Zoonotic risk, communal farming and livestock trade : the example of Rift Valley fever in north-eastern KwaZulu-Natal

Abstract

The emergence and spread of Rift Valley fever (RVF) present a significant challenge to both animal and human health across Africa and the Middle East. This zoonotic disease, caused by the RVF virus (RVFV), primarily affects livestock but can also infect humans, leading to substantial economic losses through livestock deaths and trade restrictions. In South Africa, major outbreaks occurred in 1950-51, 1974-76, and 2010-2011, resulting in significant livestock losses and human infections. Recent studies have found that RVFV is endemic among livestock and wildlife in the northern coastal areas of the KwaZulu-Natal (KZN) province. To investigate factors potentially impacting the risk of RVFV spread in and out of northern KZN, three interconnected studies were conducted focusing on the uMkhanyakude District. The first examined communal livestock farmers' knowledge, attitudes, and practices regarding livestock and zoonotic diseases. Surveying 504 farmers across 45 dip tanks, the research revealed moderate overall knowledge (53.2%) of animal disease transmission. Despite this, over 40% of farmers were unaware of the zoonotic risks from wildlife and livestock. This finding highlighted the critical need for targeted educational interventions. Building on these insights, the second study analysed livestock movement patterns within the wildlife-livestock interface area. The analysis of movement permits from 2015 to 2018 revealed 3,598 movements involving 33,561 animals. Sixty-three percent of these movements were directed outside the study area, including into areas which have previously experienced RVF outbreaks, with distinct patterns for cattle and goats. The study demonstrated the potential for disease spread across provincial boundaries and identified certain dip tanks acting as key movement nodes, emphasizing the need for enhanced surveillance measures. The final study evaluated the risk of RVFV spread from north-eastern KZN using a stochastic risk assessment model to evaluate the monthly probability of at least one viraemic animal arriving at a destination outside the study area via a legal animal movement. Temporal modelling showed peak risks in January-March for goats (0.77) and February for cattle (0.44), aligning with high movement and favourable vector conditions. Within the study area, coastal and riverine areas presented moderate, variable risk, while mountain areas remained consistently low. Sensitivity analysis identified RVFV infection incidence rate, monthly animal movement volume, duration of viraemia, and duration of transport as the most influential parameters in terms of variability. These findings collectively underscore the importance of adopting a One Health approach to RVF control, integrating disease surveillance, environmental monitoring, movement control, and community education. The research highlights the critical need for enhanced surveillance systems, particularly in identified high-risk areas, and emphasizes the importance of collaborative efforts between veterinary and public health authorities. Furthermore, the studies suggest that effective disease control strategies must consider both the ecological factors driving disease transmission and the social contexts in which livestock farming occurs.