Quantification of transmission of foot-and-mouth disease virus caused by an environment contaminated with secretions and excretions from infected calves

Foot-and-mouth disease virus (FMDV) infected animals can contaminate the environment with their secretions and excretions. To quantify the contribution of a contaminated environment to the transmission of FMDV, this study used calves that were not vaccinated and calves that were vaccinated 1 week prior to inoculation with the virus in direct and indirect contact experiments. In direct contact experiments, contact calves were exposed to inoculated calves in the same room. In indirect contact experiments, contact calves were housed in rooms that previously had held inoculated calves for three days (either from 0 to 3 or from 3 to 6 days post inoculation). Secretions and excretions from all calves were tested for the presence of FMDV by virus isolation; the results were used to quantify FMDV transmission. This was done using a generalized linear model based on a 2 route (2R, i.e. direct contact and environment) SIR model that included information on FMDV survival in the environment. The study shows that roughly 44% of transmission occurs via the environment, as indicated by the reproduction ratio R^02Renvironment that equalled 2.0, whereas the sum of R^02Rcontact and R^02Renvironment equalled 4.6. Because vaccination 1 week prior to inoculation of the calves conferred protective immunity against FMDV infection, no transmission rate parameters could be estimated from the experiments with vaccinated calves. We conclude that a contaminated environment contributes considerably to the transmission of FMDV therefore that hygiene measures can play a crucial role in FMD control.

Electronic supplementary material

The online version of this article (doi:10.1186/s13567-015-0156-5) contains supplementary material, which is available to authorized users.     

No foot-and-mouth disease virus transmission between individually housed calves

The foot-and-mouth disease outbreak in The Netherlands in 2001 most likely started on a mixed veal-calf/dairy-goat farm. The outbreak among the 74 calves on this farm appeared to be limited to four animals, and no clinical signs of FMD were reported. Also on a second veal-calf farm minor clinical signs and limited virus transmission were observed. Since FMD is known to be a very contagious disease, and can cause severe lesions, these observations were disputed. Therefore, we carried out two experiments to determine whether the Dutch FMD virus isolate from 2001 does spread among individually housed calves with limited contacts, either indirect (experiment 1) or direct (experiment 2). In experiment 1, four pairs of calves were housed in an individual box at 1m distance from each other. In experiment 2, two groups of three calves were housed in individual boxes, directly bordering each other. We infected one animal per pair in experiment 1, and the calf in the middle in experiment 2. We recorded clinical signs, virus shedding in saliva and the development of antibodies. In addition, we determined whether the virus was transmitted from the inoculated calves to the neighbour(s). All inoculated calves showed mild signs of FMD--fever, and some vesicles on hooves and/or in the mouth--but only one calf showed signs that were visible without physical examination. All inoculated calves shed virus in the saliva and developed neutralising antibodies. None of the contact animals seroconverted, indicating that virus transmission did not occur. These experiments showed that no virus transmission among individual housed calves can occur. This finding supports the hypothesis of the route of virus introduction to The Netherlands in 2001 and show that the observations on the two veal-calf farms were not impossible.     

Leaf-trait responses to irrigation of the endemic fog-oasis tree Myrcianthes ferreyrae: can a fog specialist benefit from regular watering?

Myrcianthes ferreyrae is an endemic, endangered species, with a small number of individuals located only in hyperarid, fog-oases known as lomas along the Peruvian desert in southern Peru, where fog is the main source of water. Following centuries of severe deforestation, reforestation with this native species was conducted in the Atiquipa lomas, Arequipa-Perú. On five slopes, five 2-year-old seedlings were irrigated monthly with water trapped by raschel-mesh fog collectors, supplementing natural rainfall with 0, 20, 40, 60 and 80 mm month(-1) from February to August 2008. We measured plant growth, increment in basal diameter, height and five leaf traits: leaf mass area (LMA), leaf carbon isotope composition (δ(13)C), nitrogen per leaf area, total leaf carbon and stomatal density; which are indicative of the physiological changes resulting from increased water supply. Plant growth rates, estimated from the variation of either shoot basal diameter or maximum height, were highly correlated with total biomass. Only LMA and δ(13)C were higher in irrigated than in control plants, but we found no further differences among irrigation treatments. This threshold response suggests an on-off strategy fitted to exploit pulses of fog water, which are always limited in magnitude in comparison with natural rain. The absence of a differential response to increased water supply is in agreement with the low phenotypic plasticity expected in plants from very stressful environments. Our results have practical implications for reforestation projects, since irrigating with 20 mm per month is sufficient to achieve the full growth capacity of this species.     

Simple assay for analyzing five microcystins and nodularin in fish muscle tissue: hot water extraction followed by liquid chromatography-tandem mass spectrometry

A simple, specific, and sensitive procedure for determining six cyanotoxins, that is, microcystins RR, LR, YR, LA, and LW and nodularin, in fish muscle tissue is presented. This method is based on the matrix solid-phase dispersion technique with heated water as extractant followed by liquid chromatography (LC)-tandem mass spectrometry (MS) equipped with an electrospray ion source. Target compounds were extracted from tissue by 4 mL of water acidified to pH 2 and heated at 80 degrees C. After acidification and filtration, 0.2 mL of the aqueous extract was injected in the LC column. MS data acquisition was performed in the multireaction monitoring mode, with at least two precursor ion > product ion transitions selected for each target compound. Analyte recovery ranged between 61 and 82% and was not substantially affected by either the analyte concentrations or the type of fish. The nonexcellent recovery of some of the microcystins was traced to binding of these compounds to protein phosphatases in fish tissue occurring during sample treatment. The existence of covalently bound microcystins in fish has been evidenced by several studies. Compared to an older sample preparation procedure, this one extracted larger amounts of the analytes in a simpler and much more rapid way. On the basis of a signal-to-noise ratio of 10, limits of quantification were estimated to range between 1.6 and 4.0 ng/g. The effects of temperature and volume of the extractant on the analyte recovery were studied.     

One-step triplex-polymerase chain reaction assay for the authentication of yellowfin (Thunnus albacares), bigeye (Thunnus obesus), and skipjack (Katsuwonus pelamis) tuna DNA from fresh, frozen, and canned tuna samples

A one-step triplex-polymerase chain reaction (PCR)-based assay was developed to discriminate between three tuna species, Thunnus albacares, Thunnus obesus, and Katsuwonus pelamis, even in highly processed food samples such as canned or cooked tuna. Diagnostic nucleotides were identified by direct sequencing and alignment of part of the mitochondrial cytochrome b gene of 30 authenticated exemplars, which allowed us to evaluate intraspecific variation and the genetic distance between three tuna species. The assay relies on a one-step triplex-PCR reaction in which in a single tube species-specific amplification products are generated only in the presence of the correct template nucleic acid and the species of origin of the DNA is indicated by the distinctive size of the PCR product. The identification of tuna species can be performed with a good accuracy, low cost, and with potential automation for large-scale high-throughput screenings in small in-house laboratories.     

Near-infrared reflectance spectroscopy (NIRS) for protein, tryptophan, and lysine evaluation in quality protein maize (QPM) breeding programs

Quality protein maize (QPM) has approximately twice the tryptophan (Trp) and lysine (Lys) concentrations in protein compared to normal maize. Because several genetic systems control the protein quality of QPM, it is essential to regularly monitor Trp and/or Lys in breeding programs. Our objective was to examine the potential of near-infrared reflectance spectroscopy (NIRS) to enhance the efficiency of QPM research efforts by partially replacing more expensive and time-consuming wet chemistry analysis. More than 276 maize samples were used to develop NIRS models for protein content (PC), Trp, and Lys. The standard error of prediction (SEP) for the calibration and the coefficient of determination for validation (R(2)(v)) were 0.26 and 0.96 for PC, 0.005 and 0.85 for Trp, and 0.02 and 0.75 for Lys. When the NIRS models were used to evaluate 266 S2 lines from five QPM breeding populations, the coefficients of determination between NIRS and the chemical data were 0.94, 0.76, and 0.80 for PC, Trp, and Lys, respectively. Therefore, the NIRS models can be used to support the QPM breeding efforts.     

A rapid multiplexed chemiluminescent immunoassay for the detection of Escherichia coli O157:H7, Yersinia enterocolitica, Salmonella typhimurium, and Listeria monocytogenes pathogen bacteria

A simple and rapid multiplexed sandwich chemiluminescent enzyme immunoassay has been developed for the simultaneous detection of Escherichia coli O157:H7, Yersinia enterocolitica, Salmonella typhimurium, and Listeria monocytogenes. To achieve the multiplexed detection of the four pathogens, a new polystyrene 96 well microtiter plate format has been designed, in which each main well contains four subwells in the bottom. The monoclonal antibodies specific for each bacteria were separately immobilized in each subwell. When the samples were added to the main wells, the bacteria able to specifically bind to the corresponding monoclonal antibody were captured in one of the four subwells. Subsequently, a mixture of peroxidase-labeled polyclonal antibodies against the four bacteria was added and the peroxidase activity of the bound polyclonal labeled antibodies in each well was measured by an enhanced luminol-based chemiluminescent cocktail using a low-light charge-coupled imaging device. The assay was simple and fast, and the limit of quantification was in the order of 104-105 CFU/mL for all bacterial species. The accuracy of the method, evaluated by comparison of the results with a conventional culturing methodology, was satisfactory, with recovery values ranging from 90 to 120%. This method can be used as a screening test to evaluate the presence of these pathogen bacteria in different foodstuffs.     

Formation of Oligosaccharides and Polysaccharides by Lactobacillus reuteri LTH5448 and Weissella cibaria 10M in Sorghum Sourdoughs

Gluten‐free breads, which are composed of gluten‐free flours, starch, and hydrocolloids, differ from wheat and rye breads in relation to texture, volume, and crumb structure. Moreover, the dietary fiber content is lower compared with wheat or rye breads. Cereal isolates of lactic acid bacteria frequently produce oligo‐ and homopolysaccharides from sucrose, which can improve the nutritional and technological properties of gluten‐free breads as prebiotic carbohydrates and hydrocolloids, respectively. Sorghum sourdough was fermented with Lactobacillus reuteri LTH5448 or Weissella cibaria 10M, which synthesize fructooligosaccharides (FOS) and levan, and isomaltooligosaccharides and dextran, respectively. The gluten‐free bread was produced with 14% sourdough addition. L. reuteri LTH5448 formed FOS and 1.5 g of levan/kg DM in quinoa sourdoughs. FOS were digested by the baker's yeast during proofing, and the levan could be qualitatively detected in the bread. W. cibaria 10M produced >60 g of isomaltooligosaccharides/kg DM and 0.6 g of dextran/kg DM, which could still be detected in the bread. Breads prepared with W. cibaria 10M were less firm compared with breads prepared with L. reuteri LTH5448 or a FOS and levan‐negative mutant of L. reuteri LTH5448. The addition of sourdoughs fermented with oligo‐ and polysaccharide forming starter cultures can increase the content of prebiotic oligosaccharides in gluten‐free breads.     

Nematicidal potential of materials from <Emphasis Type="Italic">Medicago</Emphasis> spp.

The nematicidal effect of soil amendments with dry top and root material from Medicago sativa and/or Medicago arborea was evaluated on the root-knot nematode Meloidogyne incognita and on the cyst nematode Globodera rostochiensis in potting mixes. All amendments suppressed root and soil population densities of both nematode species compared to non-treated and chemical controls. The suppressiveness of M. sativa differed between top and root material and among the amendment rates. In field conditions soil amendments with 20 or 40 t ha⁻¹ of a pelleted M. sativa meal increased tomato crop yield and reduced soil population densities and root galling by M. incognita. It is suggested that saponins were at least partly responsible for the nematicidal activity.     

Salmon cells SHK‐1 internalize infectious pancreatic necrosis virus by macropinocytosis

We have previously shown that infectious pancreatic necrosis virus (IPNV) enters the embryo cell line CHSE‐214 by macropinocytosis. In this study, we have extended our investigation into SHK‐1 cells, a macrophage‐like cell line derived from the head kidney of Atlantic salmon, the most economically important host of IPNV. We show that IPNV infection stimulated fluid uptake in SHK‐1 cells above the constitutive macropinocytosis level. In addition, upon infection of SHK‐1 cells, IPNV produced several changes in actin dynamics, such as protrusions and ruffles, which are important features of macropinocytosis. We also observed that the Na+/H+ pump inhibitor EIPA blocked IPNV infection. On the other hand, IPNV entry was independent of clathrin, a possibility that could not be ruled out in CHSE 214 cells. In order to determine the possible role of accessory factors on the macropinocytic process, we tested several inhibitors that affect components of transduction pathways. While pharmacological intervention of PKI3, PAK‐1 and Rac1 did not affect IPNV infection, inhibition of Ras and Rho GTPases as well as Cdc42 resulted in a partial decrease in IPNV infection. Further studies will be required to determine the signalling pathway involved in the macropinocytosis‐mediated entry of IPNV into its target cells.