The global product manager for veterinary products at Huvepharma NV, Wouter Depondt, looks at strategies for the eradication of this costly disease
Swine dysentery is usually easily recognisable on farms if the clinical signs, such as blood and mucus in the diarrhoea, are displayed. However, the disease can also stay sub-clinical, meaning that none of the obvious symptoms are visible. If a farm is found positive for the disease, this often means huge economic losses because of higher mortality, poor growth rate, higher FCR and treatment costs. This is why eradication of the disease is the best option.
The causative organism is Brachyspirae hyodysenteriae, a bacterium that’s spread from faeces to mouth. The organism is very resistant in the environment. During wintry temperatures it can survive several months in organic material, such as faeces. However, in a dry and warm environment, the survival time falls dramatically. This is why summer is the ideal season to start an eradication programme. The main spread of the disease is an infected pig, but the organism has also been found in mice, rats, dogs and flies.
The bacteria might be resistant to certain antibiotics, however most isolates are still sensitive to pleuromutilins such as tiamulin (Vetmulin). An eradication programme should be based on biosecurity measures and a medication programme, both going hand in hand. First, an effective rodent control should be established in good time before the eradication is started. Dogs and cats can also be carriers of the pathogen and should be kept away from the herd.
The success of the eradication scheme is based on cleaning, disinfection and drying of the environment. Make sure there’s as little manure in the slurry pits as possible, and sows and gilts should be intensively washed when the treatment starts.
The production system will highly influence the success rate of the eradication scheme. The best chance for success is an indoor three-site production system. An outdoor breeder-finishing unit will logically be more difficult. Anyway, as with all eradication and control schemes, they start in the breeder herd. Once these are negative, logically their progeny will also be negative. They can only be infected by the pathogens still present in the environment or by animals still shedding it.
The breeding animals and weaners can be treated via the feed or water, and suckling piglets and non-eating animals by injection. Medication of all animals, including sows, gilts, boars, weaners and suckling piglets, should be started at the same time.
The sows should be treated for at least 14 days. The dose is 8.8mg tiamulin (tiamulin hydrogen fumarate or THF) per kg bodyweight as Vetmulin premix or water-soluble granules per day. A dose can be expressed as grams per ton of feed or as grams per 1,000 litres of water. But, if dosed in this way, can often lead to under- or over-dosing.
Older pigs eat and drink less per kilo bodyweight. This means that the same grams per ton will be fewer grams per kilo bodyweight for an older animal. Dosing, for example, 176g of active ingredient per tonne of feed, corresponds to a 20kg pig receiving 8.8mg/kg kilo bodyweight, while for a 100kg pig these 176g/t correspond to 4.4mg/kg liveweight.
Dosing should always be done in g/kg liveweight. This may seem a difficult thing to do, but there are dose calculators available to help with this task, such as Huvepharma’s dose calculator app that’s compatible with iPhone and Android devices.
In the case of batch farrowing, the treatment period should be as much as possible out of the farrowing period, because feed intake is reduced for several days before and after farrowing. If treatment is done via the feed, give the sows at least two feeds per day. This will ensure a constant concentration in the gut. Tiamulin is a time-dependent antibiotic and its efficacy is improved if the bacterium is constantly exposed to the drug. If animals refuse to eat during treatment, injection with tiamulin (Vetmulin injectable) is required.
The suckling piglets are treated weekly with tiamulin (Vetmulin injectable). Weaners are treated orally with THF (Vetmulin) for 21 days at 8.8mg/kg bodyweight. Again, if animals are not eating they should be injected. Lame and severely diseased animals should be euthanised at once, and removed from the premises.
For grower and finishing units, producers have following options: 1, Completely depopulate, clean and disinfect. The premises should be kept empty for at least two weeks. 2, Establish barriers between pigs already originating from sows after eradication and pigs still infected with Brachyspira hyodysenteriae. After the last dysentery positive pigs are sold, the herd should be negative. It’s clear there can be absolutely no contact between a “clean” and “dirty” group. A depopulated house is advised between the two groups. 3, Treat all growing and fattening pigs for at least 14 days at 8.8 mg/kg bodyweight. However, this will probably only lower the infection pressure. Most likely the bacterium will still be present in the environment. Again strict barriers between the groups, cleaning, disinfection and vacancy are mandatory.
The success rate of the eradication is dependent on preventing reinfection of the animals after stopping the medication by cleaning, disinfection and other biosecurity measures.
A second factor influencing the success rate is the sensitivity of the bacterium to the antibiotic used. Normally most isolated strains are sensitive to tiamulin. However, in case of decreased susceptibility, combining apramycin (Apravet) with Vetmulin significantly lowers the MIC values.
Huvepharma’s technical department recently tested the synergistic effect of these two molecules. Thirty strains of Brachyspira hyodysenteriae were tested for their sensitivity to tiamulin. Addition of 4µg/ml Apravet, resulted in a lower MIC for 50% of the strains.
This eradication plan gives only a general outline and makes no allowance for specific herd problems. Your pig vet should be able to prepare a herd-specific programme for the eradication of swine dysentery.
