ABSTRACT
Rift Valley fever (RVF) is a zoonotic, viral disease, transmitted by mosquitoes, characterized by high mortality rates in young animals. RVF is an endemic and enzootic disease in the Arabian Peninsula and Africa, causing public health and economic instability. Therefore, it is important to develop vaccines to minimize outbreaks and combat the disease. We documented the stability of the thermo-stability of live attenuated RVF CL13T and recombinant arMP-12ΔNSm21/384 vaccine candidates at different temperatures, including these vaccine viruses in liquid and lyophilized form. The study revealed that both CL13T and recombinant arMP-12ΔNSm21/384 strains were stable for more than 18 months at 4°C. We show that at room temperatures (37°C and 45°C) the CL13T was less temperature sensitive than MP-12NSm-del in both lyophilized and liquid form. These findings are useful for the preparation of RVF vaccines that will avoid the need for a cold chain and therefore, will improve the application of the vaccines under field conditions.
ABSTRACT
Peste des Petits Ruminants virus (PPRV) is a member of the Morbillivirus subgroup of the family Paramyxoviridae, and is one of the most contagious diseases of small ruminants throughout Africa and the rest of the world. Different cell lines have previously been used to isolate PPRV but with limited success. Thus, to improve the isolation of Morbilliviruses, human, canine, and goat homologues of the lymphocyte receptor signaling lymphocyte activation molecule (SLAM) have been introduced into cells that can support virus replication. However, the amino acid sequence of SLAM varies between species, and often requires adaptation of a particular virus to different versions of the receptor. The protein sequence of Nectin-4 is highly conserved between different mammals, which eliminate the need for receptor adaptation by the virus. Cell lines expressing Nectin-4 have previously been used to propagate measles and canine distemper viruses. In this study, we compared infections in Vero cells expressing canine SLAM (VeroDogSLAM) to those in Vero cells expressing Nectin-4 (VeroNectin-4), following inoculations with wild-type strains of PPRV. Virus isolation using VeroNectin-4 cells was successful with 23% of swabbed samples obtained from live infected animals, and was 89% effective using post-mortem tissues of infected sheep. By contrast, only 4.5% efficiency was observed from swab samples and 67% efficiency was obtained in virus isolation from post-mortem tissues using VeroDogSLAM cells. The average incubation period for virus recovery from post-mortem tissues was 3.4 days using VeroNectin-4 cells, compared with 5.5 days when using VeroDogSLAM cells. The virus titers of PPRV obtained from VeroNectin-4 cells were also higher than those derived from VeroDogSLAM cells. A comparison of the growth kinetics for PPRV in the two cell lines confirmed the superiority of VeroNectin-4 cells for PPR diagnostic purposes and vaccine virus titration.
