RESUMEN
Aedes albifasciatus (Macquart) has been considered a potential vector of western equine encephalitis (WEE) virus in Argentina because it has been found naturally infected, it is susceptible to infection per os, and its distribution and feeding habits are compatible with those of an epizootic and epidemic vector. Ae. albifasciatus females collected in the vicinity of Cordoba, Argentina, were highly susceptible to WEE virus perorally (ID50 less than 0.5 Vero cell plaque-forming units) when fed on viremic chicks. Virus transmission trials were done 9 to 16 d after infection by feeding potentially infected mosquitoes individually on chicks. Among 31 mosquitoes that survived the incubation period, six refed on susceptible chicks. Virus transmission by bite was demonstrated by five of six (83%) mosquitoes. Therefore, the final piece of evidence incriminating Ae. albifasciatus as a natural vector of WEE virus has been obtained. This is the first mosquito species to be incriminated as a vector of WEE virus in South America.
Asunto(s)
Aedes/microbiología , Virus de la Encefalitis Equina del Oeste/patogenicidad , Encefalomielitis Equina/transmisión , Animales , Argentina , Pollos , Femenino , Insectos VectoresRESUMEN
Since the introduction of Aedes albopictus into North and South America, 18 viruses in 3 families have been used in vector competence studies involving 10 North American and 4 South American geographic strains of Ae. albopictus. This review summarizes the results of these studies and discusses the potential of Ae. albopictus to become a vector of arboviruses of public health importance in areas of the Western Hemisphere where it has recently become established.
Asunto(s)
Aedes , Infecciones por Arbovirus/transmisión , Insectos Vectores , Animales , Femenino , Humanos , América del Norte , América del Sur , Especificidad de la EspecieRESUMEN
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.
Asunto(s)
Brotes de Enfermedades/veterinaria , Virus de la Encefalitis Equina del Este , Encefalomielitis Equina/epidemiología , Enfermedades de los Caballos/epidemiología , Animales , Argentina/epidemiología , Encefalomielitis Equina/diagnóstico , Encefalomielitis Equina/etiología , Caballos , Pruebas SerológicasRESUMEN
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)
Asunto(s)
Animales , Encefalomielitis Equina/epidemiología , Enfermedades de los Caballos/epidemiología , Virus de la Encefalitis Equina del Este , Caballos , Argentina/epidemiología , Encefalomielitis Equina/etiología , Encefalomielitis Equina/diagnóstico , Pruebas SerológicasRESUMEN
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
Asunto(s)
Animales , Enfermedades de los Caballos/epidemiología , Virus de la Encefalitis Equina del Este , Encefalomielitis Equina/epidemiología , Argentina/epidemiología , Encefalomielitis Equina/diagnóstico , Encefalomielitis Equina/etiología , Caballos , Pruebas SerológicasRESUMEN
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.
RESUMEN
The transmission cycle of western equine encephalitis (WEE) virus in South America is unknown. A WEE virus strain was isolated from Aedes albifasciatus in Argentina during the WEE epizootic of 1982-83. Also, Culex pipiens from Argentina was reported to be able to transmit WEE virus experimentally, but other results indicate that Cx. pipiens from the USA is refractory to this virus. We determined the susceptibility of Argentina strains of Ae. albifasciatus and Culex pipiens complex mosquitos to infection by WEE virus by the oral route. Adult females were fed on chicks infected with a WEE virus strain isolated in Cordoba Province, Argentina, or were fed on a blood/virus suspension. Each mosquito ingested between 10(1.6) to 10(6.4) vero cell plaque-forming units of virus. Each of 28 Ae. albifasciatus was positive for virus from the fourth day postfeeding, and there was evidence for virus replication. In contrast, 0/44 Cx. p. quinquefasciatus and only 1/15 Cx. p. pipiens was positive. Aedes albifasciatus is susceptible to infection by WEE virus and should be considered a potential vector of this virus in Argentina. Both subspecies of Cx. pipiens are refractory to peroral infection by WEE virus and probably do not play a role in the WEE virus cycle in Argentina.
Asunto(s)
Aedes/microbiología , Culex/microbiología , Virus de la Encefalitis Equina del Oeste/patogenicidad , Encefalomielitis Equina/transmisión , Aedes/fisiología , Animales , Argentina , Pollos/microbiología , Culex/fisiología , Conducta AlimentariaRESUMEN
Three strains of Aedes albopictus from Brazil were examined for their ability to vertically transmit dengue 1 (DEN-1) and dengue 4 (DEN-4) viruses. Parental females were uniformly infected by parenteral inoculation of virus, and 8,121 F1 progeny from DEN-1 and DEN-4 infected mothers were pooled in lots of approximately 50 and tested for virus. Seven of 60 pools were positive for DEN-1 virus, and 1 of 121 pools was positive for DEN-4 virus. In DEN-1 assays, the minimum infection rate (MIR) for larvae (2 pools tested) was 1:84. Among positive cohorts of adults, pooled by sex and by geographic strain of mosquito, the MIR ranged from 1:193 to 1:626 for males and from 1:187 to 1:311 for females. Only a single pool of adult females was positive for DEN-4 virus (MIR 1:1022 for an adult female cohort from Santa Teresa). These results indicate that Brazilian Ae. albopictus have the potential to play a role in the maintenance of dengue viruses in nature.
Asunto(s)
Aedes/microbiología , Virus del Dengue/aislamiento & purificación , Insectos Vectores , Animales , Antígenos Virales/análisis , Brasil , Virus del Dengue/inmunología , Femenino , Larva/microbiología , Masculino , Especificidad de la EspecieRESUMEN
A combination of virus infection and transmission experiments showed that a Houston, Texas strain of Aedes albopictus is a competent vector for dengue (DEN), yellow fever (YF) and Ross River (RR) viruses. However, at 14 days incubation, DEN virus infection rates in a Puerto Rican strain of Aedes aegypti were significantly higher for each of the four DEN serotypes, except DEN-1, than in Houston Ae. albopictus fed simultaneously on the same virus suspensions. The degree of correlation between disseminated DEN infection rates in Houston Ae. albopictus and transmission to an in vitro system ranged from 42 to 88% for the four DEN serotypes. No significant difference was noted in YF virus infection rates or transmission rates in the two mosquito species fed on the same virus suspensions and incubated for the same time period. Also, RR virus infection and transmission rates in Houston and Hawaiian strains of Ae. albopictus were generally comparable.
Asunto(s)
Aedes/microbiología , Alphavirus/aislamiento & purificación , Virus del Dengue/aislamiento & purificación , Insectos Vectores , Virus del Río Ross/aislamiento & purificación , Virus de la Fiebre Amarilla/aislamiento & purificación , Aedes/inmunología , Animales , Antígenos Virales/análisis , Virus del Dengue/clasificación , Femenino , Ratones , Serotipificación , Texas , Infecciones por Togaviridae/transmisión , Fiebre Amarilla/transmisiónRESUMEN
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.
Asunto(s)
Arbovirus/aislamiento & purificación , Culicidae/microbiología , Encefalomielitis Equina/transmisión , Aedes/microbiología , Animales , Anopheles/microbiología , Argentina , Virus de la Encefalitis de San Luis/aislamiento & purificación , Virus de la Encefalitis Equina Venezolana/aislamiento & purificación , Virus de la Encefalitis Equina del Oeste/aislamiento & purificación , Insectos Vectores/microbiologíaRESUMEN
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.
Asunto(s)
Virus Bunyamwera/aislamiento & purificación , Bunyaviridae/aislamiento & purificación , Virus de la Encefalitis de California/aislamiento & purificación , Encefalomielitis Equina/microbiología , Enfermedades de los Caballos/microbiología , Virus de la Estomatitis Vesicular Indiana/aislamiento & purificación , Animales , Argentina , Pruebas de Fijación del Complemento , Culex/microbiología , Culicidae/microbiología , Encefalomielitis Equina/veterinaria , Femenino , Técnica del Anticuerpo Fluorescente , Caballos/microbiología , Humanos , Pruebas de Neutralización , Células Vero/microbiología , Ensayo de Placa ViralAsunto(s)
Culicidae/microbiología , Insectos Vectores/microbiología , Meningoencefalitis/transmisión , Animales , Arbovirus/aislamiento & purificación , Pollos , Virus de la Encefalitis/aislamiento & purificación , Femenino , Mordeduras y Picaduras de Insectos , Meningoencefalitis/microbiología , Ensayo de Placa ViralRESUMEN
Prospective surveys for arboviruses were carried out in Santa Fe, Corrientes, and Chaco provinces, Argentina, aperiodically during 1977-1980. A total of 313,233 mosquitoes and 598 biting flies other than mosquitoes were collected and tested for virus in 5,197 and 45 pools, respectively. Forty virus strains were isolated, all from mosquitoes, as follows: Santa Fe Province: 4 Gamboa group viruses from Aedeomyia squamipennis, 1 strain each of St. Louis encephalitis virus from Culex pipiens quinquefasciatus and Culex (Culex) spp.; Corrientes Province: a single strain of a newly discovered Anopheles A serogroup virus, Las Maloyas, from Anopheles albitarsis; and Chaco Province: 4 Gamboa group viruses from Ad. squamipennis, 6 strains of new Bunyaviridae (1 Antequera, 1 Barranqueras, and 4 Resistencia) from Culex (Melanoconion) delpontei, 3 strains of a new subtype of western equine encephalitis virus and 1 strain of Para virus from the Cx. (Mel.) ocossa group, 12 strains of a newly discovered subtype (VI) of the Venezuelan equine encephalitis complex from Cx. (Mel.) delpontei, and 1 strain each from Ad. squamipennis, Aedes scapularis, Ae. spp., Cx. (Cux.) spp., Cx. (Mel.) ocossa group, Mansonia spp., and Psorophora spp. Bloodmeals from 265 engorged mosquitoes were identified by precipitin test. These data, coupled with data on engorgement rates for 25,995 mosquitoes from bait collections, provide information on the host feeding patterns of several mosquito species. This information is discussed, along with data on relative abundance of mosquito species, within the context of the vector relationships of the species from which viruses were isolated. The association of Cx. (Mel.) delpontei with 18 strains of 4 different viruses in Chaco Province, plus its catholic feeding habits, clearly indicate for the first time the importance of this species as an arbovirus vector.
Asunto(s)
Arbovirus/aislamiento & purificación , Artrópodos/microbiología , Culicidae/microbiología , Aedes/microbiología , Animales , Anopheles/microbiología , Argentina , Aves/microbiología , Sangre/microbiología , Bunyaviridae/aislamiento & purificación , Pollos/inmunología , Cricetinae , Culex/microbiología , Virus de la Encefalitis Equina Venezolana/aislamiento & purificación , Virus de la Encefalitis Equina del Oeste/aislamiento & purificación , Femenino , Sueros Inmunes/inmunología , Masculino , Ratones , Conejos/inmunologíaRESUMEN
Forty viruses isolated from mosquitoes between 1977 and 1980 in Argentina have been identified and characterized. Nineteen strains of VEE virus, identical by neutralization (N) tests, were shown by hemagglutination-inhibition tests with anti-E2 glycoprotein sera to represent a new subtype VI of the VEE complex. RNA oligonucleotide fingerprints of this virus were distinct from subtype I viruses. The virus was not lethal for English short-haired guinea pigs, indicating that it is probably not equine-virulent. Three strains of a member of the WEE virus complex were shown to differ by N tests in 1 direction from prototype WEE virus. The new WEE subtype was also found to be distinct by RNA oligonucleotide mapping. Its vector relationships indicate that it is an enzootic virus, and it has not been associated with equine disease. A new member of the Anopheles A serogroup was identified, shown to be most closely related to Lukuni and Col An 57389 viruses, and given the name Las Maloyas virus. A strain of Para virus (Bunyaviridae, Bunyavirus) was identified. Six isolates, representing 3 new viruses morphologically resembling bunyaviruses are described; the names Antequera, Barranqueras, and Resistencia are proposed for these agents, which were all isolated from Culex (Melanoconion) delpontei in Chaco Province. No serologic relationships between these viruses and other bunyaviruses were found. Since they are antigenically interrelated, they form a new (Antequera) serogroup. Eight Gamboa serogroup viruses and 2 strains of St. Louis encephalitis virus were also identified.
Asunto(s)
Arbovirus/aislamiento & purificación , Bunyaviridae/aislamiento & purificación , Virus de la Encefalitis Equina Venezolana/aislamiento & purificación , Virus de la Encefalitis Equina del Oeste/aislamiento & purificación , Aedes/microbiología , Alphavirus/inmunología , Animales , Anopheles/microbiología , Arbovirus/genética , Argentina , Bunyaviridae/genética , Pruebas de Fijación del Complemento , Cricetinae , Culex/microbiología , Culicidae/microbiología , Patos , Virus de la Encefalitis Equina Venezolana/genética , Virus de la Encefalitis Equina del Oeste/genética , Cobayas , Pruebas de Inhibición de Hemaglutinación , Sueros Inmunes/inmunología , Insectos Vectores/microbiología , Ratones/inmunología , Pruebas de Neutralización , ARN Viral/aislamiento & purificación , Conejos/inmunología , Ensayo de Placa ViralRESUMEN
Serologic surveys of wild and domestic birds, wild mammals, and horses were conducted during arbovirus field studies in Argentina from 1977 through 1980, a non-epizootic interval. The prevalence of neutralizing antibodies to eastern equine encephalitis (EEE) was consistently higher than to western equine encephalitis (WEE) virus in all species and all areas. The presence of antibodies in short-lived avian species and in young unvaccinated horses and the demonstration of seroconversions in horses during the period, indicated that these viruses are either enzootic in, or annually reintroduced into, Argentina. Antibodies to AG80-646, a new subtype of WEE virus isolated in the subtropical north (Chaco Province) from Culex (Melanoconion) mosquitoes, were found in horses and rodents in that region. Antibodies to the TC-83 strain of Venezuelan equine encephalitis (VEE) virus were found in all areas studied. The presence of antibodies in some horses was probably related to vaccination, but the demonstration of seroconversions in sentinel horses and of antibodies in birds and wild mammals indicates active transmission of VEE virus. In 1980 a new enzootic subtype of VEE virus (AG80-663) was isolated from mosquitoes in Chaco; neutralizing antibodies to this virus were prevalent in horses and rodents in this area. Infections with Aura and Una viruses were most common in the subtropical northern provinces. Infection with St. Louis encephalitis was prevalent and widespread, and birds, principally passerine and columbiform species, appear to be the principal hosts. An interesting and unexplained finding was the absence of arbovirus antibodies, in particular SLE antibodies in house sparrows (Passer domesticus). Antibody prevalences in horses exceeded 50% in all areas, and 12% of horses surveyed in Santa Fe Province developed antibody in a 17-month period. Antibodies to other flaviviruses were rare. A high prevalence of immunity to Maguari virus was found in horses; this agent is considered to be a potential equine pathogen. Antibodies to 2 new viruses, Barranqueras and Resistencia, which had been isolated from Cx. (Melanoconion) in Chaco Province, were found in rodents there. Immunity to Gamboa group viruses was prevalent, and birds were implicated as principal hosts.
Asunto(s)
Arbovirus/fisiología , Alphavirus/inmunología , Animales , Animales Salvajes/microbiología , Anticuerpos Antivirales/inmunología , Infecciones por Arbovirus/inmunología , Infecciones por Arbovirus/microbiología , Infecciones por Arbovirus/veterinaria , Arbovirus/inmunología , Argentina , Aves/microbiología , Bunyaviridae/inmunología , Culex/microbiología , Culicidae/microbiología , Virus de la Encefalitis de San Luis/inmunología , Virus de la Encefalitis Equina Venezolana/inmunología , Virus de la Encefalitis Equina del Oeste/inmunología , Encefalitis de San Luis/veterinaria , Encefalomielitis Equina/veterinaria , Encefalomielitis Equina Venezolana/veterinaria , Flavivirus/inmunología , Cobayas/microbiología , Enfermedades de los Caballos/microbiología , Caballos/microbiología , Insectos Vectores/microbiología , Pruebas de Neutralización , Roedores/microbiología , Vacunación/veterinariaRESUMEN
This is the introductory paper to a series on the ecology of arboviruses in Argentina. Epizootics of equine encephalitis have occurred since at least 1908, principally in the Pampa and Espinal biogeographic zones, with significant economic losses; human cases of encephalitis have been rare or absent. Both western equine and eastern equine encephalitis viruses have been isolated from horses during these epizootics, but the mosquitoes responsible for transmission have not been identified. A number of isolations of Venezuelan equine encephalitis (VEE) virus were reported between 1936 and 1958 in Argentina, but the validity of these findings has been seriously questioned. Nevertheless, serological evidence exists for human infections with a member of the VEE virus complex. Serological surveys conducted in the 1960s indicate a high prevalence of infection of humans and domestic animals with St. Louis encephalitis (SLE), and 2 SLE virus strains have been isolated from rodents. Human disease, however, has rarely been associated with SLE infection. Only 7 isolations of other arboviruses have been described (3 of Maguari, 1 of Aura, 2 of Una, and 1 of an untyped Bunyamwera group virus). In 1977, we began longitudinal field studies in Santa Fe Province, the epicenter of previous equine epizootics, and in 1980 we extended these studies to Chaco and Corrientes provinces. The study sites are described in this paper.
Asunto(s)
Infecciones por Arbovirus/epidemiología , Animales , Infecciones por Arbovirus/microbiología , Arbovirus , Argentina , Aves , Bovinos , Niño , Clima , Ecología , Virus de la Encefalitis de San Luis , Virus de la Encefalitis Equina Venezolana , Virus de la Encefalitis Equina del Oeste , Encefalitis de San Luis/epidemiología , Encefalitis de San Luis/microbiología , Encefalomielitis Equina/epidemiología , Encefalomielitis Equina/microbiología , Encefalomielitis Equina/veterinaria , Encefalomielitis Equina Venezolana/epidemiología , Encefalomielitis Equina Venezolana/microbiología , Encefalomielitis Equina Venezolana/veterinaria , Geografía , Enfermedades de los Caballos/epidemiología , Enfermedades de los Caballos/microbiología , Caballos/microbiología , HumanosRESUMEN
A large net trap was used to sample mosquito populations attracted to horses at three sites each in Santa Fe and Rio Negro Provinces, Argentina, during the austral summer of 1984. These provinces, as well as others in Argentina, were affected by a severe epizootic of western equine encephalitis (WEE) during 1982-83. Totals of 2,752 and 6,929 mosquitoes were collected in Santa Fe and Rio Negro Provinces during five and three trap nights, respectively. Culex mosquitoes of the subgenus Culex were predominant (45.8% of total) in the Santa Fe collections, although Aedes albifasciatus also was prevalent (21.7%). The latter species was predominant (95.7% of total) in the Rio Negro collections. The mosquito fauna was less complex (minimum of 6 species) in Rio Negro Province as compared to Santa Fe Province (minimum of 18 species). The advantages of the net trap indicate that this trap can become a useful tool in arbovirus ecology studies in other areas.