Modeled impacts of rapid and accurate cattle tracing in a Foot-and-Mouth Disease outbreak in the US.

The purpose of this study was to estimate the impacts of rapid and accurate tracing of cattle movements during a Foot-and-Mouth Disease (FMD) outbreak in the United States (US). To simulate introduction and spread of FMD we utilized InterSpread Plus, a spatially explicit disease transmission model, and a national livestock population file. The simulations began in one of four regions of the US via beef or dairy cattle as the index infected premises (IP). The first IP was detected 8, 14, or 21 days after introduction. The tracing levels were defined by the probability of a successful trace and the time to trace completion. We evaluated three tracing performance levels, a baseline that represents a mix of paper and electronic interstate shipment records, an estimated partial implementation of electronic identification (EID) tracing, and an estimated full implementation of EID tracing. To evaluate the potential to decrease the size of control areas and surveillance zones with full EID use, we compared the standard size for each to a reduced geographical area for each. The total number of IPs in an outbreak varied with the location of the index farms. Within index farm locations and across tracing performance levels, early detection (day 8) resulted in fewer IPs and a shorter duration of the outbreak. The impact of improving tracing was most evident within introduction region when detection was delayed (day 14 or 21). Full EID use decreased the 95th percentile but had a smaller impact on the median number of IPs. Improved tracing also decreased the number of farms impacted by control efforts in control areas (0-10 km) and surveillance zones (10-20 km) by decreasing outbreak size (total IPs). Decreasing the control area (0-7 km) and surveillance zone (7-14 km) sizes while using full EID tracing further decreased the number of farms under surveillance but increased the number of IPs slightly. Consistent with previous results, this supports the potential value of early detection and improved traceability to control FMD outbreaks. Further development of the EID system in the US is necessary to achieve the modeled results. Further research into the economic impacts of enhanced tracing and decreased zone sizes are needed to determine the full impact of these results.

Rift Valley Fever Virus: Propagation, Quantification, and Storage.

Rift Valley fever virus (RVFV) is an arthropod-borne, zoonotic disease endemic to sub-Saharan Africa and the Arabian Peninsula. Outbreaks of Rift Valley fever have had up to 100% mortality rates in fetal and neonatal sheep. Upon infection of ruminant and human hosts alike, RVFV infection causes an at times severe hepatitis and pathology in many other organs. The enveloped virion contains a tripartite, predominantly negative-sense, single-stranded RNA genome, which codes for the proteins the virus needs to replicate both in mammalian hosts and insect vectors. Endemic countries often use attenuated RVFV strains for vaccination of livestock but there are no commercially licensed vaccines for humans or livestock in non-endemic areas. In the laboratory, RVFV can be readily propagated and manipulated in vitro using cell culture systems. Presented in this article are techniques routinely used in RVFV research that have proven successful in our laboratories. © 2019 by John Wiley & Sons, Inc. Basic Protocol 1: Propagation of Rift Valley fever virus in mammalian cells Basic Protocol 2: Quantification of Rift Valley fever virus by plaque assay Basic Protocol 3: Quantification of Rift Valley fever virus by 50% tissue culture infectious dose (TCID50 ) assay Basic Protocol 4: Quantification of Rift Valley fever virus by focus-forming assay Basic Protocol 5: Storage and disinfection Alternate Protocol 1: Propagation of Rift Valley fever virus in MRC-5 cells Alternate Protocol 2: Propagation of RVFV in mosquito-derived cells Alternate Protocol 3: TCID50 detection using fluorescence visualization Support Protocol 1: Calculation of the amount of virus needed to infect a flask at a chosen multiplicity of infection Support Protocol 2: Calculation of the virus titer by plaque assay or focus-forming assay Support Protocol 3: Calculation of the TCID50 titer by the method of Reed and Muench Support Protocol 4: Calculation of the antibody volume for the focus-forming assay.