Experimental infection of highly pathogenic avian influenza virus H5N1 in black-headed gulls (Chroicocephalus ridibundus)

Historically, highly pathogenic avian influenza viruses (HPAIV) rarely resulted in infection or clinical disease in wild birds. However, since 2002, disease and mortality from natural HPAIV H5N1 infection have been observed in wild birds including gulls. We performed an experimental HPAIV H5N1 infection of black-headed gulls (Chroicocephalus ridibundus) to determine their susceptibility to infection and disease from this virus, pattern of viral shedding, clinical signs, pathological changes and viral tissue distribution. We inoculated sixteen black-headed gulls with 1 × 10⁴ median tissue culture infectious dose HPAIV H5N1 (A/turkey/Turkey/1/2005) intratracheally and intraesophageally. Birds were monitored daily until 12 days post inoculation (dpi). Oropharyngeal and cloacal swabs were collected daily to detect viral shedding. Necropsies from birds were performed at 2, 4, 5, 6, 7, and 12 dpi. Sampling from selected tissues was done for histopathology, immunohistochemical detection of viral antigen, PCR, and viral isolation. Our study shows that all inoculated birds were productively infected, developed systemic disease, and had a high morbidity and mortality rate. Virus was detected mainly in the respiratory tract on the first days after inoculation, and then concentrated more in pancreas and central nervous system from 4 dpi onwards. Birds shed infectious virus until 7 dpi from the pharynx and 6 dpi from the cloaca. We conclude that black-headed gulls are highly susceptible to disease with a high mortality rate and are thus more likely to act as sentinel species for the presence of the virus than as long-distance carriers of the virus to new geographical areas.

Electronic supplementary material

The online version of this article (doi:10.1186/s13567-014-0084-9) contains supplementary material, which is available to authorized users.     

Faecal pH throughout the reproductive cycle of sows in commercial pig herds

Despite the importance of swine intestinal health, there are no easy-to-use and cost-efficient methods to evaluate it under field conditions for sows. To provide some indication about intestinal health, pH of faeces could be used but reference values for the currently high-performing commercial sow breeds are missing. In response, faecal pH of healthy sows from three different herds (herd A: 230 sows, herd B: 350 sows, herd C: 500 sows) was measured throughout the reproductive cycle. Within each herd, 10 sows were selected and rectal faeces samples were collected at different time points during the reproductive cycle: day 90 of gestation, day 1, 7, 14 and 21 of lactation, 7 days post-weaning and day 30 of the next gestation. In addition, data on sow body condition (back fat), feed composition and coarseness of the feed were collected. For individual pH measurements, the pH ranged from 6.30 to 7.93. However, for all herds together, the average faecal pH value of the sows throughout the reproductive cycle ranged from 6.89 to 7.15. Also, the variations due to sow and time of sampling during the reproductive cycle were low with coefficients of variation of less than 5%. The results from the pairwise comparisons of the statistical model showed that in the last stages of lactation (i.e., at day 21), significantly lower average pH values (p ≤ .05) are expected when compared to earlier stages of lactation (days 3 or 7), or at day 7 post-weaning or compared to day 30 of the next gestation. Bearing its limitations, our study provided reference faecal pH values from high-performing commercial sows under field conditions and as such they could be used directly in the field. Yet, further research is needed to provide more information on the factors affecting pH values throughout the reproductive cycle of the sow.     

Copper,iron, zinc and tannin concentrations throughout the digestive tract of tropical goats and sheep fed a high-fibre tannin-rich diet

The dry season in tropical regions urges livestock to feed on nutritionally very poor diets. It has not been explored how tropical sheep—assumed grazers—and tropical goats—intermediate browsers—cope with a high-fibre tannin-rich diet. This study was designed to determine the effects of a high-fibre and tannin-rich diet on the flow of important microminerals iron (Fe), zinc (Zn) and copper (Cu) throughout the digestive tract of tropical sheep and goats. The feeding trial was set up with twelve adult male animals, six sheep with mean body weight (BW) of 30.3 ± 1.6 kg and six goats with mean BW of 26.4 ± 2.2 kg. The feed consisted of 36% leaves of Millettia ferruginea, 61% hay and 3% concentrate and was offered at 3% of BW (all on dry matter (DM) basis). The total faecal collection was carried out for 7 consecutive days. At the end of the experimental period, the animals were slaughtered to collect liver and digesta samples from the gastrointestinal tract. Feed, digesta and faecal samples underwent analysis of Fe, Zn, and Cu and total tannins (TT). Goats had significantly higher reticulum Cu concentrations expressed on DM as compared to sheep. Faecal Cu concentrations were higher for goats compared to sheep. Reticulum and colon digesta Zn levels were higher in goats than sheep. Abomasum and colon Fe levels were higher in sheep than goats when expressed on DM. These results suggest differences in feed intake, micromineral absorption, secretion and excretion between sheep and goats, pointing to a divergent mineral metabolism as an adaptation to the challenge of a dry season diet having very low nutritive value.     

Modeling combined continuous and ordinal outcomes in a clustered setting

Measurements of both continuous and categorical outcomes appear in many statistical problems. One such example is the study of teratology and developmental toxicity, where both the probability that a live fetus is malformed (ordinal) or of low birth weight (continuous) are important measures in the context of teratogenicity. Although multivariate methods of the analysis of continuous outcomes are well understood, methods for jointly continuous and discrete outcomes are less familiar. We propose a likelihood-based method that is an extension of the Plackett-Dale approach. Specification of the full likelihood will be avoided using pseudo-likelihood methodology. The estimation of safe dose levels as part of quantitative risk assessment will be illustrated based on a developmental toxicity experiment of diethylene glycol dimethyl ether in mice.