Application and evaluation of enzyme-linked immunosorbent assay and immunoblotting for detection of antibodies to Treponema hyodysenteriae in swine

The use of ELISAs for monitoring exposure of pig herds to Brachyspira hyodysenteriae

Background

Swine dysentery (SD), a mucohaemorrhagic diarrhoeal disease of pigs, results from infection of the large intestine with the spirochaete Brachyspira hyodysenteriae. ELISA systems using whole spirochaete cells (WC) and the B. hyodysenteriae outer membrane lipoprotein Bhlp29.7 previously have been established as potential diagnostic tools for SD. However, their true value in identifying infected herds remains unclear. The present study aimed to compare the performance of whole-cell and Bhlp29.7 based ELISAs in detecting specific immunoglobulin class IgG and IgM to B. hyodysenteriae in growing pigs, and additionally evaluated whether meat juice could serve as a source of specific antibodies.

Results

Levels of circulating IgG and IgM reacting with WC spirochaete preparations and recombinant Bhlp29.7 peaked 4-6 weeks post-infection in the experimentally challenged pigs, and remained elevated in the present study. In a cohort of pigs on an infected farm levels of antibody directed against both antigens showed a progressive increase with time. However, other than for the level of IgG against WC antigen, a significant increase in antibody levels also was observed in a cohort of pigs on a non-infected farm. In addition, assays using meat juice had 100% specificity and equivalent sensitivity to those based on serum, and likewise the best performance was achieved using the WC IgG ELISA.

Conclusions

IgG ELISAs using either WC or Bhlp29.7 as plate-coating antigens were shown to be useful for monitoring the dynamics of B. hyodysenteriae infection in grower pigs. Of the two antigens, the WC preparation tended to give better discrimination between pigs from infected and non-infected farms. Testing of meat juice was shown to have potential for identifying infected herds.

Serologic detection ofBrachyspira (Serpulina) hyodysenteriaeinfections

Swine dysentery (SD) caused by the intestinal spirocheteBrachyspira hyodysenteriaeis an economically important disease in pig-producing countries throughout the world. To date, no specific serologic assay is commercially available for the diagnosis of pigs with SD. Several serologic techniques have been identified in the past; however, these tests have all used either whole-cell proteins or lipopolysaccharide (LPS) as the antigen. Whole-cell antigens are plagued with false-positive reactions due to cross-reactivity with common proteins shared with other spirochetes. LPS antigens produce fewer false-positives; however, false-negatives may result due to LPS components being serogroup-specific. Generally, these techniques are useful for detecting infected herds, but are unreliable for the detection of individual infected pigs. In order to develop improved serologic tests it will be necessary to identify suitable diagnostic antigens, in particular immunogenic cell-surface structures which are specific toB. hyodysenteriaebut common amongst different strains of the species. Recently, we identified and cloned a 30-kDa outer membrane lipoprotein (BmpB) which is specific toB. hyodysenteriaeand is recognized by experimentally and naturally infected pigs. In this review we summarize the available serologic tests for SD, and speculate on the use of recombinant BmpB as an antigen for future development of an improved serologic test for SD diagnosis.

Identification of the swine pathogen Serpulina hyodysenteriae in rheas (Rhea americana)

Recently intestinal spirochetes were isolated from rheas in Ohio and Iowa with a necrotizing typhlocolitis. These intestinal spirochetes, strains R1 and NIV-1, were characterized and compared with other intestinal spirochetes, including strains of S. hyodysenteriae. Both rhea spirochetes were indole positive, strongly beta-hemolytic, grew under a 1% O2:99% N2 atmosphere, and were morphologically similar to spirochetes in the genus Serpulina. Analysis of rRNA gene restriction patterns (ribotypes), and immunoblots of whole cell proteins, indicated both spirochetes were similar to Serpulina hyodysenteriae strains from swine. Comparisons of nearly complete sequences (> 1458 bases) of the 16S rRNA gene of the two rhea spirochetes with S. hyodysenteriae strains confirmed that rhea spirochetes R1 and NIV-1 were strains of S. hyodysenteriae. These results indicate that S. hyodysenteriae has a broader host range than previously recognized.

Swine dysentery: more unknown than known

Swine dysentery (SD) is an economically important disease. It is caused by the spirochete Serpulina hyodysenteriae. In order to minimize the economic damage of SD, several methods to control this disease are recommended. Whereas hygienic measures and use of antimicrobials are actually practised for prevention, detection and exclusion of carriers of S. hyodysenteriae and vaccination against the disease still needs further attention. The last two methods require reliable and sensitive diagnostic tests and understanding of the pathogenesis of and immune development against SD. At present the detection of all individual carriers of S. hyodysenteriae is not yet assured, since the tests for screening individual animals are not satisfactorily evaluated as far as sensitivity and/or specificity are concerned. Studies on the pathogenesis of SD have been performed to develop a vaccine. Besides hemolysin/cytotoxin production, no other virulence factors have been identified with certainty for S. hyodysenteriae. Recently however, further indications for a role of motility in the pathogenesis of SD have been obtained. In this manuscript we summarize the most relevant recent findings.

Evaluation of different serological tests for detection of antibodies against Serpulina hyodysenteriae in pig sera

Swine dysentery is a mucohemorrhagic diarrheal disease caused by S. hyodysenteriae. The detection of asymptomatic carriers in herds is possible by serological tests. However, cross-reactions between S. hyodysenteriae and S. innocens pose a major problem in serological diagnosis. Several serological tests were evaluated for detection of antibodies to S. hyodysenteriae such as: indirect hemagglutination, passive hemolysis, conglutination and microagglutination tests. Among the tests used, only the microagglutination test was able to detect antibodies to S. hyodysenteriae. 70 to 95% of the pigs were invariably seropositive in a single dilution of 1:10 in actively infected herds whereas the number of seropositives did not exceed 10% in presumably non-infected herds. The test was found to be simple, and reliable to be used with confidence for detection of herd infection using boiled cell suspension as an antigen.

DNA probe and polymerase chain reaction procedure for the specific detection of Serpulina hyodysenteriae

Serpulina (Treponema) hyodysenteriae, a Gram-negative anaerobic spirochete, is the causative agent of swine dysentery, a mucohaemorrhagic diarrheal disease in which lesions are confined to the large intestine of pigs. A DNA probe and polymerase chain reaction (PCR) amplification procedures which are specific, rapid , and sensitive for the detection of S.hyodysenteriae have been developed. Clone pF12 from a plasmid library of S.hyodysenteriae B204 genomic DNA was identified as a clone specific for S.hyodysenteriae but not for S.innocens by differential hybridization screening with S.hyodysenteriae and S.innocens genomic DNA probes. A DNA probe consisting of a 1.3 kb restriction fragment from pF12 was found to be highly specific for S. hyodysenteriae and detected 10(5) bacterial cells. A PCR procedure using primers derived from this fragment yielded a single product which was specifically generated for S.hyodysenteriae template DNA and not for other control cells DNA. PCR provided increased sensitivity with the direct detection of as few as 10 S.hyrodysenteriae cells. The PCR procedure could detect S.hyodysenteriae cells in seeded faecal matter. Moreover the PCR assay was able to detect most S. hyodysenteriae field isolates of serotypes 8 and 9. These tools have diagnostic application in veterinary microbiology.

Characterization of two DNA probes specific for Serpulina hyodysenteriae

Two DNA probes, one 1.1- and one 0.75-kb probe, specific for Serpulina hyodysenteriae were isolated from a genomic library generated from virulent S. hyodysenteriae 5380. These probes are highly specific and react with all S. hyodysenteriae strains tested. Under stringent conditions, the DNA probes did not react with the nonpathogenic species Serpulina innocens or with other species of enteric bacteria, including Escherichia coli. Both probes are able to detect S. hyodysenteriae in colony blot hybridizations, and when applied to fecal specimens, they can detect 10(4) S. hyodysenteriae cells in 0.1 g of seeded fecal matter. Both probes can detect S. hyodysenteriae in fecal specimens from swine with clinical signs of swine dysentery after experimental challenge and from swine from a herd with an acute outbreak of swine dysentery. These probes have application as a diagnostic tool in veterinary microbiology.