Swine dysentery and colitis are two nagging health issues that are both caused by Brachyspira bacteria. No commercial vaccines are available against the bacteria. A targeted approach with antibiotics is therefore the way to overcome the infection.
Enteric infections caused by Brachyspira bacteria are a challenge 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, B. pilosicoli) cause disease in the large intestine of pigs.
SD: Clinical signs and diagnosis
Swine dysentery (SD) is caused by B. hyodysenteriae and B. hampsonii and affects grower-finisher pigs mainly between eight and 14 weeks of age. SD is characterised by severe muco-haemorrhagic diarrhoea, fibrino-necrotic colitis and typhlitis. The animals will get orally infected by ingesting infectious faeces of affected or healthy carrier pigs. The first clinical symptom is strong and high mucus production without blood. Infection spread leads to a haemorrhagic phase of infection (bloody stools accompanied by mucus). Pigs show rapid loss of bodily condition.
Diagnosis of swine dysentery is based on clinical signs (bloody mucoid diarrhoea), post-mortem examination (mucosa proliferation / hyperaemia / haemorrhage and mucus) and laboratory analysis of rectal swabs (culture and PCR).
PCR: Clinical signs and diagnosis
Porcine colonic spirochaetosis (PCS, also known as colitis) is caused by B. pilosicoli. PCS is a mild to moderate enteric infection mainly affecting young weaned animals (20 - 40 kg). Disease transmission is based on ingestion of infectious faeces. Sloppy grey-coloured faeces occur, with loss of body condition and poor growth. Reduced absorptive capacity of 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). As for SD, serological tests for PCS diagnosis are not available.
Disease management and control
Pigs infected with Brachyspira species, as well as their faeces and anything contaminated with infected faeces (e.g., vehicles, boots and equipment) can easily spread infection between farms. Infected pig farms threaten other farms due to the spreading on vehicles or by pig movements.
Healthy carriers can excrete Brachyspira pathogens over a long time period (at least 90 days following recovery from clinical disease). They are the main source of new infections on pig farms. Consequently all new stock introduced into pig farms should be screened for one of the Brachyspira species and subjected to quarantine.
Several vectors (rodents, birds, flies, cats and dogs) are identified, which help spread the pathogens of swine dysentery and colitis. Strict biosecurity measures on farms are required to reduce transmission by preventing contact between the pigs on the farm and potential reservoirs of infection (wild birds, chickens, rodents). No commercial vaccines against B. hyodysenteriae, B. hampsonii and B. pilosicoli are currently available.
Antimicrobial therapy is the best option available to veterinarians to control SD and PCS effectively. Accurate antimicrobial susceptibility testing of Brachyspira species for the different antibiotic treatment options is of critical importance. However, Brachyspira species are slow-growing fastidious anaerobic spirochetes that require specialist equipment, media and expertise for successful culturing, isolation and final susceptibility testing in laboratories.
Brachyspira species isolates are highly susceptible to tiamulin. All published in vitro test assays show low tiamulin minimum inhibitory concentration (MIC) values. Tiamulin pharmacokinetic data, tiamulin MIC data and their pharmacokinetic / pharmacodynamic (PK/PD) relationship are essential to predict the probability of therapeutic success for the varying clinical situations of Brachyspira infections. Figure 1 shows the most recent MIC results from US investigations on B. hyodysenteriae and B. hampsonii isolated in different US states together with tiamulin pharmacokinetic data based on oral administration. For prediction of successful treatment against SD, the tiamulin colon contents concentration 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 in excess of the determined MIC ranges and MIC90 values for B. hyodysenteriae and B. hampsonii isolates. They are sufficient to inhibit SD development and for effective SD treatment when given at registered dosage.
A challenge in pig farms worldwide
SD and PCS are a challenge in pig farms worldwide. Treatment, control and elimination of both diseases rely on the use of antibiotics, as no commercial vaccines are available. Vetmulin tiamulin is the preferred antibiotic for SD and PCS 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 weapon in the eradication of Brachyspira-based infections.