Brachyspira Infections in Swine - A Threat to the Pig Industry Worldwide

Figure 1. A) Pig affected by swine dysentery B) Necropsy of large intestine showing mucosa reddened with excessive mucus

Figure 2. A) Porcine colonic spirochaetosis infection: diarrhea with a consistency similar to wet cement 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 characterized by severe muco-hemorrhagic diarrhea, fibrino-necrotic colitis and typhlitis. 

Colitis (porcine colonic spirochaetosis (PCS) is caused by Brachyspira pilosicoli. Colitis is a mild to moderate enteric infection mainly affecting young, weaned animals (20 - 40 kg). 

Table 1. Disease associations of different pathogenic Brachyspira species

Disease development, clinical signs, and diagnosis

Swine dysentery: Animals are orally infected by the ingestion of infectious feces from affected or healthy carrier pigs.

The first clinical symptom is abundant mucus production in the feces without blood. Infection spread leads to the hemorrhagic 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 diarrhea), post-mortem examination (mucosa proliferation / hyperemia / hemorrhage and mucus) and laboratory analysis of rectal swabs (culture and PCR). 

Colitis: Disease transmission is based on ingestion of infectious feces. 

Sloppy, grey-colored feces are found with loss of body condition and poor growth. Reduced absorptive capacity of the intestine results in diarrhea. Mortality is rare.

Colitis is diagnosed based on clinical signs (non-fatal diarrhea 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 feces and anything contaminated with infected feces (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 carriers 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). 

Table 2. Tiamulin colon concentration determined in pharmacokinetic studies (oral and parenteral administration)

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.

Figure 3. Tiamulin MIC values against US B. hyodysenteriae (n=83) and US B. hampsonii (n=53) isolates and PK/PD relationships

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.