Development of a control strategy for Leptospira hardjo infection in a closed beef herd.

Serological evidence of infection with a leptospire belonging to the Sejroe serogroup was identified in a closed population of Luing cattle in the west of Scotland, and the geographical isolation of the population presented an opportunity to control and possibly eradicate the infection in a large beef herd farmed under extensive conditions. Serological and bacteriological studies revealed that infection was present at a high level throughout the herd, and that the infecting serovar was hardjo. Unlike endemic hardjo infection in dairy herds, new infections were still occurring in older age-groups. Investigations of other domestic and free-living species sharing the habitat demonstrated that the maintenance of an endemic focus of hardjo was restricted to the cattle. Changes in management to prevent the transmission of infection to successive cohorts of young animals were impractical and risky, and antibiotic treatment followed by removal to clean pasture failed to prevent new cases. Thus vaccination offered the only means of control and possible eradication, and the epidemiological characteristics of the infection dictated that the programme be applied to the whole herd.

Control of Leptospira hardjo infection in beef cattle by whole-herd vaccination.

A whole-herd vaccination programme to control Leptospira hardjo infection was applied to a closed herd of approximately 800 beef cattle on the island of Luing in Scotland. An experimental vaccine was produced and the herd was vaccinated annually for five years. Progress was monitored by means of a catalytic model using data for age-specific serological prevalences and geometric mean titres. Any cattle introduced to the herd were subject to antibiotic treatment and quarantine, and at the end of the trial the whole herd was treated prophylactically with antibiotics to minimise the risk of residual infection. There was a progressive right shift in age-specific serological prevalences, and by the end of the trial all young stock entering the breeding herd were seronegative. The age-specific geometric mean titres demonstrated the cessation of an endemic cycle of hardjo infection in the herd. Birth cohort analysis supported the serological evidence of a high level of control, and bacteriological monitoring at the end of the trial indicated that hardjo had been eliminated from the herd.

Serological studies on British isolates of the Sejroe serogroup of leptospira. II. An evaluation of the factor analysis method of identifying leptospires using strains belonging to the Sejroe serogroup.

Twelve British isolates of leptospira belonging to the Sejroe serogroup were examined using a series of six factor sera prepared by a number of different absorption methods. Ten of the isolates were identified as Leptospira interrogans serovar hardjo and two as L. interrogans serovar saxkoebing. These isolates had previously been identified using the cross agglutination absorption method.

Serological studies of British leptospiral isolates of the Sejroe serogroup. III. The distribution of leptospires of the Sejroe serogroup in the British Isles.

Some 94 strains of leptospires belonging to the Sejroe serogroup isolated in the British Isles were identified to the serovar level using specific factor sera. Seventy strains were identified as Leptospira interrogans serovar hardjo, 66 from cattle, 2 from pigs and 1 each from a sheep foetus and a human. Twenty-four strains were identified as L. interrogans serovar saxkoebing, most strains were isolated from either wood mice, bank or field voles but strains were also isolated from badgers, a fox and a dog.

Serological studies on British leptospiral isolates of the Sejroe serogroup. I. The identification of British isolates of the Sejroe serogroup by the cross agglutinin absorption test.

Using the cross agglutinin absorption test 12 British leptospiral isolates of the Sejroe serogroup were identified to serovar level. Six strains isolated from cattle, two from pigs and one from a human were identified as Leptospira interrogans serovar hardjo. Two isolates from wildlife were identified as Leptospira interrogans serovar saxkoebing. One further strain isolated from wildlife closely resembled serovar saxkoebing, but specific identification was not possible. These are the first reported isolations of serovar saxkoebing in the United Kingdom. The problems associated with the cross agglutinin absorption test, and possible alternative typing procedures are discussed.

Tuberculosis in East Sussex. IV. A systematic examination of wild mammals other than badgers for tuberculosis.

A detailed investigation of the possible role of wild mammals, other than badgers, in the maintenance of Mycobacterium bovis in an area on the South Downs of East Sussex was carried out over 3 years. Estimates of population sizes were made where possible and minimum sample sizes were selected to be 95% certain of including at least one infected animal if the prevalence was at least 5%. Samples of wild mammals were taken from populations which had the highest potential direct or indirect contact rate with known infected badgers. M. bovis was not isolated from any of the 15 species of wild mammals. It was concluded that badgers are able to maintain M. bovis in an area independently of other species, and that in the area studied other species were not a source of infection for the cattle herds.

Problems associated with the serological diagnosis of Leptospira interrogans serovar hardjo infection in bovine populations.

Data combining sequential bacteriology and serology from a longitudinal study of a dairy herd were used to demonstrate the limitations of serology as a diagnostic method in cross-sectional sampling of bovine populations. Whole-herd point serological prevalences showed considerable variation over a two-year sampling period (38.8 to 76.2 per cent), and this was mainly due to varying age-specific prevalence. Owing to the rapid decline in titres and the varying persistence of infection, point serological prevalences failed to approximate to cumulative infection rates (either past or present) at different times of the year. A higher estimate of the number of susceptible animals in the herd than is the case results in inaccurate information on true incidence rates and can confuse assessments of the susceptibility of different age groups, especially if only small numbers are sampled. A sampling exercise demonstrated that a 10-cow sample usually provided little useful information other than establishing the presence or absence of hardjo in the herd. Increasing the sample size markedly improved epidemiological information, investigations of clinical disease, assessments of vaccination needs and public health tracebacks. Preferably 10 sera from each of the yearling, first calver, second calver and older age groups should be tested. Serology was an inadequate indicator of infection in individual animals. Group geometric mean titres taken from a mean serological response curve were shown to have limited application in the interpretation of field data, unless infection had occurred in the previous two months.

Consequences on emergence of resistant bacteria from the use of antibacterials in animal husbandry.

Concern over the appearance of resistant bacteria in domestic animals and birds led in Great Britain to the establishment of a Government Committee of Enquiry on the use of antibiotics in Animal Husbandry and Veterinary Medicine known as the Swan Committee. This Committee made a number of recommendations about surveillance and control of diseases of animals communicable to man which included the establishment of a system of data collection. These recommendations were incorporated in a legal statute, the Zoonoses Order of 1975. Data on the incidence of salmonellosis and of antibiotic resistance in Great Britain are presented in this paper together with a consideration of the epidemiology of salmonellosis and its control.

Differentiation of reference strains of leptospires of the Pomona serogroup by cross-agglutination absorption and restriction endonuclease analysis.

The serological classification of all reference strains that have been described as representing separate serovars of Leptospira interrogans within the Pomona serogroup was investigated using cross-agglutination absorption and bacterial restriction endonuclease analysis (BRENDA). Comparative cross-agglutination absorption studies indicated that cornelli CB, monjakov Monjakov and kennewicki LT1026 were homologous with pomona Pomona, and dania K1 and tsaratsova B81/7 were homologous with mozdok 5621. BRENDA confirmed these results, except that pomona Pomona and monjakov Monjakov showed a difference in the high molecular weight region. It is proposed that four serovars be currently recognised within the Pomona serogroup: pomona, mozdok, proechimys and tropica. The relative merits of the use of cross-agglutination absorption and BRENDA with respect to identification of Pomona serogroup isolates are discussed.

Identification by cross-agglutination absorption and restriction endonuclease analysis of leptospires of the Pomona serogroup isolated in the United Kingdom.

Five strains of Leptospira interrogans isolated in the United Kingdom and belonging to the Pomona serogroup were subjected to cross-agglutination absorption and bacterial restriction endonuclease DNA analysis (BRENDA) for their identification. British isolates were compared with reference strains representing the known serovars in the Pomona serogroup and also with isolates of the Pomona serogroup obtained from other countries. Three strains isolated from wildlife in England produced equivocal results when the cross-agglutination absorption and BRENDA results were compared. According to the World Health Organisation definition of a serovar the three English strains represented two new serovars, whereas by BRENDA all three had DNA electrophoresis patterns indistinguishable from serovar mozdok. Serovar pomona has not as yet been isolated in Great Britain and the epidemiology of the Pomona serogroup infections that have been detected by serology suggests that a serovar such as mozdok, maintained by wildlife, may be the causal agent. Two strains isolated in Northern Ireland were identified as pomona by the cross-agglutination absorption test. Further studies are needed to investigate the homogeneity of field and reference strains that are designated as pomona using the cross-agglutination absorption test.

Infection by leptospires of the Pomona serogroup in cattle and pigs in south west England.

Leptospires belonging to the Pomona serogroup were isolated from calves involved in two outbreaks of acute haemolytic disease which were characterised by jaundice, haemoglobinuria and high death rates. Retrospective case studies in which serological evidence of Pomona serogroup infection was found are also presented. Serovar pomona is the leptospire of the Pomona serogroup most commonly incriminated in clinical disease in domestic species, but the organisms isolated in this study were antigenically different to pomona and may represent a new serovar. The limited information available on the epidemiology of sporadic infection with leptospires of the Pomona serogroup in domestic species in the south west of England supports the contention that a serovar other than pomona is involved.

Infection of free-living carnivores with leptospires of the Australis serogroup.

Leptospires belonging to the Australis serogroup were isolated from badgers (Meles meles), mink (Lutreola lutreola) and a fox (Vulpes vulpes). Most isolates were identified by cross-agglutination absorption as serovar muenchen but one isolate from a fox from Surrey and one isolate from a badger from Northern Ireland were identified as serovar bratislava. Maintenance of serovar muenchen by a wide range of free-living species is an ecological condition unique to Great Britain.

Leptospira interrogans serovar hardjo in pigs: a new host-parasite relationship in the United Kingdom.

The first isolations of Leptospira interrogans serovar hardjo from pigs are recorded. Evidence that hardjo may be a sporadic cause of porcine reproductive disease is presented.

Serovar identification of leptospires of the Australis serogroup isolated from free-living and domestic species in the United Kingdom.

Eighteen isolates from the Australis serogroup from free-living and domestic animals were identified using the cross agglutination absorption test. Serovar muenchen was found only in England and Wales in wood mice, short tailed and bank voles, a grey squirrel and a pig. Serovar bratislava was found in hedgehogs in England, Wales and Northern Ireland and also in a brown rat from Northern Ireland. Serovar bratislava was isolated from sheep in both England and Northern Ireland and from horses in Northern Ireland. The distribution of these serovars in relation to possible maintenance hosts is discussed.

Identification of a reservoir of leptospira interrogans serovar muenchen in voles (Microtus agrestis and Clethrionomys glareolus) in England.

Infection with leptospires of the Australis serogroup is widespread in voles in Southern England and the serovar identification of five randomly-selected isolates was determined by cross agglutination absorption. Two isolates from short-tailed voles (Microtus agrestis) and three isolates from bank voles (Clethrionomys glareolus) were all identified as serovar muenchen. The only previous isolation of this serovar is that from a human in Germany.

Laboratory study of Mycobacterium bovis infection in badgers and calves.

Two experiments with badgers infected with Mycobacterium bovis are described. In the first, badgers were infected by intravenous inoculation of a bovine isolate of M bovis. The course of the disease in these and its spread to healthy badgers and calves was monitored by clinical, immunological and bacteriological means. In the second experiment a group of naturally infected badgers were observed for a period of up to four years. They were found to excrete M bovis in their faeces for periods of between 165 and 1305 days before they died of tuberculosis or were killed. M bovis was also shed in the urine. The badgers in both experiments were examined regularly and blood samples were taken for complement fixation tests. Faeces, urine, pus and sputum were also collected for cultural and biological tests and the badgers were skin tested using Weybridge bovine and avian tuberculin. The skin tests were uniformly negative while the complement fixation test were positive in some infected badgers but gave very variable results. Only the isolation of M bovis gave a definite diagnosis of tuberculosis in the living badger but a number of badgers which were found to have tuberculosis at post mortem were not detected while alive by this method. Environmental samples from the yards, including badger faeces, soil, hay, scrapings from feeding bowls and water were regularly examined for the presence of M bovis but apart from faeces only one water sample was positive, indicating that the organism did not persist for long in the environment. In both experiments calves developed sensitivity to bovine tuberculin after six months' exposure to infected badgers. The experiments further demonstrate the potential of a badger population to become endemically infected with M bovis and to act as a source of infection for cattle.