Distribution of Rift Valley Fever in Africa. Blue, countries with endemic disease and substantial outbreaks of RVF; green, countries known to have some cases, periodic isolation of virus, or serologic evidence of RVF.
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Rift Valley fever

Rift Valley fever (RVF) is a viral zoonosis (affects primarily domestic livestock, but can be passed to humans) causing fever. It is spread by the bite of infected mosquitoes. The disease is caused by the RVF virus, a member of the genus Phlebovirus (family Bunyaviridae). more...

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The disease was first reported among livestock in Kenya around 1915, but the virus was not isolated until 1931. RVF outbreaks occur across sub-Saharan Africa, with outbreaks occurring elsewhere infrequntly (but sometimes severely - in Egypt in 1977-78, several million people were infected and thousands died during a violent epidemic; in September 2000 an outbreak was confirmed in Saudi Arabia and Yemen).

In humans the virus can cause several different syndromes. Usually sufferers have either no symptoms or only a mild illness with fever, headache, myalgia and liver abnormalities. In a small percentage of cases (< 2%) the illness can progress to hemorrhagic fever syndrome, meningo-encephalitis (inflammation of the brain), or affecting the eye. Patients who become ill usually experience fever, generalized weakness, back pain, dizziness, and weight loss at the onset of the illness. Typically, patients recover within 2-7 days after onset.

Approximately 1% of human sufferers die of the disease. Amongst livestock the fatality level is significantly higher. In pregnant livestock infected with RVF there is the abortion of virtually 100% of fetuses. An epizootic (animal disease epidemic) of RVF is usually first indicated by a wave of unexplained abortions.

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Outbreak of Rift Valley Fever — Saudi Arabia, August-October, 2000
From Morbidity and Mortality Weekly Report, 10/13/00

On September 10, 2000, the Ministry of Health (MOH), Kingdom of Saudi Arabia, and subsequently the Ministry of Health of Yemen received reports of unexplained hemorrhagic fever in humans and associated animal deaths from the southwestern border of Saudi Arabia and Yemen. Signs and symptoms of ill persons included low grade fever, abdominal pain, vomiting, diarrhea, jaundice with liver and renal dysfunction often progressing to disseminated intravascular coagulation, hepatorenal syndrome, and death. On September 15, using ELISA (antigen detection and IgM), polymerase chain reaction, virus isolation, and immunohistochemistry, CDC confirmed the diagnosis of Rift Valley fever (RVF) in all four serum samples submitted from Saudi Arabia. This report summarizes the preliminary results of the collaborative epidemiologic investigation performed by the Saudi Arabian MOH, CDC, and the National Institute of Virology, South Africa, of the first confirmed occurrence of RVF outside Africa.

As of October 9 in Saudi Arabia, 316 persons with suspected severe RVF [*] have been reported from primary health-care centers and hospitals. All suspected severe cases have been hospitalized for care and management. Of the 316 case-patients, 245 (78%) were male; the median age was 46 years (range: 11-95 years); 15 (5%) were aged [less than]16 years; 253 (80%) were Saudi citizens and 63 (20%) were Yemen citizens. At least 66 (21%) patients have died. Suspected severe case-patients investigated to date resided in or visited the floodplains of the wadis (i.e., seasonal riverbeds) that emanate from the foothills of the Sarawat mountains and extend south of Jeddah to the border of Yemen (Figure 1). Of the 316 suspected cases, 304(96%) have been reported from the southern coastal province of Jizan (1992 population: 860,000) and the contiguous Asir and Al Quenfadah health regions. Cases from four other health regions have documented travel to these areas. The onset of the earliest suspected case was August 27 (Figure 2).

The activities of the MOH, Ministry of Agriculture and Water, and Ministry of Municipalities to contain the outbreak included an intensive mosquito-control program; restriction of movement of domestic animals; a comprehensive educational campaign to eliminate contact with sick animals and mosquitoes (including provision of free permethrin-impregnated bednets); encouragement to seek early medical evaluation of persons with febrile illnesses; and information for health-care providers on the clinical presentation and management of suspected cases. Studies are in progress to identify risk factors for infection, severe disease, and mortality. Animal, human, and vector surveillance is being strengthened throughout the country, including establishment of central human and veterinary virology laboratories in Riyadh and Jizan, respectively. A kingdomwide survey among domestic ungulates, primarily sheep and goats, is under way to define the boundaries for a veterinary vaccination program. Additional studies are planne d to assess the magnitude of the outbreak, to define infection rates among high-risk groups, such as veterinarians and slaughterhouse workers, and to determine evidence for nosocomial transmission.

Reported by: H Arishi, MD, A Ageel, MD, MA Rahman, MD, AA Hazmi, MD, AR Arishi, MD, B Ayaola, MD, C Menon, MD, J Ashraf, MD, O Frogusin, MD, F Sawwan, M Al Hazmi, MD, King Fahd Central Hospital, Jizan; A As-Sharif, MS. M Al Sayed, A Raheem Ageel, MD, Regional Health Affairs, Jizan; ARA Alrajhi, MD, King Faisal Specialist Hospital and Research Center, Riyadh; MA AI-Hedaithy, MD, College of Medicine, King Khalid Univ Hospital, Riyadh; A Fatani, MBBS, A Sahaly, MBBS, A Ghelani, MBBS, TAI Basam, MBBS, A Turkistani, BDS, N Al Hamadan, MBBS, Saudi Arabia Field Epidemiology Training Program, Riyadh; A Mishkas, MBBS, Infectious Diseases; MH AI-Jeifri, MBBS, Parasitic and Infectious Diseases; VYAI Mazroa, MD, MMA Alamri, MM AI-Qahtani, MBBS, A Al Drees, Laboratories and Blood Banks, Riyadh; T Madden, MD, G Al Gazebo, QA Shubokshi, MD, Ministry of Health, Saudi Arabia. P Jupp, PhD, A Kemp, MS. F Burt, PhD, R Swanepoel, PhD, Pathogens Unit, National Institute of Virology, Johannesburg, South Africa. Infectious Disease P athology Activity, Special Pathogens Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases, CDC; and an EIS Officer.

Editorial Note: RVF is a mosquitoborne zoonotic viral disease predominantly causing abortion and deaths of young animals (e.g., sheep and goats) [1]. Epizootic and epidemic transmission is associated with periodic heavy rainfall. Human infection is predominately not apparent or is associated with a brief self-limited febrile illness. However, complications such as retinitis, hemorrhagic fever, or encephalitis occur in some patients (approximately 15%, 1%, and 1%, respectively) [1]. Transmission is primarily by contact with infected animal body fluids and mosquito bites, although virology laboratory workers also are at risk. Person-to-person transmission has not been reported. The Saudi Arabian MOH is evaluating the feasibility of a randomized, placebo-controlled trial using intravenous ribavirin in patients with suspected severe RVF. Although ribavirin has not been administered to humans with RyE, evidence suggests its efficacy in animal models [2]. Intravenous ribavirin has been shown to treat effectively ot her viral hemorrhagic fevers, including Lassa fever, hemorrhagic fever with renal syndrome, and CrimeanCongo hemorrhagic fever [2].

This outbreak on the Arabian Peninsula represents the first cases of RVF outside Africa. The potential of RVF virus to establish transmission and cause disease in new areas first was documented during its emergence in Egypt in 1977; previously, the disease was limited to sub-Saharan Africa. The virus isolated from the blood of the first patients had a RNA sequence similar to the RVF viruses isolated during 1997-1998 East African outbreaks [3]. Cross-sectional community surveys for asymptomatic and milder illnesses and laboratory evidence of infection are in progress to assess the magnitude and geographic extent of infection.

(*.) Screening case definition for RVF: unexplained illness [greater than]48 hours in duration associated with three times elevation in transaminases (aspartate aminotransferase, alanine aminotrans ferase, and gamma glutamyl transpeptidase) or clinical jaundice; or unexplained illness [greater than]48 hours in duration associated with abortion or bleeding manifestations (e.g., from puncture sites, ecchymosis, petechiae, purpura, epistaxis, gastrointestinal bleeding, or menorrhagia); or unexplained acute visual loss or scotoma; or unexplained illness [greater than]48 hours in duration associated with neurologic manifestations (e.g., vertigo, confusion, disorientation, amnesia, lethargy, hallucination, meningismus, choreiform movements, ataxia, tremor, convulsions, hemiparesis, decerebrate posturing, locked-in syndrome, or coma); or unexplained illness [greater than]48 hours in duration associated with fever, diarrhea, nausea, vomiting, or abdominal pain and any one of the following laboratory values: 1) hemogl obin [less than]8 gm/dL; 2) platelets [less than]100,000 [mm.sup.3] ([less than]10 x [10.sup.10]/L); 3) LDH 2 x upper limit of normal; 4) creatinine [greater than]150 mol/L; 5) CPK 2 x upper limit of normal; or unexplained death with history of fever, lethargy, diarrhea, abdominal pain, nausea, vomiting, or headache in the preceding 2 weeks.


(1.) Peters CJ. Emergence of Rift Valley fever. In Saluzzo JF, Dodet B, eds. Factors in the emergence of arboviruses, 1997. Paris, France: Elsevier, 253-64.

(2.) Huggins JW. Prospects for treatment of viral hemorrhagic fevers with ribavirin, a broad-spectrum antiviral drug. Reviews of Infectious Diseases 1989;11(suppl 4):S750--S761.

(3.) CDC. Rift Valley fever--East Africa, 1997-1998. MMWR 1998;47:261--4.

COPYRIGHT 2000 U.S. Government Printing Office
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