A review - intestinal spirochaetal infections of pigs: An overview with an Australian perspective

Intestinal spirochaetes have become recognized over the last 25 years as an important group of enteric pathogens. These bacteria cause disease in a variety of animal species, especially pigs, poultry, dogs and human beings (Hampson and Stanton, 1996). In pigs, the bacteria cause two well-recognized conditions, swine dysentery (SD), and intestinal spirochaetosis (IS) (Taylor et al., 1980; Hampson, 1991). A third condition, referred to here as spirochaetal colitis (SC), is less clearly defined, but is associated with certain weakly beta-haemolytic spirochaetes other than those causing IS. Swine dysentery is one of the most significant production-limiting diseases of pigs and is a common problem throughout the world. The significance of IS and SC in reducing production is less clear; certainly, clinical manifestations of the conditions are much less severe than with SD. The prevalence of the diseases is not known, but the authors' observations suggest that IS occurs commonly in pigs in Australia and North America, whilst cases of IS and SC also have been reported in Europe (Taylor, 1992)

Genomic analysis of Mycobacterium bovis and other members of the Mycobacterium tuberculosis complex by isoenzyme analysis and pulsed-field gel electrophoresis.

Initially, multilocus enzyme electrophoresis was used to examine genetic relationships among 63 isolates of Mycobacterium bovis and 13 other members of the M. tuberculosis complex. The isolates were divided into five electrophoretic types, with a mean genetic diversity of 0.1. The strains were genetically homogenous, indicating that members of the complex were closely related. This supported the suggestion that they should be considered as subspecies of a single species. Pulsed-field gel electrophoresis (PFGE) was then used to differentiate these isolates, as well as 59 additional isolates of M. bovis from different parts of the world. PFGE differentiated these strains into 63 patterns (53 patterns for M. bovis). Isolates of M. bovis from Western Australia (n = 46) were more homogenous than isolates from other regions. Eight strains were identified in that state, and one predominantly bovine strain was isolated from two human beings and a feral pig. Although M. bovis isolates from different parts of the world had distinct DNA patterns, some were very similar. PFGE is a highly discriminatory technique for epidemiological studies of bovine tuberculosis. For example, it allowed differentiation between isolates of M. bovis cultured from animals in separate outbreaks of tuberculosis, it suggested the transmission of infection between certain properties, and it demonstrated the existence of multiple infections with different strains at certain farms

Colonic antibody responses in pigs with swine dysentery

Swine dysentery (SD) is a mucohaemorrhagic colitis of pigs resulting from infection of the large intestine with the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. The infection has been reported to result in the development of specific IgG, IgA and IgM antibodies in serum and the production of secretory IgA in the gut mucosa (Rees et al., 1989). The hypothesis tested in this experiment was that colonic antibody levels can be used as a diagnostic tool to assist the diagnosis of SD. The experimental design involved testing samples from non-infected pigs to define appropriate cut-off values for the assays, and then using these in assays of serum and colonic samples from pigs that had been experimentally exposed to B. hyodysenteriae

Diagnosis of swine dysentry and intestinal spirochaetosis by the use of polymerase chain reaction tests on faecal samples

The polymerase chain reaction (PCR) is a technique based on amplification of specific DNA sequences/ the products of which may be detected using electrophoresis (Saiki et al., 1985). The DNA sequences from Serpulina hyodysenteriae, the causative agent of swine dysentery (SD) (Combs and Hampson/ 1992), and from the spirochaete previously called "Anguillina coli" (Lee et al., 1993), which is associated with intestinal spirochaetosis (IS) (Park et al., 1995), were used to design PCR tests, and these were applied to the detection of these bacteria in pigs

Isolation of Serpulina pilosicoli from environmental and other sources on a piggery

The intestinal spirochaete Serpulina pilosicoli causes intestinal spirochaetosis (IS), a diarrhoeal disease of pigs and other species. This condition is widespread, though often undiagnosed, and causes losses to the pig industry through reduced growth rates and poor feed conversion (3). Very little is known about the epidemiology. Porcine intestinal spirochaetosis (PIS) is a diarrhoeal disease of weaners and growers, associated with a mild colitis. Control of the aetiological agent, Serpulina pilosicoli, has relied mainly on the use of antimicrobial agents. In contrast, besides the use of antimicrobials and appropriate management practices, it is our experience that the closely related Serpulina hyodysenteriae (the agent of swine dysentery) can also be partially controlled by bacterin vaccines (1), whilst experimentally-infected pigs totally resist challenge if fed• a diet based on cooked white rice and animal protein (4, 5). This diet results in reduced microbial fermentation in the large intestine, and it appears that these conditions inhibit colonisation by the spirochaete. The purpose of the present study was to assess whether the use of a bacterin vaccine or a rice-based diet could similarly inhibit colonisation by S. pilosicoli

Genetic and antigenic studies on Haemophilus parasuis

Haemophilus parasuis, an organism dependent upon nicotinamide adenine dinucleotide (NAD) or V-factor for in-vitro growth, is the causative agent of porcine polyserositis and arthritis (Glasser's disease) (Nicolet, 1992). The principal lesions associated with this disease are fibrinous or serofibrinous meningitis, serositis, pleuritis, pericarditis, peritonitis and arthritis that can occur in various combinations or occasionally singly (Nicolet, 1992)

Evidence that the 36kb plasmid of Brachyspira hyodysenteriae contributes to virulence

Swine dysentery (SD) results from infection of the porcine large intestine with the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. Recently the genome of virulent Australian B. hyodysenteriae strain WA1 was sequenced, and a 36. kilobase (kb) circular plasmid was identified. The plasmid contained 31 genes including six rfb genes that were predicted to be involved with rhamnose biosynthesis, and others associated with glycosylation. In the current study a set of PCRs was developed to amplify portions of nine of the plasmid genes. When used with DNA extracted from virulent strain B204, PCR products were generated, but no products were generated with DNA from avirulent strain A1. Analysis of the DNA using pulsed field gel electrophoresis (PFGE) identified a plasmid band in strains WA1 and B204, but not in strain A1. These results demonstrate that strain A1 does not contain the plasmid, and suggests that lack of the plasmid may explain why this strain is avirulent. To determine how commonly strains lacking plasmids occur, DNA was extracted from 264 Australian field isolates of B. hyodysenteriae and subjected to PCRs for three of the plasmid genes. Only one isolate (WA400) that lacked the plasmid was identified, and this absence was confirmed by PFGE analysis of DNA from the isolate and further PCR testing. To assess its virulence, 24 pigs were experimentally challenged with cultures of WA400, and 12 control pigs were challenged with virulent strain WA1 under the same conditions. Significantly fewer (P= 0.03) of the pigs challenged with WA400 became colonised and developed SD (13/24; 54%) compared to the pigs infected with WA1 (11/12; 92%). Gross lesions in the pigs colonised with WA400 tended to be less extensive than those in pigs colonised with WA1, although there were no obvious differences at the microscopic level. The results support the likelihood that plasmid-encoded genes of B. hyodysenteriae are involved in colonisation and/or disease expression

Intestinal spirochaetes of the genus Brachyspira share a partially conserved 26 kilobase genomic region with Enterococcus faecalis and Escherichia coli

Anaerobic intestinal spirochaetes of the genus Brachyspira include both pathogenic and commensal species. The two best-studied members are the pathogenic species B. hyodysenteriae (the aetiological agent of swine dysentery) and B. pilosicoli (a cause of intestinal spirochaetosis in humans and other species). Analysis of near-complete genome sequences of these two species identifi ed a highly conserved 26 kilobase (kb) region that was shared, against a background of otherwise very little sequence conservation between the two species. PCR amplification was used to identify sets of contiguous genes from this region in the related Brachyspira species B. intermedia, B. innocens, B. murdochii, B. alvinipulli, and B. aalborgi, and demonstrated the presence of at least part of this region in species from throughout the genus. Comparative genomic analysis with other sequenced bacterial species revealed that none of the completely sequenced spirochaete species from different genera contained this conserved cluster of coding sequences. In contrast, Enterococcus faecalis and Escherichia coli contained high gene cluster conservation across the 26 kb region, against an expected background of little sequence conservation between these phylogenetically distinct species. The conserved region in B. hyodysenteriae contained five genes predicted to be associated with amino acid transport and metabolism, four with energy production and conversion, two with nucleotide transport and metabolism, one with ion transport and metabolism, and four with poorly characterised or uncertain function, including an ankyrin repeat unit at the 5’ end. The most likely explanation for the presence of this 26 kb region in the Brachyspira species and in two unrelated enteric bacterial species is that the region has been involved in horizontal gene transfer

Emergence of Brachyspira species and strains: reinforcing the need for surveillance

This short review discusses the increasing complexity that has developed around the understanding of Brachyspira species that infect pigs, and their ability to cause disease. It describes the recognition of new weakly haemolytic Brachyspira species, and the growing appreciation that Brachyspira pilosicoli and some other weakly haemolytic species may be pathogenic in pigs. It discusses swine dysentery (SD) caused by the strongly haemolytic Brachyspira hyodysenteriae, particularly the cyclical nature of the disease whereby it can largely disappear as a clinical problem from a farm or region, and re-emerge years later. The review then describes the recent emergence of two newly described strongly haemolytic pathogenic species, “Brachyspira suanatina” and “Brachyspira hampsonii” both of which appear to have reservoirs in migratory waterbirds, and which may be transmitted to and between pigs. “B. suanatina” seems to be confined to Scandinavia, whereas “B. hampsonii” has been reported in North America and Europe, causes a disease indistinguishable from SD, and has required the development of new routine diagnostic tests. Besides the emergence of new species, strains of known Brachyspira species have emerged that vary in important biological properties, including antimicrobial susceptibility and virulence. Strains can be tracked locally and at the national and international levels by identifying them using multilocus sequence typing (MLST) and comparing them against sequence data for strains in the PubMLST databases. Using MLST in conjunction with data on antimicrobial susceptibility can form the basis for surveillance programs to track the movement of resistant clones. In addition some strains of B. hyodysenteriae have low virulence potential, and some of these have been found to lack the B. hyodysenteriae 36 kB plasmid or certain genes on the plasmid whose activity may be associated with colonization. Lack of the plasmid or the genes can be identified using PCR testing, and this information can be added to the MLST and resistance data to undertake detailed surveillance. Strains of low virulence are particularly important where they occur in high health status breeding herds without causing obvious disease: potentially they could be transmitted to production herds where they may colonize more effectively and cause disease under stressful commercial conditions