Interacting Factors That Influence Long-term Storage of Live Pasteurella tularensis Vaccine and Rift Valley Fever Virus

Abstract

Studies were conducted on the interaction of various parameters which affect the storage stability and growth potential of liquid cultures of Pasteurella tularensis live vaccine strain (LVS) and Rift Valley fever virus Van Wyk strain (RVFV). Storage variables studied with LVS included four storage temperatures (4,-20,-65,-175 C), single and multiple freeze-thaw cycles, two freezing and two thawing rates (slow and fast), various inoculum levels (1, 3, 5, and 10%) for the determination of growth potential, and the retention of immunizing potential (mice and guinea pig) after storage. Neither the freezing rate nor the number of freezethaw cycles seriously affected the growth of LVS after storage at-175 C; however, the slow rate of thaw proved deleterious as were all temperatures of storage except-175 C after 1 year of storage, as shown by both criteria of evaluation. RVFV produced in two combinations of cell lines and media (LM cell line-199 peptone medium and LDR cell line-Eagle's minimum essential medium) was stored at three serum levels (10, 20, 40%), three pH values (6.2., 7.0, 7.8), and three temperatures (-20,-65,-175 C). These studies indicated: (i) virus produced in the LDR cell line and Eagle's medium was more stable than that produced in the LM cell line and 199 peptone medium for either shortor long-term storage; (ii) serum levels did not affect stability; and (iii) low pH resulted in losses during long-term storage under all conditions tested. Thus, cryogenic storage is advantageous for stock culture maintenance of bacteria and viruses and for other similar applications.

Rift Valley fever virus (Bunyaviridae: Phlebovirus): an update on pathogenesis, molecular epidemiology, vectors, diagnostics and prevention

“…Infection of lambs via the intestinal tract by ingestion of RVFV-containing gelatin capsules was also unsuccessful but is a possible route of infection. However, the acidity of the stomach lumen is deleterious for RVFV, which is very susceptible to inactivation in solutions with a pH of less than 6.8 [ 143 , 186 ].…”

The use of Nanotrap particles for biodefense and emerging infectious disease diagnostics

“…Preserving only the genome limits analysis of viability and pathogenicity. Early studies by the US Army on RVFV confirmed its stability in serum for long term, cryogenic storage at a neutral pH (Klein et al, 1969). Subsequent studies demonstrated blood or serum could preserve virulent RVFV for up to 2 months at 4°C (Shimshony & Barzilai, 1983).…”