A new arbovirus from Aedes albopictus, an Asian mosquito established in the United States.

Ten strains of a new arbovirus belonging to the Bunyamwera group (Bunyaviridae) were recovered from field-collected Aedes albopictus mosquitoes in Potosi, Missouri. This evidence indicates that this species may serve as an arbovirus vector in the United States. The urban-suburban distribution, aggressive biting behavior, and broad viral susceptibility of Ae. albopictus may lead to the transmission of viruses of known public health importance and perhaps of viruses hitherto not transmitted to humans because of the feeding pattern of their usual vectors.

Seroepidemiology of La Crosse virus infection in humans in western North Carolina.

On the Cherokee Indian Reservation and surrounding area of western North Carolina, an area-wide serosurvey was conducted to determine the prevalence of neutralizing antibody to La Crosse (LAC) virus. A questionnaire was used to identify risk factors important in exposure to virus-infected mosquitoes in populations near the reservation. Of 1,008 serum samples tested, 9.6% were positive for LAC virus antibody. For samples solely collected from on (n = 311) or off (n = 697) the reservation, the prevalence of seropositive samples was 20.6% on the reservation and only 4.7% off the reservation. Seropositivity increased directly with age, indicating that transmission of LAC virus was highly endemic. Age and location residence (on versus off the reservation) were significant risk factors for exposure to LAC virus. Persons on the reservation were 5.5 times more likely to have been exposed to LAC virus than were people who reside off the reservation. An additive increase in risk of 1.5 times over each age group was found, so that the oldest age group ( > or = 75 years) was 7.5 times more likely to have been exposed to LAC virus than was the youngest age group ( < 1-14 years).

Arbovirus surveillance in six states during 1972.

A virus surveillance project was established and maintained during 1972 along 10 major river drainages in six states. Mosquitoes, biting flies, and blood specimens from sentinel equines were collected during 83 field trip visits to 141 arthropod collecting sites and 22 sentinel locations from April into December 1972. There were 173,074 mosquitoes tested and 303 arboviruses isolated from 11 of 41 species. From 13,388 biting flies tested, 8 arbovirus isolations were obtained in 1 of 5 species. There was no isolation of Venezuelan equine encephalitis (VEE) virus. Western equine encephalitis (WEE) virus isolates were the most numerous and were followed by Turlock, St. Louis encephalitis, Hart Park, California encephalitis, and Bunyamwera (BUN) group viruses. The first isolation of WEE from the mosquito Cullex (Mel). erraticus is reported, as is the extension of the ranges for Buttonwillow virus from California to New Mexico and Texas. Also a single isolation of the BUN group from Culicoides variipennis extends the range of this virus-vector relationship from California to Texas. New distribution records for mosquito species previously unreported for Arizona, Louisana, New Mexico, and Oklahoma are reported. The sentinel burros detected WEE serologic conversions at two sites in New Mexico and at one in Texas. The surveillance project provided state and federal officials with current information on the status of arbovirus activity, including the absence of VEE activity during 1972, and it demonstrated the existence of the potential for WEE epizootics and epidemics throughout a wide geographic area of the Western United States.

Transovarial transmission of St. Louis encephalitis virus by Culex pipiens complex mosquitoes.

Experiments were conducted to determine whether transovarial transmission (TOT) of St. Louis encephalitis (SLE) virus occurs in Culex pipiens complex mosquitoes, the principal vectors of SLE virus in the central-eastern United States. In 1978, field-collected mosquitoes from Memphis, Tennessee, and McLeansboro, Illinois, were used; during 1979, colonized mosquitoes from Chicago, Illinois, and Memphis, Tennessee, were used. Mosquitoes were infected by feeding on viremic chicks inoculated with an SLE virus strain isolated from Cx. pipiens complex mosquitoes collected from Memphis, Tennessee, in 1976. During the 1979 experiments, progeny larval and adult mosquitoes were held at two temperatures, 18 and 25 degrees C. Progeny were tested for virus by plaque assay in duck embryo cell cultures and by inoculation of Aedes albopictus C6/36 cells and examination by immunofluorescence. In 1978, most of the progeny tested were from the first ovarian cycle, and a single occurrence of TOT was documented. In 1979, a single TOT occurred from 46,856 first ovarian cycle progeny, whereas 7 of 9,234 progeny of the second ovarian cycle were infected. The rate of TOT was higher for progeny of Memphis than Chicago mosquitoes, and for mosquitoes held at 18 degrees C than at 25 degrees C; however, these differences were not statistically significant. Four positive pools were females, and three were fed on chicks for transmission attempts. The positive Chicago mosquito pool failed to transmit, but both Memphis pools successfully transmitted virus. The overall rates of TOT of SLE virus in progeny of the first and second ovarian cycle were, respectively, 1/45, 151 and 1/1,460. The significance of these results as they relate to the natural history of SLE virus is discussed.

Identification of hitherto unrecognized arboviruses from Ecuador: members of serogroups B, C, Bunyamwera, Patois, and Minatitlan.

Three hundred seventy-nine virus isolates were obtained from mosquitoes collected and sentinel hamsters exposed in coastal Ecuador from 1974 to 1978. These included four alphaviruses [Venezuelan equine encephalitis 1B (1), Venezuelan equine encephalitis 1D (35), western equine encephalitis (1) and eastern equine encephalitis (4)]; two flaviviruses [St. Louis encephalitis (3) and Naranjal (6)]; 11 bunyaviruses [Maguari (243), Playas (3), Vinces (33), Turlock (2), Abras (5), Babahoyo (3), Acara (2), Guajara (3), San Juan (6), Pueblo Viejo (3), 18 unspecified Gamboa serogroup viruses, Palestina (7)]; and one vesiculovirus (vesicular stomatitis New Jersey). All but Venezuelan equine encephalitis virus were new to Ecuador, and Naranjal (serogroup B), Playas (Bunyamwera serogroup), Vinces (serogroup C), Abras and Babahoyo (Patois serogroup), San Juan and Pueblo Viejo (Gamboa serogroup) and Palestina (Minatitlan serogroup) are newly recognized viruses. These isolates have enabled us to 1) expand our knowledge of the geographic distribution of recognized viruses, 2) expand our knowledge of the members of certain serogroups and 3) establish two new serogroups (Gamboa and Minatitlan).

Experimental studies on the transmission of hepatitis B by mosquitoes.

Culex tarsalis and Aedes aegypti mosquitoes were fed on chimpanzees carrying hepatitis B surface antigen (HBS Ag) of known infectivity and pools were tested by radioimmunoassay daily for the presence of HBS Ag. HBS Ag continued to be detected at low levels in mosquito tissue after digestion of the blood meal. Inoculation of susceptible chimpanzees with macerated pools of A. aegypti mosquitoes at two intervals after digestion of the blood meal did not produce hepatitis or serologic evidence of hepatitis B virus infection. Mechanical transmission studies by interrupting feeding of A aegypti from HBS Ag-carrier chimpanzees and transferring them to susceptible chimpanzees did not produce hepatitis. These findings do not support the hypothesis that mosquitoes are involved in either biological or mechanical transmission of hepatitis B.

Ecologic studies of mosquitoes and birds as hosts of Ockelbo virus in Sweden and isolation of Inkoo and Batai viruses from mosquitoes.

Field studies were conducted in central Sweden from 1983 through 1985 to obtain information on the etiologic agent of Ockelbo disease, described in Sweden in the 1960s and probably identical to Pogosta disease in Finland and to Karelian fever in the western USSR. Mosquitoes (63,644) collected during this 3 year period yielded 21 virus strains. Ockelbo virus isolations were from Culiseta morsitans (5 strains), Culex pipiens and/or Cx. torrentium (6 strains), and Aedes cinereus (3 strains). Inkoo (6 strains) and Batai (1 strain) viruses were recovered from Ae. communis. Blood samples collected March-May from migrating birds on the southeast and est coast of Sweden and in July and August from resident birds in east-central Sweden were tested for neutralizing antibody to Ockelbo virus. Antibody was not detected in 328 birds sampled during spring migrations. Two of 58 (3.4%) birds bled in July and 8 of 78 birds (10%) bled in August had antibody to Ockelbo virus. Ockelbo virus circulates in a mosquito-bird-mosquito cycle, with Cs. morsitans and Cx. pipiens and/or Cx. torrentium as enzootic vectors. Antibody was detected in passerine birds. Other classes of birds or other vertebrates were not sampled. Aedes cinereus may serve primarily to transmit virus to people. The role of other mosquito species as vectors for people is unknown.

Isolation of Tete serogroup bunyaviruses from Ceratopogonidae collected in Colorado.

Two viruses were isolated from ceratopogonid midges collected in northern Colorado. Electron microscopy indicated that both isolates were bunyavirus-like. Indirect fluorescent antibody and serum dilution-plaque reduction neutralization tests showed that these isolates were members of the Tete serogroup, most closely related antigenically to Tete and Batama viruses but distinguishable from both and from each other. We suggest the name Weldona virus for these isolates. Antibody in both waterfowl and passerine birds in northern Colorado indicates the enzootic presence of these viruses in northern Colorado and raises unanswered questions about the introduction and establishment of Tete serogroup viruses in the Americas.

Viruses isolated from Aedeomyia squamipennis mosquitoes collected in Panama, Ecuador, and Argentina: establishment of the Gamboa serogroup.

Twenty-four virus strains were isolated from Aedeomyia squamipennis mosquitoes collected in Ecuador. One additional strain each was isolated from this species from Panama and ARgentina. All 26 isolates were shown to be related serologically to prototype Gamboa virus, originally isolated from Ad. squamipennis mosquitoes collected in Panama. Antigenic comparisons of eight strains, including prototype Gamboa virus, indicated the existence of four distinct viruses. Neutralization tests with sera from a variety of mammalian and avian species from Argentina provided further evidence that Gamboa serogroup viruses are transmitted between Ad. squamipennis and birds.

Yellow fever in the Gambia, 1978--1979: entomological aspects and epidemiological correlations.

An entomological survey was conducted in the Gambia in January 1979, during the last phase of a yellow fever (YF) outbreak which began during the previous rainy season. In the dry conditions which prevailed in January, Aedes aegypti was the only YF vector present. Two YF virus strains were isolated from females of this mosquito species caught in a village of western Gambia, where active human cases were documented. The ae. aegypti breeding sites were exclusively of the domestic type. Larval indices varied greatly from place to place, but generally appeared to correlate with the incidence of disease. A better understanding of the conditions that prevailed at the onset and during the early phase of the epidemic will require further entomological investigations. Nevertheless, it appears probable that initial transmission as by sylvatic vectors such as the Ae. furcifer-taylori group and possibly others such as Ae. luteocephalus, Ae. metallicus, and Ae. vittatus. As the outbreak progressed, interhuman transmission by Ae. aegypti also occurred, and this mixed epidemiological pattern later gave way to transmission by Ae. aegypti only when sylvatic vector populations declined in the dry season. We speculate that a prolongation of the rainy season during 1976--1978 was important in the origin of the outbreak. The relationship of this epidemic to the established focus of sylvatic YF in southeastern Senegal is discussed. The Gambian outbreak is considered the result of a recent northwesterly extension of the YF Emergence Zone.

Characterization of Fort Morgan virus, an alphavirus of the western equine encephalitis virus complex in an unusual ecosystem.

An alphavirus isolated from nestling Cliff Swallows (Petrochelidon pyrrhonota) and House Sparrows (Passer domesticus) and from cimicid bugs (Oeciacus vicarius) in eastern Colorado, for which we propose the name Fort Morgan (FM) virus, is sensitive to the action of sodium deoxycholate, unstable at pH 2.0-4.0, and demonstrates no characteristics of temperature-sensitive mutants. Unpassaged field strains are nonpathogenic, or of low pathogenicity, for suckling mice; however, plaque-purified FM virus is pathogenic for a variety of laboratory hosts. By hemagglutination-inhibition (HI), complement-fixation, and neutralization tests, cross-reactions were observed between FM virus and members of the western equine encephalitis (WEE) virus antigenic complex. Short-incubation HI tests indicated that the new isolate shared closer antigenic relationships with WEE complex virus strains from the eastern United States (Highlands J virus) than with other WEE complex viruses. On the basis of these serological findings, as well as characterization of the structural polypeptides and oligonucleotides, we suggest that FM is a distinct virus belonging to the WEE antigenic complex. A reconsideration of the taxonomy of the WEE complex and discussion of the epizoologic significance of FM virus are presented.

Identification of a new Venezuelan equine encephalitis virus from Brazil.

Two strains of recently isolated Venezuelan equine encephalitis (VEE) complex virus from southern Brazil, avirulent for 6- to 8-week-old mice and short-haired guinea pigs, were characterized by biologic, serologic, and biochemical means. They were shown serologically to represent a single, newly recognized variant of subtype I. Two-dimensional polyacrylamide gel electrophoresis (PAGE) of ribonuclease T1 digests of viral ribonucleic acid showed considerable homology between the genomes of the new variant prototype and variant IA. Three structural proteins were visualized by discontinuous sodium dodecyl sulfate-PAGE (SDS-PAGE). Although the smallest protein of both recent isolates migrates with the capsid proteins of other subtype I viruses, the larger structural proteins of the new variants differ in molecular weight from the E1 and E2 envelope glycoproteins of the other subtype I variants. The new isolates produced peptide fragment patterns that were identical to each other, but different from the patterns of other subtype I viruses, following SDS-PaGE of dissociated virions digested with Staphylococcus aureus V8 protease. Since these two isolates were from Culex (Melanoconion) species mosquitoes and from a bat (Carollia perspicillata), were postulated that this is an enzootic VEE virus variant for which the classification IF is suggested.

La Crosse virus infection and disease in western North Carolina.

Active surveillance for La Crosse infection from 1977 to 1979 revealed 12 laboratory documented cases in children from the Cherokee reservation and nearby areas of western North Carolina. The annual rate of hospitalization with La Crosse virus was isolated from two of 34 pools of male and one of 34 pools of female Aedes triseriatus mosquitoes reared from larvae collected around the residences of reservation children who had been hospitalized with encephalitis. The occurrence of the recent cases, the history of cases in 1964 and 1965, and the demonstration of antibodies to La Crosse virus in sera from second grade children collected in 1968 (2%), in 1978 (4.5%), and in high school students in 1979 (11.3%), indicate that La Crosse has persisted in the Cherokee area for at least 15 years. La Crosse infection is infrequently reported from the southeast, but this may reflect inactive surveillance. More frequent testing would reveal whether La Crosse is a significant health problem in other areas of the southeast.

Investigations of the vertebrate hosts of eastern equine encephalitis during an epizootic in Michigan, 1980.

A study was undertaken to investigate an increase in reported cases of clinical encephalitis due to eastern equine encephalitis (EEE) virus in horses and to determine the natural vertebrate hosts of that virus. Horses, birds, and small mammals were sampled at sites in a contiguous area in St. Joseph and Kalamazoo counties, Michigan, from 25 August to 5 September 1980. Serum samples from four horses acutely ill with encephalitis and 16 of 39 pasture mates of ill horses had neutralizing (N) antibody against EEE virus (46.5%); no viruses were isolated from these 43 sera. None of 24 draft horses from a site in St. Joseph County 12 km southeast of the affected sites had EEE antibody. A strain of Cache Valley virus was isolated from the blood of one of the 24 draft horses. No viruses were isolated, and no antibodies to EEE virus were detected in 28 blood samples from small mammals captured at sites where equine cases of encephalitis were occurring. Six strains of EEE virus, five of Highlands J virus, and one of Flanders virus were isolated from the blood of 401 wild birds belonging to 42 species captured at eight sites in both counties. A total of 29.9% of the wild birds had EEE antibody. Five species of domestic birds, mostly chickens and ring-necked pheasants, were sampled in both counties. Six strains of EEE virus were isolated from 152 ring-necked pheasants; these included three isolates from the brains of dead birds. About 13% of 51 pheasants tested from two small flocks in backyard pens in Kalamazoo County and 9% of 103 pheasants tested from a large game farm in St. Joseph County had antibody to EEE virus. The source of the EEE virus and the factors responsible for this epizootic are unknown; however, the epizootic probably represented an explosive expansion of an enzootic level of virus transmission.

Distribution of Bunyamwera serogroup viruses in North America, 1956-1984.

We attempted to tabulate all Bunyamwera serogroup (family Bunyaviridae, genus Bunyavirus) isolates from North America. By summarizing information from the laboratories of the Centers for Disease Control, data generously shared by other laboratories, and the published literature, we were able to accumulate data regarding 1,372 Bunyamwera serogroup viruses. These were: Tensaw (664, including 8 from vertebrates), Cache Valley (396, including 6 from vertebrates), Main Drain (160, including 14 from vertebrates), Lokern (69, including 8 from vertebrates), Northway (13, including 5 from vertebrates), Tlacotalpan (7), Santa Rosa (2), Santa Cruz (1 from a horse), and 60 of undetermined serotype. Virus isolation rates by month of collection were correlated with collection efforts, but associations of viruses and arthropod vectors varied by location, vertebrate host, and arthropod distribution. Tensaw virus was isolated principally from Anopheles crucians mosquitoes (466/656 isolates from arthropods) in the southeastern United States; Cache Valley virus principally from An. quadrimaculatus (94), Coquillettidia perturbans (59), Culiseta inornata (45), Aedes sollicitans (30), Psorophora columbiae (23), An. punctipennis (18), and Ae. vexans and trivittatus (18 each) mosquitoes (total = 305/382 isolates from arthropods from all of the United States and Canada, except the southeastern United States); Main Drain virus from Culicoides variipennis (31), Culicoides (Selfia) sp. (65), and Psorophora (23) and Aedes (21) species mosquitoes in the western United States; Lokern virus from Culicoides species (55/61 isolates from arthropods) in the western United States. Relationships between vector and vertebrate host distributions are discussed briefly in regard to geographic distribution of the Bunyamwera serogroup viruses.

Recovery of Tonate virus ("Bijou Bridge" strain), a member of the Venezuelan equine encephalomyelitis virus complex, from Cliff Swallow nest bugs (Oeciacus vicarius) and nestling birds in North America.

A second virus with distinct biological, serological, and physiochemical properties was detected as a minority viral subpopulation in specimens of Cliff Swallow nest bugs (Oeciacus vicarius) and nestling bird sera containing Fort Morgan (FM) virus. The second virus, detected by a breakthrough neutralization test employing FM antiserum, was present in 5 of 11 FM virus-positive pools of nest bugs and in 4 of 38 birds from Colorado and South Dakota. The concentration of the second virus was 10-fold to 1,000-fold lower than that of FM virus. The second virus, which was provisionally named "Bijou Bridge" (BB) virus was shown by conventional serological tests to be a member of the Venezuelan equine encephalomyelitis (VEE) complex, and by tests employing antisera to the E2 viral glycoprotein to be identical with Tonate virus, previously isolated from birds and mosquitoes only in French Guiana. Experimental infection of House Sparrows and Cliff Swallows showed that they develop brief BB viremias and antibodies. Oe. vicarius bugs were resistant to oral infection with BB virus. The epidemiological significance of recovery of Tonate virus in North American is discussed.

The ecology of Colorado tick fever in Rocky Mountain National Park in 1974. II. Infection in small mammals.

Field studies of Colorado tick fever (CTF) in small mammals in Rocky Mountain National Park (RMNP) in 1974 established that Eutamias minimus and Spermophilus lateralis were the most important hosts for CTF virus and were the source of virus for immature stages of the tick vector, Dermacentor andersoni. Other species (Peromyscus maniculatus, Spermophilus richardsonii, Eutamias umbrinus) are secondary hosts. The intensity of viral activity in rodents varied greatly from locality to locality. Highest rodent infection rates were found to occur in the Moraine Park area of RMNP. Lowest infection rates occurred above 3,290 meters in altitude at Rainbow Curve and on the tundra. The prevalence of infection in rodents was constant from April--July (5--6% of animals captured were viremic) and then declined to 1.7--2.5% in August and September coincident with a decline in nymphal tick ectoparasitism. Many animals were captured which were simultaneously viremic and antibody-positive. Under field conditions, neutralizing antibody seroconversion does not always occur.

Identification of new Guama and Group C serogroup bunyaviruses and an ungrouped virus from Southern Brazil.

From 1975 to 1978, 36 viruses were recovered from humans, bats, birds, sentinel mice and hamsters, and from mosquitoes collected in Coastal Brazil in the state of São Paulo. Identifications of 22 of these 36 viruses have been reported. Six of the remaining 14 isolates were shown to be Guama serogroup bunyaviruses. Two of these six were strains of a newly recognized virus for which the name Cananeia virus is proposed; another is a second newly recognized Guama serogroup virus for which the name Itimirim virus is proposed; a fourth is a strain of Bertioga virus and the other two are strains of Guaratuba virus. Before these studies Guaratuba virus was considered an ungrouped bunyavirus, but cross testing by complement-fixation demonstrated that this virus, and Mirim virus as well, should be considered members of the Guama serogroup. Another six viruses were shown to be strains of a single, newly recognized Group C bunyavirus for which the name Bruconha virus is proposed. Two strains of a single virus were shown by electron microscopy to belong to the family Bunyaviridae, but serologic relationships with other members of this family of viruses were not found; the name Enseada virus is proposed for this newly recognized agent.

Yellow fever in the Gambia, 1978--1979: epidemiologic aspects with observations on the occurrence of orungo virus infections.

An epidemic of yellow fever (YF) occurred in the Gambia between May 1978 and January 1979. Retrospective case-finding methods and active surveillance led to the identification of 271 clinically suspected cases. A confirmatory or presumptive laboratory diagnosis was established in 94 cases. The earliest serologically documented case occurred in June 1978, at the extreme east of the Gambia. Small numbers of cases occurred in August and September. The epidemic peaked in October, and cases continued to occur at a diminishing rate through January, when a mass vaccination campaign was completed. The outbreak was largely confined to the eastern half of the country (MacCarthy Island and Upper River Divisions). In nine survey villages in this area (total population 1,531) the attack rate was 2.6--4.4%, with a mortality rate of 0.8%, and a case fatality rate of 19.4%. If these villages are representative of the total affected region, there may have been as many as 8,400 cases and 1,600 deaths during the outbreak. The disease incidence was highest in the 0- to 9-year age group (6.7%) and decreased with advancing age to 1.7% in persons over 40 years. Overall, 32.6% of survey village inhabitants had YF complement-fixing (CF) antibodies. The prevalence of antibody patterns indicating primary YF infection decreased with age, in concert with disease incidence. The overall inapparent:apparent infection ratio was 12:1. In persons with serological responses indicating flaviviral superinfection, the inapparent:apparent infection ratio was 10 times higher than in persons with primary YF infection. Sylvatic vectors of YF virus, principally Aedes furcifer-taylori and Ae. luteocephalus are believed to have been responsible for transmission, at least at the beginning of the outbreak. Eighty-four percent of wild monkeys shot in January 1979 had YF neutralizing antibodies, and 32% had CF antibodies. Domestic Aedes aegypti were absent or present at very low indices in many severely affected villages (see companion paper). In January, however, aegypti-borne YF 2.5 months into the dry season was documented by isolation of YF virus from a sick man and from this vector species in the absence of sylvatic vectors. Thus, in villages where the classical urban vector was abundant, interhuman transmission by Ae. aegypti occurred and continued into the dry season. A mass vaccination campaign, begun in December, was completed on 25 January, with over 95% coverage of the Gambian population. A seroconversion rate of 93% was determined in a group of vaccinees. This outbreak emphasizes the continuing public health importance of YF in West Africa and points out the need for inclusion of 17D YF vaccination in future programs of multiple immunication.

Sindbis virus isolations from Saudi Arabian mosquitoes.

A study in late 1979 to early 1980 was conducted to assess arbovirus activity in the Eastern Province of Saudi Arabia. From 38,245 mosquitoes collected at 3 locations, 16 isolations of Sindbis virus were made: 13 from Culex univittatus and one each from Cx tritaeniorhynchus, Cx pipiens complex, and Culex spp. These isolations represent the first records of a mosquito-borne virus from the Gulf of Arabia and implicate Cx univittatus as the principal vector. A potential risk of human diseases exists due to Sindbis virus in Saudi Arabia.