Enteric infections caused by Brachyspira bacteria are a constant challenge for pig producers and are responsible for major health, welfare, and production problems in the pig sector worldwide. Three bacteria of the genus Brachyspira (B. hyodysenteriae, B. hampsonii and B. pilosicoli) cause disease in the large intestine of pigs. Figures 1 and 2 show images of pigs infected with swine dysentery (SD) and colitis (porcine colonic spirochaetosis (PCS)).
B) Necropsy of large intestine showing mucosa reddened with excessive mucus
B) Necropsy of large intestine showing normal or slightly thickened mucosa
The disease
Swine dysentery is caused by Brachyspira hyodysenteriae and Brachyspira hampsonii and affects grower-finisher pigs mainly at an age between 8 and 14 weeks. SD is characterised by severe muco-haemorrhagic diarrhoea, fibrino-necrotic colitis and typhlitis.
Colitis (PCS) is caused by Brachyspira pilosicoli. Colitis is a mild to moderate enteric infection mainly affecting young, weaned animals (20 - 40 kg).
Disease development, clinical signs and diagnosis
Swine dysentery: Animals are orally infected by the ingestion of infectious faeces from affected or healthy carrier pigs.
The first clinical symptom is abundant mucus production in the faeces without blood. Infection spread leads to the haemorrhagic phase of infection (bloody stools accompanied by mucus). Pigs are gaunt, lethargic and show rapid loss of bodily condition.
The diagnosis of swine dysentery is based on clinical signs (bloody mucoid diarrhoea), post-mortem examination (mucosa proliferation / hyperemia / haemorrhage and mucus) and laboratory analysis of rectal swabs (culture and PCR).
Colitis: Disease transmission is based on ingestion of infectious faeces.
Sloppy, grey-coloured faeces are found with loss of body condition and poor growth. Reduced absorptive capacity of the intestine results in diarrhoea. Mortality is rare.
Colitis is diagnosed based on clinical signs (non-fatal diarrhoea without blood), pathological findings and laboratory investigations (culture and PCR).
Correct diagnosis requires the exclusion of other causes of enteric diseases (such as ileitis, salmonellosis, or PCV-2 infection). Serological tests for the diagnosis of SD and colitis are not available.
Disease management and control
Brachyspira spp-infected pigs, their faeces and anything contaminated with infected faeces (e.g., vehicles, boots, and equipment) can easily spread infection between farms. Infected farms threaten other pig farms due to spreading on vehicles or by pig movements.
Healthy carrier pigs can excrete Brachyspira pathogens over a long time period (at least 90 days following recovery from clinical disease) and are the main source of new infections on pig farms. Consequently, all new stock introduced into pig farms should be screened for carriage of B. hyodysenteriae, B. hampsonii and B. pilosicoli and subjected to quarantine.
As shown in Table 1, pathogenic Brachyspira species have more than one potential host species and cross-species transmission may occur. Several vectors (including rodents, birds, flies, cats, dogs) have been identified as helping spread the pathogens of SD and colitis.
Strict biosecurity measures on farms are required to reduce transmission. Contact should be prevented between the pigs on the farm and any potential sources of infection including other pigs, wild birds, chickens, and rodents.
No commercial vaccines against B. hyodysenteriae, B. hampsonii or B. pilosicoli are currently available.
Antimicrobial therapy
Antimicrobial therapy is the best option available to veterinarians to control SD and colitis effectively.
Accurate antimicrobial susceptibility testing (AST) of Brachyspira spp. for the different antibiotic treatment options is of critical importance. However, Brachyspira spp. are slow growing, fastidious, anaerobic spirochetes that require specialist equipment, media and expertise for successful culturing, isolation, and final susceptibility testing in laboratories.
Brachyspira spp. isolates are highly susceptible to tiamulin. Published in vitro test assays show low tiamulin minimum inhibitory concentration (MIC) values.
Vetmulin® (tiamulin) is one of the therapeutics registered worldwide for the treatment, metaphylaxis and control of SD and colitis. In pharmacokinetic studies, the concentration of tiamulin in the colon after oral and parenteral administration were determined (Table 2).
PK / PD relationships
Tiamulin pharmacokinetic (PK) data, tiamulin MIC data and the PK / pharmacodynamic (PD) relationship are all essential to predict the probability of therapeutic success for the varying clinical situations of Brachyspira infections. Recent MIC results from US investigations of B. hyodysenteriae and B. hampsonii isolated in different US states, together with tiamulin PK data due to oral administration are shown in Figure 3. For the prediction of successful SD treatment, the colon content concentration of tiamulin needs to be at or above the MIC90 values.
Effective tiamulin concentrations are achieved in the colon contents by feed and water medication at treatment dosages. The concentrations are far higher than the determined MIC ranges and MIC90 values for B. hyodysenteriae and B. hampsonii isolates. They are high enough to inhibit SD development and to be an effective SD treatment when given at the registered dosage.
Summary
Swine dysentery and colitis are both a challenge on pig farms worldwide. Treatment, control, and elimination of both diseases relies on the use of antibiotics as no commercial vaccines are available. Vetmulin® (tiamulin) is the preferred antibiotic for SD and colitis treatment based on its PK/PD profile. The substantial therapeutic effect of Vetmulin® (tiamulin) can be explained by its gut pharmacokinetics and the high sensitivity of Brachyspira isolates to tiamulin. It is also an important tool to eradicate Brachyspira-based infections.
