Exploratory space-time analyses of Rift Valley Fever in South Africa in 2008–2011

Metras, Raphaelle and Porphyre, Thibaud and Kemp, Alan and Pfeiffer, Dirk U. and Thompson, Peter N. and Collins, Lisa M. and White, Richard G. (2012) Exploratory space-time analyses of Rift Valley Fever in South Africa in 2008–2011. PLoS Neglected Tropical Diseases, 6 (8). e1808. ISSN 1935-2727

Full content URL: http://dx.doi.org/10.1371/journal.pntd.0001808

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Item Type:Article
Item Status:Live Archive

Abstract

Background

Rift Valley fever (RVF) is a zoonotic arbovirosis for which the primary hosts are domestic livestock (cattle, sheep and goats). RVF was first described in South Africa in 1950–1951. Mechanisms for short and long distance transmission have been hypothesised, but there is little supporting evidence. Here we describe RVF occurrence and spatial distribution in South Africa in 2008–11, and investigate the presence of a contagious process in order to generate hypotheses on the different mechanisms of transmission.

Methodology/Principal Findings

A total of 658 cases were extracted from World Animal Health Information Database. Descriptive statistics, epidemic curves and maps were produced. The space-time K-function was used to test for evidence of space-time interaction. Five RVF outbreak waves (one in 2008, two in 2009, one in 2010 and one in 2011) of varying duration, location and size were reported. About 70% of cases (n = 471) occurred in 2010, when the epidemic was almost country-wide. No strong evidence of space-time interaction was found for 2008 or the second wave in 2009. In the first wave of 2009, a significant space-time interaction was detected for up to one month and over 40 km. In 2010 and 2011 a significant intense, short and localised space-time interaction (up to 3 days and 15 km) was detected, followed by one of lower intensity (up to 2 weeks and 35 to 90 km).

Conclusions/Significance

The description of the spatiotemporal patterns of RVF in South Africa between 2008 and 2011 supports the hypothesis that during an epidemic, disease spread may be supported by factors other than active vector dispersal. Limitations of under-reporting and space-time K-function properties are discussed. Further spatial analyses and data are required to explain factors and mechanisms driving RVF spread.

Keywords:Rift Valley Fever
Subjects:D Veterinary Sciences, Agriculture and related subjects > D411 Agricultural Pests and Diseases
D Veterinary Sciences, Agriculture and related subjects > D320 Animal Health
D Veterinary Sciences, Agriculture and related subjects > D323 Animal Pathology
D Veterinary Sciences, Agriculture and related subjects > D300 Animal Science
Divisions:College of Science > School of Life Sciences
ID Code:11913
Deposited On:16 Sep 2013 16:28

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