Rift Valley fever

Rift Valley fever


Current authors:
JAW Coetzer - Professor Emeritus, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, Pretoria, Gauteng, South Africa
JT Paweska - Head Centre for Emerging Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases, South Africa
B Bird - Virologist, One Health Institute, School of Veterinary Medicine, University of California Davis, California, United States
R Swanepoel - Extraordinary Lecturer, BVSc, Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria Private Bag X04, Onderstepoort, Pretoria, Gauteng, South Africa
L Odendaal - Senior Lecturer, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, Pretoria, Gauteng, South Africa
J Fafetine - Virologist, Faculty of Veterinary Medicine, Eduardo Mondlane University, Maputo, Mozambique

Introduction and history

Rift Valley fever (RVF) is a peracute or acute disease that mainly affects domestic ruminants and humans caused by a mosquito-borne RNA phlebovirus.346 In domestic animals, the disease is most severe in sheep and goats, resulting in high mortality in new-born lambs and kids and high percentage of abortion in pregnant sheep, goats and sometimes cattle. The infection in humans is usually associated with mild to moderate febrile illness (i.e. fever, myalgia, arthralgia, lethargy), but can progress to severe sequelae including ocular lesions and loss of vision, encephalitis, a haemorrhagic disease with necrotic hepatitis and a high case fatality rate in a minority of patients. Humans usually become infected from contact with virus-contaminated tissues and body fluids from infected animals, but mosquito bites can also transmit the virus. Outbreaks of the disease tend to occur when particularly heavy rains favour the breeding of competent mosquito vectors.

Since original isolation in Kenya,135 RVF virus (RVFV) has been contained for decades within the African continent, but in the last 30 years emerged outside its historic boundaries593 including crossing significant geographic barriers: the Sahara desert into Egypt in 1977,319 the Indian Ocean to Madagascar in 1991,439, 440 and the Comoros Islands in 2007,349 and  the Red Sea to the Arabian Peninsula in 2000/01.557 The unpredictable and sudden emergence of RVFV outside traditional endemic areas, unavailability of safe and efficacious antiviral treatment and prophylactic immunization, led the World Health Organization (WHO) to identify RVF as a priority disease for development of effective therapeutics and vaccines.414

There have been multiple reviews including Henning,258 Weiss,649 Easterday,167 Peters and Meegan,499 Shimshony and Barzilai,556 and Meegan and Bailey.410 The renewed interest in RVF as a significant zoonotic threat has been a subject of numerous reviews covering various aspects of the disease, including epidemiology, pathogenesis, control/prevention, development of new diagnostic assays, therapeutics and vaccines,7, 35, 63, 66, 74, 165, 191, 271, 274, 287, 320, 331, 337, 361, 368, 383, 405, 416, 477, 485, 486, 490, 494, 503, 522, 593 molecular biology and genomics, 76, 209, 231, 270 viral and host determinants of virulence,274 surveillance, predictive models and control strategies emphasizing the One Health concept67, 203, 246, 331, 429 and ecological, climatic and anthropogenic factors that play a role in RVF emergence, re-emergence and spread.107, 384

An acute and highly fatal disease of lambs associated with heavy rains and accompanied by reports of illness in humans was first recognized in the Rift Valley in Kenya at the turn of the century, but the causative agent was not isolated until 1930.134, 431, 579 Major outbreaks were subsequently recorded in Kenya in 1930/31, 1968, 1978/79, 1997/98, 2006/07, 2014/15 and 2019 and lesser outbreaks at irregular intervals during the intervening years.145, 146, 410, 666

The disease was first recorded in southern Africa in the early 1950s when a large epidemic occurred in the western Free State, southern Gauteng and adjacent North West and Limpopo provinces of South Africa, although it was only recognized as RVF early in 1951 when humans became ill after assisting at a necropsy of a bull near Johannesburg.15, 453 Sheep farming dominates in some of the affected areas and it was estimated that 100 000 sheep died and 500 000 aborted in the epidemic, with smaller losses occurring in cattle.542 Lesser outbreaks of the disease or sporadic isolations of virus were recorded in South Africa in 1952/53, 1955/59, 1969/71, 1981, 1996, and 2018.25, 45, 283, 392, 395, 402, 629, 649 After more than a decade with minor reported RVF activity, large outbreaks affecting most of South Africa occurred in 2009/10.30, 82, 418, 657

The diversity of clinical disease presentation in humans was recognized first in Kenya, and during the 1950/51 epidemic in South Africa, when it was recognized that RVF could be accompanied by transient loss of visual acuity and serious ocular sequelae.217, 234, 539, 540 Human deaths following natural infection were first recorded in South Africa during the epidemic in 1975 when...

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