Dilution effect in bovine tuberculosis: risk factors for regional disease occurrence in Africa

Abstract

Changes in host diversity have been postulated to influence the risk of infectious diseases, including both dilution and amplification effects. The dilution effect refers to a negative relationship between biodiversity and disease risk, whereas the amplification effect occurs when biodiversity increases disease risk. We tested these effects with an influential disease, bovine tuberculosis (BTB), which is widespread in many countries, causing severe economic losses. Based on the BTB outbreak data in cattle from 2005 to 2010, we also tested, using generalized linear mixed models, which other factors were associated with the regional BTB presence in cattle in Africa. The interdependencies of predictors and their correlations with BTB presence were examined using path analysis. Our results suggested a dilution effect, where increased mammal species richness was associated with reduced probability of BTB presence after adjustment for cattle density. In addition, our results also suggested that areas with BTB infection in the preceding year, higher cattle density and larger percentage of area occupied by African buffalo were more likely to report BTB outbreaks. Climatic variables only indirectly influenced the risk of BTB presence through their effects on cattle density and wildlife distribution. Since most studies investigating the role of wildlife species on BTB transmission only involve single-species analysis, more efforts are needed to better understand the effect of the structure of wildlife communities on BTB dynamics.

Epidemiological modelling for the assessment of bovine tuberculosis surveillance in the dairy farm network in Emilia-Romagna (Italy)

“…Since bTB is a chronic disease characterized by slow transmission dynamics (see Agusto et al, 2011;Huang et al, 2013;Brooks-Pollock et al, 2014) the assumption of endemic equilibrium within a given farm is unrealistic. Then, we explicitly accounted for within-farm disease dynamics describing how epidemics evolve inside farms following the introduction of infected animals.…”

Contrasting effects of host species and phylogenetic diversity on the occurrence of HPAI H5N1 in European wild birds

“…The dilution effect, representing a "win-win" outcome for public health and nature conservation, has attracted much attention in the context of global biodiversity decline and increasing disease emergence (Huang et al, 2016;Randolph & Dobson, 2012;Wood et al, 2014). Since the dilution effect was first identified in Lyme disease (LoGiudice, Ostfeld, Schmidt, & Keesing, 2003), it has been reported in many different parasite systems, including bovine tuberculosis (Huang, de Boer, van Langevelde, Xu, et al, 2013;Huang, Xu, et al, 2014), Hantavirus (Clay, Lehmer, Jeor, & Dearing, 2009;Suzán et al, 2009)…”

Evaluating the tuberculosis hazard posed to cattle from wildlife across Europe

“…Dizney and Ruedas, 2009). Huang et al (2013) suggested that such a dilution effect may occur for TB in multiple host systems in Africa. However, that study did not include all the possible susceptible species that could be found in regions of interest.…”