Emerging infectious diseases and animal social systems

Emerging infectious diseases threaten a wide diversity of animals, and important questions remain concerning disease emergence in socially structured populations. We developed a spatially explicit simulation model to investigate whether—and under what conditions—disease-related mortality can impact rates of pathogen spread in populations of polygynous groups. Specifically, we investigated whether pathogen-mediated dispersal (PMD) can occur when females disperse after the resident male dies from disease, thus carrying infections to new groups. We also examined the effects of incubation period and virulence, host mortality and rates of background dispersal, and we used the model to investigate the spread of the virus responsible for Ebola hemorrhagic fever, which currently is devastating African ape populations. Output was analyzed using regression trees, which enable exploration of hierarchical and non-linear relationships. Analyses revealed that the incidence of disease in single-male (polygynous) groups was significantly greater for those groups containing an average of more than six females, while the total number of infected hosts in the population was most sensitive to the number of females per group. Thus, as expected, PMD occurs in polygynous groups and its effects increase as harem size (the number of females) increases. Simulation output further indicated that population-level effects of Ebola are likely to differ among multi-male–multi-female chimpanzees and polygynous gorillas, with larger overall numbers of chimpanzees infected, but more gorilla groups becoming infected due to increased dispersal when the resident male dies. Collectively, our results highlight the importance of social system on the spread of disease in wild mammals.     

Characteristics of structural proteins of infectious flacherie virus from the silkworm, Bombyx mori

Structural proteins and the characteristics of infectious flacherie virus (IFV) purified from the silkworm, Bombyx mori, are described. The purified IFV had four major structural proteins, which were detected only in high concentration gels of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and a few minor ones. Molecular weights of the major proteins were 35,200 (VP 1), 33,000 (VP 2), 31,200 (VP 3), and 11,600 (VP 4), and numbers per virion were 62, 57, 54, and 31, respectively. Amino acid compositions of VP 1, VP 2, and VP 3 were similar to each other but that of VP 4 was somewhat different. By isoelectric focusing and two-dimensional electrophoresis, high resolution of the structural proteins was obtained with silver staining. The isoelectric points of the four major proteins were determined as 7.7(VP 1), 6.7(VP 2), 4.8(VP 3), and 5.5(VP 4). This work is the first report on insect picornaviruses that presents some discriminative properties of each viral protein that was compared to those of mammalian picornaviruses.     

Integrating sample similarities into latent class analysis: a tree-structured shrinkage approach

This paper is concerned with using multivariate binary observations to estimate the probabilities of unobserved classes with scientific meanings. We focus on the setting where additional information about sample similarities is available and represented by a rooted weighted tree. Every leaf in the given tree contains multiple samples. Shorter distances over the tree between the leaves indicate a priori higher similarity in class probability vectors. We propose a novel data integrative extension to classical latent class models with tree-structured shrinkage. The proposed approach enables (1) borrowing of information across leaves, (2) estimating data-driven leaf groups with distinct vectors of class probabilities, and (3) individual-level probabilistic class assignment given the observed multivariate binary measurements. We derive and implement a scalable posterior inference algorithm in a variational Bayes framework. Extensive simulations show more accurate estimation of class probabilities than alternatives that suboptimally use the additional sample similarity information. A zoonotic infectious disease application is used to illustrate the proposed approach. The paper concludes by a brief discussion on model limitations and extensions.     

传染性单核细胞增多症患儿NLR、CD4+/CD8+比值、ADA与EBV-DNA载量的相关性分析及对肝损害的影响

摘要 目的：探讨传染性单核细胞增多症（IM）患儿外周血中性粒细胞/淋巴细胞比值（NLR）、CD4⁺/CD8⁺比值、腺苷脱氨酶（ADA）与EB病毒（EBV）-脱氧核糖核酸（DNA）载量的相关性,分析其对IM患儿肝损害的影响。方法：选择2019年1月至2022年4月我院儿科收治的102例IM患儿（IM组）,另选择同期我科收治的95例EB病毒检测阴性的发热患儿（非IM组）和体检健康的73例健康儿童（对照组）。根据是否发生肝损害将IM患儿分为肝损害组（61例）和非肝损害组（41例）。比较外周血NLR、CD4⁺/CD8⁺比值、ADA与EBV-DNA载量,Pearson法分析NLR、CD4⁺/CD8⁺比值、ADA与EBV-DNA载量的相关性。多因素Logistic回归分析IM患儿发生肝损害的影响因素。结果：IM组ADA高于非IM组和对照组（P＜0.05）,且非IM组高于对照组（P＜0.05）,NLR、CD4⁺/CD8⁺比值低于非IM组和对照组（P＜0.05）,且非IM组低于对照组（P＜0.05）,IM组EBV-DNA载量高于非IM组（P＜0.05）。IM患儿ADA与EBV-DNA载量呈正相关（r=0.493,P＜0.05）,NLR、CD4⁺/CD8⁺比值与EBV-DNA载量呈负相关（r=-0.419、-472,P＜0.05）。肝损害组ADA、EBV-DNA载量高于非肝损害组（P＜0.05）,NLR、CD4⁺/CD8+⁺比值低于非肝损害组（P＜0.05）。肝脏肿大、高EBV-DNA载量、高ADA是IM患儿肝损害的危险因素（P＜0.05）,高NLR、高CD4⁺/ CD8⁺比值是保护因素（P＜0.05）。结论：IM患儿ADA增高,NLR、CD4⁺/CD8⁺比值降低,与EBV-DNA载量增加以及肝损害有关。     

Populations and infectious diseases: Dynamics and evolution

The host-parasite or host-pathogen system was analyzed from dynamical and evolutionary viewpoints using simple mathematical models incorporating vertical transmission, immunity and its loss. We first analyzed a model without density regulation of host population. In the analysis on dynamics, the condition for the pathogen to work as a density regulating factor was obtained. In the analysis on evolution, criteria for the evolution of host and pathogen were proposed. These criteria implies that the evolution of hosts should result in an increase in infected host density, whereas the evolution of pathogens a decrease in susceptible host density. The direction of evolution at some parameters of host and that of pathogen were examined when the parameters were independently and freely changeable. Among the parameters, only reduction in additional mortality due to infection was the evolutionary trend common to both host and pathogen. In all the other parameters examined, trend of evolution predicted in host is reversed in pathogen. We then analyzed whether the obtained criteria still hold in models with density regulation of hosts. Using randomly generated parameter sets, we obtained the result that the criteria should hold very likely though they do not always hold. We discussed evolution of virulence when there is a constraint between the traits.     

Whitening,thallus decay and fragmentation in Gracilaria chilensis associated with an endophytic amoeba

Whitening of Gracilaria chilensis, accompanied by tissue softening and thallus fragmentation, was found to be associated with the presence of an endophytic amoeba. Although the symptoms developed originally in green mutant thalli, subsequent infections in the laboratory also affected normal, wild-type G. chilensis. Ultrastructural evidence indicates that the amoebae perforate the host cell walls of both cortical and medullary cells and digest their protoplasm. Feeding by the amoeba appears to involve both phagocytosis and enzymatic digestion of the host tissue. Destruction of the host tissue resulted in large cavities first, followed by thallus fragmentation. No other organism was found during the early stages of thallus invasion by the amoeba, although bacteria may appear once the amoeba reaches the inner tissues of the host.     

Integral equation models for endemic infectious diseases

Summary Endemic infectious diseases for which infection confers permanent immunity are described by a system of nonlinear Volterra integral equations of convolution type. These constant-parameter models include vital dynamics (births and deaths), immunization and distributed infectious period. The models are shown to be well posed, the threshold criteria are determined and the asymptotic behavior is analysed. It is concluded that distributed delays do not change the thresholds and the asymptotic behaviors of the models.This work was partially supported by NIH Grant AI 13233.     

Effect of Exposure Period and Algal Concentration on the Frequency of Infection of Aposymbiotic Ciliates by Symbiotic Algae from Paramecium bursaria

The effect of exposure period and concentration of algae on the frequency of infection of aposymbiotic ciliates by algae obtained from the same clone of Paramecium bursaria syngen 2, was studied. The frequency of infection was roughly proportional to the algal concentration and to the exposure time of ciliates to algae. The relationship of algal concentration to infection frequency closely fitted the Poisson distribution curve for N = 1, suggesting that the minimum number of algae required to infect a single ciliate is 1. However, the data also strongly suggested that the average number of algae required to initiate infection of an average ciliate was ? 1,000. Three possible resolutions of this situation are: (a) the selection by the ciliate of a rare infective variant from a heterogeneous population: (b) the rare escape of an alga from digestion by the ciliate; and (c) the requirement for a large number of algae-ciliate contacts to induce susceptibility in the ciliate. Splitting the exposure of ciliates to algae into 2 periods of 0.5 h, separated by 5 h in the absence of algae, produced a much higher frequency of infection than a single l-h exposure, supporting the suggestion that the large number of algae is required to induce susceptibility in the ciliate which can then be infected by as few as a single algal cell.