The presence or absence of the biting midge Culicoides sonorensis Wirth & Jones (Diptera: Ceratopogonidae), a primary vector of bluetongue viruses (genus Orbivirus, family Reoviridae, BTV) in North America, was assessed on ranches and farms across the Northern Great Plains region of the United States, specifically Nebraska, South Dakota, and North Dakota, as part of a 2-yr regional study of BTV exposure among cattle. Blacklight/suction trap samples totaling 280 2-night intervals were taken at 140 aquatic sites (potential larval habitat for C. sonorensis) on 82 livestock operations (ranches and farms) that span a south-to-north gradient of expected decreasing risk for exposure to BTV. In Nebraska, C. sonorensis populations were common and widespread, present at 15 of 18 operations. Of 32 operations sampled in South Dakota, seven of which were sampled in successive years, 18 were positive for C. sonorensis; 13 of 14 operations located west of the Missouri River were positive, whereas 13 of 18 operations east of the river were negative. Of 32 operations sampled in North Dakota, seven of which were sampled both years, 12 were positive for C. sonorensis. Six of eight operations located west and south of the Missouri River in North Dakota were positive, whereas 18 of 24 operations east and north of the river were negative for C. sonorensis. These data illustrate a well-defined pattern of C. sonorensis spatial distribution, with populations consistently present across Nebraska, western South Dakota, and western North Dakota; western South Dakota, and North Dakota encompass the Northwestern Plains Ecoregion where soils are nonglaciated and evaporation exceeds precipitation. In contrast, C. sonorensis populations were largely absent east of the Missouri River in South Dakota and North Dakota; this area comprises the Northwestern Glaciated Plains Ecoregion and Northern Glaciated Plains Ecoregion where surface soils reflect Wisconsinan glaciation and precipitation exceeds evaporation. In defining a well-demarcated pattern of population presence or absence on a regional scale, the data suggest that biogeographic factors regulate the distribution of C. sonorensis and in turn BTV exposure. These factors, ostensibly climate and soil type as they affect the suitability of larval habitat, may explain the absence of C. sonorensis, hence limited risk for exposure to BTV, across the eastern Northern Plains, upper Midwest, and possibly Northeast, regions of the United States.

Bluetongue (BT) was first reported more than 125 years ago when European breeds of sheep were introduced into southern Africa. BT viruses (BTV) have been identified in many tropical and temperate areas of the world. BT, the disease, is a phenomenon of ruminants in the temperate zones. There is little clinical disease in the tropical and subtropical areas of the world. At least 24 serotypes of BTV have been described. While the viruses are classified antigenically and taxonomically as BTV, each serotype is unique and may not cause BT, the disease. The BTVs are transmitted among ruminants by competent vector species of the genus Culicoides, i.e. biting gnats or midges. BTV serotypes exist with vector species of Culicoides in predictable, but finite, geographic and ecological cycles or ecosystems around the world. Despite the almost certain movement of livestock and Culicoides species between these ecosystems, there is little evidence that introduced BTV serotypes have been established in these ecosystems. Rather, periodic cyclic extensions and remissions of these virus-vector ecosystems permit the viruses and the disease to move into and recede from adjacent non-endemic areas in a pattern characteristic of many other known arthropod-borne viruses (arboviruses).Earlier publications suggested that a carrier state occurred in cattle infected as foetuses with BTV. No subsequent natural experiences or research support the hypothesis which has not been validated. The conclusions of the research are not accepted by the scientific community. It is logical, therefore, to propose that regulatory restrictions against the movement of cattle from BTV-affected countries be relaxed or eliminated.

Equine Veterinary EducationVolume 8, Issue S2 p. 39-41 Venezuelan equine encephalomyelitis T. E. Walton, United States Department of Agriculture, Agricultural Research Service, Arthropod-borne Animal Diseases Research Laboratory, PO Box 3965, University Station, Laramie, Wyoming 82071–3965, USA. USDA, ARS, National Program Staff, BARC-West, Building 005, Room 203, Beltsville, Maryland, 20705, USA.Search for more papers by this author T. E. Walton, United States Department of Agriculture, Agricultural Research Service, Arthropod-borne Animal Diseases Research Laboratory, PO Box 3965, University Station, Laramie, Wyoming 82071–3965, USA. USDA, ARS, National Program Staff, BARC-West, Building 005, Room 203, Beltsville, Maryland, 20705, USA.Search for more papers by this author First published: September 1996 https://doi.org/10.1111/j.2042-3292.1996.tb01854.x AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Volume8, IssueS2September 1996Pages 39-41 RelatedInformation

A study of the epidemiology of bluetongue viruses is in progress with the collaboration of 11 Central American and Caribbean countries. To date, over 200 bluetongue virus isolates have been obtained from cattle and sheep in sentinel groups distributed in the participating countries. Bluetongue serotypes identified include 1, 3, 6, and 12, virus types not previously recorded in the Western Hemisphere. Although the clinical impact of bluetongue virus infections in this hyperendemic environment appears to be minimal, the ubiquity of infection causes restrictions on the export of ruminant livestock and germ plasm. The stability of the Caribbean region ecosystem and the long-range implications of the interface with the northern temperate bluetongue virus ecosystem are reviewed.

The arthropod-borne virus (arbovirus) diseases of livestock have worldwide impact. The prevention of an introduction of an exotic disease and the control of one subsequent to an introduction will require the attention, cooperation, and support of the livestock industry, regulatory agencies, and researchers. The most effective protection of our livestock industries is to prevent the introduction of an exotic disease agent. This implies complete restriction of animal imports and exports. However, "zero risk" is an unacceptable option in today's world of internationally integrated and interdependent agriculture. Scientifically sound and factually based regulatory decisions must be combined with continued vigilance and preparedness, as well as appropriately directed surveillance and research, to protect the world agricultural marketplace. Two exotic arbovirus diseases that are of current concern to the livestock industries and regulatory officials of the North American and Caribbean Basin countries are VEE and AHS. Devastating epizootics of VEE in equines have occurred frequently in the Western Hemisphere, but no recent epizootic activity has been documented. Naturally occurring foci of sylvatic, equine nonpathogenic VEE virus subtypes, however, do exist in the tropical countries of the hemisphere. The relationship of these sylvatic virus foci to the origin of equine virulent epizootic VEE virus subtypes is unknown. AHS epizootics had been confined to Africa, the Middle East, and the Indian subcontinent until recent outbreaks in 1966 and 1987-1990 in Spain. With the recurrence of AHS in Spain for the past four years, concern about the possible introduction into potential vector species and equines in the Western Hemisphere has increased. This review addresses the current VEE and AHS virus activity and the potential for outbreaks in the Western Hemisphere.