Commercial heat treatment procedures for molluscan shellfish are based on data obtained for the inactivation of hepatitis A virus (HAV) in cockles. However, the most frequently reported illness associated with consumption of bivalve molluscs is gastroenteritis caused by small round structured viruses (SRSVs) of the Norwalk group. Conditions for inactivation of SRSVs are unknown. In this study a feline calicivirus was used as a model for the SRSV group and conditions for its heat inactivation determined. Experiments showed that feline calicivirus is more readily inactivated in shellfish than HAV, and confirmed that current heating recommendations to the UK shellfish industry are adequate. A reverse transcription polymerase chain reaction (RT-PCR) assay for the detection of calicivirus in shellfish was developed and results compared with isolation in cell culture. The RT-PCR detected virus in some samples that failed to yield virus on culture. This has important implications if molecular virology techniques are to be used in the design and monitoring of shellfish treatment procedures and for routine testing of food samples.

Viral haemorrhagic disease of rabbits (VHD), a potential biological control for wild rabbits in Australia and New Zealand, escaped from quarantined field trials on Wardang Island and spread to the mainland of Australia in October 1995. This study looked for any evidence of infection or illness in people occupationally exposed to the virus. Two hundred and sixty-nine people were interviewed and 259 blood samples were collected. Exposures to VHD-infected rabbits ranged from nil to very high. No VHD antibodies were detected in any of the 259 sera when tested by VHD competitive enzyme immunoassay, which had been validated with 1013 VHDV-specific antibody negative sera. A questionnaire designed to elicit symptoms of disease in a range of organ systems found no significant differences between illness in those exposed and those not exposed to VHD, nor could an association be found between exposure and subsequent episodes of illness. The findings are consistent with the view that exposure to VHD is not associated with infection or disease in humans.

Bank voles (Clethrionomys glareolus) serve as the reservoir for Puumala (PUU) virus, the aetiologic agent of nephropathia epidemica. The animals are believed to be persistently infected and the occurrence of serum antibodies is usually taken as an evidence of active infection. We found serum antibodies to PUU virus in 42 of 299 wild bank voles captured in a PUU virus endemic area. PUU virus RNA was demonstrated in lung specimens of 11 of these 42 animals and in 2 of them antigen was also found. Thus in the lungs of 31 of 42 seropositive animals neither PUU virus RNA nor antigen was detected. In 2 of 257 seronegative animals, lung specimens showed presence of PUU virus antigen and RNA. Isolation of PUU virus from lung tissue was successful in all 4 antigen-positive bank voles but in none of 16 tested antigen-negative animals. In conclusion, only a minority of bank voles with serum antibodies to PUU virus showed evidence of current infection.

Following the occurrence of an outbreak of Crimean–Congo haemorrhagic fever (CCHF) among workers at an ostrich abattoir in South Africa in 1996, 9 susceptible young ostriches were infected subcutaneously with the virus in order to study the nature of the infection which they undergo. The ostriches developed viraemia which was demonstrable on days 1–4 following infection, with a maximum intensity of 4·0 log10 mouse intracerebral LD50/ml being recorded on day 2 in 1 of the birds. Virus was detectable in visceral organs such as spleen, liver and kidney up to day 5 post-inoculation, 1 day after it could no longer be found in blood. No infective virus was detected in samples of muscle, but viral nucleic acid was detected by reverse transcription-polymerase chain reaction in muscle from a bird sacrificed on day 3 following infection. It was concluded that the occurrence of infection in ostriches at abattoirs could be prevented by keeping the birds free of ticks for 14 days before slaughter.

The seroprevalence of canine parvovirus (CPV), canine distemper virus (CDV), canine adenovirus (CAV) and canine herpesvirus (CHV) infections in red foxes (Vulpes vulpes) was determined in fox sera collected between 1991 and 1995. A total of 500 sera were selected and the seroprevalences were estimated to be 13% (65 of 500 sera) for CPV, 4·4% (17 of 383 sera) for CDV, 3·5% (17 of 485 sera) for CAV, and 0·4% (2 of 485 sera) for CHV, respectively. No statistically significant differences were observed between the two (rural and suburban) areas under study.

Parvovirus DNA sequences were amplified from tissues of free-ranging foxes and compared to those of prototype viruses from dogs and cats. We report here a parvovirus sequence indicative of a true intermediate between the feline panleukopenia virus-like viruses and the canine parvovirus-like viruses. The red fox parvoviral sequence, therefore, appears to represent a link between those viral groups. The DNA sequence together with a significant seroprevalence of parvovirus infections in foxes supports the hypothesis that the sudden emergence of canine parvovirus in the domestic dog population may have involved the interspecies transmission between wild and domestic carnivores.

The prevalence of antibody to the viruses of bovine virus diarrhoea (BVD), bovine herpes virus type1 (BHV1), rift valley fever (RVF), bovine ephemeral fever (BEF) and bluetongue (BT) and to Leptospira sp. was determined in wildlife populations in Zimbabwe. Evidence of infection with BVD virus was found in 14 of the 16 species examined but was greatest in eland Taurotragus oryx, nyala Tragelaphus angasi and bushbuck Tragelaphus scriptus. Persistent infection with BVD virus was found in 1 of 303 antibody-free eland but not in the smaller sample of 102 antibody-free buffalo Syncerus caffer. Antibody to BHV1 was widespread, being found in 10 of 16 species with the highest prevalence being in buffalo and eland. Antibody to RVF was most prevalent in black rhino Diceros bicornis and white rhino Ceratotherium simum, buffalo and waterbuck Kobus ellipsiprymnus. Both BEF and BT were widespread in all the species examined. Evidence of infection with Leptospira sp. was found in 7 species. Infections were due to up to 3 of 8 different serovars.

In the epidemiology of bovine viral diarrhoea (BVD), immunotolerant – persistently infected animals (IPI) appear to be major sources of contamination. These animals produce large quantities of replicating virus and have therefore been proposed as being responsible for generating antigenic variability. However, limited studies have failed to detect antigenic or genetic changes in viruses isolated at different times from IPI. An hypothesis is that the immunotolerance of IPI against their homologous strain is accompanied by immune elimination of antigenic variants. The presence of an IPI in a herd could therefore limit antigenic variation, eventually leading to the existence of herd specific strains. To verify this hypothesis we characterized, against a panel of monoclonal antibodies, 37 BVD virus strains isolated from IPI of 12 herds in Eastern Belgium. Intra-herd antigenic variation was compared to inter-herd variation. Antigenic variation within herds was found to be surprisingly high but, nevertheless, significantly lower than variation between herds.

Two groups of pigs were infected with a recent Italian isolate of swine vesicular disease virus (SVDV). Blood, nasal swabs and faeces were collected for up to 6 months after exposure to infection and animals were killed at regular intervals to obtain tissues post-mortem. These samples were examined for virus by conventional means and for viral RNA (vRNA) by reverse transcription-nested polymerase chain reaction (RT-nPCR). Virus was identified intermittently from both clinically and subclinically infected animals in nasal swabs, faeces and tonsillar tissue by either virus isolation or RT-nPCR up to 63 days post infection (dpi). Between 63 and 119 dpi virus was not detected in the secretions, excretions or tissues of any pigs. Following mixing of the two groups of animals at 119 dpi, SVDV was again identified in faeces for up to 7 days suggesting that the stress of mixing reactivated the excretion of virus in pigs from which the agent could no longer be identified. Minor antigenic changes were identified between the parental virus and isolates recovered late in the course of infection. Altered antigenicity corresponded with deduced amino acid substitutions identified from differences in nucleotide sequence between early and late isolates. This investigation demonstrates that SVDV and vRNA can be present in pigs for considerably longer after exposure to infection than has previously been recognized and provides preliminary evidence for a carrier state in swine vesicular disease.

A set of 723 diagnostic sera from human patients, submitted for the microscopic agglutination test (MAT) for antibodies to a group of 6 leptospiral serovars, was also tested by MAT for antibodies to the recently-discovered Leptospira fainei serovar hurstbridge. MAT titres of [ges ]128 to serovar hurstbridge were detected in 13·4% of these sera, and titres of [ges ]512 in 7·2%. In contrast, none of 62 sera obtained from a control population of laboratory staff gave titres of [ges ]128. The difference between the number of titres of [ges ]128 given by the two groups of sera was highly significant (P<0·01). The titres observed may have been due to cross-reactions with other leptospiral serovars, but this could not be demonstrated. An alternative explanation is that serovar hurstbridge is present in the human population.

This study sought to determine whether the decline in prevalence of hepatitis A virus (HAV) antibodies detected in Israel in 1977, 1984, and 1987 has continued. The anti-HAV antibody prevalence of a systematic sample of 578 male and female recruits inducted into the Israel Defence Force in 1996 was 38·4%. The reduction in antibody prevalence from 1977 (64%) was highly significant (P<0·001). There was a smaller decrease rate in recruits of European, North American, Australian and South African origin than from elsewhere. A ‘strategy’ that uses active immunization against hepatitis A (inactivated vaccine, instead of gamma globulin) should be considered, particularly in high risk groups such as field units during military service.

To investigate to what extent wild passerine birds are carriers of Chlamydia psittaci, 312 faecal samples from 18 bird species were collected. Using the PCR technique and subsequent DNA sequencing, C. psittaci DNA was demonstrated in faecal samples from 9 (2·9%) birds of 6 different species. Sera from 65 bird-ringers, highly exposed to wild birds, were tested by microimmunofluorescence assay for the occurrence of IgG and IgM antibodies to C. psittaci. No such antibodies were found. This results indicate that a significant proportion of wild passerine birds are carriers of C. psittaci, but rarely infectious to humans.