Retrospective Study On Rift Valley Fever in Selected States in Sudan With Reference to Spatial and Animal Patterns

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 investigate the seroprevalence of Rift Valley Fever (RVF) from 2007 to 2016. The risk factors that identied for RVF were locality, species, and animal population. For example, locality and species were signicantly associated with seroprevalence of RVF (P-value = 049)(P-value = 0.000) respectively, While animal population was not associated in Gezira state (P-value = .415) and χ 2 value was (12.629), however it was signicantly associated in other regions. The highest seroprevalence estimated for RVF was 0.7% in River Nile state, while lowest seroprevalence for RVF recorded was 0.01% in Khartoum and Sennar states, respectively. against RVF is used in case of outbreak and suspected cases in livestock; however there is no available vaccine for human usage. The current study is retrospective survey to investigate the seroprevalence, risk factor and spatial and animal patterns in selected states in Sudan. 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. The risk factors that identied for RVF were locality, species, and animal population. For instance, locality and species were signicantly associated with seroprevalence of RVF (P-value = 049), (P-value = 0.000) respectively, While animal population was not associated in Gezira state (P-value = .415). Environmental risk factors i.e. annual temperature and annual rain fall were compared to RVF occurrence in study area with average mean of 29.0ºC and 398.8 mm respectively.


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 investigate the seroprevalence of Rift Valley Fever (RVF) from 2007 to 2016. The risk factors that identi ed for RVF were locality, species, and animal population. For example, locality and species were signi cantly associated with seroprevalence of RVF (P-value = 049)(P-value = 0.000) respectively, While animal population was not associated in Gezira state (P-value = .415) and χ 2 value was (12.629), however it was signi cantly associated in other regions. The highest seroprevalence estimated for RVF was 0.7% in River Nile state, while lowest seroprevalence for RVF recorded was 0.01% in Khartoum and Sennar states, respectively.

Methods
The current study was carried out in selected states in Central Sudan to investigate the epidemiology of RVF. Also it was focused on livestock in particular sheep, goat and cattle. Study design was retrospective to investigate seroprevalence, risk factors and spatial and animal patterns associated with RVF from 2007 to 2016.

Result
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. The risk factors that identi ed for RVF were locality, species, and animal population. For example, locality and species were signi cantly associated with seroprevalence of RVF (P-value = 049)(P-value = 0.000) respectively, While animal population was not associated in Gezira state (P-value = .415). Environmental risk factors i.e. annual temperature and annual rain fall were compared to RVF occurrence in study area with average mean of 29.0ºC and 398.8 mm

Conclusion
Rift valley fever is arthropod-born zoonosis disease. It affects livestock like sheep, goat, cattle and camel .it usually occurs following heavy rainfall and cause storm of abortion in pregnant animals. The principle vector of RVF is Mosquitoe and also it is transmitted through tissues of infected animal and human and also through of undercooked milk. In spite of there is no con rmed cases that can be transmitted from person to person by direct contact. It is characterized in human by in uenza-like illness, in moderate cases can develop retinitis and eye infection and severe complication can cause hemorrhagic form with oozing of blood from natural ori ces, the morbidity and mortality rate is varying from 5-100% in livestock, death rate can reach up to 10% and case fatality rate is less than one percent. The vaccination Introduction 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 rst isolation of RVFV was done in Kenya (2). RVFV is a negative sense RNA virus. The principle vector of RVF is mosquitoes and midges. It is characterized by storm abortion in pregnant animals, following heavy rain falls season. It is in uenza like illness in human and can exceed that to cause retinitis and eyes infection in patient who are diagnosed with RVF infection. Also, in severe cases could development hemorrhagic fever form and oozing of blood from natural ori ces RVF is reported in Sudan in Kosti in 1977 whereas involved human and animal cases, and spread across River Nile up to Khartoum. The morbidity and mortality rates are ranging from 5 to 100% in pregnant animals and death rate reach up to 10% and case fatality rate is less than one percent. This study was retrospective study to analyze previous information available for RVF and using it in planning for early warning system and contingency planning and preparedness strategies for prevention and control of the disease in present and future point in time. Also the current study was to estimate the seroprevalence in study area , Gezira , Khartoum , Blue Nile, White Nile, River Nile and Sennar , determine the spatial and temporal patterns of the disease in Sudan.

Objective
This paper is aimed to understand Rift valley fever epizootiology in selected states of Sudan and evaluate spatial and temporal patterns which are considered as important to explain the distribution of the disease by designing geographical maps for disease in previous years and investigate the risk factors associated with RVF occurrence.

Study area
The current study was investigated Rift Valley Fever susceptible localities in the Sudan. White Nile, Gizera, Blue Nile, Khartoum and Sennar States were surveyed, (Figure 1).

Study population
The study was focus on livestock population in Sudan with special emphasis on most susceptible species for Rift Valley Fever like small ruminants (sheep and goats), as well as cattle.

Study design
Retrospective study design was carried out to investigate, sero-prevalence, associated risk factors, spatial distribution from 2007 to 2016.
Sampling methods and sample size A total of 3393 sera samples were observed from records of sheep, goat and cattle population in River Nile, Khartoum, Gezira, White Nile, Blue Nile and Sennar states by non-probability multistage cluster sampling method choosing state as stratum and within stratum animal species were selected conveniently as a sampling unit based on presence and absence status of Rift Valley Fever.
Detection of RVF Antibodies using ELISA Enzyme Lined Immunosorbent Assay (ELISA) was used according to manufacturer's instruction to detect RVF antibodies in tested sera from sheep, goat and cattle.
Retrospective study design was carried out to investigate spatial and temporal distribution from 2007 to 2016. ArcView software was used to reproduce the distribution of geographic maps.

Statistical analysis
ArcGis software version 10.2 was utilized to reproduce geographical maps for investigation and surveillance of the spatial distribution of Rift Valley Fever in the Sudan. Descriptive statistics, univariate analysis was utilized to determine risk factor associated with RVF seroprevalence by using SPSS version 20. 0.4.

Risk factor analysis in selected states
In univariate analysis, locality and species were signi cantly associated with seroprevalence of RVF (Pvalue < 0.05), Where animal population was not in Gezira state. In Sennar and Blue Nile, species were found to be statistically associated with seroprevalence of RVF (P-value > 0.05), ( χ 2 = 3.879) and (χ 2 = 22.959) respectively. While locality and Animal population were not associated. In White Nile state, locality and animal population were highly statistically associated with RVF seroprevalence (P-value > 0.05),(χ2 = 76.034) and (χ 2 = 29.507) respectively, while species was not. Whereas, in Khartoum state, locality, species and animal population were not statistically associated with RVF seroprevalence (Pvalue < 0.05) ( Table 3).

Risk estimation of RVF in Sudan
The likelihood of RVF to occur in Sudan is likely to occur, however, there is free zone from the disease.

Export risk analysis
RVF is unlikely to happen in the Sudan at this scenario, in condition for exported livestock that are vaccinated against RVF, quarantined with veterinary certi cation before its consignment to importing country.

Import risk analysis
In this scenario, RVF is likely to occur through livestock and livestock products that are carrying RVFV from endemic country to Sudan without consignment regulation for heath and veterinary certi cations.
In case of suspicion in RVF, surveillance for the disease by epidemiologists in relevant units in Animal Health Epidemiological Disease Control Directorate is carried out to investigate the suspected cases or outbreak. Also, eld investigations are routinely done as a project designated to investigate and provide epidemiological data for priority disease e.g. RVF. There is a program for autumn diseases; whereas water associated diseases are investigated. The program is including health and veterinary situation in states.
In addition, there are projects for entomological control, extension and preparation for eld teams for rapid intervention.    ( 3) and (7). In this study, highest overall seroprevalence estimated for RVF was 0.7% in River Nile state, while lowest overall seroprevalence for RVF recorded was 0.01% in Khartoum and Sennar states. This was in agreement with study done to investigate spatial and temporal distribution or pattern of RVF from 1930 to 2007 in Tanzania by (8), whereas distribution of disease has been investigated by geographical information to understand its epidemiology at different areas and seasons. Also clustering had been reported in Gizera state, where foci or pockets of the disease were evident; this had come into consent with research done by (4), whereas clustering can estimate the incidence of RVF in study area for a certain period of time which provides understanding for the spatial and temporal distribution and epidemiology of RVF and provide explanation for circulation of the virus in certain region. In addition, annual temperature and annual rain fall were signi cant in all study area execept, rain fall was not signi cant in Gezira state, although this could be as a confounding factor.This was in agreement with report of RVF in Senegal and Mauritania by (6), where it associated with building of dam across senegal river and in Gezira is associated with Agricultural scheme and abundance of channels and irrigation system which considere abreeding site for mosquitoes the vector for RVFV .Also, altering of ecological condition was mostly contributing to distribution of RVF into new environment whereas humans and livestock at large were often exposed to get the infection with RVF. Eventually, early warning system was used to forecast and predict occurrence of RVF, satellite imagery were utilized to explore RVF in East africa. Before 1976, susceptible cases for RVF were unknown, and could be mixed up with similar symptoms in differential diagnosis to other similar syndromes that cause hemorrhage e.g. wesselborn, pest des petites Ruminant virus, brucellosis Malaria, yellow fever, Anthrax, hemorrhage septicemia, (5) .In addition, sentinel herds were in use to monitor exposure for susceptible hosts and identify potential vector for RVF. Records, documentation and longitudinal data were useful tools for studying epidemiology of RVF. This report is important to understand the risk factors associated with RVF in sudan, in spite of further studies were required to fully investigate it.

Conclusion
The current study has concluded that RVF is endemic in some areas of sudan; and further surveillances is needed to throughly understand the dynamic and epidemiology of the disease. Also more epidemiological tools were emphasized to investigate the determinants of the disease in the sudan and to estimate the cost effective measurments of prevention and control of the disease.