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Neospora caninum and Toxoplasma gondii in brain tissue of feral rodents and insectivores caught on farms in the Netherlands

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Abstract

We investigated the presence of both Neospora caninum and Toxoplasma gondii in 250 brain tissue samples from 9 species of feral rodents and insectivores caught on 10 organic farms in the Netherlands in 2004. Collected samples were conserved in 4% paraformaldehyde solution and analysed by real-time PCR. For N. caninum, 31 samples originating from 6 species tested positive (12.4%): common shrews (33.3%), wood mice (17.6%), harvest mice (16.7%), house mice (15.4%), white-toothed shrews (10.8%) and common voles (4.2%). For T. gondii, the overall contamination level was 4%, and only three species were found to be positive: house mice (9.0%), common voles (4.2%) and white-toothed shrews (2.0%). Most N. caninum infected samples (27/31; 87%) were found on farms where dogs were present. Due to the observation that rodents and insectivores can contract both parasites, they might function as indicator species for the parasitic load on farms.

Introduction

On farms, the emergence of protozoan parasites such as Neospora caninum (N. caninum) and Toxoplasma gondii (T. gondii) may have severe consequences. N. caninum can be a major cause of abortion in cattle and this parasite can either be vertically transmitted in utero or horizontally by uptake of oocysts excreted by canids (either domestic or feral). Earlier studies have already suggested that rodents may play a role in the dissemination of N. caninum throughout the environment (Huang et al., 2004, Hughes et al., 2006, Jenkins et al., 2007).

As felids are the definitive hosts for T. gondii, they may excrete oocysts contaminating the farm environment. T. gondii is a major cause of abortion and foetal abnormalities in sheep (Hide et al., 2009), but even more importantly, when taken up by livestock (e.g. pigs) this parasite may be transmitted to humans through the consumption of raw or undercooked meat (Kijlstra and Jongert, 2008), leading to significant health problems.

Rodents can transfer many pathogens either directly or indirectly (Meerburg, 2010, Meerburg et al., 2009), and can be considered as one of the main pathways of T. gondii transmission to livestock. First, some farm animals may accidentally eat rodents. Pigs are omnivorous animals that are able to catch and eat rodents. They might even consume dead animals, thus ingesting tissue cysts. Moreover, congenital transmission rates in a natural population of rodents were recently found to be 75% (Hide et al., 2009). Another study demonstrated that strict rodent control on three pig farms had a direct influence on the Toxoplasma seroprevalence of the resident pigs: significant less pigs were T. gondii seropositive when an active rodent control campaign was instated, showing the importance of rodent control to acquire safer meat (Kijlstra et al., 2008).

Here, we investigate the presence of both T. gondii and N. caninum in brain tissue samples of feral rodents and insectivores caught on organic farms in the Netherlands in order to better understand the potential role of these small mammals in the transmission of both parasites. We also focus on the locations on the farms where these animals were caught in order to facilitate future risk assessment studies.

Section snippets

Samples

A total of 250 feral rodents and insectivores were trapped in live-traps on 10 organic farms (9 pig farms, 1 poultry farm) in the Netherlands in 2004 (Meerburg et al., 2006). The animals were humanely euthanized using CO2. Their heads (without skin) were stored in 4% PBS buffered paraformaldehyde solution until tested. For each sampled animal, the location of the farm where it was captured was recorded: feeding passage (near the feed trough), storage (inside the stable), outdoor area (next to

Results

In total 250 brain samples were collected and analysed, representing 7 species of rodents captured on various locations on or around the farm: house mouse (Mus musculus), common vole (Microtus arvalis), wood mouse (Apodemus sylvaticus), brown rat (Rattus norvegicus), harvest mouse (Micromys minitus), bank vole (Myodes glareolus), field vole (Microtus agrestis); and 2 species of insectivores: common shrew (Sorex araneus) and white-toothed shrew (Crocidura russula). Those samples originated from

Discussion

This is one of the first studies where the presence of both N. caninum and T. gondii was studied at the same time in a large number of rodents and insectivores captured on livestock farms. Remarkably, N. caninum was more often demonstrated than T. gondii in the tested samples. Before the experiment, it was expected that small mammals and insectivores play a more significant role in the transmission of T. gondii (with felids as final parasite host) than in the transmission of N. caninum (with

Acknowledgements

This work was supported by the Belgian Federal Public Service for Health, Food Chain Safety and Environment and grants from the Dutch Ministry for Agriculture, Nature, and Food Quality and the European Union Integrated Project Quality Low Input Food (QLIF). We also wish to acknowledge Nicolas Desmet and Francisca Garcia from the laboratory for Toxoplasmosis and David Duijsings from Wageningen University for their technical assistance and the farmers for their willingness to participate in this

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