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United States Department of Agriculture

Agricultural Research Service

2009 Annual Report

1a.Objectives (from AD-416)
The goal of research is to protect U.S. livestock from vector-borne pathogens through knowledge of species vector competence, defining the influence of environmental factors on vector competence and distribution, and understanding insect susceptibility to pathogen infection at cellular and molecular levels. Within this objective, research will:.
1)clarify and define the role of insects as vectors and reservoirs of pathogens that adversely affect livestock, humans, and wildlife;.
2)determine the effects of environmental factors on transmission of pathogens by biting midges and mosquitoes; and.
3)identify and characterize insect genomic and proteomic determinants that affect infection, replication, and transmission of arboviruses of concern to the U.S. livestock industry.

1b.Approach (from AD-416)
Ecological data will be developed for criteria used to incriminate insect species that serve as vectors of obscure or little studied pathogens in nature. Emphasis will be placed on clarifying the role of sand flies, grasshoppers, and Culicoides as vectors and reservoirs of vesicular stomatitis viruses, as well as the role of both blood feeding and non-blood feeding insects in the natural transmission of prions. The role of environmental factors as determinants of insect vector distribution and susceptibility to arboviruses will be developed using geographic information system approaches to estimate vector distribution and pathogen susceptibility, thus enabling prediction of livestock risk for pathogen exposure. The midgut microbial flora of biting midges will be assessed using non-culture based molecular tests, such as T-RFLP, quantitative PCR or macro-arrays, and correlated with insect susceptibility to arbovirus infection. Arbovirus susceptibility and infection pathways in insect vectors will be investigated by identifying salivary gland and midgut proteins that will be analyzed by mass spectrometry and compared with available protein databases and compared between blood-fed and non-blood fed individuals. RNA interference (RNAi) will be used to down regulate genes and thus identify the role of gene products in the susceptibility of insects to arbovirus infection.

3.Progress Report
Vertical (transovarial) transmission of vesicular stomatitis virus has been confirmed in Culicoides sonorensis biting midges with virus detected in eggs, larvae, pupae and adult progeny of infected females. Results are being analyzed and a manuscript is in preparation.

A study looking at mechanical transmission of vesicular stomatitis virus is nearly complete. Virus has been detected in the frass of Culicoides sonorensis.

Salivary proteins, D7 and maltase, were identified as major allergens in Culicoides saliva. These proteins were cloned, expressed in baculovirus expression systems, and purified. Purified proteins were then tested in horses and in a sweet itch diagnostic assay system.

The effect of BTV infection on C. sonorensis fecundity was examined, and a manuscript is in preparation. Results indicate that infection with BTV causes no change in midge survival, fecundity, survival of progeny insects, or duration of developmental stages. The effect of BTV infection on C. sonorensis feeding behavior is discussed below in the accomplishments section of this report.

Molecular techniques to differentiate Aedes mcintoshi and Ae circumluteolus are still underway. The single copy nuclear gene EF1a shows promise and is being further tested for efficacy in distinguishing these two species.

Topical repellents and ear tags were tested for efficacy in repelling C. sonorensis on sheep. These trials have lead to registration of PYthon impregnated ear tags for use on sheep in Wyoming and Montana. A manuscript reporting these results has been completed and submitted.

A mixture of 5% Dimilin and 5% permethrin in an oil based solution (Clean-UpTM from KMG Chemicals, Houston, TX) was found to be highly effective in controlling lice of ponies (Bovicola equi) as well as lice of guinea pigs (G. porcelli). One publication for these results is in press and another has been published.

The host preference of Lutzomyia (Helcocyrtomyia) apache was tested. This sandfly species was found to preferentially feed on reptiles in the laboratory. Results are in press.

Predator avoidance behavior for larval Culicoides sonorensis, Aedes aegypti and Culex tarsalis was examined.

The effects of ivermectin on the susceptibility of Culicoides sonorensis (Diptera: Ceratopogonidae) to bluetongue and epizootic hemorrhagic disease viruses was examined and results published.

Vector competence of C. sonorensis for Weldona virus was tested. Midges became infected but could not transmit virus. A portion of the viral genome was used to determine the relationship of Weldona virus with other related viruses. Sera from 8 out of 95 sheep originally taken for BTV antibody testing also tested positive for neutralizing antibodies against Weldona virus. Results are in press. A near infrared spectroscopy tool for age grading C. sonorensis was developed in collaboration with the USDA-ARS agricultural engineering unit in Manhattan, KS. Results are in press.

1. Degree Day Model for West Nile Virus Risk Analysis. This work was accomplished by collaboration with scientists at the University of Wyoming through specific cooperative agreement 5410-32000-014-15S, “Use of Geographic Information System (GIS) Methods to Understand Spatial Patterns of Mosquito Vectors of West Nile Virus.” West Nile and Rift Valley fever viruses are transmitted by mosquitoes and can cause disease in humans and animals. Predicting the start of West Nile transmission season is helpful in protecting humans and animals from disease, and predicting the risk of RVF transmission will be helpful in controlling the virus should it be introduced. Research in this project centered on the development of habitat and temperature-based models that can be used for risk assessment in mosquito-borne illness, specifically West Nile and Rift Valley fever viruses. Geographic Information System (GIS) technologies were developed to create point-based and spatially explicit models of both mosquito habitat and risk of virus transmission. Case studies were performed in Wyoming and California for West Nile Virus using a retrospective approach. Theoretical models for future risk based on global climate change were developed for both West Nile Virus and Rift Valley fever.

2. Blood feeding of BTV infected Culicoides sonorensis. Culicoides sonorensis (Diptera: Ceratopogonidae) is the primary vector of Bluetongue virus in North America. To determine whether infection with BTV affects blood-feeding behavior, midges injected with either BTV-infected or BTV-free cell lysates were allowed to blood feed for short (10 min) or long (60 min) periods of time on 2, 4, and 7 days post inoculation. BTV-infection caused a significant delay in blood feeding, as seen by a reduced percentage of females that blood fed when allowed only 10 min to feed compared to those allowed 60 min. Uninfected midges showed no difference in feeding success between 10 and 60 min feeds. Results also indicate that midges held 7 days also exhibit a delayed feeding response, as a significantly greater proportion of females fed when allowed 60 min to feed versus 10 min. This was not observed when midges were held 2 or 4 days. Changes in blood-feeding behavior caused by viral infection could potentially have a significant impact on virus transmission.

6.Technology Transfer

Number of the New/Active MTAs (providing only)3

Review Publications
Reeves, W.K. 2008. Osmoregulatory Organs of Immature Culicodes Sonorensis (Diptera: Ceratopogonidae). Entomological News, Vol. 119: 371-374

Nelder, M.P., Reeves, W.K., Adler, P.H., Wozniak, A., Wills, W. 2008. Ectoparasites of free-roaming and captive animals in South Carolina zoos and an assessment of their threat to animals welfare and public health. Vector-Borne and Zoonotic Diseases. 9(5):469-477.

Langner, K.F., Jarvis, D.L., Schuberth, H., Nimtz, M., Heselhaus, J.E., Mcholland, L.E., Leibold, W., Drolet, B.S. 2009. Identification, expression, and characterization of a major salivary allergen (Cul s 1) of the biting midge Culicoides sonorensis relevant for summer eczema in horses. International Journal for Parasitology. Vol 39 (2009) 243–250.

Reeves, W.K., Kato, C.Y., Gilchriest, T. 2008. Pathogens and bionomics of Lutzomyia apache (Diptera: Psychodidae) from Wyoming, USA. Journal of the American Mosquito Control Association. Vol 24:444-447.

Reeves, W.K., Miller, M.M. 2009. Control of Bovicola Equi (Phthiraptera: Trichodectidae) with Dimilin and Permethrin. Journal of Vector Ecology. Vol 34: 160.

Konrad, S.K., Miller, S.N., Reeves, W.K., Tietze, N.S. 2009. Spatially explicit West Nile virus risk modeling in Santa Clara County, California. Vector-Borne and Zoonotic Diseases. 9(3):267-274.

Reynolds, J.W., Reeves, W.K., Spence, R.M. 2009. The Earthworms (Oligochaeta: Lumbricidae)of Wyoming, USA, Revisited. Megadrilogica. Vol. 13(4): 25-35.

Bennett, K.E., Hopper, J.E., Stuart, M.A., West, M.S., Drolet, B.S. 2008. Blood Feeding Behavior of Vesicular Stomatitis Virus Infected Culicoides Sonorensis (Diptera: Ceratopogonidae). Journal of Medical Entomology. 2008 Sep 45(5):921-6

Reeves, W.K., Nol, P., Miller, M.M., Jones, G.Z. 2009. Effects of Ivermectin on the Susceptibility of Culicoides Sonorensis (Diptera: Ceratopogonidae) to Bluetongue and Epizootic Hemorrhagic Disease Viruses. Journal of Vector Ecology. Vol 34: 161-163.

Last Modified: 9/10/2014
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