RIFT VALLEY FEVER: LESSONS TO BE LEARNED
Rift Valley Fever (RVF) is primarily a disease that affects animals (sheep, cattle and other domestic animals) and occasionally humans. RVF epizootics can be recognized in a season when mosquitoes are abundant, and when there are abortions and neonatal death in sheep and cattle, and/or cases of fever in man, sometimes complicated by hemorrhagic fever, encephalitis, and retinitis.1 Prior to 17 September 2000, when RVF was first reported in the Jizan region in South Western Saudi Arabia, the disease had been confined to the African continent.2 The disease is caused by the RVF virus, a member of the genus Phelebovirus in the Family Bunyaviridae and was first reported among livestock in the early 1900s.
Since 1930, when the virus was first isolated during an investigation into an epidemic among sheep on a farm in the Rift Valley of Kenya, there have been serious outbreaks in sub-Saharan and North Africa.3 The most notable epizootic occurred in Kenya in 1950-1951 and resulted in the death of about 100,000 sheep. In 1977, the virus was detected in Egypt and caused a serious outbreak of RVF among animals and humans. The first epidemic of RVF in West Africa was reported in 1987, and was linked to construction of the Senegal River Project. This caused flooding in the lower Senegal River area and altered interactions between animals and humans, resulting in transmission of the RVF virus to humans.4 The clinical and pathological features of RVF have been described since 1931, and a large body of basic information has been accumulated over several decades.5,6 All information indicated that RVF is vector borne, and that at least 26 species of arthropods, mostly mosquitoes, may be or have been found to be infected. It has also been documented that transmission of RVF virus by aerosol from blood and other infected body fluids was implicated in the frequent infections of virologists, veterinarians, and abattoir workers. A sero-prevalence study conducted among butchers in Makkah during Hajj in 1419 (1997) revealed that 17% were sero-positive to RVF. A high infection rate was reported among non-African butchers.7
Very shortly after the report of RVF outbreak in the Jizan area in Saudi Arabia, few cases with hemorrhagic fever were reported in “ Mour Valley” in Yemen. Later on, these cases were confirmed as RVF, thus initiating the enquiry about the circumstantial factors behind the existence of the disease in both Saudi Arabia and Yemen. The precise mechanism by which RVF was introduced into Saudi Arabia in the year 2000 is not known.
Predictions regarding further spread can therefore, only be speculative. It has been previously pointed out that the RVF virus can be spread by infected arthropod vectors transported by aeroplanes or on winds in the intertropical Convergence Zone, which in some seasons may carry mosquitoes for hundreds of kilometers.8 Based on the previous possibility, the Mediterranean Basin or South-West Asia were supposed to be at highest risk. For an area to be receptive for RVF epidemic it should have an abundance of vectors and a high concentration of domestic animals to amplify the transmission cycle.
Some researchers reported the role of rats and rodents as reservoirs or natural hosts for RVF virus during an RVF outbreak in Egypt in 1977-1978.9
The anticipated occurrence of Rift Valley Fever disease, particularly in Saudi Arabia, was previously reported.3 As a result of the advances in the virological knowledge and the experience gained from the extensive epidemic of RVF in Egypt in 1977, it was assumed that the virus was capable of spreading to areas outside its former range in sub-Saharan Africa.6 We should have been mindful of these concerns particularly because of the existence of conditions suitable to the occurrence of RVF in Jizan. These include: the free movement of sheep and cattle, the high arthropod densities and the existence of the virus from a poorly understood cycle. There are other environmental factors including poor housing, and poor environmental sanitation that affect the incidence of the disease. Poverty and illiteracy also are possible contributing factors.
The promising preventive approach is vaccination of sheep and cattle using either killed or live attenuated vaccines. The advantages and disadvantages in choosing either type should be considered. Priority should be directed towards the efficacy and effectiveness of the vaccine in limiting an epizootic spread. However, the use of human inactivated vaccine should be restricted to exposed laboratory workers, veterinarians and vulnerable occupational groups. Where an epizootic of RVF is in progress, in addition to mosquito control, the movements of animals from affected areas should be restricted. The cooperation between public health authorities, particularly through an active surveillance system together with the effort of veterinarians and municipal authorities, will be invaluable in preventing future epidemics. We hope that further research will be conducted to ascertain the natural maintenance cycle of RVF as well as to improve the existing knowledge of the possible enzootic and/or epizootic vectors.Strategic multi-disciplinary ministerial approaches were planned and adopted to control the current RVF epizootic within and outside the primarily affected region. These efforts included primarily disseminating information about the disease to all medical and health personnel, and those connected with the livestock industry. Veterinary and public health workers were put at a particularly alert status as the disease may be recognized through increased rates of abortion in sheep and cattle before it infects people. Alerting and informing the general population of the existence of rift valley fever and educating them regarding the possible channels of transmission and ways of prevention was, and still is, of particular importance. Such educational efforts were launced at various levels and by all possible means with particular emphasis on the content of the message which was geared to be simple, sound and reliable. However, public fear and phobia was evidenced by the overall decline in red meat and, to a lesser extent, dairy products consumption, as well as to the refusal of sending children to school in some afflicted regions. Of the utmost importance was the cooperation and open communication between the Ministrries of Health, Agriculture and Municipality which are all involved in the control of rift valley fever. Movements of animals from the Jizan region which currently had an epizootic RVF was restricted, sick animals were allowed to recover or die and be buried under veterinary supervision. Slaughtering of clinically affected animals was prohibited to reduce the risk of infection through exposure to aerosolized infectious blood and other bloody fluids. However, total restriction of animal movement was broken in few illegitimate incidents. Unauthorized animal movement, to avoid complying with the legislation of exporting and importing countries, are a real problem. Supervision of slaughter houses and carcasses was activated to ensure the safety of meat for human consumption.
Emergency measures for mosquitoes control were initiated and implemented by ground and aerial insecticide spraying with the use of larvicides; these were directed against possible local breeding sites. The public were advised to use indoor insecticides with residual contact effort which are available in the markets. Vulnerable people were encouraged to use bed-nets which were distributed and made available for them. Mesh screens were also suggested to be fitted to doors and windows. The proliferation of mosquitoes is usually associated with problems arising from rapid urbanization with deficiency in water management. Environmental control measures therefore constitute the most important long-term means for controlling vectors of epizootic or epidemic of RVF.10
Precautionary environmental sanitation measures have been taken into consideration for the construction and maintenance of drains to allow free flow and disposal of unwanted water. Scattered, small water collections in and around the afflicted areas were eliminated. Effective refuse control was undertaken to reduce the possible sources of mosquitoes breeding foci.
All national control efforts were made available in order to contain the current epidemic of RVF. Jizan region has gained particular attention of the highest authority in Saudi Arabia as witnessed by the Royal Decree for establishing a higher committee to investigate the needs of that region.
Inspite of the effectiveness of employed measures in limiting the spread of RVF to other regions of Saudi Arabia, future uprecedented occurrence into previously free areas cannot be guaranteed. Epidemiologists should draw attention to the potential of RVF occurrence in receptive areas.
The adoption of active surveillance for human and animal disease will add more knowledge regarding the transmission of the virus among mosquitoes and the role of vertebrates in propagating it in order to predict and control future outbreaks of RVF. Furthermore, if the virus persists or becomes enzootic, the role of a reservoir should be investigated. Under the assumption that future RVF epidemics will continue to result in human fatalities, more research will be needed to investigate the unrestricted use of vaccines and to have specific therapeutic approaches rather than the currently available simple supportive ones.
Dr. Awatif A. Alam, ABCM Dr. Ashry G. Mohammed, PhD Department of Family & Community Medicine
College of Medicine, King Saud University
Riyadh, Saudi Arabia
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