Assessment of past Rift Valley fever outbreak using Modeling, Risk analysis and decision tree in Sudan
Authors: Ahmed mohamed E , Baumann Maximilian PO , Selhorst Thomas , Abdellah Tamador M , Abdelgadir Atif A 
Published: June 2020

Abstract
Background A retrospective study was performed in selected states of the Sudan that include Gezira state, White Nile, Blue Nile, Khartoum, River Nile and Sennar states in order to determine the seroprevalence of Rift Valley Fever (RVF) and associated risk factors as well as an attempt was made to apply mapping, risk analysis tool to investigate the disease .Those epidemiological tools were used for purpose of good management strategies and policy makers as well. The source of data was epidemiological reports and archives from the Federal Ministry of Animal resources, universities and Non Governmental Organizations for outbreaks of RVF also and laboratory reports of serum samples tested by ELISA. The test performance characteristics were 99% test sensitivity and 99% test specificity.A total of 3393from, sheep, goats and cattle were sampled and selected to be examined. Estimated Seroprevalence of RVF was 0.15% (n=905) in sheep, 0.20 %( n=776) in goats and 0.13 %( n=638) in cattle respectively. Also information gathered was used to determine the distribution of the disease, transmission and recovery rate of infection over point in time. Method This study was retrospective survey designed to investigate previous outbreaks of RVF. The method used was risk analysis, modeling and decision tree to explain the distribution of chronology of the disease. Result The current study was carried out quantitative risk analysis to investigate RVF. Risk analysis revealed that RVF is likely to occur in the Sudan, and vaccination was estimated with highest rollback to reduce the seroprevalence of RVF to be unlikely with expected value of $ US 4368789. A frequency of 0.12%, 0.12% and 0.1% from cattle, goats and sheep population were entered in SIR model respectively. The adjustable parameters were susceptible, infected, recovery rate and death rate; the result concluded that the curve of susceptible(S) was declining, infected (I) was increasing; while recovered(R) was increasing. A total of 2487 mosquitoes were pooled, represented by 600 mosquitoes in the final model, recovery rate of mosquito overtime was 0.22 which is statistically not significant, (P-value =0.9825), and rate of infection was 0.83 %. In the current study, the Basic reproductive number (R0) was estimated by one. Uncertainty for RVF model was ranged between 0.01 to 610.65 with confidence of 95%. This study concluded that RVF is endemic in the Sudan.Conclusion Rift Valley Fever (RVF) is arthropod-borne viral zoonosis disease. It affects small ruminants, sheep and goats, and large ruminants like cattle and camel, and also can affect human. Rift Valley Fever virus (RVFV) belongs to the family Bunyviridae, genus Phlebovirus. The first isolation of RVFV was done in Kenya (4). RVFV is a negative sense RNA virus. RVFV genome is structured from three partites, small, medium and large. It is peracute or acute febrile disease that is characterized by numerous abortions in female and high mortality among young animals and humans. Mosquitoe is the principle vector of the disease. It is transmitted by direct contact with infected tissues or organs of animals and ingestion of uncooked or row milk (1). The study was carried out to investigate the risk related to RVF seroepidemiology and distribution of the disease among livestock and to determine the most efficient policies in management of RVF outbreak by using retrospective data, however more further serosurveillances were required to thoroughly understand the epidemiology of the disease.