This is the second of three papers describing the use of electron microscopy and antigenic analyses intended to characterize and place in taxa more than 60 previously unclassified viruses. The first paper of the series describes the viruses we classified as provisional members of the families Arenaviridae, Paramyxoviridae, or Poxviridae; another paper, published separately, discusses the Rhabdoviridae. In this paper we report that electron microscopy provided sufficient evidence to place 17 of these viruses (Belem, Erve, Estero Real, Mojui dos Campos, Nyando, Odrenisrou, Okola, Pacora, Para, Santarem, Tanga, Telok Forest, Termeil, Thiafora, Thottapalayam, Wanowrie, and Yacaaba) in the family Bunyaviridae and to support the observations of others that Yogue and Kasokero viruses are members of this virus family. Subsequent antigenic studies allowed us to place some of these viruses in recognized antigenic groups and to establish new antigenic groups for others.
During approximately 35 years, investigators in various laboratories studying arbovirus ecology and epidemiology accumulated many virus isolates, more than 60 of which were not characterized or placed in taxa. By a combination of electron microscopic and antigenic studies we collected information sufficient to provisionally classify 60 isolates. Electron microscopic observations suggest that 20 are members of the virus family Bunyaviridae, 20 Rhabdoviridae, 14 Reoviridae, one Togaviridae, one Paramyxoviridae (Mapuera virus, from a bat), and one Poxviridae (Yoka virus, from mosquitoes). Serologic studies provided evidence sufficient to place some of these viruses in recognized antigenic groups, within families and genera, and to establish new antigenic groups and taxa for others. Three viruses were found to have morphologic and morphogenetic characteristics consistent with those of members of the family Arenaviridae: Quaranfil virus, a human pathogen, Johnston Atoll virus, isolated from birds and ticks, and Araguari virus, isolated from an opossum. This, the first in a series of three papers, described methods used for these investigations and also presents descriptions of viruses provisionally placed in the families Arenaviridae, Paramyxoviridae, or Poxviridae. Descriptions of viruses provisionally placed in families Bunyaviridae and Reoviridae are published in the second and third papers, respectively. Viruses of the family Rhabdoviridae have been described separately.
A major epidemic of Venezuelan equine encephalitis occurred in south Texas in the summer of 1971. More than 1500 equines died of VEE in Texas, and 110 human cases with no deaths were reported. Vector studies in south Texas and northern Tamaulipas revealed that the overall mosquito infection rates during the peak of the epidemic were about 1:100, one of the highest rates observed for a major epidemic. Mosquito infection rates of this magnitude could easily explain the intensity of VEE outbreaks in both equines and man. A total of 943 VEE virus isolations were made from mosquitoes. Eight of the 12 mosquito species found infected were implicated in the epidemic cycle of VEE for the first time. Sufficient laboratory and field evidence is available to prove that Psorophora confinnis was one of the primary vectors of VEE. The lack of laboratory evidence necessitates the use of the term "probable" primary vectors for other species apparently equally as involved on the basis of field infections; these include Aedes sollicitans, Aedes thelcter and Psorophora discolor. Eight other species from which less than 10 VEE virus isolations were made were considered auxiliary vectors. Mosquitoes of some species were tested individually; such tests showed 2-4% of the probable primary vectors to be infected. The first isolation of VEE virus of the epidemic was made from P. confinnis on June 28, 1971. Highest mosquito infection rates occurred during the week of July 5. Mosquito infection rates declined precipitously in the last 3 weeks of July 1971, signaling the end of the epidemic in the study area. One explanation for the decline was that equines, the principal epidemic hosts, were eliminated as a source of virus by death or by acquisition of natural or induced immunity. Mosquito control appeared to be effective in reducing the infected mosquito population while the immunization of equines with TC 83 VEE vaccine was accomplished. Quarantines appeared to be effective in restricting the VEE virus activity to south Texas. Undoubtedly all of the control measures contributed to stopping the epidemic. Continued VEE surveillance by various government and other agencies failed to reveal any further epidemic VEE activity in the US in 1972. Other arboviruses isolated during the VEE studies in south Texas included St. Louis encephalitis virus, and San Angelo subtype of the California Group. A virus of the Bunyamwera Group was also isolated from Palo Blanco, Tamaulipas.
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