The disease is caused by Leptospira bacteria, and in Australia four types, or serovars of the bacteria have been identified in pigs. Serovar pomona causes abortions, foetal deaths, premature farrowings, stillbirths and the birth of feeble piglets, which grow poorly or do not survive. Serovar bratislava is linked to stillbirths, while it is not certain if reproductive problems are caused by another common serovar, hurstbridge. Serovar tarrosovi is rarely found in Australian pigs compared with the other three, but as with pomona and hurstbridge, it presents a risk to human health.

Non-immune pigs become infected when bacteria enter their bodies via the mouth, nose, or eyes or through breaks in the skin. The bacteria multiply in the kidney and thereafter are shed in the urine at rates of up to one billion per litre. Peak infection occurs in pigs 12-16 weeks old.

Infected pigs are seldom visibly ill, and the only noticeable signs may be loss of appetite, listlessness and a mild scour lasting a couple of days. The significance of the disease, apart from the hazard to human health, is that infected pregnant sows abort or produce stillborn or weak pigs that often die soon after birth. Abortions generally occur in the last three weeks of pregnancy, but may be as early as day 16 of pregnancy in susceptible pigs that have received a massive dose of bacteria.

Most frequently, leptospirosis is introduced into previously non-infected piggeries in the urine of carrier pigs or occasionally by rodents. Cattle or horses can infect externally housed pigs if their paddocks drain into those where the pigs are kept.

Outbreaks are more serious in herds with poorly drained paddocks and where sows lie in pools of urine, or where sows are group housed with open drains (drying kills the bacteria). Stalling sows largely overcomes these problems, but sows are still exposed to boar urine at mating.

Leptospirosis can only be positively diagnosed at a laboratory by identifying the bacteria in urine, aborted foetuses, newborn piglets or in the kidneys. High antibody levels in the blood are an indication of infection though moderately high levels may be detected for a few weeks after vaccination.

Chronic leptospirosis is the major cause of kidney inflammation, which produces small, pale lesions on the kidneys. These lesions are observable at slaughter, and are routinely recorded by Australia's pig health monitoring services. However, the presence or absence of these spots is not diagnostic, as they could have other causes and some types of leptospires do not cause kidney spots.

It is important to note that unvaccinated carrier pigs present a serious health risk to piggery and abattoir staff and transport drivers. Human infection can cause prolonged and severe symptoms similar to those of flu, together with ongoing fatigue and joint soreness, and may involve severe complications such as kidney failure.

People working with pigs should avoid pig urine and afterbirth making contact with their eyes, nose and mouth, or any open wound. Afterbirth and aborted foetuses and membranes should be handled with gloves. Gloves are also a good idea with assisted matings and artificial inseminations.

Management

Incoming stock should be properly vaccinated and medicated. Rats and mice should be adequately controlled and pigs should not have access to cattle or horse paddocks or areas into which these paddocks may drain. It is also a good idea to avoid contact between pigs and dogs or cats.

Open drains and communal drinking troughs should be avoided in order to limit spread between pens, and pigs should be mixed as little as possible.

Maintenance of pens is important to prevent wound entry of bacteria and to keep urine from pooling on pitted floors.

Vaccination

Effective vaccines are available and their use is strongly recommended even in herds with no evidence of leptospirosis. Under normal circumstances, vaccinating the breeding herd twice a year gives good protection, but in some circumstances weaners also need to be vaccinated. Every animal should receive an initial dose with a follow-up injection four to six weeks later; thereafter booster doses every six months to maintain immunity. Care needs to be taken to ensure that gilts receive two injections four to six weeks apart when they enter the breeding herd.

Swellings often occur at the site of injection. These gradually subside over a period of months. The vaccine is 'killed' and so there is no danger of farmers contracting the disease from the vaccine.

The dose for breeding pigs is generally 2 mL, given under the skin (subcutaneously). Pigs should be injected in the neck region close to the base of the ear, but breeding stock can be injected at any convenient site provided it is clean.

Follow the manufacturer's recommendations concerning vaccinating procedures.

Manufacturers suggest that sows should be vaccinated before farrowing. In practice it has been found that whole herd vaccination twice a year gives satisfactory protection and has the following advantages:

• it is easier to ensure that all breeding pigs are injected
• less vaccine is wasted - at the end of a vaccination session partially used bottles should be discarded
• less time is spent vaccinating each animal - the job can be done quickly when automatic or semi-automatic syringes and flexible needle extension tubes are used
• breeders can be vaccinated against combinations of erysipelas, parvovirus and E. coli at the same time and in the same injection.

It is advisable to delay injecting sows due to farrow within a few days and those suckling very young litters.

If leptospirosis is widespread in the growing herd, give two vaccinations between 8 and 12 weeks, followed by in-feed tetracyclines upon veterinary advice.

Economics of vaccination

Due to considerable variation in severity of outbreaks it is impossible to put a figure on the financial losses incurred when leptospirosis strikes.

In an outbreak of a 50-sow herd, it is realistic to expect 10 sows to abort and 5 sows to wean only 5 piglets, a total loss of approximately 110 piglets. As the disease can be introduced into any piggery at any time, preventive vaccination is well advised. However, vaccination alone will not eliminate the organism and must be an ongoing procedure.

A single dose of streptomycin at 25 mg/kg of body weight eliminates leptospires in most pigs, and, in association with vaccination, is recommended for incoming breeders, even if they appear to be healthy. A more practical and effective alternative for wider treatment is in-feed medication with tetracyclines (800 g/tonne) for 10-14 days. Seek veterinary advice.