Sequence and phylogenetic analyses of highly virulent infectious bursal disease virus

The nucleotide sequences of the genome segments A and B encoding the precursor polyprotein (NH2-VP2-VP4-VP3-COOH) and VP1 were determined for a highly virulent strain of infectious bursal disease virus (IBDV). The precursor polyprotein and VP1 coding regions of highly virulent OKYM strain consisted of 3039 nucleotides (1012 deduced amino acids) and 2640 nucleotides (879 deduced amino acids), respectively. Comparison of the deduced amino acid sequences of the highly virulent IBDV (HV-IBDV) with other serotype 1 and 2 sequences revealed 17 amino acid residues which were conserved only in the HV-IBDV. Among the 17 unique amino acid differences, 8 were in VP1, 4 were in VP2, 3 were in VP3 and 2 were in VP4. Although it is impossible to predict the effect of the unique amino acid residues without detailed knowledge of the three-dimensional structure and function of the proteins, they could affect the virulence of HV-IBDV. Alignment of the nucleic acid sequences of precursor polyprotein, VP1, VP2, VP3 and VP4 coding regions followed by distance analysis allowed the generation of phylogenetic trees. The same tree topology was obtained for the nucleotide sequence of precursor polyprotein, VP2, VP3 and VP4. On the other hand, the tree topology of VP1 was quite different from that obtained for the nucleotide sequence of precursor polyprotein, VP2, VP3 and VP4. These findings indicate that not a genetic recombination but a genetic reassortment may play an important role in the emergence of HV-IBDV.     

Estimating the rate constants in a two-compartment stochastic model

A procedure is described for estimating the rate constants of a two-compartment stochastic model for which the covariance structure over time of the observations is known. The proposed estimation procedure, by incorporating the known (as a function of the parameters to be estimated) covariance structure of the observations, produces regular best asymptotically normal (RBAN) estimators for the parameters. In addition, the construction of approximate confidence intervals and regions for the parameters is made possible by identification of the asymptotic covariance matrix of the estimators. The explicit form of the inverse of the covariance matrix, which is required in the estimation procedure, is presented. The procedure is illustrated by application to real as well as simulated data, and a comparison is made to the widely used nonlinear least squares procedure, which does not account for correlations over time.     

Estimating the rate of evolution of the rate of molecular evolution

A simple model for the evolution of the rate of molecular evolution is presented. With a Bayesian approach, this model can serve as the basis for estimating dates of important evolutionary events even in the absence of the assumption of constant rates among evolutionary lineages. The method can be used in conjunction with any of the widely used models for nucleotide substitution or amino acid replacement. It is illustrated by analyzing a data set of rbcL protein sequences.     

Ehrlichiosis: a new infectious disease

Human ehrlichiosis is transmitted by ticks. For the first time it was described in 1987. The ethiologic agent is Ehrlichia chaffeenisis. The course of the disease may be mild, self-limited or sometimes severe finishing with dead. The main symptoms are: fever, leucopenia, thrombocytopenia, or pancytopenia. Tetracyclines are mostly efficient in the treatment.     

In vitro attenuation of highly virulent infectious bursal disease virus: some characteristics of attenuated strains

Some strains of highly virulent infectious bursal disease virus (HV-IBDV) were adapted through serial passage in embryonated eggs. The embryonated egg-adapted HV-IBDV was successfully adapted to grow in chicken embryo fibroblast (CEF) cell cultures showing a cytopathic effect by preparing the CEF cells from the virus-infected embryos. The embryonated egg- and cell culture-adapted strains significantly reduced their pathogenicity to, and did not kill any, young chickens in experimental infection. The bursal lesions of the adapted strain-infected chickens were similar to those observed in classical strain-infected chickens. Cross-virus neutralization analysis showed antigenic diversity between the cell culture-adapted HV-IBDV strains and classical strains. In immunization tests, the adapted strain-immunized chickens showed good protection against the fatal infection of HV-IBDV. Especially, in case of challenge at 3 days postimmunization, the adapted strains showed effective immunogenicity. The adapted strains appear to provide a new and effective live vaccine against HV-IBDV infection.     

关于传染病的预防

根据我国<传染病防治法>(1989年发布)的规定,预防、控制和消除传染病的发生与流行是各级医务人员的神圣职责.因此临床医师在搞好临床诊断与治疗工作的同时,也应努力做好传染病的预防工作.传染病预防措施可分为:①疫情未出现时的预防措施;②疫情出现后的防疫措施;③治疗性预防措施.     

Analysis of a dengue disease transmission model

A model for the transmission of dengue fever in a constant human population and variable vector population is discussed. A complete global analysis is given, which uses the results of the theory of competitive systems and stability of periodic orbits, to establish the global stability of the endemic equilibrium. The control measures of the vector population are discussed in terms of the threshold condition, which governs the existence and stability of the endemic equilibrium.     

A model for predicting the transmission rate of malaria from serological data

A model is developed to estimate the duration for which malaria antibody levels in the blood remain high in a closed population. This estimate can be used to calculate the transmission rate within a region, in conjunction with the serological information contained in the population. The model is used on data obtained from a study of malaria in the Philippines and shows excellent agreement. It is subsequently utilised for predictions and seems to be an appropriate vehicle for this purpose.     

A disease management case study in infectious disease

One of the earliest attempts at risk sharing between a managed-care organization and a pharmaceutical company is the infectious disease management program developed since late 1993 by Intergroup of Arizona and Eli Lilly and Company (Indianapolis, Indiana) in conjunction with the Center for Pharmaceutical Economics at The University of Arizona (Tucson, Arizona) and other entities. In the first phase of the program, protocols were built around eight infectious disease states, and it was recognized that second-line antibiotics were often prescribed when more economical first-line antibiotics would be equally effective. The second phase of the program emphasized developing treatment algorithms focused on patient outcomes, using merged medical and pharmacy claims databases to determine the effects of the antibiotic changes. To implement the program successfully, some significant shifts in corporate, medical, and patient mind-sets had to be addressed. A primary goal was to encourage a movement from a rebate, volume-driven, cost structure to a shared-risk, appropriate-use, reimbursement method in which both managed-care and the pharmaceutical company incentives could mesh as far as possible. Over the long term, it is hoped that this project will lay the groundwork for other disease management programs for high-impact, frequently occurring diseases.     

Applied infectious disease epidemiology in Germany

Applied epidemiology emphasizes the study of the distribution and determinants of disease and health in populations and the application of this study to the control of health problems of immediate public health consequence. Outbreak investigation symbolizes the use and methodology of applied epidemiology for public health. The steps of an outbreak investigation are summarized. Development of a network for applied infectious disease epidemiology involving health departments and other institutions is being built in Germany through epidemiologic training, building communication systems, providing support for outbreak investigation, development of national reference laboratories, and building a comprehensive research program.     

Global progress in infectious disease control

There is both good news and bad news concerning infectious disease control globally. The good news is that smallpox has been eradicated, eradication of poliomyelitis and guinea worm disease is on track, and many infectious diseases are under effective control in much of the world. The advances are primarily the result of improved sanitation, effective use of vaccines, and introduction and use of specific therapies (whose impact has primarily been on mortality, rather than incidence). The bad news is that infectious diseases are still the leading cause of death world-wide, new diseases are emerging, old diseases are re-emerging, there are ominous interactions between diseases, and antibiotic resistance is emerging as a major problem. There are many promising developments for the future, including new and improved vaccines, new specific therapies, and new strategies to deal with infectious disease. However, unless eradicated, infectious diseases remain a threat and require continuous efforts to be kept under control. Given the ability of infectious agents to evolve, it is certain that the future will also hold new problems and new diseases.