Will K. Reeves

Evaluation of the efficacy, potential for vector transmission, and duration of immunity of MP-12, an attenuated Rift Valley fever virus vaccine candidate, in sheep

ABSTRACT Rift Valley fever virus (RVFV) causes serious disease in ruminants and humans in Africa. In North America, there are susceptible ruminant hosts and competent mosquito vectors, yet there are no fully licensed animal vaccines for this arthropod-borne virus, should it be introduced. Studies in sheep and cattle have found the attenuated strain of RVFV, MP-12, to be both safe and efficacious based on early testing, and a 2-year conditional license for use in U.S. livestock has been issued. The purpose of this study was to further determine the vaccines potential to infect mosquitoes, the duration of humoral immunity to 24 months postvaccination, and the ability to prevent disease and viremia from a virulent challenge. Vaccination experiments conducted in sheep found no evidence of a potential for vector transmission to 4 North American mosquito species. Neutralizing antibodies were elicited, with titers of >1:40 still present at 24 months postvaccination. Vaccinates were protected from clinical signs and detectable viremia after challenge with virulent virus, while control sheep had fever and high-titered viremia extending for 5 days. Antibodies to three viral proteins (nucleocapsid N, the N-terminal half of glycoprotein GN, and the nonstructural protein from the short segment NSs) were also detected to 24 months using competitive enzyme-linked immunosorbent assays. This study demonstrates that the MP-12 vaccine given as a single dose in sheep generates protective immunity to a virulent challenge with antibody duration of at least 2 years, with no evidence of a risk for vector transmission.

Investigation of a bluetongue disease epizootic caused by bluetongue virus serotype 17 in sheep in Wyoming

OBJECTIVE To characterize a 2007 bluetongue disease (BT) epizootic caused by bluetongue virus (BTV) serotype 17 in sheep in the Big Horn Basin of Wyoming. DESIGN Cross-sectional study. ANIMALS 1,359 sheep from ranches in Wyoming and Montana. PROCEDURES Information on clinical signs and history of BT in sheep was obtained from ranchers and attending veterinarians. At 3 to 6 months after the 2007 BT epizootic, blood samples were collected from rams, ewes, and lambs within and outside the Big Horn Basin; blood samples were also collected from lambs born in the spring of 2008. Sera were tested for anti-BTV antibodies by use of a competitive ELISA to determine the seroprevalence of BTV in sheep and to measure antibody titers. Virus isolation and reverse transcriptase PCR assays were used to determine long-term presence of the infectious virus or viral genetic material in RBCs of sheep. RESULTS The percentage of sheep seropositive for BTV closely matched morbidity of sheep within flocks, indicating few subclinical infections. Flocks separated by as little as 1 mile had substantial variation in infection rate. Rams were infected at a higher rate than ewes. There was no evidence of BTV successfully overwintering in the area. CONCLUSIONS AND CLINICAL RELEVANCE This epizootic appears to be a new intrusion of BTV into a naïve population of sheep previously protected geographically by the mountains surrounding the Big Horn Basin. Rams may have a higher infection rate as a result of increased vector biting opportunity because of the large surface area of the scrotum.

Control of Culicoides sonorensis (Diptera: Ceratopogonidae) Blood Feeding on Sheep with Long-Lasting Repellent Pesticides

Abstract Culicoides sonorensis is the primary vector of bluetongue and epizootic hemorrhagic disease viruses in North America. Bluetongue disease is one of the most economically important arthropod-borne diseases of sheep in North America, because it causes significant morbidity and mortality and can lead to local quarantines and international trade restrictions. Long-lasting repellent pesticides could be applied to sheep as they are moved down from mountain pastures to protect them from biting midges until the 1st frost. We tested long-lasting pesticides on sheep as repellents against C. sonorensis. Both PYthon ear tags with 10% zeta-cypermethrin (9.8 g/tag) synergized with 20% piperonyl butoxide (PBO) and a 12-ml low-volume spray application of ready-to-use sheep insecticide (Y-TEX) with 2.5% permethrin and 2.5% PBO in an oil-based formulation were repellent to C. sonorensis for at least 3–5 wk after a single application.

Epizootic Hemorrhagic Disease Outbreak in a Captive Facility Housing White-Tailed Deer (Odocoileus virginianus), Bison (Bison bison), Elk (Cervus elaphus), Cattle (Bos taurus), and Goats (Capra hircus) in Colorado, USA

Abstract An ungulate research facility in Fort Collins, Colorado, USA, experienced mortality in white-tailed deer (Odocoileus virginianus) because of epizootic hemorrhagic disease virus (EHDV) infection from 20 August 2007 through 26 September 2007. Epizootic hemorrhagic disease virus (EHDV) was detected by reverse transcriptase polymerase chain reaction and virus isolation from the spleen and lung tissues of two white-tailed deer. Virus neutralization tests were performed on pre- and postoutbreak sera from other species maintained in the same facility, including bison (Bison bison), elk (Cervus elaphus), domestic cattle (Bos taurus), and domestic goats (Capra hircus), as well as postoutbreak sera from the surviving white-tailed deer. Serum samples that represented all species in the facility neutralized EHDV-1 and EHDV-2 either before or after the outbreak. The animals that neutralized EHDV-1 did not neutralize EHDV-2. No clinical signs attributable to EHDV infection were noted in any of the species other than the deer during the outbreak. Although experimental EHDV infections have been reported in bison and elk, natural exposures have not been previously documented in these species in North America. The roles that elk, bison, cattle, and goats might play in the epidemiology of EHDV in a close-contact multispecies situation remain unknown.

Pathogen screening and bionomics of Lutzomyia apache (Diptera: Psychodidae) in Wyoming, USA.

ABSTRACT Phlebotomine sand flies are vectors of bacteria, parasites, and viruses. Lutzomyia apache, a North American sand fly, was incriminated as a vector of vesicular stomatitis viruses (VSV) due to overlapping ranges of the sand fly and recent outbreaks of VSV. We report on the discovery of 2 populations of L. apache in Wyoming from Albany and Fremont counties. We attempted to isolate VSV and phleboviruses from sand flies from Albany County and screened select flies by polymerase chain reaction for Bartonella and blood meals. We did not isolate viruses or detect DNA from vertebrate hosts or Bartonella. Flies were also tested for insect pathogens and other microbes. We detected a Rickettsia sp. in all flies that were examined and a parasitic protozoon, Ascogregarina sp., from the midgut of a larva. Eustigmaeus lirella, a stigmaeid mite, parasitized 2 field-caught females.

Osmoregulatory Organs of Immature Culicoides sonorensis (Diptera: Ceratopogonidae) in North America

ABSTRACT Aquatic insects must regulate the ion concentrations of their haemolymph, and freshwater insects tend to loose ions to their aquatic environment. The osmoregulatory organs of larvae and pupae of C. sonorensis have not been previously reported. Silver nitrate was used to detect tissues in immature stages of C. sonorensis with active chloride exchange. Larvae of C. sonorensis actively exchanged ions with their anal papillae, cutaneous chloride cells, and to a lesser extent the hindgut. Only the cutaneous chloride cells were stained in their pupae.

Aqueous 2% geraniol as a mosquito repellent failed against Aedes aegypti on ponies.

Abstract Organic insect repellents are of interest to many agricultural producers and animal owners. Geraniol, a plant-derived alcohol, is naturally produced by a wide range of plants and is a US Environmental Protection Agency minimum risk pesticide. Previous studies have shown various concentrations of geraniol repel or kill mosquitoes; however, geraniol might cause allergic contact dermatitis in humans or animals. We tested a commercially available 2% aqueous solution of geraniol on ponies as a mosquito repellent. Five trials were conducted on ponies treated with a 60-ml aerosol mist (30 ml per side) of 2% geraniol or as untreated controls. Animals were observed 3 h postapplication to check for skin irritation. Aedes aegypti, in feeding tubes, were held on the ponies for 7 min. The average percent of biting on control animals was 56%, with a range of 16–90%, and the average for the treatments was 13%, with a range of 0–86%. Based on statistical models, there was no significant difference (P  =  0.081) in the percent bites between treated and untreated animals after 3 h. Based on our data, 2% geraniol was not an adequate mosquito repellent for horses. We did not observe any skin irritation on the animals treated with 2% geraniol.

Mosquitoes of Thule Air Base, Greenland.

Abstract Thule Air Base in western Greenland had a previously uncharacterized mosquito pest problem. Swarms of bloodfeeding mosquitoes have been reported from June to late August, but the species were unknown. We conducted a base-wide mosquito vector survey from June to July 2012. One species of mosquito, Aedes impiger, was collected and >3,000 were processed for polymerase chain reaction–based virus surveillance. Active mosquito breeding sites were located throughout the base and surrounding valley. Two pools of mosquitoes from Thule Air Base tested positive for an Orthobunyavirus; however, DNA sequencing of the viral amplicons was not complete enough to fully identify the agent.

New Records for Micronesian Mosquitoes

Abstract The mosquito fauna of Micronesia is diverse and subject to introductions of exotic species and local extinctions. We report on 2 recently identified populations of exotic mosquitoes, Aedes albopictus and Anopheles campestris, to the Republic of the Marshall Islands and Guam.

EFFECTS OF MELEZITOSE AND STACHYOSE ON ADULT LONGEVITY AND VIRUS PERSISTENCE IN CULICOIDES SONORENSIS (DIPTERA: CERATOPOGONIDAE)

ABSTRACT. A wide variety of blood-feeding Diptera feed on extrafloral sugar sources such as homopteran honeydew. The significance of these sugar sources to insect survival and disease transmission is poorly known. Culicoides sonorensis, a biting midge, can survive on plant sugars but might also feed on homopteran honeydew. The survival of C. sonorensis fed 10% melezitose or 10% stachyose was compared to that of C. sonorensis fed 10% sucrose. A significantly greater number of C. sonorensis survived longer when fed melezitose than when fed either stachyose or sucrose. The effect of sugar meals on vector competence was measured using bluetongue and epizootic hemorrhagic disease viruses. There was no significant difference in viral persistence. However, if C. sonorensis feeds on homopteran honeydew in the wild, a larger number of midges could survive to transmit orbiviruses.