B.G. Meerburg

Rodent-borne diseases and their risks for public health

Rodents are the most abundant and diversified order of living mammals in the world. Already since the Middle Ages we know that they can contribute to human disease, as black rats were associated with distribution of plague. However, also in modern times rodents form a threat for public health. In this review article a large number of pathogens that are directly or indirectly transmitted by rodents are described. Moreover, a simplified rodent disease model is discussed.

The role of rodents and shrews in the transmission of Toxoplasma gondii to pigs

Inadequate rodent control is considered to play a role in Toxoplasma gondii infection of pigs. This issue was addressed in the current study by combining a 4-month rodent control campaign and a 7-month longitudinal analysis of T. gondii seroprevalence in slaughter pigs. Three organic pig farms with known rodent infestation were included in the study. On these farms, presence of T. gondii in trapped rodents was evaluated by real-time PCR. All rodent species and shrews investigated had T. gondii DNA in brain or heart tissue. Prevalence was 10.3% in Rattus norvegicus, 6.5% in Mus musculus, 14.3% in Apodemus sylvaticus and 13.6% in Crocidura russula. Initial T. gondii seroprevalence in the slaughter pigs ranged between 8% and 17% and dropped on the three farms during the rodent control campaign to 0-10%, respectively. After 4 months of rodent control, T. gondii infection was absent from pigs from two of the three farms investigated and appeared again in one of those two farms after the rodent control campaign had stopped. This study emphasizes the role of rodents and shrews in the transmission of T. gondii to pigs and the importance of rodent control towards production of T. gondii-free pig meat.

Changing climate—changing pathogens: Toxoplasma gondii in North-Western Europe

In this review, we describe the effects of global climate change for one specific pathogen: the parasite Toxoplasma gondii. It is postulated that an increase of T. gondii prevalence in humans can occur in some regions of North-Western Europe as a result of changing environmental conditions. Such a change can be predicted by using Global Climate Change models. We have elaborated such a prediction for one scenario (SRES A1) by using one specific model (CCSR/NRIES) as an example. Next to environmental factors, also anthropogenic factors may contribute to increased prevalence of T. gondii in this region. In order to counter the potential severe consequences of a potential increase resulting from the combination of climatic and anthropogenic factors, there is an urgent need for the development of a human vaccine. Until a vaccine that offers complete protection is developed, the emphasis should be on treatment optimization and prevention.

The Year of the Rat ends : time to fight hunger!

This paper investigates the importance of ecologically based rodent management in the light of the current food crisis, and the potential effects of this approach on the position of the undernourished. Hunger and food prices are on the rise owing to shortages that can be traced to reasons such as climatic extremes, use of crops for biofuels, reduced growth in yields which lag behind population growth, reduced world stocks and lack of sufficient investment in maintaining the irrigation infrastructure. For the undernourished this is problematic as they are most vulnerable to the rise in food prices. Very often, agricultural experts focus on an increase in agricultural production to reduce food prices. It is postulated in this article that almost 280 million undernourished could additionally benefit if more attention were paid to reducing pre- and post-harvest losses by rodents. Moreover, rodent-borne diseases would decrease, diseases that can be catastrophic to the livelihoods of the poorest of the poor.

Towards sustainable management of rodents in organic animal husbandry

From 26 to 28 May 2004 an international seminar was held in Wageningen, the Netherlands, about current knowledge and advice on rodent management on organic pig and poultry farms in Western Europe. This paper summarizes the discussions. Rodent management is necessary to protect the food production chain from health hazards to livestock and humans. Some organic farmers prefer biological rodent control, but since rodents can also transmit diseases this bears certain risks for the production of healthy livestock and safe food. Effective rodent management requires a thorough understanding of the biology of the pest species concerned. These can be divided into two groups: field rodents, such as voles, and commensal rodents like house mice and rats. The objective of managing field rodents is to mini- mize livestock exposure to these vectors, and to regulate their populations in case their density is expect-

The Ethics of Rodent Control

Because western societies generally see animals as objects of moral concern, demands have been made on the way they are treated, e.g. during animal experimentation. In the case of rodent pests, however, inhumane control methods are often applied. This inconsistency in the human-animal relationship requires clarification. This paper analyses the criteria that must be met when judging the use of animals during experiments, and investigates whether these can be applied in rodent control. This is important, because, until now, animal welfare has been less of an issue in pest control: effectiveness, hygiene and cost efficiency have been leading principles. Two options are available to solve the inconsistency: the first is to abandon the criteria used in animal experimentation; the second is to apply these criteria to both animal experimentation and rodent control. This latter option implies that rodent control methods should not lead to intense pain or discomfort, and any discomfort should have a short duration and should allow escaped rodents to lead a natural life. Adherence to this option will, however, require a shift in the design of rodent control methods: effectiveness will no longer be the leading principle. It will have to share its position with animal welfare and humaneness.

Animal-friendly production systems may cause re-emergence of Toxoplasma gondii

Toxoplasmosis is still one of the most common parasitic infections in the world, although in Europe improvements in hygiene and the introduction of ‘total’ indoor farming in livestock production have rapidly diminished the problem during the past decades. As a result of public dislike, however, introduction of alternative and more acceptable animal-friendly livestock production systems including outdoor access are gaining ground. Potentially these systems can lead to increased prevalence of certain zoonotic diseases, including Toxoplasmosis. To retain prevalence of this disease in humans at current levels, emphasis should be on disease control at farm-level. This article provides an analysis of various risk factors for farm animals to get infected with Toxoplasma gondii. Access of cats to the farm premises, the use of compost and goat whey, and rodent control were identified as possible risk factors that should be addressed. Consumers should be aware of the fact that Toxoplasma infection, besides through meat, can also be caused by the uptake of contaminated water, soil, fruit and vegetables.

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

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.

The Need and Potential of Biosensors to Detect Dioxins and Dioxin-Like Polychlorinated Biphenyls along the Milk, Eggs and Meat Food Chain

Dioxins and dioxin-like polychlorinated biphenyls (DL-PCBs) are hazardous toxic, ubiquitous and persistent chemical compounds, which can enter the food chain and accumulate up to higher trophic levels. Their determination requires sophisticated methods, expensive facilities and instruments, well-trained personnel and expensive chemical reagents. Ideally, real-time monitoring using rapid detection methods should be applied to detect possible contamination along the food chain in order to prevent human exposure. Sensor technology may be promising in this respect. This review gives the state of the art for detecting possible contamination with dioxins and DL-PCBs along the food chain of animal-source foods. The main detection methods applied (i.e., high resolution gas-chromatography combined with high resolution mass-spectrometry (HRGC/HRMS) and the chemical activated luciferase gene expression method (CALUX bioassay)), each have their limitations. Biosensors for detecting dioxins and related compounds, although still under development, show potential to overcome these limitations. Immunosensors and biomimetic-based biosensors potentially offer increased selectivity and sensitivity for dioxin and DL-PCB detection, while whole cell-based biosensors present interpretable biological results. The main shortcoming of current biosensors, however, is their detection level: this may be insufficient as limits for dioxins and DL-PCBs for food and feedstuffs are in pg per gram level. In addition, these contaminants are normally present in fat, a difficult matrix for biosensor detection. Therefore, simple and efficient extraction and clean-up procedures are required which may enable biosensors to detect dioxins and DL-PCBs contamination along the food chain.

Opinion paper: The role of livestock in a sustainable diet: a land-use perspective

In 2000, the Food and Agricultural Organisation (FAO) projected that global demand for animal source food (ASF) would double by 2050 (Alexandratos and Bruinsma, 2012). Although these projections were revised slightly during recent years, they form the basis of many scientific and policy documents related to livestock production. Those projections, however, are based on global trends for a growing population and increasing incomes and urbanization, but not based on ensuring global nutrition security in a sustainable way. Currently, the world’s livestock sector adds to the total anthropogenic emissions of greenhouse gases and competes for scarce resources, such as land, water and fossil energy. Without changes to reduce the environmental impact, concerns about the environment will only increase further. We asked ourselves, how and why livestock production is essential and what would be the proportion of ASF in human diets to ensure nutrition security in a sustainable way? As land is a strict limitation of nutrition security, we took a landuse perspective, irrespective of socio-economic or technical constraints. In 2012, about 4.92 billion ha was used for agriculture, of which about 70% was used for livestock production, mainly for pasture and production of feed crops (FAO stat). Of the 4.92 billion ha of agricultural land about 1.56 billion ha is used for crop production. Assuming 9.7 billion people in 2050, then about 0.16 ha of cropland is available per person. Production of a vegan diet, for example, requires about 0.14 ha/person. Expanding the area for crop production will lead to loss of grazing areas or deforestation in the tropics, for example, resulting in loss of biodiversity and increased carbon emissions. High productive croplands, therefore, must be used to produce human food instead of livestock feed. No matter how efficiently food is produced, direct consumption of cereals by humans is more efficient ecologically than consumption of livestock fed these cereals. Should we shift, therefore, to vegan diets? Not necessarily! Grass-based ruminant systems on marginal land, that is, land not suitable for crop production, produce human digestible protein more efficiently than food crops (Van Zanten et al., 2015a). Furthermore, compared with a vegan diet, consumption of a small amount of ASF reduced land use per person when livestock were mainly fed with co-products (Van Kernebeek et al., 2015). In addition to biomass from marginal land and co-products, livestock can also upgrade two other biomass streams that humans do not currently consume: crop residues and food waste. Using crop residues as livestock feed, however, can lead to depletion of soil organic carbon, and, therefore, should be left on the field. To be safe, we assumed all crop residues are left on the field. We focus, therefore, on the potential of livestock to convert co-products from human food, food waste and biomass from marginal land, referred to as ‘leftover streams,’ into high-quality ASF. Livestock that eat these leftover streams do not compete with humans for cropland, and, therefore, contribute to sustainable nutrition security. By feeding only leftover streams to livestock, the number of humans fed per hectare is maximized. How much ASF can we consume, however, when we want to avoid feed–food competition by feeding only leftover streams to livestock? To illustrate that we can produce a sufficient amount of ASF, we calculated amount of ASF produced from co-products and food waste, and amount of ASF produced from 100% grass-based systems. Amount of ASF produced from co-products and food waste depends on availability, which depends on consumption patterns of humans. If the 1.56 billion ha of cropland is used for human food production, people consume a vegan diet because no cropland is used for feed production. Consumption of a vegan diet requires annual production of about 129 kg co-products/person (see Supplementary Material S1). We chose those food ingredients in a vegan diet, whose co-products had a high nutritional value for livestock. We assumed, for example, that oil production originates from soy cultivation resulting in soybean meal. Soybean meal compared with other co-products from oil processing, for example, sunflower meal, has a high nutritional value for livestock. This assumption not only has an † E-mail: hannah.vanzanten@wur.nl Animal (2016), 10:4, pp 547–549