Towards assessing fine-scale indicators for the spatial transmission risk of Fasciola hepatica in cattle

Abstract

Abstract. In order to improve the spatial resolution of current risk maps for fasciolosis in cattle, more knowledge is needed with respect to farm-level factors that determine infection risk. In this study, we visited 39 dairy farms within a predefined low-and high-risk area for fasciolosis in Belgium and assessed their infection status by an indirect bulk tank milk enzyme-linked immunosorbent assay (ELISA). Management factors were collected and all pastured lands of the farms were visited to identify and georeference potential snail habitats. The habitats were visually characterised, investigated for the presence of the intermediate host snails of Fasciola hepatica (i.e.Galba truncatula and Radix spp.) and used in a geographical information system (GIS) to construct overlays including information on soil and hydrology. A linear regression model was used to evaluate associations between bulk tank milk ELISA results and farm level management and habitat factors. A logistic, mixed model was used to identify possible risk factors for the presence of intermediate host snails on a potential habitat. Potential snail habitats were found in 35 out of 39 farms. A total of 87 potential habitats were identified and on 29% of these, intermediate host snails were found. The number of potential habitats, the presence of snails, drainage of pastures, month of turnout of the cows, stocking rate, type of watering place and risk area were significantly associated with the bulk tank milk ELISA result and explained 85% of the observed variation. Intermediate host snails were more likely to be present with increasing surface of the potential habitat and on loamy soils. This study confirms the importance of farm management factors in the infection risk for F. hepatica in cattle and highlights that the combination of management factors with characterization of snail habitats is a powerful means to predict the infection risk with F. hepatica at the individual farm level. Further research is needed to investigate how this knowledge can be incorporated in nation-wide spatial distribution models of the parasite.

Distribution of Fasciola hepatica in Swedish dairy cattle and associations with pasture management factors

“…In cows, however, there was no association between length of the grazing period and liver fluke seropositivity. This is not surprising, as dairy cows are generally kept on frequently re-seeded grass leys, where expo- Charlier et al, 2011). Our data suggest an association with mowing of pasture and herd size, but not at a significant level.…”

“…It has been shown that significant production losses occur in herds with a prevalence of F. hepatica infection of 25% or higher (Vercruysse and Claerebout, 2001). Detection of antibodies to liver fluke by the enzyme-linked immunosorbent assay (ELISA) in bulk tank milk (BTM) samples (Duscher et al, 2011) is currently the most common method for F. hepatica diagnosis in dairy production at the herd level (Forbes and Charlier, 2006;Charlier et al, 2007Charlier et al, , 2011Charlier et al, , 2014Salimi-Bejestani et al, 2007;Bennema et al, 2009). The simplicity of BTM collection provides an easy tool for spatial liver fluke screening at different regional scales.…”

Fine-scale mapping of vector habitats using very high resolution satellite imagery: a liver fluke case-study

“…SWBs smaller than 1 m 2 were not considered. Water troughs were also not included in this study, since these systems did not contain snails in a previous study performed by Charlier et al (2011).…”

“…the study by McCann et al (2010) where the risk was estimated using post codes with a mean surface area of 2,000 km 2 . Mapping potential habitats at a finer spatial scale could substantially improve the temporal and spatial resolution of current risk maps and create novel possibilities for improved disease management based on better understanding of transmission dynamics at the local habitat scale (Lacaux et al, 2007;Simoonga et al, 2009;Charlier et al, 2011;Estallo et al, 2012). Flexible, automated and operational tools capable of characterising vector habitats at high resolutions are, however, currently lacking.…”

“…The life-cycle of the liver fluke Fasciola hepatica depends on the intermediate snail host Galba truncatula. The highly dynamic small water bodies (SWBs), such as ponds, ditches and wet pasture areas constitute the main habitat of this vector (Torgerson and Claxton, 1999;Schweizer et al 2007;Charlier et al, 2011;Rondelaud et al 2011). Knowledge of the local occurrence and dynamics of the freshwater vector habitats is hence of key importance for studying spatial variation in disease transmission.…”