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Approximately 250 isolates of a newly recognized virus, related to western equine encephalitis virus (family Togaviridae, genus Alphavirus), were obtained from cimicid bugs, Oeciacus vicarius; Cliff Swallows, Hirundo pyrrhonata; and House Sparrows, Passer domesticus in a study area in west-central Oklahoma at Buggy Creek and Caddo Canyons. Antigenicity of the virus strains varied slightly from isolate to isolate. This paper summarizes the ecology of the area by describing in general the flora and fauna there.

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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.

The ability of the sibling species Culex pipiens (L.) and Culex torrentium (Martini) from central Sweden to transmit Ockelbo (OCK) virus was determined. Both species became infected after ingesting OCK virus from a viremic chicken; they transmitted this virus to chickens after 21-28 d of extrinsic incubation. In Cx. torrentium, infection rates were 90% or higher, and all 10 refeeding mosquitoes transmitted virus after feeding on chickens with a viremia of at least 10(3.0) plaque-forming units (PFU)/ml. In contrast, only 1 of 28 (4%) of the Cx. pipiens that ingested blood containing 10(3.0-3.9) PFU/ml became infected, and none of 16 refeeding mosquitoes transmitted virus. However, 98 of 184 (53%) of the Cx. pipiens that ingested a blood meal containing at least 10(6.0) PFU/ml became infected. Transmission rates in Cx. pipiens increased with increasing virus concentration in the blood meal to a maximum of 37% in mosquitoes that ingested greater than 10(8.0) PFU/ml. Based on these data, both Cx. pipiens and Cx. torrentium are capable of transmitting OCK virus in an enzootic cycle involving birds as hosts. However, Cx. torrentium appears to be physiologically a more efficient vector than Cx. pipiens.

During 1973 and 1974, we looked for cases of Colorado tick fever throughout Colorado; 228 cases were identified. Although 90% of the patients reported exposure to ticks before illness, only 52% were aware of an actual tick bite. Typical symptoms of fever, myalgia, and headache were common, but gastrointestinal symptoms were also prominent in 20% of the patients. Twenty percent were hospitalized; no deaths or permanent sequelae were noted. Persistent viremia (greater than or equal to 4 weeks) was found in about half of the cases; this finding was not associated with the occurrence of prolonged symptoms (greater than or equal to 3 weeks), which were also reported in half of the cases. One patient became reinfected with the virus. Increasing tourism in endemic areas and the frequent occurrence of prolonged or biphasic illnesses provide the potential for patients with Colorado tick fever to seek medical care anywhere in the United States.

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Field studies were conducted during an epizootic of vesicular stomatitis virus (VSV) in Colorado to further assess the possible role of insects in the transmission of VSV. Insects associated with domestic livestock were collected at 11 premises along the Front Range of the Rocky Mountains in Colorado during the 1982 epizootic of vesicular stomatitis. Insects were pooled by date, location, species, and sex and were processed for virus isolation in three cell culture systems. Thirty-four isolates of vesicular stomatitis virus, New Jersey serotype, were obtained from 51,036 insects. Of these, 27 isolates were from Musca domestica (126 pools/5,285 specimens), 5 from other nonhematophagous Diptera (56 pools/936 specimens), and 2 from unengorged black flies (Simuliidae) (55 pools/1,221 specimens). Results suggest that nonblood-feeding insects, such as houseflies, play a role in VSV transmission and that black flies also serve as vectors. KEY WORDS Insecta, VSV, VSV from nonhematophagous insects, VSV from Simuliidae VESICULAR STOMATITIS (VS) is a disease of cattle, horses, swine, and various wild vertebrates; it is caused by several viruses of the family Rhabdoviridae, genus Vesiculovirus, found in North and South America and Asia (Yuill 1981). VS is enzootic in the tropical and subtropical regions of the Americas, but it can spread northward into the United States and Canada during the summer months, appearing first in states along the Gulf of Mexico in April or May and later as far north as Manitoba, Canada. The natural history of VS virus in North America, including endemic maintenance and epizootic transmission, remains uncertain despite many years of study. Outbreaks often have appeared more or less simultaneously within a broad geographical area. The seasonal occurrence of disease and the spotty geographic distribution of cases suggest insect transmission. VS Indiana (VSI) virus has been isolated frequently from sand flies (Diptera: Psychodidae) caught in the wild in tropical America (Yuill 1981) and from mosquitoes (Diptera: Culicidae) collected in New Mexico (Sudia et al. 1967). Replication of the virus and transmission by bite have been demonstrated in sand flies (Tesh et al. 1971), and high rates of vertical (transovarial) transmission also have been found (Tesh et al. 1972). The New Jersey serotype (VSNJ) has been isolated from black flies (Diptera: Simuliidae) in Colombia (Theiler & Downs 1973) and from mosquitoes collected in Ecuador (Calisher et al. 1983) and Guatemala (C.H.C., unpublished data). Dur