The effect of cowpox virus infection on fecundity in bank voles and wood mice.

Although epidemic infectious diseases are a recognized cause of changes in host population dynamics, there is little direct evidence for the effect of endemic infections on populations. Cowpox virus is an orthopoxvirus which is endemic in bank voles (Clethrionomys glareolus), wood mice (Apodemus sylvaticus) and field voles (Microtus agrestis) in Great Britain. It does not cause obvious signs of disease nor does it affect survival, but in this study we demonstrate experimentally that it can reduce the fecundity of bank voles and wood mice by increasing the time to first litter by 20-30 days. The pathogenic mechanisms causing this effect are at present not known, but this finding suggests that natural subclinical infection could have a considerable effect on the dynamics of wild populations.

Transmission dynamics of a zoonotic pathogen within and between wildlife host species.

The transmission dynamics of the cowpox virus infection have been quantified in two mixed populations of bank voles (Clethrionomys glareolus) and wood mice (Apodemus sylvaticus), through analyses of detailed time-series of the numbers of susceptible, infectious and newly infected individuals. The cowpox virus is a zoonosis which circulates in these rodent hosts and has been shown to have an adverse effect on reproductive output. The transmission dynamics within species is best described as frequency dependent rather than density dependent, contrary to the 'mass action' assumption of most previous studies, both theoretical and empirical. Estimation of a transmission coefficient for each species in each population also allows annual and seasonal variations in transmission dynamics to be investigated through an analysis of regression residuals. Transmission between host species is found to be negligible despite their close cohabitation. The consequences of this for the combining ability of hosts as zoonotic reservoirs, and for apparent competition between hosts, are discussed.

Cowpox: a re-evaluation of the risks of human cowpox based on new epidemiological information.

Human cowpox is a rare but relatively severe infection of interest because of its links with Edward Jenner and the introduction of smallpox vaccine and, more recently, because of re-evaluation of the epidemiology of the infection. This indicates that cowpox is not enzootic in cattle, relegates the cow to a minor role, and emphasizes the importance of feline cowpox as a source of human infection and of wildlife as virus reservoirs. The evidence available suggests that the virus is of low infectivity for humans and should not become an increasing problem despite the cessation of smallpox vaccination and increasing numbers of immunocompromised individuals.

The Jenner bicentenary: the introduction and early distribution of smallpox vaccine.

This review describes the background to Jenner's first vaccination, his later work, and the dissemination of information about vaccination and the vaccine itself. Although based on relatively slender evidence, Jenner's theories were basically sound and he merits the credit given him. Given the circumstances, particularly the slow speed of travel and the lack of information about the duration of immunity, vaccination became established very quickly in many countries.

Gastro-enteritis due to Cryptosporidium: a prospective survey in a children's hospital.

During a 10 months' survey of children with gastro-enteritis, 27 cases of cryptosporidiosis (1.4% of those tested) were found. Only one patient was infected with another potential enteropathogen. In most cases the faeces were described as green, watery and offensive. Clinical features also included anorexia, vomiting and abdominal pain. The diarrhoea was moderate to severe in 15 cases and resulted in dehydration in 9 patients of whom two were more than 5% dehydrated. The diarrhoea was prolonged and persisted on average for 13 days. Excretion of oocysts did not stop with cessation of diarrhoea but continued for a further 11 days. Human beings appeared to be as important a source for Cryptosporidium as animals and it seemed possible that patients were infective throughout the period that they were excreting oocysts.

Cowpox in British voles and mice.

Serosurveys indicate that bank voles, field voles and woodmice are probably reservoir hosts of cowpox virus in western Europe, although virus has not yet been isolated from these species. In this study, bank voles, field voles, woodmice and laboratory mice were shown to be susceptible to combined intradermal and subcutaneous inoculation with 3-20 plaque-forming units (pfu) of cowpox virus. Bank and field voles, but not laboratory mice, were also susceptible to combined oral and nasal inoculation with 50 pfu. Few clinical signs were seen and virus was generally recovered only from inoculation sites. Bank voles were not susceptible to injection of ectromelia virus (5000 pfu) into the skin (as described above). These results provide information on which further pathogenesis and transmission studies can be based, and support the view that the orthopoxvirus antibody detected in British wild voles and woodmice indicates infection with cowpox virus. However, further investigation of the pathogenesis of cowpox in these species is needed to understand better the epidemiology of the disease.

Pox virus infection of a domestic cat.

Pox virus infection of a domestic cat is reported. It was manifest clinically as a skin infection which resolved within two months. Histopathology and electron microscopy of the epidermis revealed inclusion bodies typical of pox virus infection. Serological examination of convalescent serum confirmed recent pox virus infection. Cow pox virus was considered as the most likely infectious agent in this case.

Poxvirus infection in the domestic cat: some clinical and epidemiological observations.

The clinical findings from 30 cases of feline poxvirus infection in the UK are reviewed and some epidemiological observations described and discussed. In most cases the clinical signs consisted of skin lesions only, although systemic signs were also occasionally seen. Over half the cats had a history of a single recent lesion, assumed to be primary, on the head, neck or a forelimb. Twenty-nine of 30 cats developed more widespread secondary skin lesions. Cat-to-cat transmission was apparently rare. More cases were recognised in the autumn than at other times of the year. The possibility of a wild mammal reservoir of infection is discussed.

Serological survey for orthopoxvirus infection of wild mammals in areas where a recombinant rabies virus is used to vaccinate foxes.

Several fox vaccination campaigns against rabies have been undertaken in Belgium by using a vaccinia-rabies recombinant virus distributed in baits in the field. However, foxes and other wild animals that may ingest the baits could be infected at the same time by another orthopoxvirus, such as cowpox virus, which circulates in wildlife. Recombination between the two viruses could therefore occur. A serological survey for antibodies to orthopoxvirus, and particularly to cowpox virus, was undertaken in foxes and in several other wild species. Antibodies were detected only in two rodent species, in 16 of 25 bank voles (64 per cent) and in two of 29 woodmice (7 per cent). The risk of virus recombination in wildlife can therefore be considered to be extremely low.