Risk Factors of Rift Valley fever Among the Samtah Population, Jazan, Saudi Arabia

Rift Valley Fever (RVF) was reported for the first time in Saudi Arabia after several cases of unexplained hemorrhagic fever appeared in the southwestern border (Jazan Region). Cases wet reported by all governorates of Jazan, including Samtah Governorate. nested case control study was conducted to identify risk factors for acquiring RVF.

All RVF cases diagnosed and confirmed serologically at Samtah General Hospital were reviewed and their addresses located. A list of PHCCs with its census was provided from the Samtah Health District. Four controls were selected for each case, proportional to the census of each PHCC, regardless of the location of cases. At each PHCC an accumulative number was assigned to each medical record. A random number chart was used to select controls. The name, medical record number, and location were registered according to sequences of the selection. All study participants were interviewed face to face using a standard questionnaire. Parents were interviewed on behalf of young children. The questionnaire included demographic information, history of underlining medical conditions, and risk Factors of RVF.

The final study sample included 39 Cases and 238 Controls. Among the cases. 28 (72%) were males; median age was 43 years (range 7-85 years); 31 (80%) were Saudis and 8 (20%) were Yemenis. Among the controls, 126 (53%) were males; median age was 18 years (range 2-92 years); almost all of them 237 (99.6%) were Saudis, except for one Indonesian. The majority of both cases and controls had no history of chronic diseases.

Table I demonstrates behavioral and community risk factors for acquiring RVF. Only 10 cases and 195 controls reported sleeping inside the houses. Those who reported sleeping outside the house were at a higher risk of RVF. whether they slept outside regularly, (OR -14.2, P-value <0.05) or occasionally (OR-11.1, P value <0.05). Those who sprayed insecticides were protected from RVF, but use of a bednet was not protective. Those who drank raw milk without boiling or pasteurizing were at a higher risk of RVF, whereas handling raw meat while cooking, eating raw meat or other raw animal organs had no effect. Mosquito bites were not associated with acquiring RVF. However, those who owned sheep among those bitten by mosquitoes had a ten times risk of acquiring the disease. Stagnant water had no effect on acquiring the disease, regardless of its proximity to houses.

Individuals who owned animals were twice at risk of RVF than those who did not (Table 2). Sheep were the most implicated animal for their owners to acquire the disease. The risk increased the higher the number of animals, regardless to their type. Owning animals led to other risk factors that increased susceptibility for RVF (Table 3), such as shepherding, the risk increasing the longer the time spent in shepherding. Also, allowing animals inside the house increased the risk, which further increased the longer they are allowed in the house. Reported aborted animals, animal deaths, helping in animal birthing, or slaughtering were also associated with risk of RVF. However, milking was not statistically associated with acquiring RVF.

This study was targeted to identify possible risk factors of acquiring RVF. Although there is a difference between cases and controls in age, sex, and nationality, these factors have not been proved to contribute to acquiring RVF in the few studies that have been conducted.[1,2-4] This study was primarily designed to select controls that represented the population and had been exposed to the same risk factors.

At the time this study was conducted, there was no available information on the prevalence of RVF. It is well known that the majority of cases may acquire the infection without developing complications,[1] and may recover without recognition. Up to date, the risk of acquiring RVF is mainly through exposure to or contact with fresh tissue of infected animals, or by infective mosquito bites. Although the study showed that those bitten by mosquitoes were two times at risk of RVF, this, however, could not account for those bitten by mosquitoes but were not affected by RVF. It is uncertain what role, if any, mosquitoes play in the transmission of RVF to humans.[5,6] If they do play a role, the presence of stagnant water close to houses should have been a risk factor, since it is the main mosquito breeding area. Mosquitos may, however, play a role in transmission of RVF to humans if livestock develop high viremias, coinciding with the presence of a high density of mosquitoes. This may explain why those who reported sleeping outside the houses were at a higher risk of acquiring RVF, the risk increasing when this occurs on a daily basis. Spraying insecticide, which diminishes the density of mosquitos, was found to play an important role in the prevention of RVF. However, use of a bednet, which may play a role in prevention of mosquito bites, was not a common practice among the study population.

Some studies suggest the possibility of transmission of RVF to humans by drinking infected milk [1,2] which was proved in our study. Those who drank raw milk were twelve times at risk, pointing to the presence of the virus in milk.[4]

Although direct contact with tissues and organs of infected animals is thought to transmit the disease, this may only be true if the person has an open wound through which the virus can penetrate. Handling raw meat while cooking was not associated with

RVF infection, nonetheless, pre should be taken in case of epidemics. Eating raw meat or other raw animal organs was not proved to be a risk factor, however, this habit should be stopped immediately, particularly in endemic areas. The possibility of acquiring the disease by contact with infected fresh animal organs could not be ruled out, since those who helped in animal birthing or slaughtering had more than twice the risk of infection.

Owning animals was considered a major risk for RVF, especially sheep and goats. However, an opposite result was found among owners of cattle (cows), since their larger size kept them away from houses. Abortions or unexplained deaths among animals were significant risk factors, and could be used as indicators to the possibility of animal infection, thus allowing early detection, and should be considered in Community education to prevent future epidemics. Slaughtering animals was a significant risk factor, in case of which infection may occur as a result of injury or the possibility of airborne transmission.[1,2,3]

Educating the population in endemic areas of the importance of sleeping inside houses and spraying insecticides is recommended. Animal owners should be educated on the importance of keeping animals away from houses, immunizing them against RVF, immediate reporting to the local health authority if recurrent abortions or unexplained deaths occur among animals, the importance of wearing gloves during animal birthing, and proper disposal of abortuses or dead animals. We also recommend educating the public on the importance of boiling milk before drinking. Additional studies should be carried out to identify the role of mosquitoes in RVF transmission.