Background and history

Leptospira are long slender spiral-shaped bacteria, found in most mammalian host species. Over 160 serotypes are known, generally called serovars, with cross infections occurring between some host species. Each serotype has one or more (usually only two or three) reservoir hosts which multiply it up and maintain it. A serotype can remain as a life-long infection in its reservoir host.

The pig is a reservoir host for Leptospira pomona, L. tarassovi, L. bratislava and L. muenchen, the last two being very closely related and are widespread throughout the pigs of the world. It is not a reservoir host for L. icterohaemorrhagiae but it can be infected from rats urine and become ill. It can also become infected by other serotypes from other animals urine, for example L. canicola from dogs and L. hardjo from cattle, but the infections are subclinical and do not result in disease. The pig is then an incidental host i.e. does not perpetuate the infection and is only responsible for minimal spread.

L. bratislava and L. muenchen cause a different syndrome to L. pomona and L. tarassovi and affect mainly pregnant gilts and second litter females because they will not previously have encountered it.

All leptospira require moisture, not only for indirect transmission, but also to survive. Desiccation kills them in 48 hours.

Once these organisms are introduced into a herd the pigs become permanent carriers with infection of the kidneys and intermittent excretion of the organism into the urine. Leptospira may become localised in the uterus during pregnancy, causing either abortions or increases in stillborn piglets. L. bratislava/muenchen also permanently inhabit the fallopian tube of sows and the reproductive organs of boars and they are spread in semen. This may be an important medium for the maintenance of infection in the herd and be responsible for sows failing to conceive.

Disease is uncommon in the sucking pig and would only infect individuals.

The symptoms of leptospirosis can be mistaken for other causes of infertility including:

• Chronic porcine reproductive and respiratory syndrome (PRRS).
• Endometritis.
• Non-infectious causes.
• Summer infertility.
• Management failures.

Remember that this disease can be transmitted to people.

L. pomona

This is enzootic in many pig rearing parts of the world including North, Central and South America, Australia, New Zealand, South East Asia and Eastern and Central Europe. If you are involved in pig farming in any of these areas it is not an exotic organism and your herd is at risk.

L. pomona is definitely not present in the UK or Ireland and is thought not to be present in other countries of Western Europe with the possible exception of Italy.

Once L. pomona establishes itself in a herd it is difficult to eliminate. It causes reproductive failure with consequent loss in production and income.

If you are involved in exporting pigs from countries of Western Europe, the pigs for export will probably have to be blood-tested for antibodies to L. pomona. You will probably be frustrated to find that a small number will be positive. This is because they have encountered the mosdok serovar, which is present in some species of wildlife, which sometimes cross-infects pigs causing little or no clinical disease. This is so closely related to L. pomona of pigs that it stimulates a positive immune response. It never develops into a herd problem. The pig can be thought of as an end host.

Alternatively, you might be required to put all the pigs for export on a course of streptomycin to eliminate the carrier state.The problem with this latter is that in some countries (e.g. the USA) streptomycin is not allowed to be used in pigs.

In America the skunk is an alternative reservoir host.

L. tarassovi

This appears to be a pig adapted strain that causes reproductive problems similar to but milder than L. pomona.

There are very few recent reports of this in pigs. It seemed to be confined to Central and Eastern Europe, Australia and New Zealand and presumably is still there. It is believed to be still present in Hungary and Western Russia so if you live in these countries your pigs may be at risk.

Clinical signs

Piglets

• Uncommon.
• Illness.
• Inappetence.
• Jaundice.
• Blood in urine.
• Severely infected pigs die.

Sows

• Inappetence.
• Fever.
• Depression may be observed.
• Abortions.
• Stillbirths.
• Increase in poor, non-viable pigs.

Weaners and growers

• Acute jaundice.
• Haemorrhage.
• Rapid death.
• Pale pigs.

Signs associated with L. bratislava disease:

• Repeat breeders are common particularly in first and to some extent second pregnancy gilts.
• This often follows embryo loss and there may be copious vaginal discharges.
• Late term abortions.
• An increase in premature piglets.
• An increase in stillbirths.
• Mixed litters of live poor pigs and dead piglets at birth.
• An increase in mummified pigs.
• An increase in repeat breeding animals.
• Often there is a two year cycle of disease.
• Reproductive failure occurs in second litter females, rather than gilts following their introduction to older carrier boars.
• Disease is less common in older animals.
• In long standing carrier herds disease can be difficult to recognise.

It is important to appreciate that many infections are sub-clinical but the organisms may persist in the kidneys and reproduction tracts to cause problems later.

If any of the pig workers on the farm go down with flu-like symptoms and develop a bad headache call the doctor immediately. Fortunately the disease in people responds to antibiotics if caught soon enough.

Diagnosis

Leptospirosis can be a very difficult disease to diagnose because pigs are often infected but there are no clinical signs to be seen.

The main method of diagnosis is to assess the antibody levels in a cross section of breeding females and the isolation of the organism from diseased tissues. The micro-agglutination test is carried out on serum, and recently affected animals will show titres of up to 1:1000 or more. At the onset of clinical signs a blood sample should be taken and a further one, two weeks later. If the second sample shows a rise in antibody levels at least two fold, this would be indicative of leptospira involvement (e.g. 1st sample result 1:100; 2nd result 1:1000).

In chronic disease however, the significance of titre levels are very difficult to assess.

There is a method of detecting leptospira under the microscope using the fluorescent antibody test (FAT).

It is important to note that if you carry out a serological test in your herd and the result is positive, for example to L. bratislava, this does not necessarily mean you have disease – only that the animal has been infected and responded by producing antibodies. If you carry out a serological test with positive results for L. pomona, this may be a cross reaction to other non-pig serotypes in the same group.

Alternatively, if you have an infertility problem that clinically suggests leptospira as the cause, then such test results would support a diagnosis of disease if there were rising titres in the serum of the affected sows. However, this may not be the case because pregnant females seroconvert early in the infection and by the time they abort or show symptoms the serum levels may be falling.

The following will support diagnosis:

• Records – Study the levels of abortions, repeats, stillbirths, week piglets and the age of occurrence in sows and gilts.
• Study the clinical picture.
• Blood sample ten females that have a history of infertility.
• Test the aborted foetuses, urine or kidneys and fallopian tubes of slaughtered gilts by FAT.
• Eliminate other diseases – Chronic PRRS, endometritis.
• Eliminate non-infectious causes of infertility – Summer infertility, management failures.

The leptospirosis must be distinguished from other causes of infertility.

Causes

• Introduction of infected gilts and boars.
• The presence of PRRS in the herd.
• Artificial insemination (AI):
  • A herd can also be contaminated by L. bratislava/muenchen by AI if no antibiotics are used in the semen.

Prevention

• Vaccination – Routine vaccination of breeding stock is practised commonly in countries in which the organism is enzootic but not so much in fringe and free areas. The vaccine, like all bacterial vaccines (bacterins) does not provide a solid immunity but usually raises the resistance sufficiently to prevent clinical signs. Vaccines used are inactivated and contain an adjuvant. In many countries vaccines are available that contain five or six different types of leptospira.
• Alternatively, where vaccines are not available, it is necessary to use antibiotic therapy.
• Whilst it can be difficult to prevent L. bratislava/muenchen from infecting the herd, nevertheless the more serious types such as L. pomona and L. tarassovi can be kept out of the herd by careful isolation of incoming stock, serological testing, veterinary liaison and a knowledge of the source herd.
• Once leptospira are active and present in the herd, hygiene, the constant removal of urine and good management become important methods of control.
  • The most effective method of control is to provide two wallows per paddock and use an electric fence which by movement will allow each to dry out and rest alternately.

• In indoor housing, poor concrete surfaces that allow the collection of urine and water are ideal sources for maintaining high levels of infection.
  • Provide well drained concrete surfaces particularly in defecating areas and boar pens.

• If the sow is only exposed to low numbers of organisms, infection probably takes place with little disease.
• Keep rodents under control.
• Contamination from pig lorries are a minor risk as compared to other infections unless the lorry has other pigs present.
• Remove slurry regularly.

Strategic medication.

• Where there is a history of periodic infertility, in-feed medication can be targeted just prior to the expected time of disease.
• Inject sows at weaning time with streptomycin if available at 25mg/kg. Boars should be treated with this drug once every six weeks. Alternatively semi-synthetic penicillins could be used.
• Introduce antibiotic into the anterior vagina post-service. This is the same procedure to that described under vaginal discharges, and involves the use of an AI catheter and the deposition of antibiotic into the anterior vagina 6–18 hours after the last mating. Ampicillin, amoxycillin or penicillin/dihydrostreptomycin could be used. Discuss with your veterinarian.

Eradication can be done but it is unreliable and is probably contraindicated for L. bratislava.

Treatment

Medicate the feed with tetracycline's, either oxytetracycline or chlortetracycline at levels of 800g/tonne. Feed for a period of three weeks followed by a further course six weeks later, and repeat this for four treatment periods.

Human health

L. pomona infects people with a disease sometimes called "swine herds' disease", a severe flu-like condition which sometimes causes meningitis. There is another disease in the human called Weil's disease and this is caused by L. icterohaemorrhagiae.