Distribution of Culicoides sonorensis (Diptera: Ceratopogonidae) in Nebraska, South Dakota, and North Dakota: clarifying the epidemiology of bluetongue disease in the northern Great Plains region of the United States.

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.

The impact of diseases on the importation of animals and animal products.

For decades the veterinary services of the United States and other nations protected their livestock and poultry industries from the ravages of introduced animal diseases by rigorous import restrictions. This policy of zero risk frequently translated to no or reduced trade in animals and animal products or dramatic trade inequities. However, GATT articles enforced by the WTO require that imported products be treated no less favorably than domestically produced goods with regard to animal health restrictions. Under authority from the WTO, the OIE establishes recommendations and guidelines for the regulation of trade in animals and products of animal origin through the OIE International Animal Health Code, sets animal health standards, and reports global animal health situations and statuses. Diseases often have a dramatic impact on the animal agricultural industries of a nation--disease outbreaks may be deleterious to the competitiveness of the products of one nation but offer opportunities for others. The potential dangers of lax vigilance, insufficient scientifically valid data, inadequate SPS measures, and errors in assessing risk can turn the heady experience of seemingly unlimited growth in international markets and demand for one's products into a catastrophic return to reality. The experience of the United Kingdom and countries of Europe with bovine spongiform encephalopathy is a case in point. It is estimated that the cost of the outbreak of this disease to the economy of the UK has been more than $3 billion. Responses of their trading partners, including the US, to this outbreak were abrupt and restrictive. Although the decision was controversial, the US stopped importation of live cattle from the UK in the late 1980's and subsequently, in 1997, importation of all products of ruminant origin was stopped from all countries of Europe. The transmission of the disease to continental Europe and the disclosure that the pathogen was associated with a fatal human illness, rocked consumer confidence in the safety of the UK beef supply, brought down the ruling political party in the UK, and forced major changes in the beef industry.

Venezuelan equine encephalomyelitis and African horse sickness. Current status and review.

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.

Epidemiology of bluetongue viruses in the American tropics. Regional Bluetongue Team.

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.

Overwintering mechanism for bluetongue virus: biological recovery of latent virus from a bovine by bites of Culicoides variipennis.

Bluetongue virus (BTV) was biologically transmitted by the bites of colonized Culicoides variipennis gnats to recipient sheep from a Hereford bull with latent infection. Four biological recoveries of BTV were mediated over 2 years by multiple feedings of the vector during a 4- to 72-hour interval. Initial stimulation by gnat bites at 0 hour permitted biological recovery of BTV by gnats that fed at later intervals. The 4th biological recovery of the virus from the bull clearly indicated a vector-mediated viral recovery mechanism in which initial vector bites at 0 hours stimulated a "showering" of BTV into the blood stream of the bull. The BTV carrier bull developed no overt signs of illness during these studies. The pertinent BTV assay and serologic results for the 4 1/3 years of the bull's life are summarized in this report.

Epizootic vesicular stomatitis in Colorado, 1982: epidemiologic studies along the northern Colorado front range.

Epidemiologic evaluations were made of farm personnel on vesicular stomatitis-affected premises along the front range of the Rocky Mountains in Colorado during the 1982 epizootic. A similar antibody prevalence was noted to that of veterinarians and research and regulatory personnel who were involved with the same epizootic. Risk of infection resulted from intimate physical contact with infected horses or cows. Incidence and infection rates in horses were 45%; rates in cows were much lower, only 5%. Some epidemiologic clues were gained by a detailed study of an equine ranch. The pasture was incriminated as the area of highest risk, where 100% infection rates were noted. Horses in open pens and barns were at lower risk. Severe clinical disease in horses resulted in higher neutralizing antibody titers than inapparent or mild infection. Maternal antibody was detected in foals up to 4 months of age, and the level of antibody in the foal was a reflection of the dam's antibody level.

Epizootic vesicular stomatitis in Colorado, 1982: epidemiologic and entomologic studies.

An epizootic of vesicular stomatitis (VS) caused by the New Jersey serotype of VS virus affected livestock and humans in 14 western states in 1982-1983. Epidemiological observations were made on at least 10% of the cattle in 4 dairy herds that were located in the vicinity of Grand Junction, Colorado. High rates of neutralizing antibody to the New Jersey serotype were seen in all cattle regardless of whether livestock in the dairy had clinical VS or a decrease in mild production. Antibody titers remained high in these cattle for as long as 2 years after the epizootic. No virus isolations were made from 32 humans with clinical signs compatible with viral disease. Entomological information was obtained during the epizootic from 23 premises in northwestern Colorado. Insect collections yielded 4 isolates from Culicoides spp. midges, 2 from C. variipennis, and 1 each from C. stellifer and C. (Selfia) spp. This is the first report of VS virus isolations from field-collected Culicoides.

Electrophoretic comparison of the genomes of North American bluetongue viruses, one Australian bluetongue virus, and three other related orbiviruses.

The genomes of U.S. bluetongue viruses, an Australian bluetongue virus, and three other related orbiviruses were analyzed by polyacrylamide gel electrophoresis. The genomes were comprised of ten segments of double-stranded (ds) RNA. Estimates of the molecular weights of the dsRNA segments revealed that the U.S. bluetongue serotypes were remarkably similar. Although the dsRNA profiles of the viruses exhibited common segments, each virus had a distinct dsRNA profile. The usefulness of the genome analysis as a diagnostic tool for identification and for epidemiologic studies is discussed.

Isolation of arboviruses from Culicoides midges (Diptera: Ceratopogonidae) in Colorado during an epizootic of vesicular stomatitis New Jersey.

An arbovirus survey was conducted in Colorado and Utah during an epizootic of vesicular stomatitis New Jersey (VSNJ) that occurred in the western United States in 1982-1983. From 120,422 insect specimens assayed, 106 viruses were isolated. Four were rhabdoviruses (VSNJ), three were orbiviruses (bluetongue serotype-11), 92 were Bunyamwera group (65 Main Drain and 27 Lokern), and seven were Simbu group (Buttonwillow) bunyaviruses. Culicoides spp. accounted for 105 viral isolates (C. (Selfia) spp., C. variipennis (Coquillett), C. stellifer (Coquillett), and C. cockerellii (Coquillett], and one was from Simulium bivittatum Malloch. C. (Selfia) spp. accounted for 59% of all pooled specimens and was the source of 89.6% (95) of the isolates. Insects from two sites accounted for 44% (52,802) of all pooled specimens and 67% (71) of the viral isolates. The isolations of VSNJ, Main Drain, Lokern, and Buttonwillow viruses from C. (Selfia) spp. are the first arbovirus isolations reported for this subgenus; this is the first time these viruses have been isolated from Culicoides species other than C. variipennis.

Venezuelan equine encephalomyelitis virus: concentration, partial purification, inactivation and immunogenicity.

Venezuelan equine encephalomyelitis (VEE) TC-84 vaccinal virus, from 10-1. quantities of infected duck embryo fibroblast cell culture fluids, was isolated by combined continuous-flow centrifugation with isopycnic banding in sucrose. Most of the recovered infectivity and hemagglutinating activity were in a single band at a buoyant density (rho) of 1.2. About 90% of the total input protein (450-520 mg) was removed with the effluent, whereas most of the remaining 10% also banded at a rho of 1.2. Infectivity was inactivated with formalin at a final concentration of 0.05% at 37 degrees C for 24 hr. Formalin-inactivated virus retained its immunogenicity and induced VEE virus-specific antibody in horses and guinea pigs. The horses and those guinea pigs that received equivalent doses of vaccine survived after a challenge of their immunity with virulent VEE virus.

Efficacy of trivalent inactivated encephalomyelitis virus vaccine in horses.

Twenty-nine horses were vaccinated with a trivalent (Venezuelan, eastern, and western) inactivated equine encephalomyelitis virus vaccine. The vaccine purchased for this study was the only one licensed and commercially available in May, 1975. Plaque-neutralizing and hemagglutinin-inhibiting antibodies in response to each of the 3 equine encephalomyelitis viruses were determined after vaccination. Horses had rising levels of plaque-neutralizing and hemagglutinin-inhibiting antibodies shortly after injection with the 1st and 2nd doses of the vaccine (given 3 weeks apart) and were refractory to challenge of immunity with virulent homologous virus at 3, 8, and 12 months after vaccination. After 12 months, 8 horses were revaccinated; maximum antigenic stimulation was achieved with the 1st dose of the 2nd series of vaccinations.

Bluetongue virus in bovine semen: viral isolation.

Vero cell cultures and embryonating chicken eggs were used for direct isolation of bluetongue virus from cattle blood and from semen samples. Cell culture and embryonating chicken eggs each were more effective than was the blood autograft inoculation of susceptible sheep with selected blood and semen samples. Evaluation of the cell culture technique indicated that the quality of the distilled water was the primary factor responsible for the increased sensitivity of the Vero cell cultures for the present blue-tongue viral isolations. Test results showed that urine was a poor specimen for viral isolation when assayed in chicken eggs. A comparison of tests for precipitating and complement-fixing antibodies to bluetongue virus indicated that the precipitin test was the more accurate of the two tests.

Experimentally induced infection with bluetongue virus serotype 11 in cows.

The consequences of inoculation of bluetongue virus (BTV) serotype 11 into 16 susceptible cows either at the time of breeding or at specified stages of pregnancy were studied. The cows were free of BTV or epizootic hemorrhagic disease virus, and none had antibodies to BTV before virus inoculation. A group of 4 cows was mated naturally to a bull reported to shed BTV-11 (CO75B300 strain) in the semen. The bull was suspected of infecting cows at mating with BTV-11, which subsequently transplacentally infected the developing fetuses and induced persistently infected and congenitally malformed progeny. Two groups of 4 pregnant cows were inoculated with an insect-derived strain of BTV-11 (CO75B300), one group by direct deposit into the uterus at estrus, the other, by intradermal and SC administrations. A 90-day fetus was inoculated in utero with virus from the same pool. Four pregnant cows were inoculated with sheep blood-passaged virus of the same BTV-11 strain (CO75B300) by intradermal and SC routes. Three cows were inoculated with BTV-free suspending fluids and ovine erythrocytes by the intrauterine and intradermal-SC routes and were used as in-contact controls. Infection with insect-derived BTV-11 was confirmed in 3 cows of 1 group by virus isolation and by detection of serum antibodies. The 4 cows inoculated with sheep blood suspension of BTV-11 developed viremia and produced antibodies to the virus. None of the cattle had clinical signs of bluetongue, other than 2 cows that had a slight rectal temperature increase on postinoculation day 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Bluetongue virus infection in pregnant ewes.

Inoculation of 53 ewes after 35, 45, 60, or 80 days of gestation with bluetongue virus serotypes 10, 11, 13, or 17, or with epizootic hemorrhagic disease virus serotypes 1 or 2, resulted in overt clinical disease in the 47 ewes inoculated with bluetongue virus but not in the 6 ewes inoculated with epizootic hemorrhagic disease virus. None of the lambs produced by these ewes had developmental defects or any evidence of persistence of viremia.

Abnormalities and virus-like particles in spermatozoa from bulls latently infected with bluetongue virus.

Abnormalities were commonly observed in spermatozoa, and bluetongue virus (BTV) was isolated from semen of 2 known BTV carrier bulls and 2 of 4 BTV seropositive field bulls. The spermatozoal abnormalities ranged from a small cavity between the acrosome and nucleus with some involvement of the nucleus, to an enlargement of the cavity accompanied by vesiculation that could affect the entire acrosome. Virus-like particles were occasionally observed in the affected spermatozoa, but were present in all samples. A positive relationship was found between infectivity of semen samples from BTV latently infected bulls and the observation of abnormalities and virus-like particles in the heads of affected spermatozoa.

Temporal relationships of viremia, interferon activity, and antibody responses of sheep infected with several bluetongue virus strains.

Sheep had viremias that were first detected on day 3 (+/- 1) after infection with several strains of bluetongue virus (BTV) representing United States serotypes 10, 11, 13, and 17. Diphasic peaks of infectivity were attained on days 6 and 10 (+/- 2). Interferon (IFN) was first detected in serum samples on day 5 (+/- 1), and reached greatest concentrations on day 6 (+/- 2), which coincided with the first viremic peak; IFN concentrations then decreased toward zero by day 10 (+/- 2). Interferon peak concentrations induced approximately a 90% decrease in virus titer. The decrease in IFN concentrations by day 9 (+/- 2) corresponded with the second viremic peak on day 10 (+/- 2). Onset of the decrease in detectable concentrations of virus after the second peak of viremia corresponded to the initial detection of serum antibody to BTV by day 10 (+/- 2). Virus titer decreased and antibody production increased until approximately days 21 to 28, when the titers plateaued and virus was not detected. Febrile responses peaked on day 7 (+/- 1) during the peak viremic period. The WBC count was depressed at the time the virus titer increased, but returned to normal values while the sheep were still viremic. Diphasic viremias in BTV-infected sheep were attributed to induction of high concentrations of IFN concurrent with the first virus titer peak, followed by production of antibody to specific BTV strains and a subsequent reduction in viremia at the second virus titer peak.

Cross-protective immunity between equine encephalomyelitis viruses in equids.

Eighteen equids were inoculated with eastern equine encephalomyelitis (EEE) and 18 equids with western equine encephalomyelitis (WEE) viruses to produce EEE virus- and WEE virus-immunized equids. Twelve surviving EEE virus-seropositive equids, 15 surviving WEE virus-seropositive equids, and 10 nonimmunized, seronegative equids (controls) were subsequently inoculated with an equine pathogenic (epizootic) strain of Venezuelan equine encephalomyelitis (VEE) virus to determine cross-protective immunity. Challenge infection produced 90% mortality in control (nonimmunized) equids, and 40% mortality in WEE virus-seropositive equids; all EEE virus-seropositive equids survived. Postchallenge exposure VEE viremia levels in EEE virus- or WEE virus-seropositive equids were lower than those in the 10 nonimmunized VEE virus-inoculated control equids. Plaque-neutralizing antibody responses to VEE virus in the EEE virus- and WEE virus-seropositive equids were similar in time of onset and titer to the antibody responses of nonimmunized equids. Neutralizing antibody to the third equine encephalomyelitis virus (either EEE virus or WEE virus) was detectable in 19 of 27 equids after inoculation with the challenge virus, VEE. Demonstration of cross-protective immunity between EEE or WEE virus and VEE virus in equids confirmed field observations made during the VEE epizootic in Texas in 1971.

Epizootic vesicular stomatitis in Colorado, 1982: some observations on the possible role of wildlife populations in an enzootic maintenance cycle.

Sera obtained from wild ungulates, carnivores, and rodents in Colorado were tested for neutralizing (N) antibody against vesicular stomatitis, New Jersey serotype (VSNJ), virus to determine their involvement in the 1982 Colorado VSNJ epizootic in domestic animals. Viremic and N antibody responses of two local rodent species to a 1982 Colorado isolate of VSNJ were determined in the laboratory. The rodents produced only weak viremias, but all developed N antibody. N antibody prevalences for VSNJ in sera from wild ungulates was sufficiently high to indicate their involvement during the epizootic. In addition, the demonstration of N antibody in elk (Cervus elaphus) and mule deer (Odocoileus hemionus) prior to the epizootic in cattle and horses suggests that an enzootic cycle may exist in Colorado.