This study was conducted to estimate the varicella morbidity and mortality rates per age group among the non-immune population in France. Morbidity and mortality data for the years 1990–9 were derived from nationwide databases and surveillance systems. An incidence/prevalence model was designed to quantify the non-immune population per age group. The incidence of varicella in the non-immune population peaks during childhood and again in the 25–35 years age group. For children aged 1–4 years, adults aged 25–34 years and those older than 65 years, the hospitalization rates are respectively 235, 1438 and 8154 per 100 000 cases, and the death rates are respectively 7, 104 and 5345 per million cases. Case fatality or case hospitalization rates were not evenly distributed among adults and increased dramatically with age.

Varicella infections cause substantial morbidity and mortality in adolescents and adults. The primary infection, chickenpox, results in lifelong immunity to chickenpox. A seroprevalence study carried on adolescents 15–18 years of age attending schools in Lebanon showed 96·6% immunity to varicella. The positive predictive value for immunity to chickenpox based on history alone was 97·4%, whereas the negative predictive value was 4·5%. Coming from a bigger family was a statistically significant predictor of immunity to chickenpox. In a developing country like Lebanon the merits and limitations of implementing universal varicella vaccination is discussed in relation to seroprevalence and socioeconomic factors.

Lepto Dri Dot is a new card agglutination test developed by the Dutch Royal Tropical Institute for the rapid diagnosis of leptospirosis. We evaluated the test in field conditions in The Andaman Islands. Patients suspected of leptospirosis who attended three primary health centres were included in the study. The test results were compared with blood culture or microscopic agglutination tests on paired serum samples; 74 of 124 patients were diagnosed as having leptospirosis based on these criteria. Lepto Dri Dot had a sensitivity of 67.6% (50/74) and a specificity of 66.0% (33/50) during week 1. During weeks 2–4 the values increased to 85.5% (47/55) and 80% (40/50) respectively. An IgM ELISA was also performed on the serum samples for comparison and this was marginally less sensitive, but more specific, during the first week of illness. The positivity rates for the Dri Dot test during days 2–3, 4–5 and 6–7 were 53.1% (17/32), 75.0% (18/24) and 83.3% (15/18), respectively. The corresponding values for ELISA were 28.1% (9/32), 54% (13/24) and 77.8% (14/18). Both Dri Dot and ELISA showed good agreement with the standard diagnostic criteria after the first week of illness (κ = 0.65 and 0.74, respectively). The overall concordance of the two tests was 89.5% (κ = 0.79). The test does not require special storage or sophisticated equipment and can be performed by relatively low skilled personnel.

In industrialized countries migrants remain a high-risk group for tuberculosis (TB). Multiple linear regression analysis was used to determine the ability of indicators of TB incidence in the country of birth to predict the incidence of TB among migrants in Australia during 1997. World Health Organization total case notifications, new smear-positive case notifications and the estimated incidence of TB by country of birth explained 55, 69 and 87% of the variance in TB incidence in Australia, respectively. Gross national income of the country of birth and unemployment level in Australia were also significant predictors of TB in migrant groups. Indicators of the incidence of TB in the country of birth are the most important group-level predictors of the rate of TB among migrants in Australia.

A total of 556 individuals in Agbalenyi Community of Oji-River local government area of Enugu State, Nigeria were studied using questionnaires, focus group discussions and key informant interviews to determine the socio-cultural factors affecting the transmission of onchocerciasis. The result revealed a low level of knowledge about the cause, prevention and complications of onchocerciasis. Respondents have developed a cultural system around the disease due to long exposure. The majority are aware of the disease which they recognize once their body starts itching or musculoskeletal pain develops but only 64·4, 34·0, 1·4 and 3·6%, respectively attributed chronic itching, nodules, bad vision and leopard skin to blackfly bite. Other perceived causes mentioned include ageing, the type of food eaten, farm work and ‘bad blood’. Only 0·8% knew diagnosis could be made through skin snips. Neither Oji-River nor any of the river systems were associated with any of the complications of onchocerciasis. Significant differences in most socio-demographic characteristics were associated with differences in the level of knowledge about the disease.

Between 1995 and 2000, a prospective survey was undertaken to investigate the levels of contamination of raw retail chickens (n=1127) with salmonella and campylobacter. The levels of contamination over the 6-year period were 11% (95% CI±6·5%) for salmonella, and 57% (95% CI±9·5%) for campylobacter. S. Bredeney (20%) and S. Enteritidis (18%) were the dominant serovars. Although salmonella contamination was higher than in an earlier survey we conducted (7%), since 1998 it has declined to 6%. Many S. Enteritidis isolates (43%) were associated with one large integrated poultry organization that appears to have successfully managed the contamination, and the serovar has not been isolated since 1998. Contamination ranged from 0 to 44% between different producers. There was no significant difference between producers contributing large and small numbers of samples, although some small producers had much poorer contamination rates than others. S. Bareilly, S. Bredeney, S. Enteritidis and S. Virchow showed associations with particular producers. Campylobacter contamination remains high. Contamination ranged from 47 to 81% between different producers. This study did not show a temporal association between contamination of chickens and human campylobacter infections, indicating that many cases of human campylobacteriosis, particularly during seasonal peaks, do not originate from chickens. Control measures that have reduced salmonella contamination have been largely ineffective against campylobacter and new interventions are needed. Most raw chickens are contaminated with these pathogens, and communicating the importance of minimizing this risk to caterers and the public is vital in reducing human infections.

Phylogenetic analyses of bartonella have suggested divergence between bartonellae that infect mammals native to the Old and New Worlds. We characterized bartonella isolated from Eastern grey squirrels (Sciurus carolinensis) in the United States and from grey and red squirrels (Sciurus vulgaris) in the United Kingdom by nucleotide sequence comparison (gltA and groEL). Isolates from grey squirrels in the United States and the United Kingdom were identical, and most similar to Bartonella vinsonii, a species associated with New World rodents. A single and novel bartonella genotype was obtained from all 12 red squirrel isolates. Although grey squirrels were first introduced into the United Kingdom over 125 years ago, they continue to be infected solely by the bartonella associated with grey squirrels native to the United States. These results illustrate that exotic species may be accompanied by the introduction and maintenance, over many generations, of their microparasites.

The spread of rabbit haemorrhagic disease (RHD) virus from quarantine on Wardang Island to mainland Australia in 1995 suggested that insects could be potential vectors. Field observations and laboratory experiments were conducted to address aspects of this hypothesis. Firstly, the variation in insect populations on the island during the field trials was examined. There was approximately a 1000-fold increase in the number of bushflies, Musca vetustissima, shortly before the spread of the virus. Secondly, M. vetustissima were tested in the laboratory as potential vectors of RHD virus, and it was demonstrated that disease could be transmitted between rabbits by flies. Finally, 13 of 16 insect samples, collected from Wardang Island and from several sites on the mainland following the spread of virus off the island, were positive for the presence of RHD virus by a specific polymerase chain reaction (PCR). Only one sample contained sufficient infectious virus to kill a susceptible rabbit. These data, combined with previously published information on fly biology, suggested that flies, particularly bushflies, may be involved in the transmission of RHD virus. Other possible routes of spread were not assessed in this study.

A number of pathogens cause chronic infection in survivors of acute disease and this is believed to be a common means of persistence, including for highly virulent agents. We present a model in which transmission from chronically infected hosts causes chronic infection in naive individuals, without causing acute disease – indeed ‘protecting’ against it. Thus the pathogen obtains the benefit of virulence (high transmission rate), but mitigates against the cost (high host mortality). Recent findings suggest that rabbit haemorrhagic disease virus (RHDV), a highly contagious and virulent pathogen, may also utilize this alternative, ‘avirulent’, mode of transmission. The model may resolve the paradox of how RHDV can be highly prevalent in some populations, in the absence of mortality. Differences in host demography determine whether avirulent transmission prevents large-scale mortality (as in most UK populations) or not. Other pathogens may exhibit similar behaviour and the implications for emerging diseases in general are discussed.

Partial sequence and restriction enzyme cleavage site analyses of the fusion protein gene were used to genotype 47 Newcastle disease virus strains isolated between 1959 and 1996 in Bulgaria. Viruses belonged to five major genotypes that appeared to be associated with epizootics characterized by temporal and/or geographical restrictions. Genotype IV viruses (responsible for the European branch of the first panzootic) dominated the scene up to the early 1980s, interspersed with sporadic outbreaks caused by genotype II (US strains causing pneumoencephalitis) viruses. Genotype V viruses (transmitted by psittacines from South America) were first shown in 1973 and persisted until the late 1980s. Genotype VI (earliest members from the Middle-East 1968/70 outbreaks) was represented by scattered isolations between 1974 and 1996. A genotype VIIb (recent Middle East epizootic) virus was isolated as early as in 1984. Newcastle disease epizootics in Bulgaria were highlighted by multiple infection with more than one genotype at any one time.