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United States Department of Agriculture

Agricultural Research Service

Research Project: Countermeasures to Prevent, Mitigate, and Control Rift Valley Fever (Rvf)

Location: Arthropod-Borne Animal Diseases Research

2012 Annual Report


1a.Objectives (from AD-416):
1. Identify epidemiological factors affecting disease outbreak and inter-epizootic maintenance of RVFV.

Sub-objective 1A: Create a network based stochastic model that accounts for mosquitoes, cattle and humans to determine the best mitigation strategies in the event of an outbreak.

Sub-objective 1B: Develop tools for rapid detection and characterization of emergent viruses.

2. Identify factors associated with RVFV infection, pathogenesis and maintenance.

Sub-objective 2A: Develop RVFV “vector-transmitted” infectious models in target ruminant species to facilitate studies of disease pathogenesis, disease transmission and vaccine efficacy.

Sub-objective 2B: Identify mammalian host innate and adaptive responses to insect transmitted RVFV.

3. Develop and validate vaccine strategies for preventing RVFV epizootics.

Sub-Objective 3.A. Develop needle-free vaccine platforms that reduce the time to effective onset of immunity.

Sub-Objective 3.B. Develop vaccine platforms that do not require refrigeration for extended periods of time.


1b.Approach (from AD-416):
The potential introduction of Rift Valley fever (RVF) virus (RVFV) is the most significant arthropod-borne animal disease threat to U.S. livestock according to the USDA-APHIS National Veterinary Stockpile (NVS) Steering Committee. A number of challenges exist for the control and prevention of RVF in the areas of disease surveillance, diagnostics, vaccines and vector control. RVFV is the third biological threat agent on the NVS Steering Committee’s priority list for generation and stockpiling of countermeasures for diagnosis, vaccination, and insect control. Understanding the epidemiological factors affecting disease outbreak and the inter-epizootic maintenance of RVFV is necessary for the development of appropriate countermeasures strategies. This includes the ability to detect and characterize emergent viruses since RVFV is an RNA virus and could evolve to adapt to a new environment. Also, the proposed research will identify determinants of RVFV infection, pathogenesis and maintenance in mammalian and insect vector hosts. Information derived from these studies will also provide a better vaccine evaluation challenge model. Vaccine formulations will be developed to improve immunogenicity, onset of immunity and stability to provide better response to outbreaks and prevent RVFV epizootics. The overall goals of this project are to utilize the unit’s unique multidisciplinary expertise to fill knowledge gaps about the interepidemic cycle of RVFV and provide the tools necessary for detecting, controlling and eradicating RVFV should it be introduced into the U.S.


3.Progress Report:
Developed a general susceptible-exposed-infected-recovered (SEIR) model which uses differential equations to transition animals and insects between states. The model can account for a variety of vector species and geographic locations. By dealing with ruminants, humans and mosquitoes in separate directed and asymmetric networks, the vital link between mosquitoes and cattle can be examined.

The ABADRU has continued through numerous national and international collaborators to develop of expressed and purified RVF viral antigens and serological diagnostic reagents. The multiplex three-gene target RVFV real-time RT-PCR assay has been improved and field-tested in South Africa and Kenya. Nanotechnology has been used to develop preliminary biosensor systems for detection of viral genetic material, proteins and immunological response to infection.

Whole RVFV genome amplification protocol has been used to identify genetically diverse strains for studies of RVF genetic reassortment in mosquitoes. This system could be used to rapidly characterize an introduced RVF or related arbovirus.

New technologies for multiplex pathogen detection and characterization have been explored and funding is being pursued to acquire this modern and expensive technology.

A commercially available intradermal injection system was evaluated. The system is not acceptable for a zoonotic pathogen delivery. An alternative method has been identified an efforts are in progress to evaluate the alternative method.

Arrangements have been made to transfer and establish a Culex tarsalis colony at ABADRU to facilitate the research in objective 2B.

RVFV MP-12 vaccine infection of lambs and calves has been conducted at BSL-3+ condition to demonstrate the safety protocols necessary for animal research with wild-type RVFV.

Only two of the ABADRU staff members have received the investigational RVF vaccinations. Two new staff members have submitted applications to be enrolled in the special immunization program that is currenlty on hold by the US Army Medical Research Institute for Infectious Diseases.

Preliminary evaluations of the stability of MP-12 in formulations of the vaccine with various adjuvants and stabilizers have been conducted.

Cell-culture studies using RVFV MP-12 vaccine strain have suggested that not only livestock, but also North American wildlife including native deer species could be susceptible to infection.

The following work aligns with the Bio-defense research and the control of zoonotic diseases components of the NP-103 Animal Health Action Plan.


4.Accomplishments
1. Development and evaluation of one-step rRT-PCR and immunohistochemical methods for detection of Rift Valley fever virus in biosafety level 2 diagnostic laboratories. Rift Valley fever virus (RVFV) is a zoonotic insect transmitted virus endemic to Africa and the Arabian Peninsula. Infection causes abortions and high mortality in newborn ruminants. Currently, regional veterinary diagnostic laboratories lack safe, modern, validated diagnostic tests to detect RVFV. An existing real-time RT-PCR (rRT-PCR) assay was modified for quick virus inactivation for use on serum and tissue samples from infected lambs and calves. Antiserum against recombinant RVFV- nucleocapsid (N) was produced to develop an immunohistochemical (IHC) assay, which was subsequently evaluated on formalin fixed lamb and calf tissues. Once validated and approved by national regulatory agencies, these assays can be safely produced and distributed to regional diagnostic laboratories, providing capacity for operator safe early detection of RVFV in suspected ruminant samples.

2. Preliminary development of biosensors for insect-transmitted viruses using nanotechnology. Gold colloids were specifically modified for use in detection of viral genes, proteins and serological responses to infection using Surface Enhanced Raman Scattering technology. Once further developed, these assays will be safer to produce and use; therefore providing tools for early detection that could be used in veterinary diagnostic laboratories and by the National Animal Health Laboratory Network.


Last Modified: 7/25/2014
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