably idiosyncratic reactions, might have had a substantial contributed to the unexpected outcome.

Posttreatment follow-up of Helicobacter pylori infection using a stool antigen immunoassay.

The Helicobacter pylori stool antigen enzyme immunoassay (HpSA) was evaluated during posttreatment follow-up of patients in a country with a very high prevalence of H. pylori infection. From among 273 dyspeptic individuals (18 to 55 years) initially recruited from a shantytown in Lima, Peru, 238 participants who met the inclusion criteria and were suspected to be H. pylori positive based on (14)C urea breath test (UBT) results underwent endoscopy. Participants with endoscopy-proven infections received standard eradication therapy and were monitored by UBT and HpSA at 1 month following treatment and at 3-month intervals for 9 months posttreatment. A second endoscopy was performed if UBT results showed evidence of treatment failure or H. pylori recurrence. Biopsy results were considered the "gold standard" in all analyses. Among patients who underwent endoscopy, HpSA had a pretreatment sensitivity of 93%. Two-hundred thirty patients completed the treatment regimen, of whom 201 (93%) were considered to have had successful treatment outcomes based on a negative follow-up UBT. Thirty-two patients with UBT-defined treatment failures or H. pylori recurrences at any point during the 9-month follow-up underwent a second endoscopy. In the posttreatment setting, HpSA had an overall sensitivity of 73% and a specificity of 67%. Agreement between UBT and HpSA diminished throughout the follow-up. Among 14 participants in whom HpSA remained positive at 1 month following treatment despite UBT evidence of treatment success, 12 (86%) became HpSA negative within 3 months posttreatment. Although this study confirmed the validity of the HpSA in the initial assessment of dyspeptic patients, the test demonstrated a reduced overall accuracy in the detection of treatment failures and H. pylori recurrences during 9 months of posttreatment follow-up. Furthermore, in some patients it may take up to 3 months after successful eradication for antigen shedding to diminish to levels within the negative HpSA range.

Yellow fever: an update.

Yellow fever, the original viral haemorrhagic fever, was one of the most feared lethal diseases before the development of an effective vaccine. Today the disease still affects as many as 200,000 persons annually in tropical regions of Africa and South America, and poses a significant hazard to unvaccinated travellers to these areas. Yellow fever is transmitted in a cycle involving monkeys and mosquitoes, but human beings can also serve as the viraemic host for mosquito infection. Recent increases in the density and distribution of the urban mosquito vector, Aedes aegypti, as well as the rise in air travel increase the risk of introduction and spread of yellow fever to North and Central America, the Caribbean and Asia. Here I review the clinical features of the disease, its pathogenesis and pathophysiology. The disease mechanisms are poorly understood and have not been the subject of modern clinical research. Since there is no specific treatment, and management of patients with the disease is extremely problematic, the emphasis is on preventative vaccination. As a zoonosis, yellow fever cannot be eradicated, but reduction of the human disease burden is achievable through routine childhood vaccination in endemic countries, with a low cost for the benefits obtained. The biological characteristics, safety, and efficacy of live attenuated, yellow fever 17D vaccine are reviewed. New applications of yellow fever 17D virus as a vector for foreign genes hold considerable promise as a means of developing new vaccines against other viruses, and possibly against cancers.

Phenotypic and molecular analyses of yellow fever 17DD vaccine viruses associated with serious adverse events in Brazil.

The yellow fever (YF) 17D virus is one of the most successful vaccines developed to data. Its use has been estimated to be over 400 million doses with an excellent record of safety. In the past 3 years, yellow fever vaccination was intensified in Brazil in response to higher risk of urban outbreaks of the disease. Two fatal adverse events temporally associated with YF vaccination were reported. Both cases had features similar to yellow fever disease, including hepatitis and multiorgan failure. Two different lots of YF 17DD virus vaccine were administered to the affected patients and also to hundreds of thousands of other individuals without any other reported serious adverse events. The lots were prepared from the secondary seed, which has been in continuous use since 1984. Nucleotide sequencing revealed minor variations at some nucleotide positions between the secondary seed lot virus and the virus isolates from patients; these differences were not consistent across the isolates, represented differences in the relative amount of each nucleotide in a heterogeneous position, and did not result in amino acid substitutions. Inoculation of rhesus monkeys with the viruses isolated from the two patients by the intracerebral (ic) or intrahepatic (ih) route caused minimal viremia and no clinical signs of infection or alterations in laboratory markers. Central nervous system histological scores of rhesus monkeys inoculated ic were within the expected range, and there were no histopathological lesions in animals inoculated ih. Altogether, these results demonstrated the genetic stability and attenuated phenotype of the viruses that caused fatal illness in the two patients. Therefore, the fatal adverse events experienced by the vaccinees are related to individual, genetically determined host factors that regulate cellular susceptibility to yellow fever virus. Such increased susceptibility, resulting in clinically overt disease expression, appears to be extremely rare.

Facing up to re-emergence of urban yellow fever.

PIP: Transmitted from person to person by Aedes aegypti, urban yellow fever was eliminated in the first half of this century, with the eradication of its mosquito vector from most of South America. However, reinfestation began in the 1970s is now almost complete, and vector control is considerably more difficult now than before. The threat of urban yellow fever is greatest in towns such as Santa Cruz, Bolivia, near the forest, but improved transport links increase the likelihood of spread by viremic people to nonendemic areas. Van der Stuyft et al. have reported the first instance of urban transmission of yellow fever in the Americas in 44 years. Since residents of the densely populated cities and much visited areas in coastal South America have never been vaccinated, an outbreak there would facilitate widespread dissemination of the disease, even to other continents. While urban yellow fever is a significant threat, carrying a case-fatality rate of about 20%, the constrained dynamics of transmission, early recognition of the striking clinical presentation, and efforts to control the infection should limit the impact of the disease. Laboratory-based surveillance, together with the prevention and control strategies outlined by van der Stuyft et al. are the key defensive measures against the future threat of urban epidemics.^ieng

Serologic IgG response to urease in Helicobacter pylori-infected persons from Mexico.

Helicobacter pylori urease is required to counteract acidity during colonization of the stomach, and has been suggested as a major immunodominant antigen. The aim of this study was to determine the anti-urease response in a representative national serologic survey in Mexico. The population surveyed included persons 1-90 years of age from all socioeconomic levels and geographic zones of the country. Helicobacter pylori status was determined by ELISA serology. The IgG anti-urease was studied by ELISA using a recombinant apoenzyme. We found that 2,930 of the 7,720 infected patients (38%) were seropositive for IgG urease. The rate of IgG anti-urease positivity increased with age; in children < 10 years old it was < 20% and in persons > 40 years old it was > 50%. Age and a region with a high level of development were risk factors for seropositivity, whereas gender, educational level, crowding, and socioeconomic level were not associated with seropositivity. In conclusion, in natural infection with H. pylori, the response to urease is poor, mainly during the first years of infection. This inconsistent immune response to the enzyme may favor persistence of infection. A vaccine eliciting a consistent anti-urease response might overcome immune evasion and enhance clearance of bacteria after exposure.

Western equine encephalomyelitis: virulence markers and their epidemiologic significance.

Comparative studies are described on the virulence of the western equine encephalomyelitis (WEE) complex viruses for mice. Three epizootic WEE virus strains (McMillan, Cba 87, and Cba CIV 180) and five enzootic WEE complex viruses (Highlands J [HJ], Y62-33, Aura, Fort Morgan [FM], and WEE AG80-646) were examined. The neurovirulence and the neuroinvasiveness of these viruses for adult mice were established and correlated with viremia and virus replication in brain tissue. Adult mice inoculated intraperitoneally showed differential responses that corresponded to the epidemiologic attributes of WEE viruses. Viruses associated with equine epizootics were neurovirulent and neuroinvasive, whereas enzootic viruses were neither neuroinvasive nor neurovirulent. In North America, HJ virus appears to be an antigenic link with an intermediate virulence between epizootic WEE virus and the enzootic FM virus. The HJ virus has been associated with rare cases of sporadic equine and human diseases. In South America, no virus with intermediate virulence characteristics has been described. We speculate that epizootics may arise from nonpathogenic strains such as AG80-646 maintained in enzootic transmission cycles.

Comparative infections of epizootic and enzootic strains of Venezuelan equine encephalomyelitis virus in Amblyomma cajennense (Acari: Ixodidae).

To compare the potential for an enzootic or an epizootic strain of Venezuelan equine encephalomyelitis (VEE) virus to infect Amblyomma cajennense (F.), larval ticks were fed on guinea pigs (strain 13) inoculated with an enzootic viral strain of variant I-E (68U201) or on guinea pigs inoculated with an epizootic strain of variant I-A (Trinidad donkey). Peak viremias were 10(5.2) plaque-forming units (PFU)/ml and 10(7.3) PFU/ml in guinea pigs infected with enzootic and epizootic viral strains, respectively. Ticks feeding on enzootic- and epizootic-infected hosts had viral titers of 10(2.5) and 10(3.9) PFU per tick, respectively, at drop-off. Although epizootic virus was recovered from 98% (127 of 130) of larval ticks up to 16 d after drop-off, enzootic virus was recovered from 95% (19 of 20) at drop-off (mean titer, 10(2.5) PFU per tick), with recovery rates declining rapidly to 2 of 10 (mean titer, 10(1.4) PFU per tick) by 16 d after drop-off. Transstadially transmitted epizootic virus was found in 0.4% (12 of 2,950) of unfed nymphs (mean titer, 10(2.8) PFU per tick) 63 d after drop-off, 1% (5 of 521) fed nymphs 69 d after drop-off, and 1% (4 of 400) of unfed adults (mean titer, 10(3.6) PFU per tick) 106 d after drop-off. No enzootic virus was recovered from 4,600 unfed nymphs tested 63 d after drop-off.

Venezuelan equine encephalomyelitis virus infection in and transmission by the tick Amblyomma cajennense (Arachnida: Ixodidae).

To assess a possible role of ticks as the maintenance host for epizootic strains of Venezuelan equine encephalomyelitis (VEE) virus, laboratory experiments were conducted to determine if ticks could become infected, maintain, and transmit the virus. Larval and nymphal Amblyomma cajennense (F.) and larval Dermacentor nitens Neumann ticks were exposed to epizootic VEE virus (Trinidad donkey strain) by allowing them to feed on viremic guinea pigs (strain 13). In A. cajennense, transstadial transmission was observed from larvae to nymphs and adults. Horizontal viral transmission to a mammalian host was accomplished by nymphs. Infection rates in nymphs and adults were 2% (42/2,750) and 4% (9/244), respectively, afer ingestion of virus as larvae. Virus was detected in A. cajennense adult ticks for up to 171 d after infection in the larval stage. A cajennense, exposed as nymphs, ingested virus but did not become infected (0/164 after 10 d after taking an infective bloodmeal). No virus was detected in D. nitens 7 d after exposure. These findings suggest that A. cajennense potentially could be involved in an interepizootic maintenance cycle of epizootic VEE viral strains.

Localized eastern equine encephalitis in Santiago del Estero Province, Argentina, without human infection.

In 1981, a localized epizootic of Eastern Equine Encephalitis (EEE) occurred in irrigated areas of four counties in the province of Santiago del Estero, Argentina. The diagnosis was confirmed by serology, and there was no evidence of involvement of Western or Venezuelan equine encephalitis viruses. The overall incidence of equine encephalitis was estimated 17%, the case-fatality rate at 61% and the inapparent: apparent infection ratio less than or equal to 2.9:1. This is the first localized epizootic defined in Argentina and the first in which EEE has been found as the sole etiologic arbovirus. This posed the possibility to look for human infection in the area. In spite of a careful surveillance, no evidence of human disease or infection was found, differing from the situation in USA where EEE virus is a public health problem. Nevertheless vector/s and vertebrate hosts involved in the transmission cycle in Argentina remain unknown, precluding at present speculations on the potential human risk.

Localized Eastern equine encephalitis in Santiago del Estero province, Argentina, without human infection

Se documenta una epizootia de encefalitis equina del este (EEE) localizada en una zona irrigada de cuatro departamentos de la Privincia de Santiago del Estero, Argentina, en 1981. La incidencia de casos equinos fue estimada en 17% con una tasa de casos fatales del 61% y una relación de infección inaparente: aparente de < ou = 2,9:1. El diagnóstico para el virus EEE fue confirmado por pruebas serológicas y no se encontró evidencia de casos por virus de las encefalitis del oeste o Venezuela. Esta es la primera epizootia circunscripta a una pequeña área geográfica que se ha definido en Argentina y la primera en que el virus EEE se ha encontrado como único arbovirus etiológico. Su reconocimiento brindo la posibilidad de buscar la infección humana, pero no se encontró clara evidencia de enfermedad o infección. Esto se atribuyó a la baja densidad de población humana rural, aunque no se descartaron otros factores ecológicos. La serología en otros animales no permitió determinar los huéspedes vertebrados y no se estudiaron los vectores por lo cual el ciclo de transmisión continúa desconocido, impidiendo especular sobre el riesgo potencial del virus EEE para el hombre en Argentina

Localized Eastern equine encephalitis in Santiago del Estero province, Argentina, without human infection

Se documenta una epizootia de encefalitis equina del este (EEE) localizada en una zona irrigada de cuatro departamentos de la Privincia de Santiago del Estero, Argentina, en 1981. La incidencia de casos equinos fue estimada en 17% con una tasa de casos fatales del 61% y una relación de infección inaparente: aparente de < ou = 2,9:1. El diagnóstico para el virus EEE fue confirmado por pruebas serológicas y no se encontró evidencia de casos por virus de las encefalitis del oeste o Venezuela. Esta es la primera epizootia circunscripta a una pequeña área geográfica que se ha definido en Argentina y la primera en que el virus EEE se ha encontrado como único arbovirus etiológico. Su reconocimiento brindo la posibilidad de buscar la infección humana, pero no se encontró clara evidencia de enfermedad o infección. Esto se atribuyó a la baja densidad de población humana rural, aunque no se descartaron otros factores ecológicos. La serología en otros animales no permitió determinar los huéspedes vertebrados y no se estudiaron los vectores por lo cual el ciclo de transmisión continúa desconocido, impidiendo especular sobre el riesgo potencial del virus EEE para el hombre en Argentina (AU)

Localized eastern equine encephalitis in Santiago del Estero Province, Argentina, without human infection.

In 1981, a localized epizootic of Eastern Equine Encephalitis (EEE) occurred in irrigated areas of four counties in the province of Santiago del Estero, Argentina. The diagnosis was confirmed by serology, and there was no evidence of involvement of Western or Venezuelan equine encephalitis viruses. The overall incidence of equine encephalitis was estimated 17

, the case-fatality rate at 61

and the inapparent: apparent infection ratio less than or equal to 2.9:1. This is the first localized epizootic defined in Argentina and the first in which EEE has been found as the sole etiologic arbovirus. This posed the possibility to look for human infection in the area. In spite of a careful surveillance, no evidence of human disease or infection was found, differing from the situation in USA where EEE virus is a public health problem. Nevertheless vector/s and vertebrate hosts involved in the transmission cycle in Argentina remain unknown, precluding at present speculations on the potential human risk.

Epidemic yellow fever caused by an incompetent mosquito vector.

Arbovirus epidemics in a geographic region are believed to depend on the presence of susceptible or "competent" arthropod vectors. We demonstrate that an urban, Aedes aegypti-borne, epidemic of yellow fever occurred in 1987 although the mosquito vector was relatively resistant to infection and transmitted the virus inefficiently. Twenty-six percent of the experimental mosquitoes from the epidemic area that ingested yellow fever virus became infected and only 7% of these transmitted the virus. In contrast, 80% of an exotic susceptible strain of Ae. aegypti became infected and 43% were able to transmit. We also show that no other potential vectors were active during the epidemic and that the local Ae. aegypti were present in extremely large numbers. These results document, for the first time, that, in the presence of high population density an incompetent mosquito vector can initiate and maintain virus transmission resulting in an epidemic.

Arbovirus isolations from mosquitoes collected during and after the 1982-1983 epizootic of western equine encephalitis in Argentina.

Mosquitoes were collected in Santa Fe and Rio Negro provinces, Argentina, in 1982-1983 during a western equine encephalitis (WEE) epizootic. Totals of 153,084 mosquitoes from Santa Fe Province and 484 from Rio Negro Province were tested for virus in 2,351 pools. Seventeen virus strains were isolated, all from Santa Fe collections, as follows: 4 WEE, 6 Venezuelan equine encephalitis, 1 St. Louis encephalitis, 2 Antequera, 1 Maguari, 1 Melao, 1 new vesiculovirus (Calchaqui), and 1 Gamboa. The WEE virus isolates were from Aedes albifasciatus, Anopheles albitarsis, Mansonia species, and Psorophora pallescens. Collections during the spring and summer (1983-1984) following the epizootic yielded 49,707 mosquitoes from Santa Fe, 15,961 from Rio Negro, and 2,019 from Chubut provinces. Twenty-two virus strains were isolated, all from Santa Fe mosquitoes, as follows: 3 strains of SLE virus and 19 strains of Turlock (TUR) virus. All but one of the TUR virus isolates appear to have come from mosquitoes that engorged on a viremic chicken following entry into a bait trap. The vector relationships of each virus isolated during and after the WEE epizootic are discussed.

A newly recognized vesiculovirus, Calchaqui virus, and subtypes of Melao and Maguari viruses from Argentina, with serologic evidence for infections of humans and horses.

In 1983, 17 virus strains were isolated from mosquitoes collected during an outbreak of western equine encephalitis in Santa Fe Province, Argentina. Strains of western equine encephalitis, Venezuelan equine encephalitis, St. Louis encephalitis, and Antequera viruses were isolated, as were several bunyaviruses of the California and Bunyamwera serogroups and a new vesiculovirus. Complement fixation and neutralization tests were used to identify the California serogroup virus as a subtype of Melao virus, the Bunyamwera serogroup virus as a subtype of both Maguari and Playas viruses, and the vesiculovirus as a newly recognized agent for which the name Calchaqui virus is proposed. A limited serosurvey of horses and humans in Santa Fe Province and horses from the adjacent Santiago del Estero Province was performed to determine the prevalence of neutralizing antibody to the subtypes of Melao and Maguari viruses and to Calchaqui virus. The high prevalence of antibodies to these three agents indicates the need for further studies of their disease potential in horses, because they are closely related to several other viruses that are known equine pathogens.

Yellow fever: a medically neglected disease. Report on a seminar.

In 1984 the Pan American Health Organization (PAHO) sponsored an international seminar on the treatment and laboratory diagnosis of yellow fever. The meeting, held April 2-6 in Brasilia, was attended by 37 participants representing Bolivia, Brazil, Colombia, Peru, Venezuela, the United States, PAHO, and the World Health Organization. The objectives of the seminar were to review the current status of the disease, with emphasis on diagnosis and on the care and management of patients, and to formulate recommendations for improvements in diagnosis and management and for future research. A unique aspect of the seminar and one that distinguished it from previous, epidemiologically oriented meetings on yellow fever was the emphasis on clinical medicine and the participation of individuals representing academic medicine in relevant specialties such as hepatology, hematology, cardiology, and nephrology.

Genetic and epidemiological studies of dengue type 2 viruses by hybridization using synthetic deoxyoligonucleotides as probes.

A rapid nucleic acid hybridization procedure was developed for examining the genotypic variation of dengue type 2 viruses (DEN 2) having distinct RNase T1 fingerprints and isolated from different geographical areas. Synthetic DNA hybridization probes were constructed complementary in nucleotide sequence to common and unique RNase T1 oligonucleotides of topotype viruses from Puerto Rico/South Pacific, Jamaica, the Seychelles, Thailand/Burma and Africa. Hybridization probes with both type- and topotype-specific reactivities were observed, as were probes specific for two or more of the DEN 2 topotypes. These results confirm geographical movement of topotype virus strains and suggest possible origins. Detection of DEN 2 RNA by hybridization is a rapid and reproducible method that can be modified and applied as a viable alternative to the laborious T1 oligonucleotide fingerprinting.

Genetic and epidemiological studies of dengue type 2 viruses by hybridization using synthetic deoxyoligonucleotides as probes

A rapid nucleic acid hybridization procedure was developed for examining the genotypic variation of dengue type 2 viruses (DEN 2) having distinct RNase T1 fingerprints and isolated from different geographical areas. Synthetic DNA hybridization probes were constructed complementary in nucleotide sequence to common and unique RNase T1 oligonecleotides of topotype viruses from Puerto Rico/South Pacific, Jamaica, the Seychelles, Thailand/Burma and Africa. Hybridization probes with both type- and topotype-specific reactivities were observed, as were probes specific for two or more of the DEN 2 topotypes. These results confirm geographical movement of topotype virus strains and suggest possible origins. Detection of DEN 2 RNA by hybridization is a rapid and reproducible method that can be modified and applied as a viable alternative to the labourious T1 oligonucleotide fingerprinting.(AU)