Circulation of Rift Valley Fever Virus Antibody in Cattle during Inter-Epizootic/Epidemic Periods in Selected Regions of Tanzania.

Tanzania is one of the sub-Saharan countries that have experienced a number of Rift Valley fever (RVF) outbreaks at intervals of 10-20 years since the first isolation of the virus during the early 1930s. Recent studies have reported serological evidence of inter epizootic/epidemic period circulation of RVF virus (RVFV) in livestock and humans. The aim of this study was to conduct a cross-sectional survey in Tanzania during 2015/16 to further explore the possibility that RVFV was circulating among cattle during the Inter epizootic/epidemic period. A total of 443 cattle samples were collected in Manyara, Dodoma, Singida, and Mbeya regions of Tanzania. The samples were tested for RVFV antibodies using a commercial ELISA kit and a plaque reduction neutralization test. Serum samples were also tested for RVFV viral RNA by an reverse transcription polymerase chain reaction (RT-PCR) assay. An overall RVFV seroprevalence rate of 7.7% (34/443) was detected by ELISA among cattle in all four regions. The Mbeya region cattle had the highest seroprevalence of 26.4% (23/87), followed by Dodoma 5.9% (10/171) and lastly Singida 0.9% (1/101). Of 33 ELISA antibody-positive samples, only 0.2% (1/443) had IgM antibody. Of 36 ELISA antibody-positive and doubtful samples, 32 were positive for neutralizing antibody with titers between 10 and > 10,240. None of the samples were positive for RVFV viral RNA by RT-PCR. The detection of RVFV antibodies in cattle suggested that these animals were involved in an enzootic cycle during the interepidemic period and that the high antibody titers may confer protection of cattle against RVFV.

Survival of avirulent thermostable Newcastle disease virus (strain I-2) in raw, baked, oiled, and cooked white rice at ambient temperatures.

Raw white rice has not been considered a good carrier for oral vaccination, probably because of its antiviral activity. Methods are required to overcome antiviral activity in raw white rice. This study was carried out to determine the effects of various treatments of raw white rice on the survival of strain I-2 of Newcastle disease virus. These included cooking and baking the rice or mixing the rice with vegetable oil prior to coating with vaccine virus. The vaccine-coated rice was then stored for 30 min and 24 h, followed by quantitative recovery of the virus. Thirty min after mixing, uncooked, cooked, and baked rice, and rice mixed with vegetable oil showed titers of 10(6.2), 10(7.2), 10(6.6), and 10(7.0) EID(50)/0.1 ml, respectively. After storage for 24 h at 22-25oC, the titers dropped to 10(5.0), 10(6.5), 10(5.0), and 10(6.0) EID(50)/0.1 ml for uncooked, cooked, baked, and oiled rice, respectively.