Rift Valley Fever virus infection of natural hosts: evidence of genetic constraints
Juergen A. Richt, DVM, PhD
Kansas State University
The overall goal of my research is to investigate emerging diseases of livestock focusing mainly on viral and prion diseases. We work on influenza viruses, especially swine and avian influenza viruses. We try to understand molecular mechanisms of how influenza viruses are transmitted between animal species and which viral genes are critical for this process. In addition, we try to develop broader and more efficient vaccines. Reverse genetics technology is one of the techniques used in this line of research. Rift Valley Fever virus is another zoonotic pathogen we are working on. Our goal is the development of novel vaccines and diagnostic tools. The prion research conducted is based on prion protein-deficient knock-out cattle, which we previously generated. Here we try to produce knock-in cattle expressing mutated bovine prion proteins using homologous recombination. Recently, I became the director of the Center of Excellence for Emerging and Zoonotic Animal Diseases (CEEZAD), funded by the Department of Homeland Security.
Abstract
Rift Valley fever (RVF) is a zoonotic disease that causes severe epizootics in ruminants, characterized by mass abortion and high mortality rates in younger animals. The development of reliable challenge models in target... [ view full abstract ]
Rift Valley fever (RVF) is a zoonotic disease that causes severe epizootics in ruminants, characterized by mass abortion and high mortality rates in younger animals. The development of reliable challenge models in target animals is an important prerequisite for evaluation of existing and novel vaccines. We conducted studies aimed at comparing the pathogenesis of RVF virus infection in US sheep and cattle using two genetically different wild type strains of the virus, SA01-1322 and Kenya-128B-15. The Kenya-128B-15 strain manifested higher virulence compared to SA01-1322 by inducing more severe liver damage, and longer and higher viremia in both sheep and cattle. Genomic sequence analyses revealed sequence variations between the two isolates, which potentially could account for the observed phenotypic differences. These results demonstrate the establishment of virulent target host challenge models for vaccine evaluation based on the RVFV strain Kenya-128B-15.
The rather high mutation rate of RNA viruses usually results in a genetically diverse virus population (“quasispecies”) within a host that increases the virus’ ability to adapt to diverse selective pressures and different environments. In contrast, the genetic evolution of RVFV strains across all lineages is rather limited. We hypothesize that the mosquito-vertebrate-mosquito alternating lifecycle of RVFV might be the mechanism which restricts RVFV genomic evolution. Therefore, we determined the influence of host alternation on the quasi-species diversity of RVFV strain Kenya-128B-15. To this end, mosquito cell (C6/36)-propagated Kenya-128B-15 virus was used to infect cattle and sheep subcutaneously. Virus present in serum of infected ruminants was then inoculated into C6/36 mosquito cells. The full length viral genome from the original and ruminant-passaged C6/36 virus and from the ruminant sera was sequenced on the Illumina Miseq and analyzed for single nucleotide variants. Smaller quasi-species diversity was detected after passage in mosquito cells compared to the mammalian host. These data indicate that molecular evolution of RVFV seems to be restricted via its alternating insect-mammalian-insect cycle.
Session
KN-2 » Keynote (08:45 - Wednesday, 17th May, La Fonda Ballroom)
