The H strain of infectious bronchitis (IB) was one of the earliest live attenuated IB vaccines to be developed and has continued to be use in most parts of the world for almost 50 years. It was developed for used at both the 52nd (H52) and 120th (H120) vaccine levels and, because of it ability to provide heterologous cross-protection against a number of IB viruses of different serotypes, has proved to be one of the most enduring live attenuated IB vaccines. In fact, the H120 vaccine is possibly the most widely used live attenuated IB vaccine globally to this day. The use of H52 has, however, declined with the introduction of safe and highly efficacious inactivated IB vaccines. This review documents the original studies to isolate and attenuate the H strain by serial embryo passage, and describes the early studies to demonstrate its efficacy in laboratory studies and under field conditions. The efficacy of the H vaccine in providing cross-protection against some of the many IB variants now reported worldwide is also discussed, and possible future vaccination strategies for IB considered.
Safe blood transfusion still remains a major concern and so far all the efforts in this direction have failed to achieve zero residual risk of transfusion transmitted hepatitis B virus (HBV) infection. In this direction the recently published work by Silva et al. in Journal of Infection has revealed remarkable observations. 1 This report shows 3.3% HBV DNA positivity of the blood donor's samples that were anti-HBc positive, more enlightening finding is the HBV DNA positivity among the high level anti-HBs positive donors. At this tertiary care centre of Saudi Arabia out of 26 606 blood units collected during 2000-2003, isolated anti-HBc positivity was 3.2% and HBsAg positivity 1.9%, where as 10.1% of the blood units were anti-HBc and anti-HBs positive. As per policy of health ministry, the anti-HBc and anti-HBs positive blood units were utilized and the isolated anti-HBc blood units were rejected. 2 The blood units which are anti-HBc and anti-HBs positive do not appear to transmit HBV infection and there is inverse correlation between anti-HBs level and infectivity, only 10% of the blood units with low level (!0.1 IU/ml) anti-HBs are infectious. 3 The observation by Silva et al. that HBV DNA positivity among anti-HBc and high level anti-HBs positive blood donors is a pointer towards the transfusion transmitted risk involved by transfusion of anti-HBc and anti-HBs positive blood units. Though the viral load in these samples was low (!1000 copies/ml) but this can be highly infectious if transfused to an immunocomprised patient. Considering the volume of infectious blood transfused any amount of HBV DNA will be infectious as the minimum infecting dose of HBV in chimpanzees is only 100 virus particles. 4 In many of the developed countries and most of the developing countries the blood units collected are still being screened for HBsAg, anti-HBc and anti-HBs by enzyme immuno assay. On many occasions the results are indeterminate and has to be repeated leading to higher per unit cost of blood screening and lot of rejection of the invaluable units of collected blood or exclusion of the generous donor because of isolated anti-HBc positivity and still the safety of transfusion transmitted HBV is compromised. This high rate of rejection of collected blood units and the exclusion of the anti-HBc positive blood donors leads to the unceasing blood shortage in the blood banks. The HBV screening policy for the collected units of blood needs reassessment in light of the present report 1 and HBV DNA testing should be preferred instead of three enzyme immuno assay tests. HBV DNA testing by NAT of all the collected units of blood should be adopted by all the blood banks, in order to possibly achieve zero risk of transfusion transmitted HBV infection and also to reduce the rejection rate of the precious units of collected blood by testing for anti HBc. References1. Silva CMD, Costi C, Costa C, et al. Low rate of occult hepatitis B virus infection among anti-HBc positive blood donors living in a low prevalence region in Brazil. J ...
SUMMARYPost-exposure protection of rabies-infected mice was observed by proximal application of axonal flow inhibitors, particularly vinblastine, to the local nerve(s). These observations indicate that rabies virus is transported by the axonal flow of the peripheral nerves to the central nervous system, Both a fixed virus (CVS) and a street (sylvatic) virus were used.This model in mice could be used to develop an additional post-exposure local treatment of rabies infection in man, by infiltrating local nerves or ganglions with axonal flow inhibitors, with the advantage that it would not interfere with subsequent vaccination as is the case with the administration of hyperimmune serum or immunoglobulin.
SUMMARYA rabies virus persistent infection in BHK21 S13 cells was established and maintained in culture for more than 4 years. Initially, the cultures produced a large plaque virus similar to that produced by the original virus, but between the 10th and 20th passage, this was replaced by a small plaque variant. By the 200th passage, infectious virus could no longer be detected in the medium. After further cell passages O 300) no infectious particles could be detected in the medium. At various passage levels, the persistently infected cells were labelled with [35S]methionine and the virus antigens immunoprecipitated and analysed by polyacrylamide gel electrophoresis. No changes in the virus polypeptides were observed in the establishment of the persistent state. However, after the 20th passage (predominance of small plaque variant) there was an increase in the size of the glycoprotein. This was followed (164th passage) by a change in the M1 polypeptide which was subsequently further modified in the defective state (/> 300 passages). Virus isolated from the 400th passage by treatment of the cells with DEAE-dextran, was also modified in the glycoprotein and M 1 polypeptides and contained less L polypeptide than the original virus. This virus grew more slowly, to a lower titre and was no longer pathogenic in suckling mice.
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