Statistical inference and model selection for the 1861 Hagelloch measles epidemic

A stochastic epidemic model is proposed which incorporates heterogeneity in the spread of a disease through a population. In particular, three factors are considered: the spatial location of an individual's home and the household and school class to which the individual belongs. The model is applied to an extremely informative measles data set and the model is compared with nested models, which incorporate some, but not all, of the aforementioned factors. A reversible jump Markov chain Monte Carlo algorithm is then introduced which assists in selecting the most appropriate model to fit the data.     

Comparison of natural and artificial epidemics of take-all in sequences of winter wheat crops

Winter wheat was grown for six successive years (Expt 1) and for three successive years (Expt 2) in field experiments on different soil types. Artificial inoculum of the take-all fungus (Gaeumannomyces graminis var. tritici cultured on autoclaved oat grains) was incorporated in the soil of some of the plots just before, or at, sowing of the first winter wheat crop. Expt 1 tested the incorporation of similar amounts of inoculum (212 kg ha^-1) at different depths. Expt 2 tested different amounts of inoculum at the same, shallow depth. Early sowing (September), late sowing (October) and spring inoculation were additional treatments, applied to the first crop only, in Expt 2. Seasonal factors apart, the disease outcome in the first year after inoculation depended on amounts and placement of applied inoculum, as well as date of sowing. Deeper inoculum resulted in less disease (Expt 1). Severe take-all was produced in Expt 2 by incorporating inoculum shallowly in sufficient quantities (400 kg ha^-1 or more). Less inoculum (200 kg ha^-1) generated less disease, especially in earlier-sown plots. Differences in disease amongst inoculum treatments were greatest in the first year and diminished subsequently, particularly where sowing had been early in the first year. In Expt 1, where first crops exposed to artificial inoculum developed moderate-to-severe disease, disease in subsequent second and/or third crops was less. In the fourth crop a second peak of disease occurred, coinciding with a first peak in sequences without added inoculum. Take-all decline (TAD) appeared to be expressed in all sequences thereafter. In Expt 2 in sequences without added inoculum, TAD occurred after a peak of disease in the second crop. Where 400 kg ha^-1 or more of inoculum were added, disease was severe in the first year and decreased progressively in successive years. Disease was less patchy in plots that received artificial inoculum. However, it remains uncertain mat severe disease caused by artificial inoculation achieved an early onset of true TAD. The infectivity of the top 12 cm of soil in the first 3 yr of Expt 1, determined by bioassay, depended on the depth of added inoculum and amount of disease in subsequent crops. However, at the time of the naturally occurring peak of disease severity (in either inoculated or non-inoculated plots) it did not predict either disease or TAD. Differences and similarities amongst epidemics developing naturally and those developing from different amounts and placement of applied inoculum have been revealed. The epidemiological implications of adding inoculum and the potential value of artificially-created epidemics of take-all in field trials are discussed.     

Temporal Dynamics of Powdery Mildew (Oidium neolycopersici) and its Effects on the Host Growth Dynamics of Tomato

Controlled glasshouse experiments were conducted to investigate the temporal progress of powdery mildew and its effects on host dynamics of tomato, without and with one fungicide application. Healthy tomato transplants (5‐ to 6‐week old) were artificially inoculated with powdery mildew, and disease progress as well as host growth were monitored in both fungicide sprayed and unsprayed treatments and compared with non‐inoculated plants. Actual disease severity on a plant basis increased in unsprayed plants reaching maximum severity in the proportionate range of 0.53–0.83. One fungicide spray significantly reduced the maximum disease severity by two‐ to fourfolds. Despite adjustments for defoliation, declines in the proportion of disease severity between successive assessments were evident. Whereas the estimated growth rates of diseased plants were significantly lower than that of healthy plants, no significant differences were observed in the maximum leaf area formed of inoculated and non‐inoculated plants. A considerable effect of the powdery mildew epidemics was manifested through hastened shrivelling and defoliation of diseased leaves within the tomato canopy. An average of 18–29% and 40–52% of leaves had abscised from the plant canopy at the last date of assessment in sprayed and non‐sprayed plants, respectively. Accordingly, defoliation accounted for 14–33.3% and 58.3–63.1% losses in leaf area of sprayed and non‐sprayed plants, respectively. Duration of healthy leaf area and yield of inoculated plants were also significantly reduced by powdery mildew epidemics.     

研究SIR传染病数学模型的Lagrange-Noether方法

应用分析力学的方法讨论了SIR传染病数学模型方程,得到了与其对应的Lagrange函数和Noether守恒量,并根据Noether守恒量具体探讨了对感染病者和易感染病者人群的隔离率与患病者人数最大值的关系.     

SIR传染病数学模型的隔离控制

本文研究的SIR传染病隔离控制,不仅对染病者进行隔离,而且隔离易感者．对该模型闽值进行分析,探讨隔离率与患病人数最大值之间的关系,旨在消除该传染病．仿真表明此法行之有效．     

Vector borne diseases on an urban environment: The effects of heterogeneity and human circulation

We study the effect of human circulation and host/vector heterogeneities on the onset of epidemics of arboviruses. From a meta-population dynamics based on the classical Bailey–Dietz model, we derive a multi-group model under three assumptions: (i) fast host sojourn time-scale; (ii) mosquitoes do not move; (iii) time homogeneity and strong connectivity of human circulation. Within this modelling framework, three different kinds of R₀ appear: (i) the “true” or “global” R₀—derived from the corresponding next generation matrix; (ii) the uniform R₀—obtained if the patches are taken homogeneous; (iii) the local R₀s—obtained if the patches are disconnected. We show that there is relevant epidemiological information associated to all of them. In particular, they can be used to understand the effects of changing the circulation on the value of the global R₀. We also present additional results on the effects on R₀ of different vector control policies, and a simulation with data from the city of Rio de Janeiro, Brazil.     

Cucurbit Powdery Mildew: First Insights for the Identification of the Causal Agent and Screening for Resistance of Squash Genotypes (Cucurbita moschata (Duchesne ex Lam.) Duchesne ex Poir.) in Mendoza,Argentina

The cucurbit powdery mildew (CPM) caused by different fungal species is a major concern for cucurbit crops around the world. In Argentina CPM constitutes the most common and damaging disease for cucurbits, especially for squash crops (Cucurbita moschata). The present study displays initial insights into the knowledge of the disease in western Argentina, including the determination of the prevalent species causing CPM, as well as the evaluation of the resistance of squash cultivars and breeding lines. Fungal colonies were isolated from samples collected in Mendoza province, Argentina. A field trial was also performed to assess the resistance of five squash accessions, including commercial cultivars and breeding lines. The severity of CPM was analyzed and epidemiological models were built based on empirical data. The morphological determinations and analysis with specific molecular markers confirmed Podosphaera xanthi as the prevalent causal agent of CPM in Mendoza. The results od the field trial showed differences in the resistance trait among the squash accessions. The advanced breeding line BL717/1 showed promising results as source of CPM resistance for the future development of open pollinated resistant cultivars, a crucial tool for an integrative control of the disease.     

Exploring Spatiotemporal Patterns of Phoma Black Stem in Sunflower

Field experiments were conducted over two growing seasons with three sunflower cultivars to explore the spatiotemporal dynamics of phoma black stem epidemics and to test hypotheses pertaining to (i) disease spread from a known inoculum source; (ii) spatial patterns of the disease; (iii) disease spatiotemporal association; and (iv) association between disease intensity and sunflower defoliation. The spatial patterns of disease were random in most of epidemics, and disease gradients were not detected. Our results suggest absence of secondary infections, that is, that the studied phoma black stem epidemics were monocyclic under the experimental conditions reported here. Significant associations between the number of dead leaves per plant and the number of phoma black stem lesions per plant were detected towards the end of epidemics.     

Culture change and epidemiological patterns among the Hagahai,Papua New Guinea

The role of introduced epidemic disease in highland New Guinea is considered in light of recent debate concerning pre-contact adaptations. Seroepidemiological studies of the Hagahai, a small isolated group of hunterhorticulturalists in the fringe highlands of Papua New Guinea, document the recent introduction of mumps, hepatitis B, specific types of influenza, and rotavirus. Results are related to ethnographic findings, detailing past levels of intergroup contact and recent changes in settlement patterns, travel, feasting, health care, and other cultural factors. Data suggest that intergroup disease transmission is greatly increased decades before officially recorded time of contact and that mortality levels documented soon thereafter are not indicative of the pre-contact adaptation.