Rift Valley Fever, Madagascar | CDC EID

EID Journal Home > Volume 16, Number 6–June 2010

Volume 16, Number 6–June 2010
Research
Rift Valley Fever during Rainy Seasons, Madagascar, 2008 and 2009
Soa Fy Andriamandimby, Armand Eugène Randrianarivo-Solofoniaina, Elisabeth M. Jeanmaire, Lisette Ravololomanana, Lanto Tiana Razafimanantsoa, Tsanta Rakotojoelinandrasana, Josette Razainirina, Jonathan Hoffmann, Jean-Pierre Ravalohery, Jean-Théophile Rafisandratantsoa, Pierre E. Rollin, and Jean-Marc Reynes1
Author affiliations: Institut Pasteur, Antananarivo, Madagascar (S.F. Andriamandimby, T. Rakotojoelinandrasana, J. Razainirina, J.Hoffmann, J.-P. Ravalohery, J.-T. Rafisandratantsoa, J.-M. Reynes); Ministère de la Santé et du Planning Familial, Antananarivo (A.E. Randrianarivo-Solofoniaina, L. Ravololomanana); Food and Agriculture Organization, Antananarivo (E.M. Jeanmaire); Ministère de l'Agriculture, d'Elevage et de la Pêche, Antananarivo, (L.T. Razafimanantsoa); and Centers for Disease Control and Prevention, Atlanta, Georgia, USA (P.E. Rollin)

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Abstract
During 2 successive rainy seasons, January 2008 through May 2008 and November 2008 through March 2009, Rift Valley fever virus (RVFV) caused outbreaks in Madagascar. Human and animal infections were confirmed on the northern and southern coasts and in the central highlands. Analysis of partial sequences from RVFV strains showed that all were similar to the strains circulating in Kenya during 2006–2007. A national cross-sectional serologic survey among slaughterhouse workers at high risk showed that RVFV circulation during the 2008 outbreaks included all of the Malagasy regions and that the virus has circulated in at least 92 of Madagascar's 111 districts. To better predict and respond to RVF outbreaks in Madagascar, further epidemiologic studies are needed, such as RVFV complete genome analysis, ruminant movement mapping, and surveillance implementation.
Rift Valley fever virus (RVFV) belongs to the family Bunyaviridae, genus Phlebovirus, and was first isolated in 1930 during an investigation of a large epizootic in Kenya. Virions are enveloped and contain 3 single-stranded RNA genome segments designated large (L), medium (M), and small (S) coding for the viral proteins.

Rift Valley fever (RVF) is an arthropod-borne zoonosis; it affects ruminants and is characterized by high rates of abortion and death in young and adult animals. Economic consequences of this disease can be devastating. In humans, symptoms are usually mild, but in severe cases hemorrhage, meningoencephalitis, retinopathy, and death can occur. RVFV has been detected across Africa, from Senegal to Madagascar and from Egypt to South Africa. In 2000, RVFV reached the Arabian Peninsula (1).

Animals are typically infected before humans. RVFV is transmitted between ruminants primarily by bites of mosquitoes of numerous genera and species. Humans can also be infected by these vectors as well as by contact or inhalation of aerosols generated when handling sick or dead infected animals or their fresh tissues. Treatment of human patients is based on signs and symptoms; a commercial vaccine is available for animals only. RVFV outbreaks are periodic and occur every 10–15 years. Between epidemics, the virus is believed to be maintained through vertical transmission by mosquitoes of the genus Aedes. Outbreaks are closely linked to climate variations, especially widespread increased rainfall, that favor the hatching of mosquito eggs and the subsequent emergence of a large number of adult mosquitoes (2). Moderate or large outbreaks that have been documented in the Horn of Africa (1989, 1997–1998, 2006–2007) were associated with widespread rainfall. For the purpose of predicting RVF outbreaks in this area, a model based on several satellite-derived observations has been proposed (3).

RVFV has also been detected in Madagascar. The first isolate was obtained from mosquitoes caught during the March 1979 rainy season in a forest area in the Moramanga district (no. 514; Appendix Figure), 120 km east of Antananarivo (4). Then in March 1990, an RVF epizootic occurred in Fenoarivo Atsinana (district 509) on the east coast, where an abnormally high incidence of abortions and disease in humans was reported (5,6). A year later, from February through April 1991, RVFV was responsible for abortions and deaths of cattle in the central highlands. Human cases were also confirmed (7,8). After the outbreaks of RVF in 2006 and 2007 in the Horn of Africa (9), 17 years later, the virus was again detected in Madagascar during a major outbreak. We report some features of this outbreak and the results of preliminary molecular characterization of the circulating virus. We also performed a nationwide serosurvey to determine the range of past and recent RVFV circulation.

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