Estimating Disease Prevalence Using Inverse Binomial Pooled Testing

Monitoring populations of hosts as well as insect vectors is an important part of agricultural and public health risk assessment. In applications where pathogen prevalence is likely low, it is common to test pools of subjects for the presence of infection, rather than to test subjects individually. This technique is known as pooled (group) testing. In this paper, we revisit the problem of estimating the population prevalence p from pooled testing, but we consider applications where inverse binomial sampling is used. Our work is unlike previous research in pooled testing, which has largely assumed a binomial model. Inverse sampling is natural to implement when there is a need to report estimates early on in the data collection process and has been used in individual testing applications when disease incidence is low. We consider point and interval estimation procedures for p in this new pooled testing setting, and we use example data sets from the literature to describe and to illustrate our methods.     

Low dietary silicon supplementation may not affect bone and cartilage in mature,sedentary horses

As osteoarthritis is a major cause of lameness in horses in the United States, improving collagen health prior to onset and increasing collagen turnover within affected joints could improve health- and welfare-related outcomes. Through its positive effects on bone mineral content and density and its role in increasing collagen synthesis, silicon (Si) may slow the development and progression of osteoarthritis, thereby reducing lameness. This study evaluated the hypothesis that Si supplementation would increase cartilage turnover through increased collagen degradation and formation markers, as well as bone formation markers, resulting in reduced lameness severity when compared with controls. Ten mature Standardbred geldings were assigned to either a Si-treated (SIL) or control (CON) group and group-housed on pasture for 84 d. Horses were individually fed to ensure no cross-contamination of Si other than what was present in the environment. For the duration of the study, SIL horses received a Si–collagen supplement at the rate of 0.3 g supplement/(100 kg body weight day). Serum samples were taken weekly for osteocalcin, and plasma samples were taken on days 0, 42, and 84 for plasma minerals. On days 0, 42, and 84, subjective and objective lameness exams were performed, and radiographs and synovial fluid samples were taken from reference and osteoarthritic joints. Plasma minerals were similar in both groups and were lower on day 84 than on day 0 (P < 0.05). Si supplementation, fed at the manufacturer’s recommended rate, did not improve lameness or radiographs when compared with controls, and supplemented horses did not show greater collagen degradation and/or synthesis markers in synovial fluid than controls, indicating that cartilage turnover remained unaffected. However, a minimum beneficial threshold and range for Si supplementation standardized to body weight need to be established.     

The breeding systems and some interspecific relations of a number of African Trifolium spp.

The breeding systems of 12 species and varieties of Trifolium from Africa were investigated. One annual and the three perennial species were allogamous and self-incompatible, the other annuals were autogamous.The effect of temperature on pollen germination and growth was variable. In some species high temperatures (30°C) adversely affected pollen germination and low temperatures (20°C) in others. A high humidity (93–98% R.H.) was essential for good pollen germination and growth.Approach grafts indicated that these species were closely related, however, this method of grafting may not be as reliable as the cleft graft for assessing species relations. From hybridization attempts between seven species, it appears that some interspecific hybrids may be possible within this group.     

Problems associated with the serological diagnosis of Leptospira interrogans serovar hardjo infection in bovine populations

Data combining sequential bacteriology and serology from a longitudinal study of a dairy herd were used to demonstrate the limitations of serology as a diagnostic method in cross-sectional sampling of bovine populations. Whole-herd point serological prevalences showed considerable variation over a two-year sampling period (38.8 to 76.2 per cent), and this was mainly due to varying age-specific prevalence. Owing to the rapid decline in titres and the varying persistence of infection, point serological prevalences failed to approximate to cumulative infection rates (either past or present) at different times of the year. A higher estimate of the number of susceptible animals in the herd than is the case results in inaccurate information on true incidence rates and can confuse assessments of the susceptibility of different age groups, especially if only small numbers are sampled. A sampling exercise demonstrated that a 10-cow sample usually provided little useful information other than establishing the presence or absence of hardjo in the herd. Increasing the sample size markedly improved epidemiological information, investigations of clinical disease, assessments of vaccination needs and public health tracebacks. Preferably 10 sera from each of the yearling, first calver, second calver and older age groups should be tested. Serology was an inadequate indicator of infection in individual animals. Group geometric mean titres taken from a mean serological response curve were shown to have limited application in the interpretation of field data, unless infection had occurred in the previous two months.     

Listeria monocytogenes septicemia in an immunocompromised dog

An 11‐year‐old, male castrated, Boston Terrier was presented to the North Carolina State University College of Veterinary Medicine Small Animal Emergency Service with a 2‐day history of progressive ataxia, left‐sided head tilt, and anorexia. The dog had previously been diagnosed with chronic lymphoid leukemia and suspected immune‐mediated destruction of his bone marrow precursor cells, possibly due to therapy with immunosuppressive dosages of prednisone and azathioprine. During the physical examination, abnormal findings included an increased body temperature and horizontal nystagmus. Diagnostic investigations included a computed tomography (CT) scan, which confirmed bilateral otitis media, and a blood culture, which was positive for Listeria monocytogenes serotype 4b (epidemic clone 1). Upon treatment with ampicillin/sulbactam, enrofloxacin, and minocycline, the dog became normothermic and the neurologic signs improved. L monocytogenes serotype 4b (epidemic clone 1) has been associated with outbreaks of human listeriosis originating from food contamination. Although rare case reports of Listeria spp. infection in dogs exist, an actual infection with the epidemic clone 1 strain has never before been reported in a dog. It should be included in the differential diagnoses in immunocompromised dogs with clinical signs of septicemia.     

Effects of opening size and stand characteristics on light transmittance and temperature under young trembling aspen stands

While aspen (Populus tremuloides Michx.) cover provides protection from growing season radiative frosts, reduced light levels can limit growth of understory white spruce (Picea glauca (Moench) Voss). The creation of openings around individual spruce can provide more light, but the chance of radiative frost damage increases as gaps become larger. We examined the relationship between opening size and light and temperature levels in the center of circular gaps created in young aspen stands ranging from 1.8 to 8 m tall. Models for predicting transmittance as a function of sky view factor and transmittance under intact stands are presented. Results indicated a strong relationship between light levels and opening size after considering pre-treatment light levels. The relationship between opening size and temperature was weak with minimum temperatures being more affected by the height and density of the surrounding stand than opening size.     

Indigenous Agroforestry Systems in Amazonia: From Prehistory to Today

Understanding the historical development of indigenous systems will provide valuable information for the design of ecologically desirable agroforestry production systems. Such studies have been relatively few, especially in Amazonia. The agroforestry systems in Amazonia follow a trail that begins with the arrival of the first hunter-gatherers in prehistoric times, followed by the domestication of plants for agriculture, the development of complex societies rich in material culture, the decimation of these societies by European diseases, warfare, and slavery, the introduction of exotic species, and finally, the present-day scenario of widespread deforestation, in which agroforestry is ascribed a potential role as an alternative land use. Despite the upheavals which occurred in colonial times, greatly reducing the population of native tribes, a review of anthropological and ethnobiological literature from recent decades indicates that a great variety of indigenous agroforestry practices still exist, ranging from deliberate planting of trees in homegardens and fields to the management of volunteer seedlings of both cultivated and wild species. These practices result in various configurations of agroforestry systems, such as homegardens, tree/crop combinations in fields, orchards of mixed fruit trees, and enriched fallows. Together they constitute a stock of knowledge developed over millenia, and represent technologies that evolved along with the domestication of native forest species and their incorporation into food production systems. This knowledge is the basis for the principal agroforestry practice employed by farmers in Amazonia today, the homegarden, and has potential to contribute to the development of other agroforestry systems.