Host-specificity of myxoma virus: Pathogenesis of South American and North American strains of myxoma virus in two North American lagomorph species.

The pathogenesis of South American and North American myxoma viruses was examined in two species of North American lagomorphs, Sylvilagus nuttallii (mountain cottontail) and Sylvilagus audubonii (desert cottontail) both of which have been shown to have the potential to transmit the South American type of myxoma virus. Following infection with the South American strain (Lausanne, Lu), S. nuttallii developed both a local lesion and secondary lesions on the skin. They did not develop the classical myxomatosis seen in European rabbits (Oryctolagus cuniculus). The infection at the inoculation site did not resolve during the 20-day time course of the trial and contained transmissible virus titres at all times. In contrast, S. audubonii infected with Lu had very few signs of disseminated infection and partially controlled virus replication at the inoculation site. The prototype Californian strain of myxoma virus (MSW) was able to replicate at the inoculation site of both species but did not induce clinical signs of a disseminated infection. In S. audubonii, there was a rapid response to MSW characterised by a massive T lymphocyte infiltration of the inoculation site by day 5. MSW did not reach transmissible titres at the inoculation site in either species. This might explain why the Californian myxoma virus has not expanded its host-range in North America.

Magnetic fields in astrophysical objects.

Magnetic fields are known to reside in many astrophysical objects and are now believed to be crucially important for the creation of phenomena on a wide variety of scales. However, the role of the magnetic field in the bodies that we observe has not always been clear. In certain situations, the importance of a magnetic field has been overlooked on the grounds that the large-scale magnetic field was believed to be too weak to play an important role in the dynamics. In this article I discuss some of the recent developments concerning magnetic fields in stars, planets and accretion discs. I choose to emphasize some of the situations where it has been suggested that weak magnetic fields may play a more significant role than previously thought. At the end of the article, I list some of the questions to be answered in the future.

Virulence and pathogenesis of the MSW and MSD strains of Californian myxoma virus in European rabbits with genetic resistance to myxomatosis compared to rabbits with no genetic resistance.

The pathogenesis of two Californian strains of myxoma virus (MSW and MSD) was examined in European rabbits (Oryctolagus cuniculus) that were either susceptible to myxomatosis (laboratory rabbits) or had undergone natural selection for genetic resistance to myxomatosis (Australian wild rabbits). MSW was highly lethal for both types of rabbits with average survival times of 7.3 and 9.4 days, respectively, and 100% mortality. Classical clinical signs of myxomatosis were not present except in one rabbit that survived for 13 days following infection. Previously described clinical signs of trembling and shaking were observed in laboratory but not wild rabbits. Despite the high resistance of wild rabbits to myxomatosis caused by South American strains of myxoma virus, the MSW strain was of such high virulence that it was able to overcome resistance. The acute nature of the infection, relatively low viral titers in the tissues and destruction of lymphoid tissues, suggested that death was probably due to an acute and overwhelming immunopathological response to the virus. No virus was found in the brain. The MSD strain was attenuated compared to previously published descriptions and therefore was only characterized in laboratory rabbits. It is concluded that Californian MSW strain of myxoma virus is at the extreme end of a continuum of myxoma virus virulence but that the basic pathophysiology of the disease induced is not broadly different to other strains of myxoma virus.

Monitoring the spread of myxoma virus in rabbit Oryctolagus cuniculus populations on the southern tablelands of New South Wales, Australia. II. Selection of a strain of virus for release.

To be able to study the dynamics of myxoma virus spread following a release in the field, a strain of virus is required that is both highly transmissible and readily differentiated from other field strains. Eight strains of virus of known virulence for laboratory rabbits and with previously mapped and sequenced restriction fragment length polymorphisms, were used to infect groups of seronegative wild rabbits. Based on these trials, and on the nature of the DNA polymorphism, a virus designated Brooklands/2-93 was chosen as a strain suitable for experimental release. These trials confirmed that resistance to myxomatosis within wild rabbit populations continues to be substantial and that some rabbits are highly resistant. These rabbits probably have little role in transmission of virus. Most of the virus strains tested induced very small or invisible primary lesions at the inoculation site. Thus the secondary skin sites such as eyelids, face and ears may be critical for transmission.

The epidemiology of fatalities reported to the vaccine adverse event reporting system 1990-1997.

PURPOSE: To examine the fatalities reported to the federally administered Vaccine Adverse Event Reporting System (VAERS), a passive surveillance system, in its first 7 years. METHODS: The working data set included variables such as demographic information, dates of vaccination, adverse event onset and death, vaccines administered, and vaccination facility data. Frequencies for these data and state reporting rates were calculated. RESULTS: A total of 1266 fatalities were reported to VAERS during July 1990 through June 1997. The number of death reports peaked in 1992-1993 and then declined. The overall median age of cases was 0.4 years, with a range of 1 day to 104 years. Nearly half of the deaths were attributed to sudden infant death syndrome (SIDS). CONCLUSIONS: The trend of decreasing numbers of deaths reported to VAERS since 1992-1993 follows that observed for SIDS overall for the US general population following implementation of the 'Back to Sleep' program. These data may support findings of past controlled studies showing that the association between infant vaccination and SIDS is coincidental and not causal. VAERS reports of death after vaccination may be stimulated by the temporal association, rather than by any causal relationship.

Infertility in female rabbits (Oryctolagus cuniculus) alloimmunized with the rabbit zona pellucida protein ZPB either as a purified recombinant protein or expressed by recombinant myxoma virus.

Development of immunocontraceptives for wild rabbit populations requires selection of both effective antigens and effective delivery systems. Recombinant rabbit zona pellucida glycoprotein B (ZPB) produced in eukaryotic cells in vitro was an effective antigen and induced sustained infertility in 70% of female rabbits. This required two boosts and serum antibody titers of 12 800 or greater. Antibody titers in females were low after the initial immunization, as might be expected with a self-antigen; however, male rabbits had a strong antibody response, indicating that the protein was immunologically foreign. To develop a delivery system, ZPB was delivered by infection with a recombinant myxoma virus. In contrast to the results with ZPB protein, infection of rabbits induced a similar serum antibody response to ZPB in both sexes. This indicated that presentation of ZPB in the context of a virus infection was able to overcome tolerance in females. However, the antibody titers were lower than 12 800, and only 25% of female rabbits were infertile. This antibody response was boosted by injections of recombinant ZPB protein, after which 80% of female rabbits were infertile. Infertility was associated with antibody binding to zonae and varying degrees of ovarian pathology characterized by follicular degeneration and substantial depletion of primordial follicles. Oocyte and follicular degeneration appeared to be the principal mechanism of infertility and may be primarily induced by antibodies to ZPB.

Peripheral arterial emboli and factors in their recurrence rate.

One hundred six patients who underwent a total of 141 operations, on 156 limbs for peripheral arterial emboli from 1964 to 1979 were studied. The average age of the patients was 68.5 years. The source of the emboli in 76.4% of the patients was arteriosclerotic heart disease and atrial fibrillation. The presenting clinical symptoms and signs were the most accurate determinate of limb salvage. Our overall limb salvage was 86.5% and in the survivor population 93.9%. The overall hospital mortality was 21.7%. There were much higher morbidity and mortality rates associated with each subsequent embolic event. Particular attention was paid to factors related to recurrent emboli. The use of antigoagulants in the post embolectomy period does not have a statistically significant effect of preventing recurrent emboli.